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Petroleum Reservoir Engineering----Basic Concepts
S.K.Pant
Pennsylvania 1859
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Outline
§ Introduction
§ Reservoir Propertiesú Porosity
ú Permeability
ú Capillary Pressures
ú Wettability
ú Relative Permeability
ú Reservoir Pressure
§ Basic PVT data
§ Reservoir fluid type
§ Drive Mechanism
§ Numerical simulation
Mar-2009
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Is the Party over ??
“I should stress that we are not facing a re-run of the Oil Shocks of the 1970s. They were like the tremors before an earthquake. We now face the earthquake itself. This shock is very different. It is driven by resource constraints, …”
(Dr Colin. J. Campbell)
Mar-2010
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The law of Diminishing return
Mar-2010
0
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0 500 1000 1500 2000 2500 3000 3500
Cum Wildcat wells
Cu
m D
isco
very
, G
b
Actual Hyperbolic Model
Hyperbolic Creaming Curve-North sea
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The Hydrocarbon….
§ Hydrocarbons are the simplest of the organic compounds. As the name suggests, hydrocarbons are made from hydrogen and carbon. The basic building block is one carbon with two hydrogens attached, except at the ends where three hydrogens are attached.
Mar-2010
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The Hydrocarbons…
§ When the chain is between 5 and 9 carbons, the hydrocarbon is gasoline.
§ About a dozen carbons and it is diesel.
§ Around 20 carbons is motor oil.
§ A chain of hundreds to thousands of carbon and hydrogens make plastic. This particular plastic is polyethylene.
Mar-2010
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§ “Application of scientific principles to the drainage problems arising during the development and production of oil and gas reservoirs”
§ “The art of developing and producing oil and gas fluids in such a manner as to obtain a high economic recovery.”
Definition-Reservoir Engineering
Mar-2010
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Broad Functions
Mar-2010
Reservoir Simulation
Therefore the Ultimate goal is…..•Hydrocarbon in place •Recoverable hydrocarbons reserves•Rate of exploitation
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Data Type
§ Data that pertains to the reservoir rock and its extent
ú Geologic & seismic data
ú Well Log data
ú Well test data
ú Core data
§ Data that pertains to the properties of reservoir fluids
ú Composition of HC
ú PVT
Mar-2010
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The Traps
Mar-2010
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Porosity Porosity of rock is the ratio of pore volume to bulk
volume and is usually expressed as percentage
Vp is pore volumeVb is bulbk volumeVg is grain volume
Total or Absolute Porosity:
ú It is the ratio of the volume of all the pores to the bulk volume of the material,
Effective porosity
ú It is the ratio of the interconnected pore volume to the
bulk volume
Interconnected pores
Isolated pores
Mar-2010
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A Pore
Spatial arrangement-Arrangement of pores of different sizes w.r.t each other
Connectivity of pores and throat-No of pore throat connecting to pores
Size & freq distribution-uncorrelated, correlated
Elements of Pore Throat
The texture of a rock consists of it's grain or mineral crystal size, the arrangement of the grains or crystals, and the degree of uniformity of the grains or crystals.
Mar-2010
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The role of Rock Texture…
Soi=(1-Swi)high
Soi=(1-Swi)low
Mar-2010
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Pore Network-Reconstructed using thin section IMAGE Analysis
Porosity intergranular- 0.23Porosity total- 0.28Absolute Permeability- 426md
Porosity intergranular- 0.37Porosity total- 0.39Absolute Permeability- 5600md
Mar-2010
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Saturation
§ Saturation of a phase is the fraction of the pore volume occupied by the phase So+Sg+Sw=1
Connate water saturation (Swc)
Critical Oil Saturation (Soc)
Critical gas Saturation (Sgc)
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§ Permeability is a measure of ‘ ease of flow’ or the capacity of formation to transmit fluids.
§ Its unit is Darcy named after a French scientist
Henry Darcy in 1856.
