03 Ifptraining_rcm_sem3_booklet
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Formation professionnalisante
Reservoir Characterization & Modeling
Semaine 3 Stratigraphy – Sedimentology
Une formation IFP Training pour Sonatrach / IAP
Une formation IFP Training pour Sonatrach / IAP
Stratigraphy/Sedimentology on Clastic reservoirs Laurence BOVE
Sonatrach / IAP
Summary Table of content
Basin analysis
Slides 9
Clastic depositional environments and facies
Log responses in clastic sequences
Slides 165
Clastic petrography and diagenesis
Slides 193
Fundamentals of sequence stratigraphy
Slides 249
Slides 49
© 2013 ‐ IFP Training
Sonatrach / IAP
2
Exploration‐Production: stakes and challenges 1. Where are hydrocarbons?
In reservoirs (naturals or fractured) How did they reach reservoirs? Where are they coming from? (HC generation) Why are they trapped in this place? Sedimentary basin analysis
2. How to produce them?
Geological reservoir modeling Quantification of reservoir characteristics Heterogeneities prediction Reservoir model Productivity prediction Appraisal well
Exploration Strategy
Strategy for field development design
© 2013 ‐ IFP Training
Elaboration of « exploration guides »: Plays Identification of « Prospects » Uncertainties & risks evaluation Exploration well: OOIP calculation
3
Sonatrach / IAP
Basin exploration workflow: step 1 Petroleum trilogy Source rock / Reservoir / Seal extension Risk and uncertainties → Deliverables • HC index maps for each reservoir • Petroleum system mapping → Hypotheses • Events chart • Potential SR and RR maturity (kitchen) • Migration episodes and pathways • Entrapment and timing
4 Petroleum system analysis
Sonatrach / IAP
2
Basin analysis 3 Geochemical analysis
Stratigraphic analysis Relationship between tectonic and sedimentation Exploration tools (cores, logs, well correlation) Biostratigraphy Sequence stratigraphy Risk and uncertainties → Deliverables • Basin time calibration • Chronostratigraphic chart (Wheeler) • Stratigraphic basin reconstruction
© 2013 ‐ IFP Training
Organic indicators (VR, biomarkers, X‐fluo) Thermochronology (fission tracks, mineralogy) Rock‐Eval (TOC, HI…) Risk and uncertainties → Deliverables • Organic matter origin (Kerogene type) • Maturation curve
1 Structural analysis
Exploration tools (seismic) Geodynamics Risk and uncertainties → Deliverables • Basin geometry calibration • Structural basin reconstruction
4
Exploration techniques & tools
© 2013 ‐ IFP Training
5
Sonatrach / IAP
Basin exploration workflow: step 2
Basin modeling Sequence stratigraphy framework
• Subsidence mechanisms (back‐ stripping) • Temperature evolution (maturation) • Pressure evolution (compaction) • HC accumulation • Risk and uncertainties
Deliverables • Basin thermal calibration • Kitchen extension maps • Generation timing • Φ vs. Depth evolution
Deliverables • Maps
Play concept & definition
• Play definition and mapping (traps) • Prospect definition and evaluation • Migration pathways for each play • Risk and uncertainties
- Play & prospect extension - Field shows distribution
• Volumetrics (OOIP) • Prospect ranking • Yet‐to‐find (explored area) • Economic
Basin evaluation & Play assessment strategy © 2013 ‐ IFP Training
Sonatrach / IAP
6
© 2013 ‐ IFP Training
© 2013 ‐ IFP Training
Une formation IFP Training pour Sonatrach / IAP
Clastic reservoirs Basin analysis
Sonatrach / IAP
Basin analysis
Structural and thermal evolution during burial • • • • •
Earth structure Extensive context Compressive context Transform context Thermal evolution
© 2013 ‐ IFP Training
Sonatrach / IAP
10
Map of sedimentary basins Onshore and Offshore basins
© 2013 ‐ IFP Training
Sonatrach / IAP
11
© 2013 ‐ IFP Training
Basin analysis
Structural and thermal evolution during burial • • • • •
Earth structure Extensive context Compressive context Transform context Thermal evolution
© 2013 ‐ IFP Training
13
Sonatrach / IAP
Structure of the Earth
Crust • Lithosphere (10 to 70 km) Granitic crust
Basaltic crust
Mantle
Crust
• Upper mantle: Asthenosphere (700km) • Lower mantle: Mesosphere (2 200 km)
Core • Outer core (2 200km) • Inner core (1 271 km)
< passive margin >
(LITHOSPHERE)
Mid Oceanic Ridge Atlantic Ocean
Upper mantle (ASTHENOSPHERE)
Lower mantle (MESOSPHERE)
Subduction > active margin <
Rift
Outer core
SiAl
Sonatrach / IAP
NiFe
© 2013 ‐ IFP Training
Inner core
14
Dynamics of the Earth: convection
© 2013 ‐ IFP Training
Core
15
Sonatrach / IAP
Earthquake activity
© 2013 ‐ IFP Training
Lithospheric plate boundaries = seismicity (in red) Sonatrach / IAP
16
Tectonic plates
Mid oceanic ridge
Earth‐ quakes Volcanoes
Lithospheric plate boundaries: • Divergent (extensional: mid oceanic ridges) • Convergent (compressional: subduction, collision) • Sliding/Shearing (transform, strike‐slip)
© 2013 ‐ IFP Training
Sonatrach / IAP
17
Types of margins and related basins
3 types of crustal stresses • Extensional basins • Compressional basins • Shear basins
3 types of processes • Purely thermal • Lithospheric thickness variation • Loading and unloading
© 2013 ‐ IFP Training
Sonatrach / IAP
18
Types of sedimentary basins
Basins associated with plate divergence Extensional basins • Rift, passive margin (plate divergence, ocean) • Intra‐cratonic basin (intra‐continental, intra‐plate)
Basins associated with plate convergence Compressional basins • Island arc‐type margin (two oceanic plates) • Continental active margin (ocean / continent plates) • Inter‐plate collision (two continental plates)
Basins associated with shearing (sliding movement) Trans‐tensional basins • Pull‐apart basin (trans‐tension, local distension in convergence) © 2013 ‐ IFP Training
Sonatrach / IAP
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© 2013 ‐ IFP Training
Basin analysis
Structural and thermal evolution during burial • • • • •
Earth structure Extensive context Compressive context Transform context Thermal evolution
© 2013 ‐ IFP Training
21
Sonatrach / IAP
Rift basin
Rift are areas of crustal extension and thinned continental crust. Regions of rifting are characterized by lithospheric stretching, high heat flow and volcanic activity caused by a thermal anomaly at depth
Rift zones general characteristics: • Heat flow of 90 to 110mW.m‐2 • High levels of earthquake activity and a dome‐shaped Moho • Normal faults network
Current examples in the Red Sea and in Ethiopia
© 2013 ‐ IFP Training
Sonatrach / IAP
22
Failed rift basin
Beginning of rifting mechanisms and stop of lithospheric stretching caused by a reducing and cooling of the thermal anomaly
Rift zones general characteristics: • Heat flow of 80 to 90mW.m‐2 • A reducing of seismic and volcanic activity • A normal faults network covered a disconformity
Failed rift basin
© 2013 ‐ IFP Training
Examples in the North Sea and in Rhine‐Bresse (France)
23
Sonatrach / IAP
Intra‐cratonic basin
Intra‐cratonic basins are large depressions in continental crust. They have a slow and homogeneous sedimentary filling
Generally, intra‐cratonic basins: • Have a heat flow near‐normal (60 to 80mW.m‐2) • Are seismically inactive • Have sediment overlain on faults and syn‐rift sediments
Sonatrach / IAP
Examples in Paris basin and Middle‐East
© 2013 ‐ IFP Training
24
Passive margin basin
Beginning of rifting mechanisms and stop of lithospheric stretching caused by a reducing and cooling of the thermal anomaly
Generally, passive margin zones: • Have a heat flow near‐normal (60 to 80mW.m‐2) • Are seismically inactive • Have sediment overlain on faults and syn‐rift sediments
© 2013 ‐ IFP Training
Sonatrach / IAP
Examples in West Africa and East South America
25
© 2013 ‐ IFP Training
Basin analysis
Structural and thermal evolution during burial • • • • •
Earth structure Extensive context Compressive context Transform context Thermal evolution
© 2013 ‐ IFP Training
27
Sonatrach / IAP
Foreland basin Foreland basin
Foreland basins are the result of the downward flexing of the lithosphere in response to the weight of the adjacent mountain belt, though many geological and geodynamic processes combine to control their subsequent evolution
Generally, foreland basins: • Have a heat flow near‐normal (60 to 80mW.m‐2) • Are seismically active
© 2013 ‐ IFP Training
Sonatrach / IAP
Examples in Alps, Himalayan and Appalachian chains
28
Forearc basin
This basin is located between the volcanic arc and the subduction complex
Generally, fore‐arc basins: • Are highly seismic active
Example in Andes, Java and Sumatra islands
© 2013 ‐ IFP Training
29
Sonatrach / IAP
Oceanic trench basin
Oceanic trenches are the deeper part of the ocean floor where lithosphere is in subduction under another
The age of the oceanic lithosphere controls the trench depth
Generally, oceanic trench: • Have a highly seismic activity • Have an associated accretionary prism
© 2013 ‐ IFP Training
Sonatrach / IAP
Examples in western South America and eastern Japan
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Basin analysis
Structural and thermal evolution during burial • • • • •
Earth structure Extensive context Compressive context Transform context Thermal evolution
© 2013 ‐ IFP Training
31
Sonatrach / IAP
Strike‐slip basin
Trans‐pression
Strike‐slip basins are due to transform fault movements
If the blocks move away from their initial position, it is a transtensional movement so there are normal faults associated to the flower structure
Symmetrically, transpressional movement induces reverse faults
Trans‐tension
© 2013 ‐ IFP Training
Sonatrach / IAP
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Basin analysis
Structural and thermal evolution during burial • • • • •
Earth structure Extensive context Compressive context Transform context Thermal evolution
© 2013 ‐ IFP Training
33
Sonatrach / IAP
Origin of hydrocarbons
Transformation of Organic Matter (O.M.) from dead fauna or flora
Accumulation & preservation of O.M. • Accumulation in quiet geological environments (lake, delta, sea) • Preservation depends on sediment type & rate, environment energy
Modification of depositional conditions • Burial, compaction, water expulsion • Temperature & pressure increase
Transformation of Kerogen into hydrocarbons • Oil • Gas (methane)
Maturation: chemical transformation, mainly due to temperature (and pressure) increase during burial Sonatrach / IAP
© 2013 ‐ IFP Training
Kerogen: non soluble part of O.M. (i.e. lipids)
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Origin of Organic Matter
Lipids
Cellulose
Lignine
Type III
Type II
Bacteria
Wood
Algae
© 2013 ‐ IFP Training
Plankton
Type I
Animals = maximum 10% of total generated organic biomass 35
Sonatrach / IAP
Transformation of O.M. & Kerogen
Diagenesis [< 60°C] Bacterial degradation Immature stage
Catagenesis [from 60 to 120°C] Thermal degradation → Weak chemical bonds breaking
Oil window
Metagenesis [from 120 to 200°C] Thermal degradation → Strong C–C bonds breaking (cracking)
Sonatrach / IAP
© 2013 ‐ IFP Training
Gas window
36
Van Krevelen diagram
© 2013 ‐ IFP Training
Sonatrach / IAP
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Generation & Migration of HC
© 2013 ‐ IFP Training
Sonatrach / IAP
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Hydrocarbon migration Types of migration: The word “migration” covers all types of displacements of hydrocarbons, from the source rock where they generated to the reservoir rock where they accumulate
Primary migration • Expulsion of hydrocarbons from source rocks towards adjacent rocks. This migration takes place over very short distances (few centimetres). It depends on the internal overpressure conditions, linked to the volume of HC generated
Secondary migration • Displacement of hydrocarbons after expulsion from the source‐rock, over distances ranging from few meters to several hundred kilometres, until they are trapped • This migration takes place inside permeable conditions (reservoir rocks, open fractures open unconformities…). Migration pathways are complex and specific to each basin, they are mainly driven by pressure decrease. Migration can be lateral and/or vertical
Dysmigration • Hydrocarbon displacement from a “leaking” reservoir to the surface (i.e. seepage)
© 2013 ‐ IFP Training
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Sonatrach / IAP
Origin of hydrocarbons: summary
Three origins of OM > three different types of Kerogen • Type I: lacustrine (lake algae, bacteria,…) • Type II: marine (zoo‐ & phyto‐plankton, micro‐organisms,…) • Type III: continental (terrestrial vegetation, forests, bacteria…)
Three steps of OM transformation within source rocks • Diagenesis (burial, lithification) • Catagenesis (Kerogen transformation) → ~60°C… • Metagenesis (cooking, cracking) → ~120°C…
Three factors for OM maturation
Sonatrach / IAP
© 2013 ‐ IFP Training
• Temperature (sediments cooking, anoxic conditions, bacterial activity) • Pressure (sediment compaction, water expulsion) • Time (molecular evolution, new atomic combinations – compensates for low T°)
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Key Points : The petroleum trilogy Source rock Definition
Reservoir rock
Sedimentary rocks rich in • Porous and permeable rocks OM, mature enough to • Allow displacement and generate hydrocarbons hydrocarbon accumulation
• Non‐permeable rocks (prevent hydrocarbons from migration) • Plastic rocks (can be deformed but not fractured)
• Shales or salt rocks (plastic Clastic rocks (e.g. sandstone) rocks) Carbonate rocks (e.g. • Very compact sandstones or limestones (without limestone) porosity, “tight”) Petrophysical parameters: • Porosity: Φ • Permeability: K • Saturation: S
Lateral extension and layer continuity are more important than thickness
© 2013 ‐ IFP Training
• Very fine‐grained rocks (shales, mudstones, marls,…) with interbedded • laminations Lithology • (sediment/OM) • Low permeability (internal over‐pressure > under‐ compaction) • OM production, deposition, preservation Specificity & maturation (process, parameters,…) • HC generation, expulsion & migration
Seal rock / Cap rock
41
Sonatrach / IAP
Timing between elements & processes The trap must be available before/during migration
Trap 2. Processes:
Sonatrach / IAP
Source rock
Migration
Migration pathways
Accumulation and Preservation
Reservoir and Seal
© 2013 ‐ IFP Training
1. Elements:
Generation
42
Pretroleum system events chart
400
300
200
Paleozoic
D
M
P
100
Mesozoic
P
TR
J
Geologic Time Scale Cenozoic
K
P
Petroleum System Events
N Rock Units
Reservoir Rock Seal Rock
Elements
Source Rock
Trap Formation Gen/Migration/Accum
Processes
Overburden Rock
Preservation
Magoon and Dow, 1994
Time of expulsion and migration. (Trap must already exist) Sonatrach / IAP
Critical Moment
© 2013 ‐ IFP Training
Critical Moment
43
Cross‐section of a petroleum system
© 2013 ‐ IFP Training
Sonatrach / IAP
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Map of a petroleum system
Migration pathway
© 2013 ‐ IFP Training
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Sonatrach / IAP
Petroleum system: Critical steps
Entrapment Accumulation Entrapment Preservation
Gas Cap Oil Water
Seal Rock Reservoir Rock
Migration 120° F
Generation
Source Rock
(60°C)
350° F
(120°C) 2480
Sonatrach / IAP
© 2013 ‐ IFP Training
Expulsion
46
Petroleum systems: key points Key points to keep in mind Conditions for the formation of a hydrocarbon field Necessary existence of:
one (or more) mature source rock, one (or more) reservoir rock, one seal rock,
a phase of migration (and pathways),
one (or several) traps, …and:
© 2013 ‐ IFP Training
• an adequate timing between trap formation, hydrocarbon generation and migration • sufficient quantities of generated hydrocarbons to feed the trap • preservation of trap integrity throughout geologic times
47
© 2013 ‐ IFP Training
Une formation IFP Training pour Sonatrach / IAP
Clastic reservoirs Clastic depositional environments and facies
Sonatrach / IAP
Clastic depositional environments and facies
Fluid flows and related sedimentary processes • Reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments) • Sedimentary fill hierarchy • Depositional environments
Sonatrach / IAP
© 2013 ‐ IFP Training
− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
50
Definition of siliciclastic rocks
Siliciclastics are detrital sediments that result from the accumulation of debris from erosion or alteration of existing rocks
The main mineral components are quartz, feldspars, micas and clays
Clastics are classified according to their grain size and shape: • • • •
Conglomerates / Breccias Sandstones Siltstones Shales / Claystones / Clastic muds (Sandy & shaly sediments family) © 2013 ‐ IFP Training
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Sonatrach / IAP
Textural classification
Example of shale structure (Scanning Eletron Microscope) and composition Claystones
[Shales]
The classification of clastic sedimentary rocks is complex because several variables are involved. Particle size (both average size and range of particles’ sizes), particles composition, cement and matrix must all be taken into consideration
Shales (which consist mostly of clay minerals) are generally further classified on the basis of composition and bedding
Sonatrach / IAP
© 2013 ‐ IFP Training
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Formation of clastic rocks
Weathering and erosion (of outcropping rocks ) • Chemical weathering (alteration) Agent: rain (+ dissolved CO2) − Solutions − Grains • Mechanical weathering (erosion) Agents: gravity, freeze/thaw, running water, wind, glaciers
Transport (of debris + solutions and colloidal particles) • Agents: − Continental: water (torrents, streams & rivers), wind, ice (glaciers) − Oceanic: currents, waves, tides, gravity flow deposits
Deposition © 2013 ‐ IFP Training
• Progressive decrease of current speed leads to deposition of transported load, with resulting sorting according to grain weight (and size)
53
Sonatrach / IAP
Bedforms characteristics
Bedform generation • Result of interaction of moving fluid on surface sediment • Undulation on non cohesive surface • Downstream migration
Bedform boundaries • Upper bedding surface: constructional structures − Unidirectional current − Oscillatory current • Lower bedding surface: erosional structures (sole marks) − Current marks: produced by erosion du to the current flow » Flute marks » Crescent marks
− Tool marks: objects removed by the current along the surface • Internal bedding − Horizontal stratification − Inclined stratification Sonatrach / IAP
© 2013 ‐ IFP Training
» Groove, Bounce, Brush
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Clastic depositional environments and facies
Fluid flows and related sedimentary processes • Reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments) • Sedimentary fill hierarchy • Depositional environments © 2013 ‐ IFP Training
− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
55
Sonatrach / IAP
Sediment transport
Tractive sediment transport (bedload) • Particles roll or skip on sediment surface with a low level of suspension • Motion: rolling carpets or turbid clouds • Decreasing of velocity → downstream load deposition Geometry of deposition: oblique laminae
Suspended sediment transport (suspension) • Particles in suspension (partial, continuous or intermittent) in the water depth • Motion: ascending movement due to turbulence • Decrease of turbulence → vertical decantation
Agents: Water, wind, ice…
Sonatrach / IAP
© 2013 ‐ IFP Training
Geometry of deposition: horizontal laminae
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Clastic depositional processes Cohesive
Non ‐cohesive
Transport in suspension
© 2013 ‐ IFP Training
Hjulstrom’s diagram Evolution of erosion vs deposition with stream (or current) speed and particle size
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Sonatrach / IAP
Primary sedimentary structures
Formed under influence of same hydrodynamic and/or aerodynamic conditions as entrainment, transport and deposition of sediment particles
We must answer and resolve the following questions: • Which way is up? • Orientation of process that dispersed sediment? • What process was responsible for transportation and deposition of sediment?
