Review Of Reservoir Engineering I

Review of Reservoir Engineering I

Dr. Shiferaw Regassa Jufar Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610, Perak, Malaysia | Tel: +605 368 7045 | Fax: +605 365 5670 e-mail : [email protected]

Learning objectives o To review concepts introduced in reservoir engineering I.

Review of Reservoir Engineering I, January 2017 semester

Contents o o o o o

Role and responsibilities of a reservoir engineer Reservoir classification Fluid properties Concepts of relative permeability Flow through porous media  Flow geometry  Type of regimes  Darcy’s Law  Steady-state Flow o Natural drive mechanism o Phase behavior of reservoir fluids o PVT analysis Review of Reservoir Engineering I, January 2017 semester

Role and responsibilities of a reservoir engineer o Reservoir engineering is a branch of petroleum engineering that applies scientific principles to the drainage problems arising during the development and production of oil and gas reservoirs so as to obtain a high economic recovery. source: Wikipedia

Review of Reservoir Engineering I, January 2017 semester

Role and responsibilities of a reservoir engineer o Estimating reserves and forecasting for property evaluations and development planning.

Source: AAPG WIKI Review of Reservoir Engineering I, January 2017 semester

Role and responsibilities of a reservoir engineer o Carrying out reservoir simulation studies to optimize recoveries. o Predicting reserves and performance for well proposals. o Predicting and evaluating waterflood and enhanced recovery performance. o Developing and applying reservoir optimization techniques. o Developing cost-effective reservoir monitoring and surveillance programs. o Performing reservoir characterization studies. o Analyzing pressure transients. o Designing and coordinating petrophysical studies. o Analyzing the economics and risk assessments of major development programs.

Review of Reservoir Engineering I, January 2017 semester

Characterization of Oil Reservoirs A wide variety of characterization tools and methods are usually required to properly portray the complexity found in an average hydrocarbon reservoir The major principles behind these tools depend upon: • the scale • resolution, and • nature of the measurement itself.

Review of Reservoir Engineering I, January 2017 semester

Role and responsibilities of a reservoir engineer Reservoir modeling involves assimilation of multi-scale information

Review of Reservoir Engineering I, January 2017 semester

Role and responsibilities of a reservoir engineer In physics and chemistry, multiscale modeling is aimed to calculation of material properties or system behavior on one level using information or models from different levels. On each level particular approaches are used for description of a system. The following levels are usually distinguished: level of quantum mechanical models (information about electrons is included), level of molecular dynamics models (information about individual atoms is included), coarsegrained models (information about atoms and/or groups of atoms is included), mesoscale or nano level (information about large groups of atoms and/or molecule positions is included), level of continuum models, level of device models. Each level addresses a phenomenon over a specific window of length and time. Multiscale modeling is particularly important in integrated computational materials engineering since it allows the prediction of material properties or system behavior based on knowledge of the process-structure-property relationships. Source: Wikipedia Review of Reservoir Engineering I, January 2017 semester

Reservoir Classification



Oil reservoir 



In general Tres
Gas reservoir 

In general, Tres>Tc of reservoir fluid (hydrocarbon systems)

Review of Reservoir Engineering I, January 2017 semester

10

Reservoir Classification 

Oil reservoir:



Under-saturated oil reservoir: 



Saturated oil reservoir: 



initial reservoir pressure, pi > the bubble-point pressure, pb of the reservoir fluid

pi = pb

Gas-cap reservoir or two phase reservoir 

pi < pb

Note: The appropriate quality line gives the ratio of volume of liquid (oil) to volume of gas

Review of Reservoir Engineering I, January 2017 semester

11

Reservoir Classification Gas Reservoir: Dry gas reservoir 



initial reservoir temperature higher than cricondentherm temperature (light components) even at low pressure (separator) and temperature, fluid is 100% gas

Wet gas reservoir  

initial reservoir temperature higher than cricondentherm temperature But even at low pressure (separator) and temperature, some gas condensate to liquid

Retrograde gas-condensate reservoir 

Reservoir temperature lies between Tc and Tcri (Tc
Near critical gas-condensate 

Reservoir temperature is nearly equal to critical temperature of fluid (Tr ~Tc) Review of Reservoir Engineering I, January 2017 semester