ú Absolute Permeability:When only one fluid is present in the rock. It is a property of the rock and is independent of the fluid used in the measurement. This assumes that the fluid does not interact with the rock.(K)
ú Effective Permeability:Effective permeability occurs when more than one fluid is present & is a function of the fluid saturation & the wetting characteristics of the rock. (Ko,Kw,Kg)
Permeability
Mar-2010
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Permeability
The permeability is measured by flowing a fluid of known viscosity µ through a core plug of measured dimensions (A and L) and then measuring flow rate and pressure drop. Darcy equation becomes
Mar-2010
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Permeability
Establishing a perfect Ø-K transform still remains a major challenge specially in ref to carbonates
Mar-2010
The clastics
The carbonates
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Improved Permeability estimation
0.001
0.010
0.100
1.000
10.000
0.010 0.100 1.000
Phi Group
RQ
I, m
icro
n
Phi Group - RQI Plot
HU 1
HU 7HU 6
HU 4
HU 2HU 3
HU 5
y = 18.846x2.4585
y = 30.796x2.1428y = 37.476x1.8785
y = 245.68x2.212
y = 355.42x2.0499y = 1648.1x2.3492
y = 8081.6x2.5518
0.01
0.10
1.00
10.00
100.00
1000.00
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40
Core Porosity
Core
Perm
eability,
mD
HU7,
HU6,HU5,
HU4,
HU3,HU2,
HU1,
Porosity - Permeability Plot
Mar-2010
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Capillary pressure
§ Combined effect of surface and IFT of the rock and fluid, pore size and geometry & wettability of the system.
• Major effect of Cap pres is the creation ofTransition Zone
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Capillary pressure
§ Drainage Process:
ú Non Wetting phase displacing Wetting phase
§ Imbibition Process:
ú Wetting phase displacing Non wetting phase
•Determination of Connate water•Establish Saturation –height relation•Rock Typing Mar-2010
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Wettability
§ ‘The tendency of a fluid to spread or adhere to a solid surface in presence of another immiscible fluid ‘
Mar-2010
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Relative Permeability§ When two or more phases flow simultaneously the ratio of
effective to absolute permeability is termed ‘Relative permeability’
Kro= ko/k
Kre= kw/k
Krg= kg/k
SocSwc
NwP
WP Mar-2010
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Relative Permeability-Rock typing
§ The variation in Rock Texture imparts significant changes in Rel perm estimates in core plugs of same formation
Mar-2010
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Relative Permeability-Core Condition
§ Comparison of Rel-perms of cores with natural reservoir wettability preserved against a plug cleaned, dried and resaturated.
§ Relative Permeability
Mar-2010
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Relative Permeability-wettability
0.8-1.01.5-36-8Oil Wet
0.5-0.92-43-5Mixed Wet
0.1-0.44-62-3Water Wet
KrwNwNoType
Mar-2010
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Reservoir Pressure§ Reservoir Pressure
§ The fluids confined in the pores of the reservoir rock occur under certain degree of pressure, generally called reservoir pressure
ú The maximum pressure is called the static bottom hole
pressure, the shut in pressure or static formation pressure
Mar-2010
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Well testing§ The response of the reservoir to change in production/
injection rates in a well is monitored
§ The reservoir response is measured in terms of ‘pressure’response & is usually dependent on K, Skin, Well bore storage, boundaries, fractures, dual porosity et.c
ú Evaluation: Deliverability, Properties, Size
ú Management: Refining forecast, Front movement
ú Description: Faults, barriers
ResK,s,C
ModelK,s,C
qo
t
P
P
T
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Mar-2010
Radial Flow in a porous media :
For a single phase fluid flow (radial) in a constant permeability and porosity for a fluid of small and constant compressibility, the eauation is :
Pws= Pi-162.6qµB/kh*log((T+∆t)/ ∆t)
K= 162.6qµBmh
S= 1.151[ P1hr-Pwf] –log (K / ФuCtrw2 )+3.23]m
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Pressure Build-up analysis
§ Log-log Plot(Diagnostic plot):
Log ▲t Vs Log ▲P
§ Horner Plot or MDH Plot :
Log [(tp+ ▲t)/ ▲t] Vs Pwf
▲Pskin= 0.87mS
Jactual = q .