© 2013 ‐ IFP Training
Sonatrach / IAP
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Bedforms vs flow regime Oscillatory flow: waves • Circular motion of particle at water surface • Flat orbits at bottom back and forth motion of particles • Geometry of deposit: wavy ripples, plane beds
Unidirectional flow: rivers, wind • Unidirectional downstream motion of particles • Deposition depends on grain size vs. flow velocity • Geometry of deposit: irregular ripples, plane beds
© 2013 ‐ IFP Training
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Sonatrach / IAP
Bedforms in unidirectional flow
Three main factors controlling bedforms in unidirectional currents: • Average flow velocity • Grain size • Water depth
© 2013 ‐ IFP Training
Sonatrach / IAP
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Constructional bedforms
Bedforms shape vs flow velocity
Intermittent transport
Permanent transport © 2013 ‐ IFP Training
Erosional bedforms
Lower Flow regime Upper flow regime
61
Sonatrach / IAP
Bedforms in oscillatory flow
Bedforms produced by wave action
Oscillatory flow • Flattening of wave orbits • Back and forth motion creating « lateral » motion along the sea bottom
General characteristics
Sonatrach / IAP
© 2013 ‐ IFP Training
• Symmetrical shape − Waves ripples − Hummocks (Swales) − Subplane beds • Peak or round crests • Straight crests, with bifurcation
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Bedforms in oscillatory flow
Waves ripples • Develop in velocity of waves between 9 to 90 cm/s • Height: up to 20 cm • Length: up to 1 m
© 2013 ‐ IFP Training
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Sonatrach / IAP
Bedforms in oscillatory flow
Hummocky/swaley cross‐stratification (HCS) • Broad undulations, gently dipping − Hummocks / Swales
• • • •
In fine‐grained sandstone, subparallel laminae (lower surface) Wave length: 1 to 5 m Average set thickness: ~25 cm Storm deposits: below fairweather wave base
© 2013 ‐ IFP Training
Sonatrach / IAP
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Erosional flow features
Sole marks Erosional sedimentary structures on sediment surface (preserved by burial) • Scour marks erosional turbulence • Tool marks object imprints
Visible as negative moulds on layers base (way‐up criteria)
© 2013 ‐ IFP Training
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Processes velocities
© 2013 ‐ IFP Training
Sonatrach / IAP
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Sediment maturity Key points to keep in mind
© 2013 ‐ IFP Training
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© 2013 ‐ IFP Training
Clastic depositional environments and facies
Fluid flows and related sedimentary processes • Reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments) • Sedimentary fill hierarchy • Depositional environments © 2013 ‐ IFP Training
− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
69
Sonatrach / IAP
Workshop: oscillatory bedforms
Identify depositional environment
Name bedforms
Range dimensions (λ, H, L)
Indicate flow direction
Sketch dynamic process
Sonatrach / IAP
© 2013 ‐ IFP Training
Typical Y‐shaped symmetrical ripples
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Workshop: constructional bedforms
Identify depositional environment
Name bedforms
Range dimensions (λ, H, L)
Indicate flow direction
Sketch dynamic process
© 2013 ‐ IFP Training
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Sonatrach / IAP
Workshop: beach facies analogues
Identify depositional environment
Name bedforms
Range dimensions (λ, H, L)
Indicate flow direction
Sketch dynamic process
© 2013 ‐ IFP Training
Sonatrach / IAP
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Workshop: erosional bedforms Flute marks
© 2013 ‐ IFP Training
Load structures Sonatrach / IAP
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Workshop: erosional bedforms
© 2013 ‐ IFP Training
Sonatrach / IAP
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Workshop: erosional bedforms
© 2013 ‐ IFP Training
Sonatrach / IAP
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Workshop: erosional bedforms Crescent
© 2013 ‐ IFP Training
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Workshop: Bioturbation / Way‐up criterium
© 2013 ‐ IFP Training
Sonatrach / IAP
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Workshop: beach facies analogues
© 2013 ‐ IFP Training
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Workshop: beach facies analogues
© 2013 ‐ IFP Training
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Workshop: beach facies analogues
© 2013 ‐ IFP Training
Sonatrach / IAP
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Clastic depositional environments and facies
Fluid flows and related sedimentary processes • General reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments • Sedimentary fill hierarchy • Depositional environments © 2013 ‐ IFP Training
− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
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Sonatrach / IAP
Sedimentary fill hierarchy
© 2013 ‐ IFP Training
Jeroen Schokker, Wim Westerhoff & Henk Weerts after Heinz & Aigner, 2003 Sonatrach / IAP
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How to order the sedimentary pile?
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"Facies adjacent to one another in a continuous vertical sequence also accumulated adjacent to one another laterally"
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Sonatrach / IAP
How to order the sedimentary pile? Introduction to sedimentary sequences Depositional sequence in respect to Walther's law
© 2013 ‐ IFP Training
Clastic depositional environments and facies
Fluid flows and related sedimentary processes • General reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments • Sedimentary fill hierarchy • Depositional environments © 2013 ‐ IFP Training
− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
85
Sonatrach / IAP
Sedimentary depositional environments Continental environments
Marine environments
Glacial Aeolian Lacustrine Fluvial
• Fluvial‐dominated • Wave‐dominated • Tide‐dominated
• Braided • Meandering • Anastomosed
Continental shelf • Siliciclastic • Carbonatic
Coastal plain
Slope, canyon Basin • Turbiditic fan • Abyssal plain
© 2013 ‐ IFP Training
Sea level
Sonatrach / IAP
Shoreline (coast/beach) Delta
86
Transfer mechanisms in siliciclastic environments
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Sonatrach / IAP
Alluvial fan systems
Fan‐shaped body • Cone that radiates downslope • Stream channels emerge from valleys • Rather coarse detrital sediments • Poorly sorted
© 2013 ‐ IFP Training
Sonatrach / IAP
Built up by mountain stream • At relief's foot • Change of slope gradient • Dip of alluvial fan: <10° (3 to 6°) • Length: from few 100 m to 100 km
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Typical alluvial fan sequence
Sedimentation • Beds more or less parallel to the surface • Stratification is moderately developed
Deposition mode • Debris flow or mud flow dominated • Extensive masses of mud‐supported coarse‐grained sediment, moving downward • Main channel: in upper fan and mid fan
Massive conglomerates
© 2013 ‐ IFP Training
Coarsening‐up sequence
89
Sonatrach / IAP
Alluvial fans
Alluvial fans are cone‐shaped piles of sediment formed at the foot of highlands where streams confined by narrow valleys emerge into adjacent lowland. A series of overlapping alluvial fans generates a clastic wedge
There are some differences between alluvial fans in arid and humid climates. Sedimentation on alluvial fans begins where the streams leave their confined valleys and loose some of their transport efficiency
Alluvial fans are composed of two types of sediment: • Stream deposits • Sediment gravity‐flows Current‐transported sediments usually predominate. They are deposited either from ephemeral or perennial water flow in the channel system or, after extreme rain storms, from sheet‐floods inundating large parts of the alluvial fan
Sometimes, gravel is concentrated locally to form sieve deposits (coarse gravel and boulders devoid of finer‐grained matrix). From time to time, large debris flows with a muddy‐sandy matrix reach the proximal and mid‐fan area and bury part of the pre‐ existing, radiating channel system
At their lower end, such debris flows terminate in characteristic lobes, and they often concentrate large boulders and gravel at their outer margin, forming levees. Later, new channels cut into the mass flow deposits and rework and redistribute great proportions of their material
Sonatrach / IAP
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Fan deltas Coastal alluvial fans prograding into a lake or into the sea form fan deltas. As soon as the streams, carrying a high bed‐load, reach the standing water body, they drop their coarse material at the shore face and in prodelta foresets
The intensity of reworking, sorting, and redeposition, as well as the transport of material along the shoreline, depend on the wave energy and, in marine environments, on the tidal range
In the case of lakes and protected embayments, fan progradation is little influenced by these processes. Gravel and sand accumulate at the mouths of streams until they become unstable from time to time and move as subaqueous debris flows into deeper water. There, they alternate with muddy lake or marine deposits
On high‐energy coasts, some of the coarse material dropped at the river mouth is transported alongshore adjacent beaches where it forms distinctive beach gravel; some sand and gravel is swept by storms into deeper water
Fluctuations in the water level in lakes or the sea affect both the subaerial and subaqueous facies of fan deltas. They are reflected by fluvial terraces and coarse grained river mouth deposits at varying elevations. A lowering of the lake or sea level causes the emergence of delta foresets and the subsequent cutting of fluvial channels into the foresets. These channels are commonly filled later with fluvial deposits
Sonatrach / IAP
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Exercise: identify environment and name feature
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Fluvial depositional systems Main characteristics
• Unidirectional flow regime • Transport until flow exists, with decreasing grain size of carried particles • Three types of sediment bedload: − Bedload − Suspended load − Mixed load • Sediments start to deposit when river loses energy or/and is progressively abandoned (progressive decantation) • Typical depositional sequence: basal erosional surface and fining‐upward sequence
Three main types of river (fluvial) systems (according to braided parameters and sinuosity index):
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• Braided system • Meandering system • Anastomosed system
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Fluvial depositional settings
Channel pattern is the combination of • Bedload vs suspended load • Bank stability • Slope gradient • Flow fluctuations
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Transfer mechanisms in siliciclastic environments
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Braided river systems
Braided rivers are characterized by high‐sediment load and high velocity
Typical succession of lenticular sorted conglomerates and coarse sandstones
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Typical braided river sequence Braided rivers and its bars
Several erosional channels
Stacked fining‐up sequences
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Basal lag deposit
Basal erosional surface 97
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Examples of basal conglomerates (lag deposit)
Erosion in the flood plain Sonatrach / IAP
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Erosional baseline
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Log responses – Outcrop analogue
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Typical braided river architecture
Gravel‐rich braided system • Longitudinal bars • Conglomerates dominant
Sand‐rich braided system • Transverse bars • Sandstones dominant
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Braided river systems
Braided streams usually consist of several individual channels separated by bars and islands and therefore form a wide, shallow stream bed. Braided rivers develop near areas of high relief, which deliver relatively large amounts of debris, gravel and sand into the fluvial system
From all these characteristics, it can be inferred that braided systems are bed load‐ dominated, they carry and deposit chiefly gravel and sands. Therefore, they consist predominantly of channel and channel‐flank deposits, while silty and muddy floodplain facies are subordinate
Downstream, they often display a progressive decrease in grain size, as well as in bed forms and internal sedimentary structures
The interstices in the gravel are usually later filled with sand during low water periods, but in this system sandy beds are relatively rare in the proximal zone, unless there is little gravel available in the source area. Sandy beds develop best at somewhat higher topography elevations within the braided system next to the active channel system
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Braided river systems Many bars are somewhat graded. Interbedded with the gravels are thin lenses of sand representing deposition in abandoned channels or sand wedges at the edge of bars
In places, one can observe repeated successions of fining‐upward gravel‐sand sequences 1 to 2 m thick, but in general it is difficult to identify the bottoms of former channels and the geometry of their fill. The reason is that the underlying and neighboring sediments also consist largely of gravel
Downstream, the predominantly gravelly beds grade into beds consisting partly of smaller pebbles and sand. In the lower, more active channels, bar gravels dominate, whereas sands and pebbly sands are common at higher topography elevations. In rarely flooded areas, some silt and mud may be deposited and preserved
In the total assemblage, the gravel content varies between 10 and 70 %. As a result of downstream and laterally migrating sand and gravel bars, planar and trough cross‐bedding are the most important internal sedimentary structures
Both the lateral migration and sudden abandonment of channels due to avulsion cause fining‐upward channel fill sequences a few meters thick. Such sequences are considered the most distinctive characteristic feature of this type of braided river deposit
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Braided river architecture: reservoir potential
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High Net‐to‐Gross Immature sediments; early alteration Require top‐seal/structural traps
Sheet‐like geometry Thin shaly interval at the top
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Transfer mechanisms in siliciclastic environments
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Typical meandering river sequence
Crevasse splay Point Bar
Coal Fine grained sandstone Organic shale, roots medium coarse to grained sandstone
Fining‐up sequence : point bar Sonatrach / IAP
Meandering river
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Erosion
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Generation of meanders
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Meandring river architecture: reservoir potential
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Lower Net‐to‐Gross Sediment more mature Stratigraphic trap potential
Shoe‐lace geometry becoming sheet like Shales frequent in sequence
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Meandering river systems
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Meandering river systems
Meandering river systems develop one principal, relatively narrow channel of high sinuosity (> 1.5) and are dominated by mixed load or predominantly suspended load. Their overall sand content often averages 20 to 40 %. If meandering rivers are associated with a wide floodplain, the channel sediments may be restricted to a comparatively narrow zone within the flood basin where they form a meander belt
In a sinuous channel segment, one can distinguish the following morphological features and depositional sub‐environments: − − − − − −
Channels and channel fills Point bars and lateral accretion complexes Chute bars Channel plugs (oxbow lakes) Levee and crevasse splay deposits Alluvial floodplain deposits
• Point bars accumulate on the inner sides of river bends, while on the outer side material from the bank is eroded. In this way, the curvature of the meander tends to become increasingly exaggerated until the river produces short‐cuts, leaving behind abandoned channel segments (oxbow lakes)
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• The channel floor is usually covered by lag sediments consisting of the coarsest material transported by the river during peak flood. This channel lag may also contain mud clasts or blocks eroded from the banks. Lag sands and gravel usually accumulate between scour pools and form flat, elongate bars displaying either imbrication of gravel or crudely laminated and planar cross‐bedded gravelly sand
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Meandering river systems Most of the point bar material is eroded from the upstream channel banks. It is deposited in areas of lower velocity turbulence. Because sediment moves up and out of the channel onto the bar, cross sections of point bars often show fining‐upward sequences, with sands on top of channel lags
Similarly, the internal structures grade from horizontal bedding (upper flow regime) to large‐scale and small scale trough cross‐bedding (lower flow regime). The most distinctive feature of point bars is lateral accretion)
Many meandering channels are accompanied by flat ridges sloping away from the channel into the floodplain. These levees are built up during moderate floods which just reach the elevation of the channel ridge. Due to decreasing flow velocity, sand is deposited along the channel ridges, grading into silt somewhat farther away
Locally, channel water may spill over the levees into the floodplain, forming crevasse splays. The fallout of sand and silt usually extends farther into the floodplains than the levees, but such crevasse splays can also contribute to the buildup of the levees
The prevailing internal structures of these sand sheets may resemble those of thin sandy turbidites, showing some grading, horizontal lamination and small‐scale ripple cross‐ bedding. These structures are, however, often mashed or destroyed by the roots of vegetation. Whereas distal crevasse splays become interbedded with floodplain deposits, levee sands of ten tend to be reworked by subsequent channel migration
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Crevasse splay deposits
Deposits formed during flood period, by break into the channel levees
Cones composed of sand to silty facies
Formed by stacked fining upward thin sequences with small secondary channels at top during peak of flood
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Channel levees deposits
Mississipi
Levees deposits, adjacent to the channel and formed during the flooding period, are:
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• Wedge deposits of alternating fine sand /silts and mud • Showing parallel to small current ripple laminations
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Transfer mechanisms in siliciclastic environments
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Anastomosing river systems
Develop in • Upstream area or downstream areas • Low sinuosity (less than braided) • Several wandering channels
Particularities of each channel • Stable banks (not ephemeral) • Fixed by vegetation
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Anastomosing river architecture: reservoir potential
Lower Net‐to‐Gross Sediment more mature
vertical stacked and confined sand bodies encased in mud
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Fluvial architecture and reservoir potential Key points to keep in mind
River systems • Main reservoirs located in channels and channels belts • Associated reservoirs located in − Levees deposits − Crevasse splays − Floodplains sandstones
Braided system: reservoir bodies • Vertical and lateral stacking, good connection • Geometry: Sheetlike or tabular sandbodies (stacked multistorey infill)
Meandering system: reservoir bodies • Dominant lateral accretion (point bar – levees – crevasse splays) • Geometry: “point bar – clay plug” model, isolated sandbodies
Anastomosing system: reservoir bodies • Dominant vertical aggradation, isolated narrow channels • Geometry: channel fill
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Depositional environment vs reservoir distribution
ELF 1997
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Variation of reservoir quality with depositional environment and energy (slope)
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River types vs reservoir distribution
Slims
Williams
Windorah
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River facies: reservoir potential Fluvial architecture vs reservoir potential Braided Meandering Anastomosed
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Courtesy of Pr. M. Lopez (U. of Montpellier)
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Clastic depositional environments and facies
Fluid flows and related sedimentary processes • General reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments • Sedimentary fill hierarchy • Depositional environments © 2013 ‐ IFP Training
− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
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Coastal deposits
Coastal environment: river outlet, delta • Continuous quantity of sediments provided by the river • Deposition driven by energy loss (decreasing flow rate, decantation) − From coarse‐grained sand (close to coast and beach) to fine‐grained sand and shales (towards platform and basin) − Continental environment taking over marine environment with time
• Variable distribution of river sediments according to local dominant energy factor (river flow, tidal currents, wave action)
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Clastic depositional environments
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Delta shapes & energy
Morphological classification of deltas based on delta front shape which reflects: • Relation between the relative importance of rive, tide or wave processes • Sediment supply • Duration in time
Birdfoot
Lobate
Fluvial dominated
Cuspate
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Tide dominated Estuarian
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Wave dominated
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Delta classifications
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Delta morphology reflects the relative importance of fluvial, tidal, and wave processes, as well as gradient and sediment supply • River‐dominated deltas occur in microtidal settings with limited wave energy, where delta‐lobe progradation is significant and redistribution of mouth bars is limited • Wave‐dominated deltas are characterized by mouth bars reworked into shore‐ parallel sand bodies and beaches • Tide‐dominated deltas exhibit tidal mudflats and mouth bars that are reworked into elongate sand bodies perpendicular to the shoreline
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Deltaic environments
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Key points: Fluvial‐dominated deltas
Fluvial‐dominated deltas are primarily controlled by the water density difference between the inflowing river water and the standing water on the basin. Delta – lobe progradation is significant while mouth bar distribution remains limited
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Fluvial‐dominated deltas
Different flow types that determine the distribution of sediment and sedimentary structures formed in the delta are hyperpycnal flow and hypopycnal flow • Hyperpycnal flow produced when the density of the river water entering the basin is greater than the density of the standing water in the ocean basin. This higher density river water will flow below the standing water in the basin because of the difference in density. A zone of mixing occurs along the outer edge of the flow. As the river water flows beneath the standing water, it erodes the previously deposited bottom sediments.