12

Reservoir Classification Reservoir Classification Black Oil

Volatile Oil Pressure path in reservoir

Critical point

Dewpoint line

Black Oil % Liquid

2

Volatile oil

Pressure

Pressure, psia

Pressure path in reservoir

Critical 1 point

% Liquid

33 Separator

Separator

Temperature

Temperature, °F

Pressure path in reservoir

Critical point

1

Wet gas

% Liquid Critical point 3

Dry gas

% Liquid 2

Separator

Separator Temperature

% Liquid

Pressure

2

Pressure

Pressure

Retrograde gas

Pressure path in reservoir

Pressure path in reservoir 1

1

Temperature

Retrograde Gas

Wet Gas

Review of Reservoir Engineering I, January 2017 semester

2

Separator Temperature

Dry Gas

Fluid properties Viscosity ():



A measure of resistance to flow



Symbols: o, g, w



Units: cp



Sources: Lab measurements, correlations



Range and typical values

•

0.25 to 10,000 cp, Black oil

•

0.5 to 1.0 cp, Water

•

0.012 to 0.035 cp, Gas

Pb Pressure

Review of Reservoir Engineering I, January 2017 semester

Fluid properties Fluid Compressibility (Co, Cg, Cw)

1 Vo  ln Vo  co    Vo p p

1 dV cg   V dP

T

1 1 dz cg   P z dP

Fractional change in volume due to a unit change

in pressure Symbol: co, cg, cw

Units: psi-1, microsips (1 microsip = 1x10-6 psi-1) Source: Lab measurements, correlations

Review of Reservoir Engineering I, January 2017 semester

Fluid properties Oil Formation Volume Factor (Bo)

Gas at Surface

Oil at Surface

Oil Volume in Place Bo  Oil Volume at Surface

Pb

Oil in Place Review of Reservoir Engineering I, January 2017 semester

Fluid properties Gas-Oil Ratio (GOR)

Oil at Surface

Gas Volume at Surface GOR  Oil Volume at Surface

Pb

Gas at Surface

Oil in Place Review of Reservoir Engineering I, January 2017 semester

Concepts of relative permeability

Review of Reservoir Engineering I, January 2017 semester

Concepts of relative permeability o Relative permeability is a concept used to convey the reduction in flow capability due to the presence of multiple mobile fluids. o It is dependent upon:  pore geometry  wettability  fluid distribution and  fluid saturation history o Relative permeability has important implications for flow of reservoir fluids. A number of models have been developed to relate relative permeability to other reservoir properties. Review of Reservoir Engineering I, January 2017 semester

Flow through porous media

Pressure-volume relationship Review of Reservoir Engineering I, January 2017 semester

Flow through porous media

Fluid density versus pressure for different fluid types Review of Reservoir Engineering I, January 2017 semester

Flow through porous media Flow Regimes o There are basically three types of flow regimes that must be recognized in order to describe the fluid flow behavior and reservoir pressure distribution as a function of time:  Steady-state flow  Unsteady-state flow  Pseudosteady-state flow

Review of Reservoir Engineering I, January 2017 semester

Flow through porous media Steady-State Flow

• The pressure at every location in the reservoir remains constant and does not change with time

 P    0  t i

Review of Reservoir Engineering I, January 2017 semester

Flow through porous media When It Happens? o In reservoirs, the steady-state flow condition can only occur when the reservoir is completely recharged and supported by strong aquifer or pressure maintenance

operations.

Review of Reservoir Engineering I, January 2017 semester

Flow through porous media Unsteady / Transient State Flow o The fluid flowing condition at which the rate of change of pressure with respect to time at any position in the

reservoir is not zero or constant o The pressure derivative with respect to time is

essentially a function of both position i and time t

 P     f i, t   t  Review of Reservoir Engineering I, January 2017 semester

Flow through porous media Pseudosteady-State Flow o The pressure at different locations in the reservoir is declining linearly as a function of time

 P     constant  t i

Review of Reservoir Engineering I, January 2017 semester

Flow through porous media

Flow regimes Review of Reservoir Engineering I, January 2017 semester

Flow through porous media Reservoir Geometry  The shape of a reservoir has a significant effect on its flow behavior  Most reservoirs have irregular boundaries  Rigorous mathematical description of geometry is often possible only with the use of numerical simulators  The actual flow geometry may be represented by one of the following flow geometries:

Review of Reservoir Engineering I, January 2017 semester

Flow through porous media Reservoir Geometry o Radial flow o Linear flow o Spherical and hemispherical flow

Review of Reservoir Engineering I, January 2017 semester

Flow through porous media o Flow into or away from a wellbore will follow radial flow lines from a substantial distance from the wellbore o In the absence of severe reservoir heterogeneities o fluids move toward the well from all directions and coverage at the wellbore

Three-dimensional flow structure in radialcylindrical coordinate system

Radial Flow

A typical one-dimensional, radial-cylindrical flow model Review of Reservoir Engineering I, January 2017 semester

Flow through porous media

Ideal radial flow into a wellbore.

