PetroleumResEng

Petroleum Reservoir Engineering
----Basic Concepts
S.K.Pant
Pennsylvania 1859
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Outline
§ Introduction
§ Reservoir Properties
ú 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

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

The law of Diminishing return
Mar-2010
0
5
10
15
20
25
30
35
40
45
50
0 500 1000 1500 2000 2500 3000 3500
Cum Wildcat wells
CumDiscovery,Gb
Actual Hyperbolic Model
Hyperbolic Creaming Curve-North sea

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

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

§ “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

Broad Functions
Mar-2010
Reservoir Simulation
Therefore the Ultimate goal is…..
•Hydrocarbon in place
•Recoverable hydrocarbons reserves
•Rate of exploitation

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

The Traps
Mar-2010

Porosity
Porosity of rock is the ratio of pore volume to bulk
volume and is usually expressed as percentage
Vp is pore volume
Vb is bulbk volume
Vg 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

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

The role of Rock Texture…
Soi=(1-Swi)
high
Soi=(1-Swi)
low
Mar-2010

Pore Network-Reconstructed using thin section IMAGE
Analysis
Porosity intergranular- 0.23
Porosity total- 0.28
Absolute Permeability- 426md
Porosity intergranular- 0.37
Porosity total- 0.39
Absolute Permeability- 5600md
Mar-2010

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)

§ 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

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

Permeability
Establishing a perfect Ø-K transform still remains a major challenge
specially in ref to carbonates
Mar-2010
The clastics
The carbonates

Improved Permeability estimation
0.001
0.010
0.100
1.000
10.000
0.010 0.100 1.000
Phi Group
RQI,micron
Phi Group - RQI Plot
HU 1
HU 7
HU 6
HU 4
HU 2
HU 3
HU 5
y = 18.846x2.4585
y = 30.796x2.1428
y = 37.476x1.8785
y = 245.68x2.212
y = 355.42x2.0499
y = 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
CorePermeability,mD
HU7,
HU6,
HU5,
HU4,
HU3,
HU2,
HU1,
Porosity - Permeability Plot
Mar-2010

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 of
Transition Zone

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

Wettability
§ ‘The tendency of a fluid to spread or adhere to a solid surface in
presence of another immiscible fluid ‘
Mar-2010

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

Relative Permeability-Rock typing
§ The variation in Rock
Texture imparts
significant changes in
Rel perm estimates in
core plugs of same
formation
Mar-2010

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

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

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

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
Res
K,s,C
Model
K,s,C
qo
t
P
P
T

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= 162.6qµB
mh
S= 1.151[ P1hr-Pwf] –log (K / uCtrw2 )+3.23]
m

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/ uCt)1/2
Where
t = point at the time of intersection
between two
straight lines
Horner Plot

Field Example
XYZ
2222-2250.5m (B2)
3 distinct slopes
K:588md, kh:17105 mdft
Nearest distance to heterogeneity: 130ft
Mar-2010

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)
tvdss(m)
1983-84
1993-94
1997-98
Fig-4
Mar-2010

Differing Aquifer Support
Mar-2010
MDT pressure of layer-II
2150
2160
2170
2180
2190
2200
2210
2220
2230
2240
2250
2920
2940
2960
2980
3000
3020
3040
3060
3080
3100
3120
3140
3160
3180
3200
3220
3240
3260
3280
3300
3320
3340
3360
3380
3400
3420
3440
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
3160
3180
3200
3220
3240
3260
3280
3300
3320
3340
3360
3380
3400
3420
3440
3460
3480
3500
3520
3540
3560
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

Mar-2010
Data - Fluid Properties
§ Expressing HC in
place in surface
conditions
§ Estimation of
Pb,FVF,Rs,Bg,
Viscosity
§ Laboratory or
empirical relations

Basic PVT
Properties
Mar-2010
Mar-2010

Reservoir Fluid Types
§Wet gas
§Dry gas
§Retrograde
condensate
§Near Critical Cond
gas
§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.

The Role of Heavy Components….
After Mccain,W.D

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
GOR

Phase Envelop-Low shrinkage Oil
Mar-2010
BlackColour
<35API°
35GOR-v/v
<1.2Bo v/rv

Phase Envelop-Volatile Oil
Mar-2010
Greenish-
Orange
Colour
45-55API°
350-550GOR-v/v
< 2.0Bo v/rv
GOR API

Phase Envelop-Near Critical Crude
Mar-2010
LightColour
45-55API°
> 550GOR-v/v
> 2.0Bo v/rv

Phase Envelop-Retrograde Gas
Condensate
Mar-2010
LightColour
> 50API°
1400-16000GOR-v/v
GOR API

Phase Envelop-Wet Gas
Mar-2010
LightColour
60API°
11000-
18000
GOR-v/v
GOR API

Phase Envelop- Dry Gas
Mar-2010
LightColour
>API°
>18000GOR-v/v

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

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%)

Drive mechanism
§ Water Drive:
Production of oil by
water displacing
process is & usually
most efficient process
ú Very gradual pressure
decline
ú Little change in producing
GOR
ú Early water production
from structurally lower
wells
ú High ultimate recovery
Mar-2010

Drive mechanism
§ Gravity Drainage:
As a result of difference in reservoir fluid
densities
ú 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

Asphaltene –The problem
Mar-2010

Scales for reservoir heterogeneity
RSIN3
MICRO
Thin sections
MACRO
Core
MEGA
Well logging
Well test
3D seismic
GIGA
Seismic
Basin studies
Mar-2010

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

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

Disciplinary contributions to reservoir modeling
NUMERICAL
SIMULATION
MODEL
Petrophysics Fluid
Properties
Seismic
Interpretation
Model Grid
Effects
Geological
Model
Surface
Facilities
Economics
Wells
Vertical
Horizontal
Multilateral
RSIN1 Mar-2010

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

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

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

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

Scales for reservoir heterogeneity
RSIN3
MICRO
Thin sections
MACRO
Core
MEGA
Well logging
Well test
3D seismic
GIGA
Seismic
Basin 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

History Match-First Realization
Mar-2010

History Match -Final Realization
Mar-2010

Layer-9(c)

Parallel Simulation
10 million cell 1 billion cell

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

Mar-2010
Thanks for patient hearing

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