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• Hypopycnal flow is associated with a lower river water density entering a higher density standing water in the basin. Under these conditions, the river water will flow out over the standing water, gradually depositing the suspended clay portion of the sediment load on the prodelta
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Key points: Wave‐dominated deltas
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Wave‐dominated deltas are primarily influenced by wave energy and action. The common sequence reflects reworked mouth bar into sandbodies and beaches parallel to the shoreline
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Coastal depositional environments Shoreline
Shelf
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Identify features and infer depositional environment
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Identify features and infer depositional environment
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Coastal depositional environments
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Coastal sedimentary features
Swash zone
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Sedimentary features: HCS stratifications
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Hummocky cross stratification (HCS) forms during storm events with combined wave and current activity in shallow seas
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Key points: Tide‐dominated deltas
Sonatrach / IAP
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Tide‐dominated deltas typically occur in locations of large tidal ranges or high tidal current speeds. The sediment supply is over powered by strong tidal currents, the delta tends to be very small Resulting feature of a tide‐dominated delta is that it has many linear structures parallel to the tidal flow and perpendicular to the shore
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Tidal environments
Tide • • • •
Periodic phenomenon on coastal domain Results from the gravitational attraction (Earth, Moon, Sun) Regular rise and fall of water level in the world’s oceans Effective agent of transport of sediment
Tidal range: vertical amplitude between low tide and high tide
Foreshore: area horizontally alternately covered and uncovered by the tide
Characterization • Particle transport is vigorous and rapid − Bipolar linear current (alternating tidal currents: Flood/Ebb) − Cross‐stratification in opposite directions (herringbone) : Flood / Ebb oscillation
Repeated erosion and creation of tidal channels Difficult conditions for living organisms Flaser, wavy and lenticular beddings Reactivation surface
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• • • •
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Tidal influenced bedforms & sedimentary structures
Tide‐influenced sedimentary structures: • Herringbone cross stratification → bipolar flow directions • Mud‐draped cross strata (quite common): result from alternating bedform migration during high flow velocities with mud drapes deposition during high/low tide slack water • Tidal bundles are characterized by a sand‐mud couplet of varying thickness; tidal bundle sequences consist of bundles that can be related to neap‐spring cycles
Flood
Flood‐ebb tidal deposits
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Ebb
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Sedimentary structures in tidal range
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Sedimentary structures: tide‐related laminae
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Sedimentary structures: tide‐related laminae Bundle thickness vs tide cycles
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Summary table: sedimentary features vs environments Depositional energy
Water Zone
Sediment type (GS)
Backshore
Parallel landward stratifications
High ℮
Swash zone Breaking zone
Sand
Foreshore (Tidal flat)
Lenticular Wavy Flaser
Low → High ℮
High tide (MHW) Low tide (MLW)
Mud Mud/Sand Sand
Sandwaves (trough) Megaripples(tabular) Ripples (sym/asym)
High ℮
Low tide (MLW) Fair weather zone (MFWB)
Sand (winnowed: clean, rounded & sorted)
Upper offshore
Storm HCS Wavy bedding
Low ℮
Storm weather zone (MSWB)
Silty/Shaly
Lower offshore
Wavy bedding
Low ℮
Outer shelf
Shaly (burrows)
Deep water [Turbidites]
Massive (no struct.) [Bouma, Stowe,...]
Low ℮ [High ℮ gravity flow]
Slope Basin
Muddy [Sandy/Silty]
Shoreface
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Laminae
Sedimentary features
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Environment
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Key points : Coastal systems and reservoir potentials Key points to keep in mind 2. Reservoir bodies: Mouth bar, and aggradational channels complexes located along the distributary:
Limited lateral extension
Fluvial‐ dominated
Wave‐ dominated
Tide‐ dominated
3. Reservoir bodies:
Beach barrier island, very good lateral continuity, well sorted sandbodies and clay‐free:
Isolated tidal bar, poor continuity and extension. Well sorted sandstone, but lot of clay drapes due to intertidal processes: Discontinuous reservoir
Best reservoir
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1. Reservoir bodies:
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Clastic depositional environments and facies
Fluid flows and related sedimentary processes • General reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments • Sedimentary fill hierarchy • Depositional environments © 2013 ‐ IFP Training
− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
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Gravity deposits
Continental environment: broken blocks or erosional debris falling down by gravity and/or density–turbulence current
Aquatic environment (lake, open marine) • Mass flow (debris flow, mud flow) − Low amount of water incorporated in sediments − Sedimentation without any sorting (very fast and sudden, almost instantaneous event)
• Density‐turbulence flow
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− Progressive incorporation of water (turbulent flow or current) − Sediments start to be deposited when flow velocity and related turbulence decrease: coarser grains are deposited first and finer last − One turbidite = one single event − Very good sorting in layers: fining upward sequence with well organized geometry evolution
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Marine clastic deposits: turbidites
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Fluvial vs turbiditic clastics: similar organization of sediments in deeper environments 147
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Gravity deposits vs. processes & sediment supply Step 3‐ geometries & extend of turbidites
Step 1‐ Initiation of gravity deposits
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Step 2 ‐ Processes of transport &deposition
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Turbidite system general organization
Cross‐sections: from proximal to distal turbiditic facies
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Turbiditic system organization Upper fan
Middle fan
Turbidite deposits: sedimentary facies and log responses Lower fan
New lobe
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Abyssal plain
General upward tendency: coarsening and shallowing upward
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Turbidites: depositional mechanism
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Lab reconstitution of a dynamic gravity flow (mini turbiditic current = avalanche!)
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Bedforms in unidirectional flow
Three main factors controlling bedforms in unidirectional currents: • Average flow velocity • Grain size • Water depth
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Typical turbidite depositional sequences
Main characteristics • Allochthonous sedimentation • Highly organized from proximal to distal part • Dominantly controlled by unidirectional flow • General fining upward sequence • Facies association from channels to levees and lobes
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Conventional Bouma sequence & field outcrop
Obara turbidites, Spain © 2013 ‐ IFP Training
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Conventional Bouma sequence & field outcrop
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St Jean de Luz turbidites ‐ France
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Deep sea deposits: turbidites
Turbiditic system with midfan/suprafan lobes
Simple turbiditic system without lobes
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Abundant sediments reworked from delta Sonatrach / IAP
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Turbidite outcrop
Courtesy Philippe JOSEPH
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Turbiditic sandstones (Mid fan ‐ channel)
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Turbidite outcrop
Stacked channels
Turbiditic sandstones Sonatrach / IAP
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Lower fan ‐ lobes
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Turbidite outcrop
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Bouma sequence: Tb and Tc
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Sedimentation rate and sea variations
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Fluvial and deltaic sequences
Gamma Ray log responses and depositional deltaic environments
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Sediment maturity
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Clastic reservoirs internal geometry and organization
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Clastics Key points to keep in mind
Clastic sediments are: • Allochthonous erosional products (weathering, alteration and transportation) • Transported by fluvial water, wind, ice • Deposited in basins
The main depositional process of clastic sediments is progressive decantation due to gradual decay of flow velocity (water or density current), i.e. decreasing transport energy
Fluvial, deltaic and turbiditic depositional sequences are mostly fining‐upward The evolution of a fluvial system (e.g. meander) involves both erosional and decantation processes
The development of a delta is mostly due to progradation (if constant sediment supply and sea level)
A turbidite results from a single depositional event (intermittent sediment supply) The main source of continental sediments is erosion of existing rock (outcrops) The main source of deep sea deposits is reworking of existing sediments (e.g. delta)
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Clastic reservoirs Log responses in clastic sequences
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Log responses in clastic sequences
Sedimentological & stratigraphic well log analysis • • • •
Log shapes review Depositional environment review & logs characteristics Parasequences & logs responses Clastic system tracts and logs facies responses
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Sedimentary processes
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Log responses
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Log responses
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Log responses in clastic sequences
Sedimentological & stratigraphic well log analysis • • • •
Log shapes review Depositional environment review & logs characteristics Parasequences & logs responses Clastic system tracts and logs facies responses
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Typical braided river sequence Braided rivers and related bars
Several erosional channels
Stacked fining‐up sequences Sonatrach / IAP
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Basal lag deposit
Basal erosional surface 172
Typical meandering river sequence
Crevasse splay Point bar
Coal Fine grained sandstone Organic shale, roots medium coarse to grained sandstone
Fining‐up sequence: point bar
Meandering river
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Erosion
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Typical depositional sequences of fluvial sediments Key points to keep in mind Alluvial fan
Braided river
Meandering river
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Deltaic depositional sequences
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Turbidites sequences
Main characteristics: • Allochthonous sedimentation • Highly organized from proximal to distal part • Dominantly controlled by unidirectional flow • General fining‐upward sequence • Facies association from channels to levees and lobes
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Clastic sequences Gamma Ray log responses and depositional environments
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Log responses in clastic sequences
Sedimentological & stratigraphic well log analysis • • • •
Log shapes review Depositional environment review & logs characteristics Parasequences & logs responses Clastic system tracts and logs facies responses
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Accommodation variations and related sequences PROGRADATIONAL PARASEQUENCE SET
Rate of deposition Rate of accommodation
SP
RES
SP
RES
SP
RES
> 1
RETROGRADATIONAL PARASEQUENCE SET
Rate of deposition Rate of accommodation
< 1
AGGRADATIONAL PARASEQUENCE SET
Rate of deposition
= 1
Coastal plain sandstones And mudstones Sonatrach / IAP
Shallow marine sandstones
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Rate of accommodation
Shelf Mudstones
MITCHUM and VAN WAGONER 1991
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Correlations during progradation time
Basinward
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Correlations during progradation time
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Facies distribution wave or fluvial‐dominated environment
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Facies distribution fluvial or wave‐dominated environment
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Facies distribution shoreline‐dominated environment
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Facies distribution in tidal flat‐dominated environment
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Log responses in clastic sequences
Sedimentological & stratigraphic well log analysis • • • •
Log shapes review Depositional environment review & logs characteristics Parasequences & logs responses Clastic system tracts and logs facies responses
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Hierarchy of fluvial architectural elements
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Une formation IFP Training pour Sonatrach / IAP
Clastic reservoirs Clastic Petrography & Diagenesis
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Clastic Petrography & Diagenesis
Mineral diagenesis • Definition and processes
Diagenetical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetical regimes
Heterogeneities
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• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
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Mineral diagenesis: Definition
All physical, chemical or biological processes at relatively low temperatures (less than 200‐250°C) and pressures (less than 2‐3kbars) that affect a sediment (or a sedimentary rock) after its deposition.
Compaction, dissolution, cementation, mineral replacement are major elementary processes of diagenesis activated by physico‐chemical parameters (pressure, temperature, fluid composition) and/or biological (bacterial activity, bioturbation)
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Why study diagenesis?
To understand: • Transformation mechanisms from sediment to sedimentary rock • Sedimentary basin dynamic • Reservoir quality • Nature and distribution of porosity and permeability • Fluid flow evolution • Extend of oil recovery • Interaction of secondary recovery fluids with the reservoir • Movement or binding of pollutants
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Processes
Physical • Compaction • Fluid migration • Pressure solution
Chemical • • • • •
Mineral reaction Mineral replacement Cementation Dissolution Organic matter evolution
Geological & climatic
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• Original depositional environment • Diagenetic environment • Tectonic setting and basin evolution Etc.
→ All processes are interdependent and cannot be easily separated 197
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What is lithification? Process which leads to the transformation of a non‐consolidated sediment to a rock.
It implies grain cementation in the sediment but not necessarily burial and compaction (e.g. beachrock)
Lithification is the result of diagenetic processes but diagenesis does not necessarily lead to sediment lithification.
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What type of diagenesis?