Review of Reservoir Engineering I, January 2017 semester

Flow through porous media Linear Flow o When flow paths are parallel and the fluid flows in a single direction o The cross sectional area to flow must be constant o A common application of linear flow equations is the fluid flow into vertical hydraulic fractures

Linear flow Review of Reservoir Engineering I, January 2017 semester

Flow through porous media

Ideal linear flow into vertical fracture Review of Reservoir Engineering I, January 2017 semester

Flow through porous media Spherical and Hemispherical Flow  Depending upon the type of wellbore completion configuration  possible to have a spherical or hemispherical flow near the wellbore  A well with a limited perforated interval could result in spherical flow in the vicinity of the perforations

 A well that only partially penetrates the pay zone could result in hemispherical flow Review of Reservoir Engineering I, January 2017 semester

Flow through porous media

Spherical flow due to limited entry

Review of Reservoir Engineering I, January 2017 semester

Flow through porous media

Hemispherical flow in a partially penetrating well

Review of Reservoir Engineering I, January 2017 semester

Flow through porous media Number of Flowing Fluids in the Reservoir: o Single-phase flow (oil, water, or gas)

o Two-phase flow (oil-water, oil-gas, or gas-water)

o Three-phase flow (oil, water, and gas)

Review of Reservoir Engineering I, January 2017 semester

Henry Darcy o 19th century French engineer o While designing a filter to process his town’s water demand o Vertical flow of water through packed sand o Introduce the concept of

permeability (unit: mD)

Review of Reservoir Engineering I, January 2017 semester

Darcy’s Law o What are the parameters that affect fluid flow?

Review of Reservoir Engineering I, January 2017 semester

L q

A dx

• For one-dimensional, horizontal flow through a porous medium, Darcy’s Law states that:

kA dp q  dx

q =Flow rate (cm3/s) A= Cross sectional area (cm2) μ =Viscosity of flowing fluid (cp) k =Permeability (Darcy) 𝑑𝑃/𝑑𝑥=Pressure gradient (atm/cm)

Transport eqn. implying velocity is proportional to pressure gradient and reciprocal to viscosity

Pressure vs. distance in a linear flow

Darcy’s Law for Radial Flow

kA dp k (2rh) dp q   dr  dr Curved surface open to flow

For fluid flow to occur, a pressure gradient must be established between the inner and outer boundary of the reservoir.

h

Pressure gradient dp/dr

Review of Reservoir Engineering I, January 2017 semester

Pressure gradient in radial flow

Darcy’s Law o Darcy’s Law applies only when the following conditions exist:

 Laminar (viscous) flow

 Steady-state flow  Incompressible fluids

 Homogeneous formation

Review of Reservoir Engineering I, January 2017 semester

Steady-state Flow o Represents the condition that exists when the pressure throughout the reservoir does not change with time o The applications of the steady-state flow include:  Linear flow of incompressible fluids  Linear flow of slightly compressible fluids  Linear flow of compressible fluids  Radial flow of incompressible fluids  Radial flow of slightly compressible fluids  Radial flow of compressible fluids  Multiphase flow

Review of Reservoir Engineering I, January 2017 semester

Steady-state Flow o Derive simple Linear Flow of Incompressible fluid o Understand the fluid potential concept o See how units can be converted from one system

to another

Review of Reservoir Engineering I, January 2017 semester

Linear Flow of Incompressible Fluids  The flow occurs through a constant cross-sectional area A  both ends are entirely open to flow  no flow crosses the sides, top, or bottom

Linear flow model Review of Reservoir Engineering I, January 2017 semester

Linear Flow of Incompressible Fluids •

If an incompressible fluid is flowing across the element dx, then the fluid velocity v and the flow rate q are constants at all points

•

The flow behavior in this system can be expressed by the differential form of Darcy’s equation L

kAP1  P2  q L

P2

q k dx    dP  A0  P1

OR

• In field units Permeability (mD)

Area (ft2)

0.001127kAP1  P2  q L

Flowrate (bbl/d) Viscosity (cp)

Distance (ft)

Pressure (psi)

Darcy’s units In terms of Darcy units

v= apparent fluid velocity, cm/sec; k= permeability, darcy; μ= fluid viscosity, cp; p= pressure, atm l= length, cm; ρ= fluid density, gm/cm3; g= Acceleration due to gravity, cm/sec2; and Z= elevation, cm.

