basic reservoir engineering - part i
TRANSCRIPT
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GEOPET BACHELOR PROGRAM IN
PETROLEUM ENGINEERING
BASIC RESERVOIRENGINEERING
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Learning Objectives
At the end of this lecture, you should be able to understand the
fundamentals of reservoir engineering and do some basic
analyses/calculations as follows:
PVT Analysis
Special Core Analysis
Well Test Analysis
Production Forecast
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References
1. L.P.Dake (1978). Fundamentals of Reservoir Engineering,
Elsevier Science, Amsterdam.
2. L.P.Dake (1994). The Practice of Reservoir Engineering,
Elsevier Science, Amsterdam.
3. B.C.Craft & M.Hawkins (1991). Applied Petroleum
Reservoir Engineering,Prentice Hall, New Jersey.
4. T. Ahmed (2006). Reservoir Engineering Handbook , Gulf
Professional Publishing, Oxford.
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Outline
Key Concepts in Reservoir Engineering
Fundamentals of Oil & Gas Reservoirs
Quantitative Methods in Reservoir Characterization and
Evaluation.
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Part I
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Key Concepts in
Reservoir Engineering
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Definition of Reservoir
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In petroleum industry, reservoir fluids is a mixture ofhydrocarbons (oil and/or gas), water and other non-hydrocarboncompounds (such as H2S, CO2, N2, ...)
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Definition of Engineering
Engineering is the discipline or profession of
applying necessary knowledge and utilizing
physical resources in order to design and
implement systems and processes that realize a
desired objective and meet specified criteria.
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Definition of Engineering
Engineering is the discipline and profession of
applying necessary knowledge and utilizing
physical resources in order to design and
implement systems and processes that realize a
desired objective and meet specified criteria.
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Necessary Knowledge
Knowledge about oil & gas reservoirs
Reservoir Rock Properties & Behavior during the
Production Process
Reservoir Fluid Properties & Behavior during the
Production Process
Fluid Flows in Reservoirs
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Necessary Knowledge (cont’d)
Technical & Scientific Knowledge
Quantitative Methods for Reservoir
Characterization
Quantitative Methods for Reservoir
Evaluation
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Definition of Engineering
Engineering is the discipline and profession of
applying necessary knowledge and utilizing
physical resources in order to design and
implement systems and processes that realize a
desired objective and meet specified criteria.
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Physical Resources
In-place Reservoir Resources
Reservoir’s energy source resulted from the
initial pressure & drive mechanisms during
production
Available flow conduits thanks to reservoir’s
characteristic properties such as permeability
distribution.
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Definition of Engineering
Engineering is the discipline and profession of
applying necessary knowledge and utilizing
physical resources in order to design and
implement systems and processes that realize a
desired objective and meet specified criteria.
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Design and Implementation
Design and Implement an Oil Field Development Plan
Plan for producing oil & gas from the reservoirs in the
field: Exploit reservoir energy sources; Design
appropreate well patterns; Select suitable subsurface &
surface facilities ... during the lifecycle of the oil field
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Definition of Engineering
Engineering is the discipline and profession of
applying necessary knowledge and utilizing
physical resources in order to design and
implement systems and processes that realize a
desired objective and meet specified criteria.
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Desired Objective
To Maximize the profit resulted from the
recovered oil & gas
To recover as much as possible oil & gas from
the reservoirs
To recover high-quality oil & gas
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Definition of Engineering
Engineering is the discipline and profession of
applying necessary knowledge and utilizing
physical resources in order to design and
implement systems and processes that realize a
desired objective and meet specified criteria.
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Specified Criteria
Money associated with hired manpower,
facilities, technologies, ...