Early diagenesis • Changes essentially biochemical • First meters of burying • Early in the history of sediments • Environment in marine, meteoric, salted zone and vadoze zone
Late diagenesis • Slower changes (compaction, dissolution and mineralogical transformations) • Burying diagenesis (pressure, temperature and fluids effects) • Type of rock (carbonates, clays, siliciclastics, etc.) controlled by climate, tectonic and sedimentary contexts © 2013 ‐ IFP Training
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Clastic Petrography & Diagenesis
Mineral diagenesis • Definition and processes
Diagenesical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetic regimes
Heterogeneities © 2013 ‐ IFP Training
• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
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Definition of compaction
All processes which lead to a decreasing of porosity in sediment or sedimentary rock and generate pore fluid eviction
Rearrangement
Cementation
(with volume losses)
(without volume losses)
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Mechanical compaction – 1/2
Occur at shallow burial depth
Reworking of sediments (grain repacking and rearrangement, bioturbation)
« The tightest packing of spheres is rhombohaedral (Φ=25%) while the loosest is cubic (Φ=50%) » Graton & Fraser, 1935
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Mechanical compaction – 2/2 Impact of grain size, roundness and sphericity
Mechanical compaction is generally more effective in mudrocks than sandstones (high water content in shales, rapidly expelled by compaction)
Water
Minerals
Compaction
+
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Water loss
Water
Minerals
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Rearrangement example in siliciclastics
1 mm
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Rearrangement example in carbonates
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Chemical compaction
Mainly achieved by reprecipitation of minerals in remaining pore spaces
Cementation more obvious in coarse clastics than mudrocks
Main process is pressure‐solution
P1
Where Pw = Pore fluid pressure P2
And P1 > P2 > Pw Pw
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Reprecipitation of overgrowth forms (dark blue) by diffusion of silica from the grain contact to the pore spaces
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Pressure‐solution
Development of sutured contact enhanced by presence of clays • Enhance transport of ions away from site of pressure solution (diffusion network)
Much more difficult to produce pressure‐solution in clean sandstones
In coarse clastic sediments (gravels) • High pressure contacts • Rapid porosity loss early in burial slowing down rapidly
In fine clastic sediments (sandstones & siltstones) • Higher surface area in contact = fewer nucleation sites • Rapid porosity loss at depth © 2013 ‐ IFP Training
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Pressure‐solution mechanisms Major constraint σ1 1. DISSOLUTION
2. DIFFUSION
Grain
Minor constraint σ3 3. OVERGROWTH
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Pressure‐solution in sandstone
Φ
Overgrowth
Φ © 2013 ‐ IFP Training
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Pressure‐solution in carbonate Nummulitic limestone (Eocene, Corsica) Precipitation Diffusion
Dissolution
Awl
Concept
Polarized light
Cathodoluminescence © 2013 ‐ IFP Training
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Pressure‐solution example in sandstone (polarized light)
Ex1 Lum Pola
Ex1 Lum nat
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Pressure‐solution example in sandstone (natural light)
Zoom 2
Zoom 1
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Pressure‐solution example in sandstone (natural light)
Zoom 1
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Dissolution Sonatrach / IAP
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Pressure‐solution example in sandstone (natural light)
Precipitation
500 µm
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Zoom 2
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Mineralogical dissolution example (Natural light)
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Potassic feldspar (FK) dissolution Sonatrach / IAP
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Clastic Petrography & Diagenesis
Mineral diagenesis • Definition and processes
Diagenesical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetic regimes
Heterogeneities © 2013 ‐ IFP Training
• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
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Cementation parameters – 1/2
An allogenic cementation occur during deposition
An authigenic cementation grown in situ during diagenesis
There is rarely sufficient material in the rock to account for all cements present
Degree of supersaturation of the pore fluid, example in silica • High level, soluble forms precipitate: opal and chalcedony form thin crusts and mosaics on grains • Low level: quartz precipitates (because low solubility) and slowly forms monocrystalline overgrowths
Other common cements:
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Carbonates (calcite, dolomite) Silicates (quartz, opal, potassic & sodic feldpars) Clay minerals (kaolin, illite, chlorite…) Sulphates (gypsum, anhydrite…) Oxides (haematite…)
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• • • • •
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Cementation parameters – 2/2
From fluids to cement formation: • Water salinity • Dissolution of soluble rock • Groundwater percolation • Shales expulsion • Mineral and organic reaction
Cement precipitation depends on the nucleation
A slow kinetic or an inhibitor presence can explain the no‐precipitation
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Sources of silica cement
During early diagenesis: • Skeletal remains of diatoms and radiolaria • Quartz dust abraded during transportation
During late diagenesis: • Mainly pressure‐solution
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Radiolaria Diatom Sonatrach / IAP
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Cementation in sandstone reservoir (Brent)
Uncemented sandstone
Diagenetic front
Cemented sandstone (calcitic cement) © 2013 ‐ IFP Training
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Sources of kaolin cement
Alteration and mineral recombination in porosity
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Quartz
Porosity
Quartz
Kaolin cement
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Kaolin cement
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Clastic Petrography & Diagenesis
Mineral diagenesis • Definition and processes
Diagenesical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetic regimes
Heterogeneities © 2013 ‐ IFP Training
• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
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Moldic dissolution
Initial presence of a shell, rock fragment or grain. Then, micritization by bacteria. Progression from outside to inside
Second step, dissolution of cement but not the micrite (more stable). The shape is preserved. Sparitic precipitation in the cavity
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Pseudomorph forms
Replacement of a preexisting mineral by an other one
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From halite (cubic crystal) to a “cubic” calcite (normally trigonal – hexagonal scalenohedral)
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Recrystallization
Sometimes, it is difficult to distinguish cementation and recrystallization
Change in crystal shape / orientation without compositional change
The orientation of the first crystal (as seed) govern the direction in which further crystals grows
Major effect of temperature
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How to reset all information… Sonatrach / IAP
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Clastic Petrography & Diagenesis
Mineral diagenesis • Definition and processes
Diagenesical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetic regimes
Heterogeneities © 2013 ‐ IFP Training
• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
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Near‐surface sandstone diagenesis
Particularly occurs in semi‐arid climates • Water table very low • Sediments are oxygenated for long period • Sparse vegetation (= rapid erosion) • Immature sediment producing (high amount of unstable minerals like feldspars, amphiboles…)
Processes of activation near surface • Clay infiltration (clay percolation through water) • Intrastratal mineral dissolution (partial or complete dissolution of instable minerals) • Replacement • Authigenic mineral growth (hydroxydes…) © 2013 ‐ IFP Training
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Subsurface sandstone diagenesis
Sandstone horizons correspond to fluid pathways especially for fluids from compacting mudstones
Fluids carry dissolved ions (potential cements)
Clays flatten to form a matrix (=permeability decreasing)
Effect of the fluids composition, temperature and pressure
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Diagenesis and reservoir quality Key points to keep in mind
Diagenesis have a strong impact on reservoir quality
Generally, the quality of clastic reservoirs decrease with diagenesis by compaction and cementation
Whereas in carbonate reservoirs, the quality can be also reduced or improved by physical, chemical or biological processes (dissolution, dolomitization…)
The main parameters of reservoir quality affected by diagenesis are the porosity and the permeability
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Clastic Petrography & Diagenesis
Mineral diagenesis • Definition and processes
Diagenesical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetic regimes
Heterogeneities © 2013 ‐ IFP Training
• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
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Reservoir heterogeneities: Summary
Introduction: heterogeneities in the reservoir • • • •
Homogeneous / heterogeneous reservoirs Reservoir heterogeneity concepts Classification of reservoir heterogeneities Impact of reservoir heterogeneity on hydrocarbon recovery
Reservoir heterogeneity features • Scale of reservoir heterogeneities • Small‐scale observation and analysis • Large‐scale observation and analysis © 2013 ‐ IFP Training
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Homogeneous vs. Heterogeneous reservoir
Heterogeneous reservoir (Faults, Unconformities, Layers, Facies, Diagenesis, Fractures, Super K,…)
Heterogeneity: spatial variation of rock physical properties that affect fluid flow
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Homogeneous reservoir
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Reservoir heterogeneity: concepts – 1/2
To build a consistent and relevant model: • All variations in the reservoir quality must be analyzed and classified in a manner that the main heterogeneities main are clearly highlighted • For a given study, all heterogeneities that can affect fluid flow are considered as key heterogeneities
Key heterogeneities have to be absolutely described in the geological model © 2013 ‐ IFP Training
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Reservoir heterogeneity: concepts – 2/2
Reservoir heterogeneities • All relevant factors affecting the dynamic behavior of the field • Small‐ to large‐scale geologic features • From static reservoir characterization (significant or not) • From dynamic reservoir characterization (significant)
Basic principle • Identify the smallest element that will impact production
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Reservoir heterogeneities characterization calls for the cooperation between all professionals involved in the study (i.e. from geophysicists to reservoir engineers)
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Classification of heterogeneities in reservoirs – 1/2 Classification
Weber classification (1986) « How heterogeneitiy affect oil recovery »
Heterogeneity range A: Structural
1 to 3
B: Stratigraphic
1 to 3
C: Diagenetic
1 to 3
D: Depositional
1 to 3
E: Depositional
1 to 3 1 to 3
G: Structural
1 to 3
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1 ‐ major heterogeneity 2 ‐ intermediate heterogeneity 3 ‐ negligible heterogeneity Classification objective: highlight most significant heterogeneities.
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F: Diagenetic
Prior to the modeling phase, it is necessary to perform a synthesis of heterogeneity types, for each item, taking into account their impact on fluid flow, using the following scale:
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Classification of heterogeneities in reservoirs – 2/2 Impact on recovery
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Clastic Petrography & Diagenesis
Mineral diagenesis • Definfition and processes
Diagenesical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetic regimes
Heterogeneities © 2013 ‐ IFP Training
• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
239
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Scale of reservoir heterogeneities Grain
Obervation scales:
Lamination
Bed
< 1 mm
Formation
Field
< 1 cm Small ...
< 1 m
Relative scales:
Intermediate ...
< 1000 m
Large ...
> 1000 m
Very large ...
Heterogeneities and investigation tools do not always have the same scale… Sonatrach / IAP
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(from Krause and Collins, 1984)
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Small scale heterogeneities Example of laminations and cross‐beddings
Micro scale: related to a mixture of different pore types and geometries (textural features)
Macro scale: often related to laminations and cross‐beddings (depositional features: energy) © 2013 ‐ IFP Training
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Large‐scale heterogeneities (1/5)
Faults • Juxtaposition of reservoir units and low permeability units • Clay smearing (injection of clay into the fault plane) • Cataclasis: sand grains crushing (breccia) • Diagenesis (fault‐related): cementation due to fluid circulation and precipitation creating hydraulic seals
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Cataclasis: silicification Sonatrach / IAP
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Large‐scale heterogeneities (2/5) Genetic unit boundaries → represent stratigraphic discontinuities (isolated bar, channel…)
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Large‐scale heterogeneities (3/5) Diagenesis
DOLOMITE
(power line cable)
Dolomitization front
Bedding
LIMESTONE
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Scale
5 m
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0
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Large‐scale heterogeneities (4/5) Both shale baffles and permeability streaks Lateral extension linked with depositional environment e.g. Hassi‐Messaoud reservoir (silts)
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Large‐scale heterogeneities (5/5) Seeping fractures
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Reservoir characterization and modeling Key points to keep in mind
To build a consistent and relevant model for an integrated study: • All reservoir heterogeneities must be identified and classified (main ones highlighted) • All heterogeneities that can impact fluid flow are considered as major heterogeneities • Even the smallest elements that can affect production need to be identified and modeled • The geological model must take into account all significant heterogeneities • Characterization of reservoir heterogeneities calls for integrated multi‐ disciplinary approach (cooperation and team work) © 2013 ‐ IFP Training
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Clastic reservoirs Fundamentals of sequence stratigraphy
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Fundamentals of sequence stratigraphy
Introduction to sequence stratigraphy • • • • • •
General introduction Accommodation definition Relative sea level and space available Dynamic points Sequence development Parasequence/genetic sequence © 2013 ‐ IFP Training
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Sequence stratigraphy: Introduction Sequence stratigraphy is based on the application of the systematic subdivision of the section by well defined surfaces
These surfaces are used to provide a frame work to the interpretation of the depositional settings of the sedimentary section
This interpretation is then used to predict the extent and character of the component sedimentary facies
Integrated method with all the exploration tools (geology, geophysics, palynology, geochemistry…) • Relation between geological layers in a chronostratigraphic understanding • Basic sedimentary unit: depositional sequence
Characteristics of a depositional sequence • Bounded by their unconformities and their correlative conformities • Composed by systems tracts
Each system tract • Bounded by physical surface • Composed of elementary « unit » (genetic unit or parasequence)
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Fundamentals of sequence stratigraphy
Introduction to sequence stratigraphy • • • • • •
General introduction Accommodation definition Relative sea level and space available Dynamic points Sequence development Parasequence/genetic sequence © 2013 ‐ IFP Training
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Accommodation definition
Sediment is deposited in the space between the seafloor and base level (sea level or graded stream profile) which is called accommodation
The way a basin fills with sediment and the stratal patterns that result depend upon how much space is available for the sediment to fill and how rapidly new space is added
Accommodation may vary as both the upper and lower boundaries of this space move up or down
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Fundamentals of sequence stratigraphy
Introduction to sequence stratigraphy • • • • • •
General introduction Accommodation definition Relative sea level and space available Dynamic points Sequence development Parasequence/genetic sequence © 2013 ‐ IFP Training
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Relative sea level vs space availability
Eustacy refers only to the position of the sea surface with reference to a fixed datum, such as the center of the earth, and is therefore independent from local factors
Relative sea level incorporates local subsidence by referring to the position of the sea surface with respect to a datum at or near the seafloor
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To discern the rate at which new space is added, both relative eustacy fluctuation rate combined with subsidence rate must be considered
256
Accommodation & Equilibrium point Equilibrium point : Rate of subsidence = Rate of eustatic change A platform is divided into two parts separated by an equilibrium point Basinward of : • Rate of subsidence > Rate of eustatic fall • Creation of a new space added • Area of relative sea level rise
Landward of : • Rate of subsidence < Rate of eustatic fall • No creation of new space added • Area of relative sea level fall
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Fundamentals of sequence stratigraphy
Introduction to sequence stratigraphy • • • • • •
General introduction Accommodation definition Relative sea level and space available Dynamic points Sequence development Parasequence/genetic sequence © 2013 ‐ IFP Training
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Specific dynamic points
Inflection points of the eustatic curve • Point F: maximum rate of sea level fall
F
R
− Minimum rate of creation of new space added
• Point R: maximum rate of sea level rise − Maximum rate of creation of new space added
Depositional dynamic on the shelf at these specific inflection points of the eustatic curve • Point F: minimum deposit of sediment − Maximum erosional phenomenon
Point R
• Point R: transgression and development of
Point F
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− a condensed section − Maximum drowning of the basin over the shelf − Location of the maximum flooding surface: MFS
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Theorical sequence: the Exxon “slug”
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Fundamentals of sequence stratigraphy
Introduction to sequence stratigraphy • • • • • •
General introduction Accommodation definition Relative sea level and space available Dynamic points Sequence development Parasequence/genetic sequence © 2013 ‐ IFP Training
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Sequence stratigraphy 1
3
2
4
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Sequence stratigraphy 5
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Key surfaces in sequence stratigraphy
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Sedimentation rate and sea variations
Sequence are subdivided by • Maximum Flooding Surfaces (MFS) • Transgressive Surfaces (TS) • Sequence Boundaries (SB)
Arrangement of vertical succession or stacking patterns of unconfined sheets • Prograde (step seaward) • Retrograde (step landward) • Aggrade (build vertically)
Sheets and unconfined lobes containing • Non‐amalgamated bodies
Incised topographic fill
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• Amalgamated, multi‐storied bodies (e.g. incised valleys) • Within unconfined lobes
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Theorical sequence: “Exxon Slug”
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Systems tract synthesis
Sequence stratigraphy is based on the application of the systematic subdivision of the section by well defined surfaces
These surfaces are used to provide a frame work to the interpretation of the depositional settings of the sedimentary section
This interpretation is then is used to predict the extent and character of the component sedimentary facies
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Lowstand‐fan systems tract
Lowstand fans are deposited during rapid eustatic falls which exceed the rate of subsidence at the shelf edge
Sediment bypasses the shelf and is deposited directly on the slope and in the basin in the form of point‐sourced submarine fans. This figure illustrates geologic, geographic, and eustatic conditions conducive to the formation of these deposits
The systems tract is bounded below and above by discontinuities
Internally, lowstand fans are characterized by mounded facies and may be extensively sand prone. These mounds are commonly excellent reservoirs
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Lowstand‐wedge systems tract
The lowstand‐wedge systems tract begins to form during the latter part of a rapid eustatic fall as lowstand‐fan deposition ends. Deposition is initiated when the rate of eustatic fall is again equal to subsidence at the shelf edge
This interval is characterized by resumption of a slow rise of relative sea level at the shelf edge
Deltaic deposition is localized in the upper parts of canyons or embayments cut into the shelf during rapid eustatic falls
The base of this systems tract is an unconformity. The top grades either into a transgressive depositional sequence or is a condensed section, if transgressive deposits are absent or not observed.
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Transgressive systems tract
When the rate of new shelf space added exceeds the rate of sediment supply, transgression occurs. The timing of this event depends on sediment supply and rate of eustatic rise, but it will usually occur on the rising limb of the eustatic curve when the rate of addition of new shelf space increases rapidly prior to the eustatic rise inflection point
During transgression, only pelagic or hemipelagic deposition occurs on the starved shelf and basin, generating a starved or condensed section there
Of all the systems tract types, the transgressive systems tract is the most sensitive to variations of sediment supply, and its occurrence is therefore the most difficult to predict
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Highstand systems tract
The highstand systems tract is deposited during the eustatic highstand, defined as the interval between the eustatic rise and fall inflection points. This interval is characterized by a slowly decreasing relative rise of sea level as the rate of eustatic change gradually decreases
An unconformity defines the upper surface, and a condensed section marks the lower limits of this systems tract
Reservoir facies are associated primarily with prograding beach and aggrading fluvial depositional systems. Organic‐rich facies with source potential may develop on the toes and delta plains of progradational units
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Shelf‐margin systems tract
The shelf‐margin systems tract is a regressive stratigraphic unit overlying a highstand deposit and is usually deposited following the inflection point on a gentle eustatic fall
This interval is characterized by a progressive increase in the rate of relative rise of sea level. The shelf margin systems tract is deposited on the outer part of the shelf and is marked by an abrupt basinward shift of coastal onlap at its base
The base of this systems tract is an erosional unconformity or its correlative conformity, whereas the top either grades into a transgressive systems tract or is a condensed section. The basal unconformity on the shelf is usually marked by paralic/deltaic sediments overlying fluvial deposits
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Fundamentals of sequence stratigraphy
Introduction to sequence stratigraphy • • • • • •
General introduction Accommodation definition Relative sea level and space available Dynamic points Sequence development Parasequence/genetic sequence © 2013 ‐ IFP Training
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How to order the sedimentary pile?