•

The vertical distance Δzi is assigned as a positive value when the point i is below the datum level and as a negative when it is above the datum level Review of Reservoir Engineering I, January 2017 semester

In fields units

where Φi = fluid potential at point i, psi pi = pressure at point i, psi Δzi = vertical distance from point i to the selected datum level ρ = fluid density, lb/ft3 γ = fluid specific gravity (water=1) v= apparent fluid velocity, res bbl/day/ft2; A= total cross-sectional area, ft2 B= formation volume factor, RB/STB. k= permeability, md θ= dip angle of the reservoir or formation measured counterclockwise from the horizontal to the positive flow path The negative sign in Eq. (16) accounts for the sign convention that flow is considered positive in the positive direction of the flow path length, and pressure decreases in the direction of flow

Review of Reservoir Engineering I, January 2017 semester

Linear Flow of Slightly Compressible Fluids o The relationship that exists between pressure and volume for slightly compressible fluid is:





V  Vref 1  cPref  P 

-------------- (6)

• The above equation can be modified and written in terms of flow rate as:





q  qref 1  cPref  P  -------------- (18) where qref is the flow rate at some reference pressure Pref. Review of Reservoir Engineering I, January 2017 semester

Darcy’s Unit Conversion

Review of Reservoir Engineering I, January 2017 semester

Oil Recovery Mechanisms o Each reservoir is unique:

 geometric form  geological rock properties  fluid characteristics  primary drive mechanism

Review of Reservoir Engineering I, January 2017 semester

Primary Recovery Mechanisms o Yet they can be grouped according to the primary drive mechanism.  The recovery of oil by any of the natural drive mechanisms is called primary recovery.

Review of Reservoir Engineering I, January 2017 semester

Types of Reservoir Energy o The energy of compression of the:  water and rock within the reservoir.  oil and gas within the reservoir. o Waters contiguous to and in communication with the petroleum reservoir. o The gravitational energy that causes the oil and gas to segregate within the reservoir.

Review of Reservoir Engineering I, January 2017 semester

Types of Reservoir Energy o Rank the types of energy in order of least importance to oil recovery?

o Compressed water and rock o Compressed oil o Compressed gas  Compressibility of oil=10-5 /psi  Compressibility of water=3x10-6 /psi  Compressibility of rock=6x10-6 /psi

Review of Reservoir Engineering I, January 2017 semester

Primary Recovery Mechanisms Why study Recovery Mechanisms? Knowledge of the driving mechanisms

Proper understanding of reservoir behaviour and predicting future performance Review of Reservoir Engineering I, January 2017 semester

Primary Recovery Mechanisms cont’d o The overall performance of oil reservoirs is largely determined by the nature of the energy, i.e., driving mechanism, available for moving the oil to the wellbore. o Each drive mechanism has certain typical performance characteristics in terms of:  Ultimate recovery factor  Pressure decline rate  Gas-oil ratio  Water production

Review of Reservoir Engineering I, January 2017 semester

Primary Recovery Mechanisms cont’d o There are basically six driving mechanisms that provide the natural energy necessary for oil recovery:  Rock and liquid expansion drive  Depletion drive  Gas-cap drive  Water drive  Gravity drainage drive  Combination drive

Review of Reservoir Engineering I, January 2017 semester

Primary Recovery Mechanisms cont’d o A petroleum reservoir rarely can be characterized throughout its pressure-depletion life by any single producing mechanism. o Broadly, all commercially productive petroleum reservoirs are divided into either  expansion-drive (sealed reservoir)  compaction-drive (sealed reservoir)  water drive reservoirs (unsealed reservoir)

Review of Reservoir Engineering I, January 2017 semester

Classification of Primary Recovery Mechanisms

Review of Reservoir Engineering I, January 2017 semester

Phase behavior of reservoir fluids

o VLE calculation Review of Reservoir Engineering I, January 2017 semester

PVT analysis

o Equations of state are used to model phase behavior of reservoir fluids. Review of Reservoir Engineering I, January 2017 semester

Review of Reservoir Engineering I, January 2017 semester