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Petroleum Reservoir Engineering
----Basic Concepts

Pennsylvania 1859

S.K.Pant


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

50 Hyperbolic Creaming Curve-North sea
45
40
Cum Discovery, Gb

35
30
25
20
15
10
Actual Hyperbolic Model
5
0
0 500 1000 1500 2000 2500 3000 3500
Cum Wildcat wells Mar-2010


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


Definition-Reservoir Engineering

§ “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.”

Mar-2010


Broad Functions

Reservoir Simulation

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


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 Interconnected
Vb is bulbk volume pores

Vg is grain volume Isolated
pores

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

Mar-2010


A Pore
Elements of Pore
Throat
Size & freq distribution-uncorrelated,
correlated

Connectivity of pores and throat-No of pore
throat connecting to pores

Spatial arrangement-Arrangement of pores
of different sizes w.r.t each other

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 intergranular- 0.37
Porosity total- 0.28 Porosity total- 0.39
Absolute Permeability- 426md 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

§ 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)
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

The carbonates

The clastics

Mar-2010


Improved Permeability estimation

Phi Group - RQI Plot
Porosity - Permeability Plot
10.000
1000.00
y = 8081.6x 2.5518
HU7,

Core Permeability, mD
1.000
HU 7 100.00
HU 6
HU 5 HU6, y = 1648.1x2.3492
HU 4 y = 355.42x 2.0499
10.00 HU5,
y = 245.68x 2.212
RQI, micron

HU 3
HU 2 HU4,
0.100
HU 1 1.00 y = 37.476x1.8785
HU3, y = 30.796x 2.1428
HU2,

0.10
0.010 y = 18.846x 2.4585
HU1,

0.01
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40
0.001
0.010 0.100 1.000 Core Porosity
Phi Group

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

Swc Soc

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- § Relative Permeability
perms of cores with
natural reservoir
wettability preserved
against a plug
cleaned, dried and
resaturated.

Mar-2010


Relative Permeability-wettability

Type No Nw Krw

Water 2-3 4-6 0.1-0.4

Wet

Mixed 3-5 2-4 0.5-0.9

Wet

Oil Wet 6-8 1.5-3 0.8-1.0

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

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


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
Mar-2010


Pressure Build-up analysis
§ Log-log Plot(Diagnostic plot):
Log t Vs Log P
§ Horner Plot or MDH Plot : Horner 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


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
Fig-4
L-II RFT Pressure Data

920
1983-84
940 1993-94
1997-98
960
tvds s (m )

980

1000

1020

1040
900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
Normalised pressures ( psi)

Mar-2010


Differing Aquifer Support
I4

P3
I5
MDT pressure of layer-II I4
MDT pressure of layer-IV well P3-2/06
P2

well P3-2/06
I2
I5
well I5-9/06
2150 well P2-3/06 2260 well I2-10/06
well P4-4/06
well I5-9/06
well I1-06/08
2160 well I2-10/06 2270 Well I6-07/08
31%
well I1-06/08 D1-14-10/07
Well I6-07/08
2170 D1-14-10/07
2280 Well P5-9/08
wELL p5-9/08 well p6 11/08
well p6-11/08
2180 2290
well p1-12/08

15%
2190 2300

2200 2310

2210 2320

2220 2330

2230 2340

2240 2350

2250 2360
3160
3180
3200
3220
3240
3260
3280
3300
3320
3340
3360
3380
3400
3420
3440
3460
3480
3500
3520
3540
3560
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

Mar-2010


Data - Fluid Properties

§ Expressing HC in
place in surface
conditions

§ Estimation of
Pb,FVF,Rs,Bg,
Viscosity

§ Laboratory or
empirical relations

Mar-2010


Basic PVT
Properties

Mar-2010

Mar-2010


Reservoir Fluid Types
Tr<Tc Tc<Tr<Tct Tr>Tct
§Black oil §Retrograde §Wet gas
§Low shrinkage oil condensate §Dry gas
§Volatile oil §Near Critical Cond
gas

Mole Comp. Black Oil Volatile Oil Gas. Cond Dry gas
C1 48.83 64.36 87.07 95.85
C2 2.75 7.52 4.39 2.67
C3 1.93 4.74 2.29 0.34
C4 1.6 4.12 1.74 0.52
C5 1.15 2.97 0.83 0.08
C6 1.59 1.38 0.60 0.12
C7+ 42.15 14.91 3.80 0.42

Mar-2010


The Role of Heavy Components….

After Mccain,W.D


Phase Envelop-Black Oil

Bo v/rv 1.2-1.3

GOR-v/v 35-125

API° 15-40

Colour Brown-
GOR

D.Green
API

Mar-2010
T T


Phase Envelop-Low shrinkage Oil

Bo v/rv <1.2
GOR-v/v 35
API° <35
Colour Black

Mar-2010


Phase Envelop-Volatile Oil

Bo v/rv < 2.0
GOR-v/v 350-550
API° 45-55
Colour Greenish-
Orange

Mar-2010
GOR API


Phase Envelop-Near Critical Crude

Bo v/rv > 2.0
GOR-v/v > 550
API° 45-55
Colour Light

Mar-2010


Phase Envelop-Retrograde Gas
Condensate

GOR-v/v 1400-16000
API° > 50
Colour Light

Mar-2010
GOR API


Phase Envelop-Wet Gas

GOR-v/v 11000-
18000
API° 60

Colour Light

Mar-2010
GOR API


Phase Envelop- Dry Gas

GOR-v/v >18000
API° >
Colour Light

Mar-2010


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


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%)

Mar-2010


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

MICRO
Thin sections
MACRO
Core

MEGA
Well logging
Well test
3D seismic

GIGA
Seismic
Basin studies

RSIN3

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
Seismic Fluid
Interpretation Petrophysics
Properties

NUMERICAL
Geological SIMULATION Surface
Model MODEL Facilities

Wells
Model Grid Vertical Economics
Effects 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
MICRO
Thin sections

MACRO
Grouping of fine layers for upscaling
Core 1 2 3 4
100%

80%

60%

40%

20%

0%
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

MEGA
Well logging
Well test RSIN3

3D seismic
GIGA
Seismic
Basin studies

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


Thanks for patient hearing

Mar-2010

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