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"Facies adjacent to one another in a continuous vertical sequence also accumulated adjacent to one another laterally"
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Sedimentation rate and sea variations
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Introduction to sedimentary sequences Depositional sequence in respect to Walther's law
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Parasequence: depositional processes in system tracts Progradagradation (Advancing) Retrogradation (Backstepping)
• Elementary deposition sequence (building block) • Thickness : few meters to few tens of meters • Bounded by isochrons (2 successives times surfaces)
Elementary cycles of variations accomodation Influenced by allocyclic parameters (external parameter of the basin)
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Parasequence or Genetic units :
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The genetic sequence
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The genetic sequences are short term depositional sequences (1 Ma) regrouping orders of cyclicity lower than the 4th order
They are limited by two maximum flooding surfaces or by two condensed intervals, and there thicknesses vary from a few decimeters to few meters
They record a cycle of variation of the depositional environment, interpreted as transgression and regression
The genetic sequences are deducted from essentially sedimentological but none geometric observations. They are recognized by drilling or on outcrops
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P. Homewood, P. Mauriaud, F. Lafont 2001
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The genetic sequence
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P. Homewood, P. Mauriaud, F. Lafont 2001 281
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The genetic sequence
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Definition and example
Chronostratigraphy is the branch of stratigraphy that studies the absolute age of rock strata
Chronostratigraphy is based upon deriving geochronological data for rock units, both directly and by inference
Objectives of chronostratigraphy: • Determine the ages of strata • Demonstrate the geographic extend of strata • Confirm the sequence stratigraphy interpretations © 2013 ‐ IFP Training
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Definition and example
Combination between paleontology and stratigraphy. In oil and gas industry, biostratigraphy corresponds to the study from rock samples (core and cuttings) of microfossils (pollens, spores, nannofossils, diatoms and foraminifera)
The objectives of biostratigraphy are to: • Determine the age (relative or absolute) of strata • Study the paleo‐environment during deposition and its evolution • Make correlations between layers containing the same fossil population © 2013 ‐ IFP Training
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THANK YOU FOR YOUR ATTENTION,
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Reservoir Characterization & Modeling
Semaine 3 Stratigraphy – Sedimentology
Une formation IFP Training pour Sonatrach / IAP
Une formation IFP Training pour Sonatrach / IAP
Stratigraphy/Sedimentology on Clastic reservoirs Laurence BOVE
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Summary Table of content
Basin analysis
Slides 9
Clastic depositional environments and facies
Log responses in clastic sequences
Slides 165
Clastic petrography and diagenesis
Slides 193
Fundamentals of sequence stratigraphy
Slides 249
Slides 49
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Exploration‐Production: stakes and challenges 1. Where are hydrocarbons?
In reservoirs (naturals or fractured) How did they reach reservoirs? Where are they coming from? (HC generation) Why are they trapped in this place? Sedimentary basin analysis
2. How to produce them?
Geological reservoir modeling Quantification of reservoir characteristics Heterogeneities prediction Reservoir model Productivity prediction Appraisal well
Exploration Strategy
Strategy for field development design
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Elaboration of « exploration guides »: Plays Identification of « Prospects » Uncertainties & risks evaluation Exploration well: OOIP calculation
3
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Basin exploration workflow: step 1 Petroleum trilogy Source rock / Reservoir / Seal extension Risk and uncertainties → Deliverables • HC index maps for each reservoir • Petroleum system mapping → Hypotheses • Events chart • Potential SR and RR maturity (kitchen) • Migration episodes and pathways • Entrapment and timing
4 Petroleum system analysis
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Basin analysis 3 Geochemical analysis
Stratigraphic analysis Relationship between tectonic and sedimentation Exploration tools (cores, logs, well correlation) Biostratigraphy Sequence stratigraphy Risk and uncertainties → Deliverables • Basin time calibration • Chronostratigraphic chart (Wheeler) • Stratigraphic basin reconstruction
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Organic indicators (VR, biomarkers, X‐fluo) Thermochronology (fission tracks, mineralogy) Rock‐Eval (TOC, HI…) Risk and uncertainties → Deliverables • Organic matter origin (Kerogene type) • Maturation curve
1 Structural analysis
Exploration tools (seismic) Geodynamics Risk and uncertainties → Deliverables • Basin geometry calibration • Structural basin reconstruction
4
Exploration techniques & tools
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Basin exploration workflow: step 2
Basin modeling Sequence stratigraphy framework
• Subsidence mechanisms (back‐ stripping) • Temperature evolution (maturation) • Pressure evolution (compaction) • HC accumulation • Risk and uncertainties
Deliverables • Basin thermal calibration • Kitchen extension maps • Generation timing • Φ vs. Depth evolution
Deliverables • Maps
Play concept & definition
• Play definition and mapping (traps) • Prospect definition and evaluation • Migration pathways for each play • Risk and uncertainties
- Play & prospect extension - Field shows distribution
• Volumetrics (OOIP) • Prospect ranking • Yet‐to‐find (explored area) • Economic
Basin evaluation & Play assessment strategy © 2013 ‐ IFP Training
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Clastic reservoirs Basin analysis
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Basin analysis
Structural and thermal evolution during burial • • • • •
Earth structure Extensive context Compressive context Transform context Thermal evolution
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Map of sedimentary basins Onshore and Offshore basins
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Basin analysis
Structural and thermal evolution during burial • • • • •
Earth structure Extensive context Compressive context Transform context Thermal evolution
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Structure of the Earth
Crust • Lithosphere (10 to 70 km) Granitic crust
Basaltic crust
Mantle
Crust
• Upper mantle: Asthenosphere (700km) • Lower mantle: Mesosphere (2 200 km)
Core • Outer core (2 200km) • Inner core (1 271 km)
< passive margin >
(LITHOSPHERE)
Mid Oceanic Ridge Atlantic Ocean
Upper mantle (ASTHENOSPHERE)
Lower mantle (MESOSPHERE)
Subduction > active margin <
Rift
Outer core
SiAl
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NiFe
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Inner core
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Dynamics of the Earth: convection
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Core
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Earthquake activity
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Lithospheric plate boundaries = seismicity (in red) Sonatrach / IAP
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Tectonic plates
Mid oceanic ridge
Earth‐ quakes Volcanoes
Lithospheric plate boundaries: • Divergent (extensional: mid oceanic ridges) • Convergent (compressional: subduction, collision) • Sliding/Shearing (transform, strike‐slip)
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Types of margins and related basins
3 types of crustal stresses • Extensional basins • Compressional basins • Shear basins
3 types of processes • Purely thermal • Lithospheric thickness variation • Loading and unloading
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Types of sedimentary basins
Basins associated with plate divergence Extensional basins • Rift, passive margin (plate divergence, ocean) • Intra‐cratonic basin (intra‐continental, intra‐plate)
Basins associated with plate convergence Compressional basins • Island arc‐type margin (two oceanic plates) • Continental active margin (ocean / continent plates) • Inter‐plate collision (two continental plates)
Basins associated with shearing (sliding movement) Trans‐tensional basins • Pull‐apart basin (trans‐tension, local distension in convergence) © 2013 ‐ IFP Training
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Basin analysis
Structural and thermal evolution during burial • • • • •
Earth structure Extensive context Compressive context Transform context Thermal evolution
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Rift basin
Rift are areas of crustal extension and thinned continental crust. Regions of rifting are characterized by lithospheric stretching, high heat flow and volcanic activity caused by a thermal anomaly at depth
Rift zones general characteristics: • Heat flow of 90 to 110mW.m‐2 • High levels of earthquake activity and a dome‐shaped Moho • Normal faults network
Current examples in the Red Sea and in Ethiopia
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Failed rift basin
Beginning of rifting mechanisms and stop of lithospheric stretching caused by a reducing and cooling of the thermal anomaly
Rift zones general characteristics: • Heat flow of 80 to 90mW.m‐2 • A reducing of seismic and volcanic activity • A normal faults network covered a disconformity
Failed rift basin
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Examples in the North Sea and in Rhine‐Bresse (France)
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Intra‐cratonic basin
Intra‐cratonic basins are large depressions in continental crust. They have a slow and homogeneous sedimentary filling
Generally, intra‐cratonic basins: • Have a heat flow near‐normal (60 to 80mW.m‐2) • Are seismically inactive • Have sediment overlain on faults and syn‐rift sediments
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Examples in Paris basin and Middle‐East
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Passive margin basin
Beginning of rifting mechanisms and stop of lithospheric stretching caused by a reducing and cooling of the thermal anomaly
Generally, passive margin zones: • Have a heat flow near‐normal (60 to 80mW.m‐2) • Are seismically inactive • Have sediment overlain on faults and syn‐rift sediments
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Examples in West Africa and East South America
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Basin analysis
Structural and thermal evolution during burial • • • • •
Earth structure Extensive context Compressive context Transform context Thermal evolution
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Foreland basin Foreland basin
Foreland basins are the result of the downward flexing of the lithosphere in response to the weight of the adjacent mountain belt, though many geological and geodynamic processes combine to control their subsequent evolution
Generally, foreland basins: • Have a heat flow near‐normal (60 to 80mW.m‐2) • Are seismically active
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Examples in Alps, Himalayan and Appalachian chains
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Forearc basin
This basin is located between the volcanic arc and the subduction complex
Generally, fore‐arc basins: • Are highly seismic active
Example in Andes, Java and Sumatra islands
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Oceanic trench basin
Oceanic trenches are the deeper part of the ocean floor where lithosphere is in subduction under another
The age of the oceanic lithosphere controls the trench depth
Generally, oceanic trench: • Have a highly seismic activity • Have an associated accretionary prism
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Examples in western South America and eastern Japan
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Basin analysis
Structural and thermal evolution during burial • • • • •
Earth structure Extensive context Compressive context Transform context Thermal evolution
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Strike‐slip basin
Trans‐pression
Strike‐slip basins are due to transform fault movements
If the blocks move away from their initial position, it is a transtensional movement so there are normal faults associated to the flower structure
Symmetrically, transpressional movement induces reverse faults
Trans‐tension
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Basin analysis
Structural and thermal evolution during burial • • • • •
Earth structure Extensive context Compressive context Transform context Thermal evolution
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Origin of hydrocarbons
Transformation of Organic Matter (O.M.) from dead fauna or flora
Accumulation & preservation of O.M. • Accumulation in quiet geological environments (lake, delta, sea) • Preservation depends on sediment type & rate, environment energy
Modification of depositional conditions • Burial, compaction, water expulsion • Temperature & pressure increase
Transformation of Kerogen into hydrocarbons • Oil • Gas (methane)
Maturation: chemical transformation, mainly due to temperature (and pressure) increase during burial Sonatrach / IAP
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Kerogen: non soluble part of O.M. (i.e. lipids)
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Origin of Organic Matter
Lipids
Cellulose
Lignine
Type III
Type II
Bacteria
Wood
Algae
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Plankton
Type I
Animals = maximum 10% of total generated organic biomass 35
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Transformation of O.M. & Kerogen
Diagenesis [< 60°C] Bacterial degradation Immature stage
Catagenesis [from 60 to 120°C] Thermal degradation → Weak chemical bonds breaking
Oil window
Metagenesis [from 120 to 200°C] Thermal degradation → Strong C–C bonds breaking (cracking)
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Gas window
36
Van Krevelen diagram
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Generation & Migration of HC
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Hydrocarbon migration Types of migration: The word “migration” covers all types of displacements of hydrocarbons, from the source rock where they generated to the reservoir rock where they accumulate
Primary migration • Expulsion of hydrocarbons from source rocks towards adjacent rocks. This migration takes place over very short distances (few centimetres). It depends on the internal overpressure conditions, linked to the volume of HC generated
Secondary migration • Displacement of hydrocarbons after expulsion from the source‐rock, over distances ranging from few meters to several hundred kilometres, until they are trapped • This migration takes place inside permeable conditions (reservoir rocks, open fractures open unconformities…). Migration pathways are complex and specific to each basin, they are mainly driven by pressure decrease. Migration can be lateral and/or vertical
Dysmigration • Hydrocarbon displacement from a “leaking” reservoir to the surface (i.e. seepage)
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Origin of hydrocarbons: summary
Three origins of OM > three different types of Kerogen • Type I: lacustrine (lake algae, bacteria,…) • Type II: marine (zoo‐ & phyto‐plankton, micro‐organisms,…) • Type III: continental (terrestrial vegetation, forests, bacteria…)
Three steps of OM transformation within source rocks • Diagenesis (burial, lithification) • Catagenesis (Kerogen transformation) → ~60°C… • Metagenesis (cooking, cracking) → ~120°C…
Three factors for OM maturation
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• Temperature (sediments cooking, anoxic conditions, bacterial activity) • Pressure (sediment compaction, water expulsion) • Time (molecular evolution, new atomic combinations – compensates for low T°)
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Key Points : The petroleum trilogy Source rock Definition
Reservoir rock
Sedimentary rocks rich in • Porous and permeable rocks OM, mature enough to • Allow displacement and generate hydrocarbons hydrocarbon accumulation
• Non‐permeable rocks (prevent hydrocarbons from migration) • Plastic rocks (can be deformed but not fractured)
• Shales or salt rocks (plastic Clastic rocks (e.g. sandstone) rocks) Carbonate rocks (e.g. • Very compact sandstones or limestones (without limestone) porosity, “tight”) Petrophysical parameters: • Porosity: Φ • Permeability: K • Saturation: S
Lateral extension and layer continuity are more important than thickness
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• Very fine‐grained rocks (shales, mudstones, marls,…) with interbedded • laminations Lithology • (sediment/OM) • Low permeability (internal over‐pressure > under‐ compaction) • OM production, deposition, preservation Specificity & maturation (process, parameters,…) • HC generation, expulsion & migration
Seal rock / Cap rock
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Timing between elements & processes The trap must be available before/during migration
Trap 2. Processes:
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Source rock
Migration
Migration pathways
Accumulation and Preservation
Reservoir and Seal
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1. Elements:
Generation
42
Pretroleum system events chart
400
300
200
Paleozoic
D
M
P
100
Mesozoic
P
TR
J
Geologic Time Scale Cenozoic
K
P
Petroleum System Events
N Rock Units
Reservoir Rock Seal Rock
Elements
Source Rock
Trap Formation Gen/Migration/Accum
Processes
Overburden Rock
Preservation
Magoon and Dow, 1994
Time of expulsion and migration. (Trap must already exist) Sonatrach / IAP
Critical Moment
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Critical Moment
43
Cross‐section of a petroleum system
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Map of a petroleum system
Migration pathway
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Petroleum system: Critical steps
Entrapment Accumulation Entrapment Preservation
Gas Cap Oil Water
Seal Rock Reservoir Rock
Migration 120° F
Generation
Source Rock
(60°C)
350° F
(120°C) 2480
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Expulsion
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Petroleum systems: key points Key points to keep in mind Conditions for the formation of a hydrocarbon field Necessary existence of:
one (or more) mature source rock, one (or more) reservoir rock, one seal rock,
a phase of migration (and pathways),
one (or several) traps, …and:
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• an adequate timing between trap formation, hydrocarbon generation and migration • sufficient quantities of generated hydrocarbons to feed the trap • preservation of trap integrity throughout geologic times
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Une formation IFP Training pour Sonatrach / IAP
Clastic reservoirs Clastic depositional environments and facies
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Clastic depositional environments and facies
Fluid flows and related sedimentary processes • Reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments) • Sedimentary fill hierarchy • Depositional environments
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− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
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Definition of siliciclastic rocks
Siliciclastics are detrital sediments that result from the accumulation of debris from erosion or alteration of existing rocks
The main mineral components are quartz, feldspars, micas and clays
Clastics are classified according to their grain size and shape: • • • •
Conglomerates / Breccias Sandstones Siltstones Shales / Claystones / Clastic muds (Sandy & shaly sediments family) © 2013 ‐ IFP Training
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Textural classification
Example of shale structure (Scanning Eletron Microscope) and composition Claystones
[Shales]
The classification of clastic sedimentary rocks is complex because several variables are involved. Particle size (both average size and range of particles’ sizes), particles composition, cement and matrix must all be taken into consideration
Shales (which consist mostly of clay minerals) are generally further classified on the basis of composition and bedding
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Formation of clastic rocks
Weathering and erosion (of outcropping rocks ) • Chemical weathering (alteration) Agent: rain (+ dissolved CO2) − Solutions − Grains • Mechanical weathering (erosion) Agents: gravity, freeze/thaw, running water, wind, glaciers
Transport (of debris + solutions and colloidal particles) • Agents: − Continental: water (torrents, streams & rivers), wind, ice (glaciers) − Oceanic: currents, waves, tides, gravity flow deposits
Deposition © 2013 ‐ IFP Training
• Progressive decrease of current speed leads to deposition of transported load, with resulting sorting according to grain weight (and size)
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Bedforms characteristics
Bedform generation • Result of interaction of moving fluid on surface sediment • Undulation on non cohesive surface • Downstream migration
Bedform boundaries • Upper bedding surface: constructional structures − Unidirectional current − Oscillatory current • Lower bedding surface: erosional structures (sole marks) − Current marks: produced by erosion du to the current flow » Flute marks » Crescent marks
− Tool marks: objects removed by the current along the surface • Internal bedding − Horizontal stratification − Inclined stratification Sonatrach / IAP
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» Groove, Bounce, Brush
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Clastic depositional environments and facies
Fluid flows and related sedimentary processes • Reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments) • Sedimentary fill hierarchy • Depositional environments © 2013 ‐ IFP Training
− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
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Sediment transport
Tractive sediment transport (bedload) • Particles roll or skip on sediment surface with a low level of suspension • Motion: rolling carpets or turbid clouds • Decreasing of velocity → downstream load deposition Geometry of deposition: oblique laminae
Suspended sediment transport (suspension) • Particles in suspension (partial, continuous or intermittent) in the water depth • Motion: ascending movement due to turbulence • Decrease of turbulence → vertical decantation
Agents: Water, wind, ice…
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Geometry of deposition: horizontal laminae
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Clastic depositional processes Cohesive
Non ‐cohesive
Transport in suspension
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Hjulstrom’s diagram Evolution of erosion vs deposition with stream (or current) speed and particle size
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Primary sedimentary structures
Formed under influence of same hydrodynamic and/or aerodynamic conditions as entrainment, transport and deposition of sediment particles
We must answer and resolve the following questions: • Which way is up? • Orientation of process that dispersed sediment? • What process was responsible for transportation and deposition of sediment?