P*- Pwf
Jideal = q .
P*-Pwf- ▲Pskin
Flow Efficiency = Jactual/ Jideal
D(distance of fault)=
(0.00105K ▲t/ ФuCt)1/2
Where ▲t = point at the time of intersection between two
straight lines
Horner Plot
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Field ExampleXYZ2222-2250.5m (B2)
3 distinct slopesK:588md, kh:17105 mdftNearest distance to heterogeneity: 130ft
Mar-2010
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Field ExampleXYZ2222-2250.5m (B2)
3 distinct slopesK:588md, kh:17105 mdftNearest distance to heterogeneity: 130ft
Mar-2010
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More data More Refinement
L-II RFT Pressure Data
920
940
960
980
1000
1020
1040
900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
Normalised pressures ( psi)
tvd
ss
(m
)
1983-84
1993-94
1997-98
Fig-4
Mar-2010
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Differing Aquifer Support
Mar-2010
MDT pressure of layer-II
2150
2160
2170
2180
2190
2200
2210
2220
2230
2240
2250
29
20
29
40
29
60
29
80
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00
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40
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30
80
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00
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60
31
80
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00
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80
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00
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00
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34
40
well P3-2/06
well P2-3/06
well P4-4/06
well I5-9/06
well I2-10/06
well I1-06/08
Well I6-07/08
D1-14-10/07
wELL p5-9/08
well p6-11/08
well p1-12/08
P3
I4
I5
15%
MDT pressure of layer-IV
2260
2270
2280
2290
2300
2310
2320
2330
2340
2350
2360
31
60
31
80
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00
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well P3-2/06
well I5-9/06
well I2-10/06
well I1-06/08
Well I6-07/08
D1-14-10/07
Well P5-9/08
well p6 11/08
P2
I2
31%
I5
I4
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Mar-2010
Data - Fluid Properties
§ Expressing HC in place in surface conditions
§ Estimation of Pb,FVF,Rs,Bg, Viscosity
§ Laboratory or empirical relations
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Basic PVT Properties
Mar-2010
Mar-2010
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Reservoir Fluid Types
§Wet gas
§Dry gas
§Retrograde condensate
§Near Critical Condgas
§Black oil
§Low shrinkage oil
§Volatile oil
Tr>TctTc<Tr<TctTr<Tc
Mar-2010
0.423.8014.9142.15C7+
0.120.601.381.59C6
0.080.832.971.15C5
0.521.744.121.6C4
0.342.294.741.93C3
2.674.397.522.75C2
95.8587.0764.3648.83C1
Dry gasGas. CondVolatile OilBlack OilMole Comp.
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The Role of Heavy Components….