Time
Local regulations
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Oil Fields and Their Lifecycle
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Oil Fields and Their Lifecycle
A lifecycle of an oil field consists of the following stages:
Exploration
Appraisal
Development
Production
Abandonment
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Revenue Throughout LifeCycle
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Part II
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Basic Properties and
Behaviors of
Oil & Gas Reservoirs
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Five Basic
Reservoir
Fluids
Black Oil
Criticalpoint
P r e s s u r e , p s i a
Separator
Pressure pathin reservoir Dewpoint line
% Liquid
Temperature, °F
P r e s s u r e
Temperature
Separator
% Liquid
Volatile oil
Pressure pathin reservoir
3
2
1
3
Criticalpoint
3
Separator
% Liquid
Pressure pathin reservoir
1
2Retrograde gas
Critical
point P r e s s u r e
Temperature
P r e s s u
r e
Temperature
% Liquid
2
1
Pressure pathin reservoir
Wet gas
Criticalpoint
Separator
P r e s s u r e
Temperature
% Liquid
2
1
Pressure pathin reservoir
Dry gas
Separator
Retrograde Gas Wet Gas Dry Gas
Black Oil Volatile Oil
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Classification of Reservoir Fluids
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Used to visualize the fluids production path from
the reservoir to the surface
Used to classify reservoir fluids
Used to develop different strategies to produce
oil/gas from reservoir
Pressure-Temperature Diagrams
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Phase Diagrams
Single
Liquid
Phase
Region
CriticalPoint
P r e s s u r e , p s i a
InitialReservoir
State
% Liquid
Temperature, °F
Cricondentherm
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Separator
Cricondenbar
Single
Gas
Phase
Region
Two-Phase
Region
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Black Oil
Black Oil
CriticalPoint
P r e s s u r e ,
p s i a
Separator
Pressure pathin reservoir
Dewpoint line
% Liquid
Temperature, °F
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Volatile-Oil
P r e s s u
r e
Temperature, °F
Separator
% Liquid
Volatile oil
Pressure pathin reservoir
2
1
3
Criticalpoint
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Retrograde Gas
3
Separator
% Liquid
Pressure path
in reservoir1
2Retrograde gas
Critical point
P r e s s u r
e
Temperature
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Wet Gas
P r e s s u r e
Temperature
% Liquid
2
1
Pressure path
in reservoir
Wet gas
Criticalpoint
Separator
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Dry Gas
P r e s s u
r e
Temperature
% Liquid
2
1
Pressure path
in reservoir
Dry gas
Separator
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Field Identification
Black
Oil
Volatile
Oil
Retrograde
Gas
Wet
Gas
Dry
Gas
Initial Producing
Gas/Liquid
Ratio, scf/STB
3200 > 15,000* 100,000*
Initial Stock-
Tank Liquid
Gravity, API
< 45 > 40 > 40 Up to 70 No
Liquid
Color of Stock-
Tank Liquid
Dark Colored Lightly
Colored
Water
White
No
Liquid
*For Engineering Purposes
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Laboratory Analysis
Black
Oil
Volatile
Oil
Retrograde
Gas
Wet
Gas
Dry
Gas
Phase
Change in
Reservoir
Bubblepoint Bubblepoint Dewpoint No Phase
Change
No
Phase
ChangeHeptanes
Plus, Mole
Percent
> 20% 20 to 12.5 < 12.5 < 4* < 0.8*
Oil
Formation
VolumeFactor at
Bubblepoint
< 2.0 > 2.0 - - -
*For Engineering Purposes
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0
50000
0 30
Heptanes plus in reservoir f luid, mole %
I n i t i a l p r o d
u c i n g
g a s / o i l r
a t i o ,
s c f / S T B
Dewpoint gas
Bubblepoint oil
Retrograde
gas
Volatile
oil
Wet
gas
Dry
gas
Blackoil
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Field Identification
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34 Flui
Primary Production Trends
G O R
G O R
G O R
G O R
G O R
Time Time Time
TimeTime TimeTimeTime
TimeTime
No
liquid
No
liquid
Dry
Gas
Wet
Gas
Retrograde
Gas
Volatile
Oil
Black
Oil
A P I
A P I
A P I
A P I
A P I
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Exercise 1
Based on the phase diagrams of volatile oil
and retrograde gas, describe some
characteristic properties of these two