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Bedforms vs flow regime Oscillatory flow: waves • Circular motion of particle at water surface • Flat orbits at bottom back and forth motion of particles • Geometry of deposit: wavy ripples, plane beds
Unidirectional flow: rivers, wind • Unidirectional downstream motion of particles • Deposition depends on grain size vs. flow velocity • Geometry of deposit: irregular ripples, plane beds
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Bedforms in unidirectional flow
Three main factors controlling bedforms in unidirectional currents: • Average flow velocity • Grain size • Water depth
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Constructional bedforms
Bedforms shape vs flow velocity
Intermittent transport
Permanent transport © 2013 ‐ IFP Training
Erosional bedforms
Lower Flow regime Upper flow regime
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Bedforms in oscillatory flow
Bedforms produced by wave action
Oscillatory flow • Flattening of wave orbits • Back and forth motion creating « lateral » motion along the sea bottom
General characteristics
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• Symmetrical shape − Waves ripples − Hummocks (Swales) − Subplane beds • Peak or round crests • Straight crests, with bifurcation
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Bedforms in oscillatory flow
Waves ripples • Develop in velocity of waves between 9 to 90 cm/s • Height: up to 20 cm • Length: up to 1 m
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Bedforms in oscillatory flow
Hummocky/swaley cross‐stratification (HCS) • Broad undulations, gently dipping − Hummocks / Swales
• • • •
In fine‐grained sandstone, subparallel laminae (lower surface) Wave length: 1 to 5 m Average set thickness: ~25 cm Storm deposits: below fairweather wave base
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Erosional flow features
Sole marks Erosional sedimentary structures on sediment surface (preserved by burial) • Scour marks erosional turbulence • Tool marks object imprints
Visible as negative moulds on layers base (way‐up criteria)
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Processes velocities
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Sediment maturity Key points to keep in mind
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Clastic depositional environments and facies
Fluid flows and related sedimentary processes • Reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments) • Sedimentary fill hierarchy • Depositional environments © 2013 ‐ IFP Training
− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
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Workshop: oscillatory bedforms
Identify depositional environment
Name bedforms
Range dimensions (λ, H, L)
Indicate flow direction
Sketch dynamic process
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Typical Y‐shaped symmetrical ripples
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Workshop: constructional bedforms
Identify depositional environment
Name bedforms
Range dimensions (λ, H, L)
Indicate flow direction
Sketch dynamic process
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Workshop: beach facies analogues
Identify depositional environment
Name bedforms
Range dimensions (λ, H, L)
Indicate flow direction
Sketch dynamic process
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Workshop: erosional bedforms Flute marks
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Load structures Sonatrach / IAP
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Workshop: erosional bedforms
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Workshop: erosional bedforms
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Workshop: erosional bedforms Crescent
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Workshop: Bioturbation / Way‐up criterium
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Workshop: beach facies analogues
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Workshop: beach facies analogues
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Workshop: beach facies analogues
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Clastic depositional environments and facies
Fluid flows and related sedimentary processes • General reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments • Sedimentary fill hierarchy • Depositional environments © 2013 ‐ IFP Training
− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
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Sedimentary fill hierarchy
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Jeroen Schokker, Wim Westerhoff & Henk Weerts after Heinz & Aigner, 2003 Sonatrach / IAP
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How to order the sedimentary pile?
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"Facies adjacent to one another in a continuous vertical sequence also accumulated adjacent to one another laterally"
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How to order the sedimentary pile? Introduction to sedimentary sequences Depositional sequence in respect to Walther's law
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Clastic depositional environments and facies
Fluid flows and related sedimentary processes • General reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments • Sedimentary fill hierarchy • Depositional environments © 2013 ‐ IFP Training
− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
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Sedimentary depositional environments Continental environments
Marine environments
Glacial Aeolian Lacustrine Fluvial
• Fluvial‐dominated • Wave‐dominated • Tide‐dominated
• Braided • Meandering • Anastomosed
Continental shelf • Siliciclastic • Carbonatic
Coastal plain
Slope, canyon Basin • Turbiditic fan • Abyssal plain
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Sea level
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Shoreline (coast/beach) Delta
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Transfer mechanisms in siliciclastic environments
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Alluvial fan systems
Fan‐shaped body • Cone that radiates downslope • Stream channels emerge from valleys • Rather coarse detrital sediments • Poorly sorted
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Built up by mountain stream • At relief's foot • Change of slope gradient • Dip of alluvial fan: <10° (3 to 6°) • Length: from few 100 m to 100 km
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Typical alluvial fan sequence
Sedimentation • Beds more or less parallel to the surface • Stratification is moderately developed
Deposition mode • Debris flow or mud flow dominated • Extensive masses of mud‐supported coarse‐grained sediment, moving downward • Main channel: in upper fan and mid fan
Massive conglomerates
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Coarsening‐up sequence
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Alluvial fans
Alluvial fans are cone‐shaped piles of sediment formed at the foot of highlands where streams confined by narrow valleys emerge into adjacent lowland. A series of overlapping alluvial fans generates a clastic wedge
There are some differences between alluvial fans in arid and humid climates. Sedimentation on alluvial fans begins where the streams leave their confined valleys and loose some of their transport efficiency
Alluvial fans are composed of two types of sediment: • Stream deposits • Sediment gravity‐flows Current‐transported sediments usually predominate. They are deposited either from ephemeral or perennial water flow in the channel system or, after extreme rain storms, from sheet‐floods inundating large parts of the alluvial fan
Sometimes, gravel is concentrated locally to form sieve deposits (coarse gravel and boulders devoid of finer‐grained matrix). From time to time, large debris flows with a muddy‐sandy matrix reach the proximal and mid‐fan area and bury part of the pre‐ existing, radiating channel system
At their lower end, such debris flows terminate in characteristic lobes, and they often concentrate large boulders and gravel at their outer margin, forming levees. Later, new channels cut into the mass flow deposits and rework and redistribute great proportions of their material
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Fan deltas Coastal alluvial fans prograding into a lake or into the sea form fan deltas. As soon as the streams, carrying a high bed‐load, reach the standing water body, they drop their coarse material at the shore face and in prodelta foresets
The intensity of reworking, sorting, and redeposition, as well as the transport of material along the shoreline, depend on the wave energy and, in marine environments, on the tidal range
In the case of lakes and protected embayments, fan progradation is little influenced by these processes. Gravel and sand accumulate at the mouths of streams until they become unstable from time to time and move as subaqueous debris flows into deeper water. There, they alternate with muddy lake or marine deposits
On high‐energy coasts, some of the coarse material dropped at the river mouth is transported alongshore adjacent beaches where it forms distinctive beach gravel; some sand and gravel is swept by storms into deeper water
Fluctuations in the water level in lakes or the sea affect both the subaerial and subaqueous facies of fan deltas. They are reflected by fluvial terraces and coarse grained river mouth deposits at varying elevations. A lowering of the lake or sea level causes the emergence of delta foresets and the subsequent cutting of fluvial channels into the foresets. These channels are commonly filled later with fluvial deposits
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Exercise: identify environment and name feature
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Fluvial depositional systems Main characteristics
• Unidirectional flow regime • Transport until flow exists, with decreasing grain size of carried particles • Three types of sediment bedload: − Bedload − Suspended load − Mixed load • Sediments start to deposit when river loses energy or/and is progressively abandoned (progressive decantation) • Typical depositional sequence: basal erosional surface and fining‐upward sequence
Three main types of river (fluvial) systems (according to braided parameters and sinuosity index):
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• Braided system • Meandering system • Anastomosed system
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Fluvial depositional settings
Channel pattern is the combination of • Bedload vs suspended load • Bank stability • Slope gradient • Flow fluctuations
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Transfer mechanisms in siliciclastic environments
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Braided river systems
Braided rivers are characterized by high‐sediment load and high velocity
Typical succession of lenticular sorted conglomerates and coarse sandstones
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Typical braided river sequence Braided rivers and its bars
Several erosional channels
Stacked fining‐up sequences
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Basal lag deposit
Basal erosional surface 97
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Examples of basal conglomerates (lag deposit)
Erosion in the flood plain Sonatrach / IAP
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Erosional baseline
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Log responses – Outcrop analogue
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Typical braided river architecture
Gravel‐rich braided system • Longitudinal bars • Conglomerates dominant
Sand‐rich braided system • Transverse bars • Sandstones dominant
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Braided river systems
Braided streams usually consist of several individual channels separated by bars and islands and therefore form a wide, shallow stream bed. Braided rivers develop near areas of high relief, which deliver relatively large amounts of debris, gravel and sand into the fluvial system
From all these characteristics, it can be inferred that braided systems are bed load‐ dominated, they carry and deposit chiefly gravel and sands. Therefore, they consist predominantly of channel and channel‐flank deposits, while silty and muddy floodplain facies are subordinate
Downstream, they often display a progressive decrease in grain size, as well as in bed forms and internal sedimentary structures
The interstices in the gravel are usually later filled with sand during low water periods, but in this system sandy beds are relatively rare in the proximal zone, unless there is little gravel available in the source area. Sandy beds develop best at somewhat higher topography elevations within the braided system next to the active channel system
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Braided river systems Many bars are somewhat graded. Interbedded with the gravels are thin lenses of sand representing deposition in abandoned channels or sand wedges at the edge of bars
In places, one can observe repeated successions of fining‐upward gravel‐sand sequences 1 to 2 m thick, but in general it is difficult to identify the bottoms of former channels and the geometry of their fill. The reason is that the underlying and neighboring sediments also consist largely of gravel
Downstream, the predominantly gravelly beds grade into beds consisting partly of smaller pebbles and sand. In the lower, more active channels, bar gravels dominate, whereas sands and pebbly sands are common at higher topography elevations. In rarely flooded areas, some silt and mud may be deposited and preserved
In the total assemblage, the gravel content varies between 10 and 70 %. As a result of downstream and laterally migrating sand and gravel bars, planar and trough cross‐bedding are the most important internal sedimentary structures
Both the lateral migration and sudden abandonment of channels due to avulsion cause fining‐upward channel fill sequences a few meters thick. Such sequences are considered the most distinctive characteristic feature of this type of braided river deposit
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Braided river architecture: reservoir potential
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High Net‐to‐Gross Immature sediments; early alteration Require top‐seal/structural traps
Sheet‐like geometry Thin shaly interval at the top
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Transfer mechanisms in siliciclastic environments
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Typical meandering river sequence
Crevasse splay Point Bar
Coal Fine grained sandstone Organic shale, roots medium coarse to grained sandstone
Fining‐up sequence : point bar Sonatrach / IAP
Meandering river
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Erosion
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Generation of meanders
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Meandring river architecture: reservoir potential
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Lower Net‐to‐Gross Sediment more mature Stratigraphic trap potential
Shoe‐lace geometry becoming sheet like Shales frequent in sequence
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Meandering river systems
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Meandering river systems
Meandering river systems develop one principal, relatively narrow channel of high sinuosity (> 1.5) and are dominated by mixed load or predominantly suspended load. Their overall sand content often averages 20 to 40 %. If meandering rivers are associated with a wide floodplain, the channel sediments may be restricted to a comparatively narrow zone within the flood basin where they form a meander belt
In a sinuous channel segment, one can distinguish the following morphological features and depositional sub‐environments: − − − − − −
Channels and channel fills Point bars and lateral accretion complexes Chute bars Channel plugs (oxbow lakes) Levee and crevasse splay deposits Alluvial floodplain deposits
• Point bars accumulate on the inner sides of river bends, while on the outer side material from the bank is eroded. In this way, the curvature of the meander tends to become increasingly exaggerated until the river produces short‐cuts, leaving behind abandoned channel segments (oxbow lakes)
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• The channel floor is usually covered by lag sediments consisting of the coarsest material transported by the river during peak flood. This channel lag may also contain mud clasts or blocks eroded from the banks. Lag sands and gravel usually accumulate between scour pools and form flat, elongate bars displaying either imbrication of gravel or crudely laminated and planar cross‐bedded gravelly sand
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Meandering river systems Most of the point bar material is eroded from the upstream channel banks. It is deposited in areas of lower velocity turbulence. Because sediment moves up and out of the channel onto the bar, cross sections of point bars often show fining‐upward sequences, with sands on top of channel lags
Similarly, the internal structures grade from horizontal bedding (upper flow regime) to large‐scale and small scale trough cross‐bedding (lower flow regime). The most distinctive feature of point bars is lateral accretion)
Many meandering channels are accompanied by flat ridges sloping away from the channel into the floodplain. These levees are built up during moderate floods which just reach the elevation of the channel ridge. Due to decreasing flow velocity, sand is deposited along the channel ridges, grading into silt somewhat farther away
Locally, channel water may spill over the levees into the floodplain, forming crevasse splays. The fallout of sand and silt usually extends farther into the floodplains than the levees, but such crevasse splays can also contribute to the buildup of the levees
The prevailing internal structures of these sand sheets may resemble those of thin sandy turbidites, showing some grading, horizontal lamination and small‐scale ripple cross‐ bedding. These structures are, however, often mashed or destroyed by the roots of vegetation. Whereas distal crevasse splays become interbedded with floodplain deposits, levee sands of ten tend to be reworked by subsequent channel migration
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Crevasse splay deposits
Deposits formed during flood period, by break into the channel levees
Cones composed of sand to silty facies
Formed by stacked fining upward thin sequences with small secondary channels at top during peak of flood
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Channel levees deposits
Mississipi
Levees deposits, adjacent to the channel and formed during the flooding period, are:
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• Wedge deposits of alternating fine sand /silts and mud • Showing parallel to small current ripple laminations
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Transfer mechanisms in siliciclastic environments
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Anastomosing river systems
Develop in • Upstream area or downstream areas • Low sinuosity (less than braided) • Several wandering channels
Particularities of each channel • Stable banks (not ephemeral) • Fixed by vegetation
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Anastomosing river architecture: reservoir potential
Lower Net‐to‐Gross Sediment more mature
vertical stacked and confined sand bodies encased in mud
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Fluvial architecture and reservoir potential Key points to keep in mind
River systems • Main reservoirs located in channels and channels belts • Associated reservoirs located in − Levees deposits − Crevasse splays − Floodplains sandstones
Braided system: reservoir bodies • Vertical and lateral stacking, good connection • Geometry: Sheetlike or tabular sandbodies (stacked multistorey infill)
Meandering system: reservoir bodies • Dominant lateral accretion (point bar – levees – crevasse splays) • Geometry: “point bar – clay plug” model, isolated sandbodies
Anastomosing system: reservoir bodies • Dominant vertical aggradation, isolated narrow channels • Geometry: channel fill
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Depositional environment vs reservoir distribution
ELF 1997
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Variation of reservoir quality with depositional environment and energy (slope)
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River types vs reservoir distribution
Slims
Williams
Windorah
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River facies: reservoir potential Fluvial architecture vs reservoir potential Braided Meandering Anastomosed
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Courtesy of Pr. M. Lopez (U. of Montpellier)
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Clastic depositional environments and facies
Fluid flows and related sedimentary processes • General reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments • Sedimentary fill hierarchy • Depositional environments © 2013 ‐ IFP Training
− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
121
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Coastal deposits
Coastal environment: river outlet, delta • Continuous quantity of sediments provided by the river • Deposition driven by energy loss (decreasing flow rate, decantation) − From coarse‐grained sand (close to coast and beach) to fine‐grained sand and shales (towards platform and basin) − Continental environment taking over marine environment with time
• Variable distribution of river sediments according to local dominant energy factor (river flow, tidal currents, wave action)
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Clastic depositional environments
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Delta shapes & energy
Morphological classification of deltas based on delta front shape which reflects: • Relation between the relative importance of rive, tide or wave processes • Sediment supply • Duration in time
Birdfoot
Lobate
Fluvial dominated
Cuspate
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Tide dominated Estuarian
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Wave dominated
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Delta classifications
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Delta morphology reflects the relative importance of fluvial, tidal, and wave processes, as well as gradient and sediment supply • River‐dominated deltas occur in microtidal settings with limited wave energy, where delta‐lobe progradation is significant and redistribution of mouth bars is limited • Wave‐dominated deltas are characterized by mouth bars reworked into shore‐ parallel sand bodies and beaches • Tide‐dominated deltas exhibit tidal mudflats and mouth bars that are reworked into elongate sand bodies perpendicular to the shoreline
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Deltaic environments
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Key points: Fluvial‐dominated deltas
Fluvial‐dominated deltas are primarily controlled by the water density difference between the inflowing river water and the standing water on the basin. Delta – lobe progradation is significant while mouth bar distribution remains limited
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Fluvial‐dominated deltas
Different flow types that determine the distribution of sediment and sedimentary structures formed in the delta are hyperpycnal flow and hypopycnal flow • Hyperpycnal flow produced when the density of the river water entering the basin is greater than the density of the standing water in the ocean basin. This higher density river water will flow below the standing water in the basin because of the difference in density. A zone of mixing occurs along the outer edge of the flow. As the river water flows beneath the standing water, it erodes the previously deposited bottom sediments.