After Mccain,W.D
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Phase Envelop-Black Oil
Mar-2010
Brown-D.Green
Colour
15-40API°
35-125GOR-v/v
1.2-1.3Bo v/rv
T T
API
GO
R
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Phase Envelop-Low shrinkage Oil
Mar-2010
BlackColour
<35API°
35GOR-v/v
<1.2Bo v/rv
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Phase Envelop-Volatile Oil
Mar-2010
Greenish-Orange
Colour
45-55API°
350-550GOR-v/v
< 2.0Bo v/rv
GOR API
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Phase Envelop-Near Critical Crude
Mar-2010
Light Colour
45-55API°
> 550GOR-v/v
> 2.0Bo v/rv
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Phase Envelop-Retrograde Gas Condensate
Mar-2010
LightColour
> 50API°
1400-16000GOR-v/v
GOR API
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Phase Envelop-Wet Gas
Mar-2010
LightColour
60API°
11000-18000
GOR-v/v
GOR API
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Phase Envelop- Dry Gas
Mar-2010
LightColour
>API°
>18000GOR-v/v
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Drive mechanism
§ Depletion drive:
Expansion of gas evolved from solution
ú No free gas cap and no active water drive
ú Rapid pressure decline
ú Water free production
ú Rapidly increasing GOR
ú Low ultimate oil recovery (5-20%)
Mar-2010
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Mar-2010
Drive mechanism
§ Gas Cap drive:
Expansion of Gas cap gas
ú Gas cap and no or small active water drive
ú Less rapid pressure decline
ú Water free production
ú Rapidly increasing GOR in structurally high wells
ú Moderate ultimate oil recovery (25-40%)
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Drive mechanism
§ Water Drive:
Production of oil by water displacing process is & usually most efficient processú Very gradual pressure
decline
ú Little change in producing GOR
ú Early water production from structurally lower wells
ú High ultimate recovery
Mar-2010
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Drive mechanism
§ Gravity Drainage:
As a result of difference in reservoir fluid densitiesú Low GOR in structurally low wells
ú Formation of Secondary GCG
ú High GOR in structurally high wells
ú Little or no water production
ú High ultimate recovery
ú Variable rate of pressure decline
Mar-2010
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Asphaltene –The problem
Mar-2010
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Scales for reservoir heterogeneity
RSIN3
MICROThin sections
MACROCore
MEGAWell loggingWell test3D seismic
GIGASeismicBasin studies
Mar-2010
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Reservoir simulation
§ The dictionary meaning of the word ‘simulate’ is ‘to give an appearance of’
§ Forms an integral part of Reservoir Management Functions (RMF)
Mar-2010
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Reservoir simulation§ Mimics the behavior of a real system through
a model (physical, analog, electrical or numerical) based on realistic assumptions
§ Simulation can be close to reality but it is never the reality ( should approach reality with time)
Mar-2010
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Disciplinary contributions to reservoir modeling
NUMERICALSIMULATION
MODEL
Petrophysics FluidProperties
SeismicInterpretation
Model GridEffects
GeologicalModel
SurfaceFacilities
Economics
WellsVertical
HorizontalMultilateral
RSIN1 Mar-2010
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Numerical Model§ Mathematical models System of equations describing the
physical behavior
These are complicated nonlinear partial differential equations relating pressure and saturation changes with time
Analytical solutions-generally impossible
Numerical solutions –generally the only way
Mar-2010
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Numerical Models
§ Basic equations for fluid flow
ú Conservation of mass
ú Conservation of momentum
ú Conservation of energy
ú Rate Equation
ú EOS
Mar-2010
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Numerical Models
§ Numerical solution produces answer at discrete points within the system
§ Use of ‘finite difference’ for transforming the continuous differential equation to discrete form-both space and time are discretized (grid, timesteps)
§ Common solution procedures• IMPES, Newton-Raphson
Mar-2010
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Stochastic Modeling§ Measures statistical variation in data
points-maps similar statistical properties
§ Better describes the heterogeneity of the reservoir- (variograms-trends, direction)
§ Integrates independent measurements
§ Uncertainty in measured values-assessed
§ Algorithm-Kriging, Conditional simulation,co-kriging
Mar-2010
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Scales for reservoir heterogeneity
RSIN3
MICROThin sections
MACROCore
MEGAWell loggingWell test3D seismic
GIGASeismicBasin studies
Grouping of fine layers for upscaling
0%
20%
40%
60%
80%
100%
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43
Fine layers of 'a' parasequence
<1 1 to 10 10 to 100 >100
1 432
Mar-2010
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History Match-First Realization
Mar-2010
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History Match -Final Realization
Mar-2010
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Layer-9(c)
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Parallel Simulation
10 million cell 1 billion cell
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Role & Impact
ú Corporate impact-cash flow predictions
ú Insight to the various physical process
ú Sensitivity
ú Comparing different exploitation scenarios
ú Optimize project design to maximize economic recovery
ú Real Time monitoring
Mar-2010
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Mar-2010
Thanks for patient hearing
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