reservoir fluids
Name some applications of phase diagrams
in selecting surface facilities
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Basic Properties of Natural Gas
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Equation-of-State (EOS)
Apparent Molecular Weight of Gas Mixture
Density of Gas Mixture
Gas Specific Gravity
Z-factor (Gas Compressibility or Gas Deviation
Factor)
Isothermal Compressibility
Gas Formation Volume Factor
Gas Viscosity
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Gas Equation-Of-State (EOS)
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pV nZRT =Equation of State:
Quantity Description Unit/Value
p Pressure psia
V Volume ft3
n Mole Number lb-mol
Z Gas Deviation
Factor
dimensionless
T Temperature Rankine
R Universal Gas
constant
10.73
psia.ft3 /lb-mole. °R
Apparent Molecular Weight of a
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Apparent Molecular Weight of aGas Mixture
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Normally, petroleum gas is a mixture of variouslight hydrocarbon (C1-C4). For example:
Component Mole Percent MolecularWeight
(lb/lb-mol)
Critical Critical
Pressure Temperature
(psia) (o
R) (1) (2) (3) (4)
C1 0.85 16.043 666.4 343.00
C2 0.04 30.070 706.5 549.59
C3 0.06 44.097 616.0 665.73
iC4 0.03 58.123 527.9 734.13 nC4 0.02 58.123 550.6 765.29
1
20.39 N
a i i
i
M y M =
= =∑
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Density of Gas Mixture
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Gas density is calculated from the definition ofdensity and the EOS
3 pM= = (lb/ft )g a a
g
g
m nM p
V nZRT ZRT ρ =
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Gas Specific Gravity
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The specific gravity is defined as the ratio of thegas density to that of the air
M= =
28.97
g a a
g
air air
M
M
ρ γ
ρ =
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Gas Deviation Factor (Z-factor)
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Z-factor in the EOS accounts for the difference inthe behavior of natural gases in compared with idealgases.
; pr pr
pc pc
p T p T
p T = =
Z-factor can be expressed as: Z=Z(ppr,Tpr) where
; pc i ci pc i ci
i i
p y p T y T = =∑ ∑
ppr: pseudo-reduced pressureTpr: pseudo-reduced temperatureppc: pseudo-critical pressureTpc: pseudo-critical temperature
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Standing-Katz Chart
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Step 1: Calculate pseudo-criticalpressure and temperature
Step 2: Calculate pseudo-reducedpressure and temperature:
Step 3: Use Standings-Katz chartto determine Z
; pr pr
pc pc
p T p T
p T = =
; pc i ci pc i ci
i i
p y p T y T = =∑ ∑
Dranchuk & Abou-Kassem
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Dranchuk & Abou-KassemCorrelation
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7210.0;6134.0
1056.0;1844.0;7361.0
5475.0;05165.0;01569.0
5339.0;0700.1;3265.0
1110
987
654
321
==
==−=
=−==−=−==
A A
A A A
A A A
A A A
2 5 2 2 22
1 3 4 5 11 11
3 4 5
1 1 2 3 4 5
2
2
3 6 7 8
2
4 9 7 8
3
5 10
( ) (1 ) exp( ) 1 0
0.27 / ( )
/ / / /
0.27 /
/ /
( / / )
/
r r r r r r r r
r pr pr
pr pr pr pr
pr pr
pr pr
pr pr
pr
RF R R R R A A
p ZT
R A A T A T A T A T
R p T
R A A T A T
R A A T A T
R A T
ρ ρ ρ ρ ρ ρ ρ ρ
ρ
= − + − + + − + =
=
= + + + +
=
= + +
= +
=
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Exercise 2
Component yi Mi Tci,°R pci
CO2 0.02 44.01 547.91 1071
N2 0.01 28.01 227.49 493.1
C1 0.85 16.04 343.33 666.4
C2 0.04 30.1 549.92 706.5
C3 0.03 44.1 666.06 616.4
i - C4 0.03 58.1 734.46 527.9
n - C4 0.02 58.1 765.62 550.6
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Wichert-Aziz Correction Method
R , oε −= pc pc T T
2 2
, psia(1 )
pc pc
pc
pc H S H S
p T p
T y y ε =
+ −
Corrected pseudo-critical temperature:
Corrected pseudo-critical pressure:
( ) ( )( ) ( )2 2 2 2 2 20.9 1.6
0.5 4.0120 15 , H S CO H S CO H S H S y y y y y yε = + − + + −
Pseudo-critical temperature adjustment factor
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Exercise 3
Component Mole fraction
C1 0.76
C2 0.07CO2 0.1
H2S 0.07
Given the following real gas composition,
Determine the density of the gas mixture at 1,000psia and 110 °F using Witchert-Aziz correctionmethod.