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• Hypopycnal flow is associated with a lower river water density entering a higher density standing water in the basin. Under these conditions, the river water will flow out over the standing water, gradually depositing the suspended clay portion of the sediment load on the prodelta
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Key points: Wave‐dominated deltas
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Wave‐dominated deltas are primarily influenced by wave energy and action. The common sequence reflects reworked mouth bar into sandbodies and beaches parallel to the shoreline
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Coastal depositional environments Shoreline
Shelf
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Identify features and infer depositional environment
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Identify features and infer depositional environment
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Coastal depositional environments
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Coastal sedimentary features
Swash zone
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Sedimentary features: HCS stratifications
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Hummocky cross stratification (HCS) forms during storm events with combined wave and current activity in shallow seas
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Key points: Tide‐dominated deltas
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Tide‐dominated deltas typically occur in locations of large tidal ranges or high tidal current speeds. The sediment supply is over powered by strong tidal currents, the delta tends to be very small Resulting feature of a tide‐dominated delta is that it has many linear structures parallel to the tidal flow and perpendicular to the shore
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Tidal environments
Tide • • • •
Periodic phenomenon on coastal domain Results from the gravitational attraction (Earth, Moon, Sun) Regular rise and fall of water level in the world’s oceans Effective agent of transport of sediment
Tidal range: vertical amplitude between low tide and high tide
Foreshore: area horizontally alternately covered and uncovered by the tide
Characterization • Particle transport is vigorous and rapid − Bipolar linear current (alternating tidal currents: Flood/Ebb) − Cross‐stratification in opposite directions (herringbone) : Flood / Ebb oscillation
Repeated erosion and creation of tidal channels Difficult conditions for living organisms Flaser, wavy and lenticular beddings Reactivation surface
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• • • •
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Tidal influenced bedforms & sedimentary structures
Tide‐influenced sedimentary structures: • Herringbone cross stratification → bipolar flow directions • Mud‐draped cross strata (quite common): result from alternating bedform migration during high flow velocities with mud drapes deposition during high/low tide slack water • Tidal bundles are characterized by a sand‐mud couplet of varying thickness; tidal bundle sequences consist of bundles that can be related to neap‐spring cycles
Flood
Flood‐ebb tidal deposits
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Ebb
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Sedimentary structures in tidal range
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Sedimentary structures: tide‐related laminae
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Sedimentary structures: tide‐related laminae Bundle thickness vs tide cycles
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Summary table: sedimentary features vs environments Depositional energy
Water Zone
Sediment type (GS)
Backshore
Parallel landward stratifications
High ℮
Swash zone Breaking zone
Sand
Foreshore (Tidal flat)
Lenticular Wavy Flaser
Low → High ℮
High tide (MHW) Low tide (MLW)
Mud Mud/Sand Sand
Sandwaves (trough) Megaripples(tabular) Ripples (sym/asym)
High ℮
Low tide (MLW) Fair weather zone (MFWB)
Sand (winnowed: clean, rounded & sorted)
Upper offshore
Storm HCS Wavy bedding
Low ℮
Storm weather zone (MSWB)
Silty/Shaly
Lower offshore
Wavy bedding
Low ℮
Outer shelf
Shaly (burrows)
Deep water [Turbidites]
Massive (no struct.) [Bouma, Stowe,...]
Low ℮ [High ℮ gravity flow]
Slope Basin
Muddy [Sandy/Silty]
Shoreface
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Laminae
Sedimentary features
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Environment
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Key points : Coastal systems and reservoir potentials Key points to keep in mind 2. Reservoir bodies: Mouth bar, and aggradational channels complexes located along the distributary:
Limited lateral extension
Fluvial‐ dominated
Wave‐ dominated
Tide‐ dominated
3. Reservoir bodies:
Beach barrier island, very good lateral continuity, well sorted sandbodies and clay‐free:
Isolated tidal bar, poor continuity and extension. Well sorted sandstone, but lot of clay drapes due to intertidal processes: Discontinuous reservoir
Best reservoir
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1. Reservoir bodies:
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Clastic depositional environments and facies
Fluid flows and related sedimentary processes • General reminders • Bedforms generation • Bedforms boundaries
Depositional environments & Clastic reservoirs geometry (from continental to marine environments • Sedimentary fill hierarchy • Depositional environments © 2013 ‐ IFP Training
− Fluvial systems & reservoirs geometry – Quality − Coastal / deltaic systems & reservoirs geometry – Quality − Marine systems & reservoirs geometry – Quality
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Gravity deposits
Continental environment: broken blocks or erosional debris falling down by gravity and/or density–turbulence current
Aquatic environment (lake, open marine) • Mass flow (debris flow, mud flow) − Low amount of water incorporated in sediments − Sedimentation without any sorting (very fast and sudden, almost instantaneous event)
• Density‐turbulence flow
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− Progressive incorporation of water (turbulent flow or current) − Sediments start to be deposited when flow velocity and related turbulence decrease: coarser grains are deposited first and finer last − One turbidite = one single event − Very good sorting in layers: fining upward sequence with well organized geometry evolution
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Marine clastic deposits: turbidites
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Fluvial vs turbiditic clastics: similar organization of sediments in deeper environments 147
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Gravity deposits vs. processes & sediment supply Step 3‐ geometries & extend of turbidites
Step 1‐ Initiation of gravity deposits
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Step 2 ‐ Processes of transport &deposition
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Turbidite system general organization
Cross‐sections: from proximal to distal turbiditic facies
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Turbiditic system organization Upper fan
Middle fan
Turbidite deposits: sedimentary facies and log responses Lower fan
New lobe
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Abyssal plain
General upward tendency: coarsening and shallowing upward
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Turbidites: depositional mechanism
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Lab reconstitution of a dynamic gravity flow (mini turbiditic current = avalanche!)
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Bedforms in unidirectional flow
Three main factors controlling bedforms in unidirectional currents: • Average flow velocity • Grain size • Water depth
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Typical turbidite depositional sequences
Main characteristics • Allochthonous sedimentation • Highly organized from proximal to distal part • Dominantly controlled by unidirectional flow • General fining upward sequence • Facies association from channels to levees and lobes
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Conventional Bouma sequence & field outcrop
Obara turbidites, Spain © 2013 ‐ IFP Training
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Conventional Bouma sequence & field outcrop
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St Jean de Luz turbidites ‐ France
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Deep sea deposits: turbidites
Turbiditic system with midfan/suprafan lobes
Simple turbiditic system without lobes
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Abundant sediments reworked from delta Sonatrach / IAP
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Turbidite outcrop
Courtesy Philippe JOSEPH
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Turbiditic sandstones (Mid fan ‐ channel)
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Turbidite outcrop
Stacked channels
Turbiditic sandstones Sonatrach / IAP
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Lower fan ‐ lobes
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Turbidite outcrop
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Bouma sequence: Tb and Tc
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Sedimentation rate and sea variations
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Fluvial and deltaic sequences
Gamma Ray log responses and depositional deltaic environments
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Sediment maturity
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Clastic reservoirs internal geometry and organization
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Clastics Key points to keep in mind
Clastic sediments are: • Allochthonous erosional products (weathering, alteration and transportation) • Transported by fluvial water, wind, ice • Deposited in basins
The main depositional process of clastic sediments is progressive decantation due to gradual decay of flow velocity (water or density current), i.e. decreasing transport energy
Fluvial, deltaic and turbiditic depositional sequences are mostly fining‐upward The evolution of a fluvial system (e.g. meander) involves both erosional and decantation processes
The development of a delta is mostly due to progradation (if constant sediment supply and sea level)
A turbidite results from a single depositional event (intermittent sediment supply) The main source of continental sediments is erosion of existing rock (outcrops) The main source of deep sea deposits is reworking of existing sediments (e.g. delta)
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Une formation IFP Training pour Sonatrach / IAP
Clastic reservoirs Log responses in clastic sequences
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Log responses in clastic sequences
Sedimentological & stratigraphic well log analysis • • • •
Log shapes review Depositional environment review & logs characteristics Parasequences & logs responses Clastic system tracts and logs facies responses
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Sedimentary processes
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Log responses
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Log responses
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Log responses in clastic sequences
Sedimentological & stratigraphic well log analysis • • • •
Log shapes review Depositional environment review & logs characteristics Parasequences & logs responses Clastic system tracts and logs facies responses
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Typical braided river sequence Braided rivers and related bars
Several erosional channels
Stacked fining‐up sequences Sonatrach / IAP
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Basal lag deposit
Basal erosional surface 172
Typical meandering river sequence
Crevasse splay Point bar
Coal Fine grained sandstone Organic shale, roots medium coarse to grained sandstone
Fining‐up sequence: point bar
Meandering river
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Erosion
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Typical depositional sequences of fluvial sediments Key points to keep in mind Alluvial fan
Braided river
Meandering river
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Deltaic depositional sequences
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Turbidites sequences
Main characteristics: • Allochthonous sedimentation • Highly organized from proximal to distal part • Dominantly controlled by unidirectional flow • General fining‐upward sequence • Facies association from channels to levees and lobes
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Clastic sequences Gamma Ray log responses and depositional environments
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Log responses in clastic sequences
Sedimentological & stratigraphic well log analysis • • • •
Log shapes review Depositional environment review & logs characteristics Parasequences & logs responses Clastic system tracts and logs facies responses
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Accommodation variations and related sequences PROGRADATIONAL PARASEQUENCE SET
Rate of deposition Rate of accommodation
SP
RES
SP
RES
SP
RES
> 1
RETROGRADATIONAL PARASEQUENCE SET
Rate of deposition Rate of accommodation
< 1
AGGRADATIONAL PARASEQUENCE SET
Rate of deposition
= 1
Coastal plain sandstones And mudstones Sonatrach / IAP
Shallow marine sandstones
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Rate of accommodation
Shelf Mudstones
MITCHUM and VAN WAGONER 1991
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Correlations during progradation time
Basinward
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Correlations during progradation time
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Facies distribution wave or fluvial‐dominated environment
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Facies distribution fluvial or wave‐dominated environment
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Facies distribution shoreline‐dominated environment
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Facies distribution in tidal flat‐dominated environment
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Log responses in clastic sequences
Sedimentological & stratigraphic well log analysis • • • •
Log shapes review Depositional environment review & logs characteristics Parasequences & logs responses Clastic system tracts and logs facies responses
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Hierarchy of fluvial architectural elements
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Une formation IFP Training pour Sonatrach / IAP
Clastic reservoirs Clastic Petrography & Diagenesis
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Clastic Petrography & Diagenesis
Mineral diagenesis • Definition and processes
Diagenetical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetical regimes
Heterogeneities
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• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
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Mineral diagenesis: Definition
All physical, chemical or biological processes at relatively low temperatures (less than 200‐250°C) and pressures (less than 2‐3kbars) that affect a sediment (or a sedimentary rock) after its deposition.
Compaction, dissolution, cementation, mineral replacement are major elementary processes of diagenesis activated by physico‐chemical parameters (pressure, temperature, fluid composition) and/or biological (bacterial activity, bioturbation)
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Why study diagenesis?
To understand: • Transformation mechanisms from sediment to sedimentary rock • Sedimentary basin dynamic • Reservoir quality • Nature and distribution of porosity and permeability • Fluid flow evolution • Extend of oil recovery • Interaction of secondary recovery fluids with the reservoir • Movement or binding of pollutants
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Processes
Physical • Compaction • Fluid migration • Pressure solution
Chemical • • • • •
Mineral reaction Mineral replacement Cementation Dissolution Organic matter evolution
Geological & climatic
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• Original depositional environment • Diagenetic environment • Tectonic setting and basin evolution Etc.
→ All processes are interdependent and cannot be easily separated 197
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What is lithification? Process which leads to the transformation of a non‐consolidated sediment to a rock.
It implies grain cementation in the sediment but not necessarily burial and compaction (e.g. beachrock)
Lithification is the result of diagenetic processes but diagenesis does not necessarily lead to sediment lithification.
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What type of diagenesis?
