Oil An Gas Typing

Oil & Gas typing Introduction & bulk properties

Wiekert Visser

Petroleum systems mapping work flow Oil – Oil correlation Oil – Gas correlation Gas – Gas correlation

Oil/gas family map

Oil – Source rock correlation Gas – Source rock correlation

Define Petroleum Systems

Rock Eval analyses (wells) Seismic isopachs map

Source rock quality maps

Maturity data (wells)

Source rock kitchen maps

(Once) Active Petroleum Systems maps Note: modern 3D modeling tools need much more data & deliver superior results

Objectives of oil and gas typing in Exploration Typing of oil, gas, and source rock extracts is a key element of Petroleum Systems Analysis. This work aims at:  Assessment of the source of the hydrocarbons (type and age)  Assessment of the maturity of the source at the time of expulsion  Estabishing the petroleum system (i.e. The link between source rock and trapped hydrocarbons)  Oil family mapping: is there more than 1 petroleum system in the basin?  Reduction of exploration risk by the above activities.

Example exploration question Question: Is the oil derived from the Cretaceous or the Jurassic source rock? D

B

A

C

0

Oil field

Depth (km)

1

2 Immature Mature

Top oil window (VR=0.6)

3 ? Source rock B (JJ) ? Source rock A (KK)

4

Fundamentals of oil & gas chemistry • Crude oil is a mixture of thousands of organic components. Chemical analysis of these complex mixtures gives information about:  Economic value of the oil/gas  The source & charge history  Post-trapping alterations

Bulk Characteristics of Petroleum Fluids Gas

Condensate

Oil

n.a.

>45

<45

C7+ (black oil) content

<1%

< 15 %

> 20 %

Methane content

> 95 %

60-85 %

< 20 %

> 100.000

3000 – 100.000

< 3000

API gravity

GOR (scf/bbl)

A condensate is operationally defined as any fluid which is a gas in the subsurface but a liquid at the surface. This depends on the PVT conditions. For geochemical purposes, a condensate is a fluid with most of its mass below C15.

Oil and Gas compounds, fundamentals Saturates: alkanes H | H—C—H | H

Methane

C1

Pentane C5H12

Saturates: naphtenes

H2

Non-saturates

H2 H2

H2

H2

Cyclo-hexane C6H12

n-Alkanes: CnH2n+2

Iso-C6

Paraffins/Alkanes

H2

Cyclo-pentane

Pentane

C5

n-alkanes

Cyclo-alkanes (Naphtenes)

iso-alkanes

H H H H H | | | | | H—C—C—C—C—C—H | | | | | H H H H H

Benzene C6H6

Naphtalene

Aromatics

Composition of a 35 API & a 16 API crude Down-stream purposes 35 API

16 API Volume percent 0 <2 16 42 39

Weight percent 10 3 37 50

Main boiling fractions of oil Down-stream purposes “Normal” black oil

Bulk properties of oils for E&P Geological Applications • • • • • •

API gravity (density) weight-loss on topping % Sulfur Heavy metals Carbon Isotopes Gross Composition:

(Reservoir) Engineering i

i

i

• • • • • •

Total Acid Number (TAN) Viscosity Pour point Cloud point Wax content Asphaltene content

– % Saturates, – % Aromatics – % Hetero compounds

F

API gravity - density relationship Tar API gravity

Specific gravity

Oil

Degrees API=

141,5 -131,5 specific gravity

Condensate R

Sulphur in Shaly Marine Oils API Gravity versus %S Global data set trend Hemiar: 22.2 / 1.23%

Masila: 30.5 / 0.67%

Tambaredjo Oil

Marib Light: 48 / 0.08%

The percentage of Sulphur is important for crude market price, and for corrosive effects. The variation in the percentage of Sulphur in the Yemeni crudes is related to biodegradation.

Amongst heavy oils the Tambaredjo crude is of high quality, and very exceptional in composition

These data are from the Jurassic Madbi marly shales in Yemen

Interpreting Sulfur • ―Sweet‖ low sulfur crudes indicate the source is: – High API gravity shaly marine – Lacustrine (in case of elevated wax content) – Landplant (in case of high wax content)

• ―Souer‖ high sulfur crudes indicate that: – Source is a limestone (with very low shale content) – Crude has been biodegraded (in case of low API) – Crude is a low maturity early expulsion product (in case of low API)

R

Carbon isotopes • The atom Carbon has three different isotopes 12C, 13C, 14C, with atomic weight of 12, 13, and 14 gram/mol respectively. • 12C is most abundant, and living organisms prefer 12C over 13C • 14C is least abundant and is radio-active. It can be used as dating tool.

13

 C =[

13

12

13

12

 C /  C (sample)  C /  C (standard)

] -1 *1000

The standard is the belemnite from the PeeDee Formation in South Carolina 13

PDB  C = 0

Carbon Isotopes in Nature -100

-80

-60

-40

-20

0

20

Atmospheric CO2 Marine HCO3 Marine Carbonate Minerals Marine Plants Plankton

Carbon isotopes are very useful for Oil – Oil and Oil – Source rock correlations

Land Plants (C4) Land Plants (C3) Groundwater HCO3 Non-marine Carbonate Minerals

Oils / Source Rocks

Wood

-35

-30

Peat

-25

-20

Monterey

Coal

Kimmeridge Cretaceous

Oils/SR

Bakken Shale

Bacterial Gas

Phosphoria

Thermal Gas

North Sea West Africa Williston Basin Wyoming

Ordovician Texas

Animal Bone Diamond -100

-80

-60

-40

-20

13 CPDB (‰)

0

20

R

Isomers of alkanes

Carbon atoms in molecule Isomers

C2

C4

C5

C6

C7

C8

C9

C11

C13

Possible

1

2

3

5

9

18

35

159

802

Significant in crude oils

1

2

2

3

4

5

6

7

8

The number of isomers in crude oils explodes with increasing carbon number. Analysing all these compounds required excellent separation techniques, such as liquid and/or gas chromatography, and mass spectrometry

Example of branched alkanes: C7 isomers C-C-C-C-C-C-C n-C7

Branched alkanes

C7 ring compounds

3* Mono-branched

4* Di-branched

1* Tri-branched

Long chain iso-alkanes: Pristane and Phytane Phytane CH3 H3C CH3

CH3

CH3

C20

CH3

Pristane H3C

CH3

CH3

CH3

CH3

CH3

Pristane and Phytane occur in all crude oils Both compounds are fragments of Chlorophyll, which occurs in many living organisms Pristane and Phytane are simple indicators for environment of deposition and a basic tool for correlation. They are maturity dependent, but reasonably resistant to biodegradation.

C19

Biomarkers in oil and in living organisms H3C

H3C

CH3

CH3

CH3 CH3

CH3

CH3

CH3 CH3

HO

Cholesterol

Cholestane

Present in living organisms

Present in crude oil

This biomarker occur in virtually all crude oils

Many biomarkers are detailed indicators for environment of deposition and age of the source rock and are the most important tool for correlation. They are slightly maturity dependent, but resistant to biodegradation. Biomarkers are the “work-horse” for exploration geochemists.

Conclusions

• Analyses of oil and gas are essential input for the assessment of Petroleum Systems • Fluid properties contain geological information that can be used for inpout as well as for calibration of petroleum systems models.