Early diagenesis • Changes essentially biochemical • First meters of burying • Early in the history of sediments • Environment in marine, meteoric, salted zone and vadoze zone
Late diagenesis • Slower changes (compaction, dissolution and mineralogical transformations) • Burying diagenesis (pressure, temperature and fluids effects) • Type of rock (carbonates, clays, siliciclastics, etc.) controlled by climate, tectonic and sedimentary contexts © 2013 ‐ IFP Training
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Clastic Petrography & Diagenesis
Mineral diagenesis • Definition and processes
Diagenesical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetic regimes
Heterogeneities © 2013 ‐ IFP Training
• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
201
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Definition of compaction
All processes which lead to a decreasing of porosity in sediment or sedimentary rock and generate pore fluid eviction
Rearrangement
Cementation
(with volume losses)
(without volume losses)
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Mechanical compaction – 1/2
Occur at shallow burial depth
Reworking of sediments (grain repacking and rearrangement, bioturbation)
« The tightest packing of spheres is rhombohaedral (Φ=25%) while the loosest is cubic (Φ=50%) » Graton & Fraser, 1935
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Mechanical compaction – 2/2 Impact of grain size, roundness and sphericity
Mechanical compaction is generally more effective in mudrocks than sandstones (high water content in shales, rapidly expelled by compaction)
Water
Minerals
Compaction
+
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Water loss
Water
Minerals
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Rearrangement example in siliciclastics
1 mm
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Rearrangement example in carbonates
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Chemical compaction
Mainly achieved by reprecipitation of minerals in remaining pore spaces
Cementation more obvious in coarse clastics than mudrocks
Main process is pressure‐solution
P1
Where Pw = Pore fluid pressure P2
And P1 > P2 > Pw Pw
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Reprecipitation of overgrowth forms (dark blue) by diffusion of silica from the grain contact to the pore spaces
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Pressure‐solution
Development of sutured contact enhanced by presence of clays • Enhance transport of ions away from site of pressure solution (diffusion network)
Much more difficult to produce pressure‐solution in clean sandstones
In coarse clastic sediments (gravels) • High pressure contacts • Rapid porosity loss early in burial slowing down rapidly
In fine clastic sediments (sandstones & siltstones) • Higher surface area in contact = fewer nucleation sites • Rapid porosity loss at depth © 2013 ‐ IFP Training
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Pressure‐solution mechanisms Major constraint σ1 1. DISSOLUTION
2. DIFFUSION
Grain
Minor constraint σ3 3. OVERGROWTH
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Pressure‐solution in sandstone
Φ
Overgrowth
Φ © 2013 ‐ IFP Training
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Pressure‐solution in carbonate Nummulitic limestone (Eocene, Corsica) Precipitation Diffusion
Dissolution
Awl
Concept
Polarized light
Cathodoluminescence © 2013 ‐ IFP Training
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Pressure‐solution example in sandstone (polarized light)
Ex1 Lum Pola
Ex1 Lum nat
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Pressure‐solution example in sandstone (natural light)
Zoom 2
Zoom 1
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Pressure‐solution example in sandstone (natural light)
Zoom 1
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Dissolution Sonatrach / IAP
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Pressure‐solution example in sandstone (natural light)
Precipitation
500 µm
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Zoom 2
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Mineralogical dissolution example (Natural light)
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Potassic feldspar (FK) dissolution Sonatrach / IAP
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Clastic Petrography & Diagenesis
Mineral diagenesis • Definition and processes
Diagenesical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetic regimes
Heterogeneities © 2013 ‐ IFP Training
• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
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Cementation parameters – 1/2
An allogenic cementation occur during deposition
An authigenic cementation grown in situ during diagenesis
There is rarely sufficient material in the rock to account for all cements present
Degree of supersaturation of the pore fluid, example in silica • High level, soluble forms precipitate: opal and chalcedony form thin crusts and mosaics on grains • Low level: quartz precipitates (because low solubility) and slowly forms monocrystalline overgrowths
Other common cements:
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Carbonates (calcite, dolomite) Silicates (quartz, opal, potassic & sodic feldpars) Clay minerals (kaolin, illite, chlorite…) Sulphates (gypsum, anhydrite…) Oxides (haematite…)
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• • • • •
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Cementation parameters – 2/2
From fluids to cement formation: • Water salinity • Dissolution of soluble rock • Groundwater percolation • Shales expulsion • Mineral and organic reaction
Cement precipitation depends on the nucleation
A slow kinetic or an inhibitor presence can explain the no‐precipitation
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Sources of silica cement
During early diagenesis: • Skeletal remains of diatoms and radiolaria • Quartz dust abraded during transportation
During late diagenesis: • Mainly pressure‐solution
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Radiolaria Diatom Sonatrach / IAP
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Cementation in sandstone reservoir (Brent)
Uncemented sandstone
Diagenetic front
Cemented sandstone (calcitic cement) © 2013 ‐ IFP Training
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Sources of kaolin cement
Alteration and mineral recombination in porosity
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Quartz
Porosity
Quartz
Kaolin cement
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Kaolin cement
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Clastic Petrography & Diagenesis
Mineral diagenesis • Definition and processes
Diagenesical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetic regimes
Heterogeneities © 2013 ‐ IFP Training
• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
223
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Moldic dissolution
Initial presence of a shell, rock fragment or grain. Then, micritization by bacteria. Progression from outside to inside
Second step, dissolution of cement but not the micrite (more stable). The shape is preserved. Sparitic precipitation in the cavity
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Pseudomorph forms
Replacement of a preexisting mineral by an other one
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From halite (cubic crystal) to a “cubic” calcite (normally trigonal – hexagonal scalenohedral)
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Recrystallization
Sometimes, it is difficult to distinguish cementation and recrystallization
Change in crystal shape / orientation without compositional change
The orientation of the first crystal (as seed) govern the direction in which further crystals grows
Major effect of temperature
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How to reset all information… Sonatrach / IAP
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Clastic Petrography & Diagenesis
Mineral diagenesis • Definition and processes
Diagenesical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetic regimes
Heterogeneities © 2013 ‐ IFP Training
• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
227
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Near‐surface sandstone diagenesis
Particularly occurs in semi‐arid climates • Water table very low • Sediments are oxygenated for long period • Sparse vegetation (= rapid erosion) • Immature sediment producing (high amount of unstable minerals like feldspars, amphiboles…)
Processes of activation near surface • Clay infiltration (clay percolation through water) • Intrastratal mineral dissolution (partial or complete dissolution of instable minerals) • Replacement • Authigenic mineral growth (hydroxydes…) © 2013 ‐ IFP Training
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Subsurface sandstone diagenesis
Sandstone horizons correspond to fluid pathways especially for fluids from compacting mudstones
Fluids carry dissolved ions (potential cements)
Clays flatten to form a matrix (=permeability decreasing)
Effect of the fluids composition, temperature and pressure
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Diagenesis and reservoir quality Key points to keep in mind
Diagenesis have a strong impact on reservoir quality
Generally, the quality of clastic reservoirs decrease with diagenesis by compaction and cementation
Whereas in carbonate reservoirs, the quality can be also reduced or improved by physical, chemical or biological processes (dissolution, dolomitization…)
The main parameters of reservoir quality affected by diagenesis are the porosity and the permeability
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Clastic Petrography & Diagenesis
Mineral diagenesis • Definition and processes
Diagenesical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetic regimes
Heterogeneities © 2013 ‐ IFP Training
• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
231
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Reservoir heterogeneities: Summary
Introduction: heterogeneities in the reservoir • • • •
Homogeneous / heterogeneous reservoirs Reservoir heterogeneity concepts Classification of reservoir heterogeneities Impact of reservoir heterogeneity on hydrocarbon recovery
Reservoir heterogeneity features • Scale of reservoir heterogeneities • Small‐scale observation and analysis • Large‐scale observation and analysis © 2013 ‐ IFP Training
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Homogeneous vs. Heterogeneous reservoir
Heterogeneous reservoir (Faults, Unconformities, Layers, Facies, Diagenesis, Fractures, Super K,…)
Heterogeneity: spatial variation of rock physical properties that affect fluid flow
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Homogeneous reservoir
233
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Reservoir heterogeneity: concepts – 1/2
To build a consistent and relevant model: • All variations in the reservoir quality must be analyzed and classified in a manner that the main heterogeneities main are clearly highlighted • For a given study, all heterogeneities that can affect fluid flow are considered as key heterogeneities
Key heterogeneities have to be absolutely described in the geological model © 2013 ‐ IFP Training
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Reservoir heterogeneity: concepts – 2/2
Reservoir heterogeneities • All relevant factors affecting the dynamic behavior of the field • Small‐ to large‐scale geologic features • From static reservoir characterization (significant or not) • From dynamic reservoir characterization (significant)
Basic principle • Identify the smallest element that will impact production
© 2013 ‐ IFP Training
Reservoir heterogeneities characterization calls for the cooperation between all professionals involved in the study (i.e. from geophysicists to reservoir engineers)
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Classification of heterogeneities in reservoirs – 1/2 Classification
Weber classification (1986) « How heterogeneitiy affect oil recovery »
Heterogeneity range A: Structural
1 to 3
B: Stratigraphic
1 to 3
C: Diagenetic
1 to 3
D: Depositional
1 to 3
E: Depositional
1 to 3 1 to 3
G: Structural
1 to 3
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1 ‐ major heterogeneity 2 ‐ intermediate heterogeneity 3 ‐ negligible heterogeneity Classification objective: highlight most significant heterogeneities.
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F: Diagenetic
Prior to the modeling phase, it is necessary to perform a synthesis of heterogeneity types, for each item, taking into account their impact on fluid flow, using the following scale:
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Classification of heterogeneities in reservoirs – 2/2 Impact on recovery
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© 2013 ‐ IFP Training
Clastic Petrography & Diagenesis
Mineral diagenesis • Definfition and processes
Diagenesical analysis • • • •
Effect of compaction on primary porosity Effect of cementation on primary porosity Replacement during diagenesis Fluid dynamics and diagenetic regimes
Heterogeneities © 2013 ‐ IFP Training
• Introduction: heterogeneities in the reservoir • Reservoir heterogeneity features
239
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Scale of reservoir heterogeneities Grain
Obervation scales:
Lamination
Bed
< 1 mm
Formation
Field
< 1 cm Small ...
< 1 m
Relative scales:
Intermediate ...
< 1000 m
Large ...
> 1000 m
Very large ...
Heterogeneities and investigation tools do not always have the same scale… Sonatrach / IAP
© 2013 ‐ IFP Training
(from Krause and Collins, 1984)
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Small scale heterogeneities Example of laminations and cross‐beddings
Micro scale: related to a mixture of different pore types and geometries (textural features)
Macro scale: often related to laminations and cross‐beddings (depositional features: energy) © 2013 ‐ IFP Training
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Large‐scale heterogeneities (1/5)
Faults • Juxtaposition of reservoir units and low permeability units • Clay smearing (injection of clay into the fault plane) • Cataclasis: sand grains crushing (breccia) • Diagenesis (fault‐related): cementation due to fluid circulation and precipitation creating hydraulic seals
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Cataclasis: silicification Sonatrach / IAP
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Large‐scale heterogeneities (2/5) Genetic unit boundaries → represent stratigraphic discontinuities (isolated bar, channel…)
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Large‐scale heterogeneities (3/5) Diagenesis
DOLOMITE
(power line cable)
Dolomitization front
Bedding
LIMESTONE
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Scale
5 m
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0
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Large‐scale heterogeneities (4/5) Both shale baffles and permeability streaks Lateral extension linked with depositional environment e.g. Hassi‐Messaoud reservoir (silts)
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Large‐scale heterogeneities (5/5) Seeping fractures
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Reservoir characterization and modeling Key points to keep in mind
To build a consistent and relevant model for an integrated study: • All reservoir heterogeneities must be identified and classified (main ones highlighted) • All heterogeneities that can impact fluid flow are considered as major heterogeneities • Even the smallest elements that can affect production need to be identified and modeled • The geological model must take into account all significant heterogeneities • Characterization of reservoir heterogeneities calls for integrated multi‐ disciplinary approach (cooperation and team work) © 2013 ‐ IFP Training
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© 2013 ‐ IFP Training
Une formation IFP Training pour Sonatrach / IAP
Clastic reservoirs Fundamentals of sequence stratigraphy
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Fundamentals of sequence stratigraphy
Introduction to sequence stratigraphy • • • • • •
General introduction Accommodation definition Relative sea level and space available Dynamic points Sequence development Parasequence/genetic sequence © 2013 ‐ IFP Training
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Sequence stratigraphy: Introduction Sequence stratigraphy is based on the application of the systematic subdivision of the section by well defined surfaces
These surfaces are used to provide a frame work to the interpretation of the depositional settings of the sedimentary section
This interpretation is then used to predict the extent and character of the component sedimentary facies
Integrated method with all the exploration tools (geology, geophysics, palynology, geochemistry…) • Relation between geological layers in a chronostratigraphic understanding • Basic sedimentary unit: depositional sequence
Characteristics of a depositional sequence • Bounded by their unconformities and their correlative conformities • Composed by systems tracts
Each system tract • Bounded by physical surface • Composed of elementary « unit » (genetic unit or parasequence)
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© 2013 ‐ IFP Training
Fundamentals of sequence stratigraphy
Introduction to sequence stratigraphy • • • • • •
General introduction Accommodation definition Relative sea level and space available Dynamic points Sequence development Parasequence/genetic sequence © 2013 ‐ IFP Training
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Accommodation definition
Sediment is deposited in the space between the seafloor and base level (sea level or graded stream profile) which is called accommodation
The way a basin fills with sediment and the stratal patterns that result depend upon how much space is available for the sediment to fill and how rapidly new space is added
Accommodation may vary as both the upper and lower boundaries of this space move up or down
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Fundamentals of sequence stratigraphy
Introduction to sequence stratigraphy • • • • • •
General introduction Accommodation definition Relative sea level and space available Dynamic points Sequence development Parasequence/genetic sequence © 2013 ‐ IFP Training
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Relative sea level vs space availability
Eustacy refers only to the position of the sea surface with reference to a fixed datum, such as the center of the earth, and is therefore independent from local factors
Relative sea level incorporates local subsidence by referring to the position of the sea surface with respect to a datum at or near the seafloor
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© 2013 ‐ IFP Training
To discern the rate at which new space is added, both relative eustacy fluctuation rate combined with subsidence rate must be considered
256
Accommodation & Equilibrium point Equilibrium point : Rate of subsidence = Rate of eustatic change A platform is divided into two parts separated by an equilibrium point Basinward of : • Rate of subsidence > Rate of eustatic fall • Creation of a new space added • Area of relative sea level rise
Landward of : • Rate of subsidence < Rate of eustatic fall • No creation of new space added • Area of relative sea level fall
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© 2013 ‐ IFP Training
Fundamentals of sequence stratigraphy
Introduction to sequence stratigraphy • • • • • •
General introduction Accommodation definition Relative sea level and space available Dynamic points Sequence development Parasequence/genetic sequence © 2013 ‐ IFP Training
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Specific dynamic points
Inflection points of the eustatic curve • Point F: maximum rate of sea level fall
F
R
− Minimum rate of creation of new space added
• Point R: maximum rate of sea level rise − Maximum rate of creation of new space added
Depositional dynamic on the shelf at these specific inflection points of the eustatic curve • Point F: minimum deposit of sediment − Maximum erosional phenomenon
Point R
• Point R: transgression and development of
Point F
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− a condensed section − Maximum drowning of the basin over the shelf − Location of the maximum flooding surface: MFS
260
Theorical sequence: the Exxon “slug”
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© 2013 ‐ IFP Training
Fundamentals of sequence stratigraphy
Introduction to sequence stratigraphy • • • • • •
General introduction Accommodation definition Relative sea level and space available Dynamic points Sequence development Parasequence/genetic sequence © 2013 ‐ IFP Training
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Sequence stratigraphy 1
3
2
4
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Sequence stratigraphy 5
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Key surfaces in sequence stratigraphy
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In Kendall (2004) Sonatrach / IAP
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Sedimentation rate and sea variations
Sequence are subdivided by • Maximum Flooding Surfaces (MFS) • Transgressive Surfaces (TS) • Sequence Boundaries (SB)
Arrangement of vertical succession or stacking patterns of unconfined sheets • Prograde (step seaward) • Retrograde (step landward) • Aggrade (build vertically)
Sheets and unconfined lobes containing • Non‐amalgamated bodies
Incised topographic fill
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• Amalgamated, multi‐storied bodies (e.g. incised valleys) • Within unconfined lobes
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Theorical sequence: “Exxon Slug”
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Systems tract synthesis
Sequence stratigraphy is based on the application of the systematic subdivision of the section by well defined surfaces
These surfaces are used to provide a frame work to the interpretation of the depositional settings of the sedimentary section
This interpretation is then is used to predict the extent and character of the component sedimentary facies
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Lowstand‐fan systems tract
Lowstand fans are deposited during rapid eustatic falls which exceed the rate of subsidence at the shelf edge
Sediment bypasses the shelf and is deposited directly on the slope and in the basin in the form of point‐sourced submarine fans. This figure illustrates geologic, geographic, and eustatic conditions conducive to the formation of these deposits
The systems tract is bounded below and above by discontinuities
Internally, lowstand fans are characterized by mounded facies and may be extensively sand prone. These mounds are commonly excellent reservoirs
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Lowstand‐wedge systems tract
The lowstand‐wedge systems tract begins to form during the latter part of a rapid eustatic fall as lowstand‐fan deposition ends. Deposition is initiated when the rate of eustatic fall is again equal to subsidence at the shelf edge
This interval is characterized by resumption of a slow rise of relative sea level at the shelf edge
Deltaic deposition is localized in the upper parts of canyons or embayments cut into the shelf during rapid eustatic falls
The base of this systems tract is an unconformity. The top grades either into a transgressive depositional sequence or is a condensed section, if transgressive deposits are absent or not observed.
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Transgressive systems tract
When the rate of new shelf space added exceeds the rate of sediment supply, transgression occurs. The timing of this event depends on sediment supply and rate of eustatic rise, but it will usually occur on the rising limb of the eustatic curve when the rate of addition of new shelf space increases rapidly prior to the eustatic rise inflection point
During transgression, only pelagic or hemipelagic deposition occurs on the starved shelf and basin, generating a starved or condensed section there
Of all the systems tract types, the transgressive systems tract is the most sensitive to variations of sediment supply, and its occurrence is therefore the most difficult to predict
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Highstand systems tract
The highstand systems tract is deposited during the eustatic highstand, defined as the interval between the eustatic rise and fall inflection points. This interval is characterized by a slowly decreasing relative rise of sea level as the rate of eustatic change gradually decreases
An unconformity defines the upper surface, and a condensed section marks the lower limits of this systems tract
Reservoir facies are associated primarily with prograding beach and aggrading fluvial depositional systems. Organic‐rich facies with source potential may develop on the toes and delta plains of progradational units
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Shelf‐margin systems tract
The shelf‐margin systems tract is a regressive stratigraphic unit overlying a highstand deposit and is usually deposited following the inflection point on a gentle eustatic fall
This interval is characterized by a progressive increase in the rate of relative rise of sea level. The shelf margin systems tract is deposited on the outer part of the shelf and is marked by an abrupt basinward shift of coastal onlap at its base
The base of this systems tract is an erosional unconformity or its correlative conformity, whereas the top either grades into a transgressive systems tract or is a condensed section. The basal unconformity on the shelf is usually marked by paralic/deltaic sediments overlying fluvial deposits
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Fundamentals of sequence stratigraphy
Introduction to sequence stratigraphy • • • • • •
General introduction Accommodation definition Relative sea level and space available Dynamic points Sequence development Parasequence/genetic sequence © 2013 ‐ IFP Training
275
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How to order the sedimentary pile?
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© 2013 ‐ IFP Training
"Facies adjacent to one another in a continuous vertical sequence also accumulated adjacent to one another laterally"
276
Sedimentation rate and sea variations
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Introduction to sedimentary sequences Depositional sequence in respect to Walther's law
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Parasequence: depositional processes in system tracts Progradagradation (Advancing) Retrogradation (Backstepping)
• Elementary deposition sequence (building block) • Thickness : few meters to few tens of meters • Bounded by isochrons (2 successives times surfaces)
Elementary cycles of variations accomodation Influenced by allocyclic parameters (external parameter of the basin)
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Parasequence or Genetic units :
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The genetic sequence
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The genetic sequences are short term depositional sequences (1 Ma) regrouping orders of cyclicity lower than the 4th order
They are limited by two maximum flooding surfaces or by two condensed intervals, and there thicknesses vary from a few decimeters to few meters
They record a cycle of variation of the depositional environment, interpreted as transgression and regression
The genetic sequences are deducted from essentially sedimentological but none geometric observations. They are recognized by drilling or on outcrops
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P. Homewood, P. Mauriaud, F. Lafont 2001
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The genetic sequence
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P. Homewood, P. Mauriaud, F. Lafont 2001 281
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The genetic sequence
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Definition and example
Chronostratigraphy is the branch of stratigraphy that studies the absolute age of rock strata
Chronostratigraphy is based upon deriving geochronological data for rock units, both directly and by inference
Objectives of chronostratigraphy: • Determine the ages of strata • Demonstrate the geographic extend of strata • Confirm the sequence stratigraphy interpretations © 2013 ‐ IFP Training
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Definition and example
Combination between paleontology and stratigraphy. In oil and gas industry, biostratigraphy corresponds to the study from rock samples (core and cuttings) of microfossils (pollens, spores, nannofossils, diatoms and foraminifera)
The objectives of biostratigraphy are to: • Determine the age (relative or absolute) of strata • Study the paleo‐environment during deposition and its evolution • Make correlations between layers containing the same fossil population © 2013 ‐ IFP Training
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THANK YOU FOR YOUR ATTENTION,
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