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Sutton Correction Method
20.5
o
o
1 2, R/psia
3 3
, R/psiai
i
c ci i
i ic ci i
c
i
i c
T T J y y
p p
T K y
p
= +
=
∑ ∑
∑
Step1: Calculate the parameters J and K:
7 7
7 7
7 7 7
7
20.5
2 2
2 3
1 2
3 3
0.6081 1.1325 14.004 64.434
0.3129 4.8156 27.3751
c c J
c c
C C
J J J J C J C
cK C C C
c C
T T F y y
p p
F F F y F y
T y y y
p
ε
ε
+ +
+ +
+ + +
+
= +
= + − +
= − +
Step 2: Calculate the adjustment parameters:
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S C i M h d ( )
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Sutton Correction Method (cont.)
K
J
K K
J J
ε
ε
−=
−=Step 3: Adjust the parameters J and K
J T p
J
K T
pc pc
pc
=
=2
Step 4: Calculate the adjusted pseudo-criticalterms
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Correlations for Pseudo Properties
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Correlations for Pseudo Propertiesof Real Gas Mixture
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Isothermal Compressiblity of
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Isothermal Compressiblity ofNatural Gas Mixture
1 d
d g
V c
V p= −
By definition, the compressibility of the gas is
1 1g
T
dzc
p z dp
= −
Isothermal pseudo-reduced compressibility:
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or
1 1 d
d pr
pr g pc pr pr T
z
c c p p z p
= = −
Gas Isothermal Compressiblity Correlation by
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Gas Isothermal Compressiblity Correlation by
Matter, Brar & Aziz (1975)
2
1 0.27
1
pr
pr
r T
g
pr pr r
r T
dz
d c
p z T dz
z d
ρ
ρ
ρ
= −
+
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( ) ( )4 2 2 4 21 2 3 4 8 8 82 5 2 1 exp pr
r r r r r r
r T
dzT T T T A A A
d ρ ρ ρ ρ ρ ρ
ρ = + + + + − −
3 521 1 2 43
5 6 73 4 53
;
0.27; ;
pr pr pr
pr
pr pr pr
A A AT A T A
T T T p A A A
T T T T T T
= + + = +
= = =
A1 0.3150624 A5 -0.61232032
A2 -1.04671 A6 -0.10488813
A3 -0.578327 A7 0.68157001
A4 0.5353077 A8 0.68446549
G F i V l F
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Gas Formation Volume Factor
, p T
g
sc
V B
V =
By definition, the gas FVF is
Combining the above equation with the EOS yields
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30.02827 (ft /scf)
0.005035 (bbl/scf)
g
g
zT B
p
zT B p
=
=
Gas Viscosity Correlation Method by
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Gas Viscosity Correlation Method byCarr, Kobayashi and Burrows (1954)
Step 1: Calculate pseudo-critical properties and thecorrections to these properties for the presence ofnonhydrocarbon gases (CO2, H2S, N2)
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Step 2: Obtain the (corrected) viscosity of the gas
mixture at one atmosphere and the temperature ofinterest
2 2 21 1uc N CO H S µ µ µ µ µ = + ∆ + ∆ + ∆
Step 3: Calculate the pseudo-reduced pressure and
temperature, and obtain the viscosity ratio (µg /µ1)
Step 4: Calculate the gas viscosity from µ1 and theviscosity ratio (µg /µ1)
Carr’s Atmospheric Gas Viscosity
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Carr s Atmospheric Gas ViscosityCorrelation
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G Vi it R ti C l ti
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Gas Viscosity Ratio Correlation
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Standing’s Correlation for
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Standing s Correlation for Atmospheric Gas Viscosity
( )
( )5 6
1
3 3
1.709 10 2.062 10 460
8.118 10 6.15 10 log
uc g
g
T µ γ
γ
− −
− −
= × − × − +
× − × ×
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( )2 2
2 2
2 2
3 3
3 3
3 3
9.08 10 log 6.24 10
8.48 10 log( ) 9.59 10
8.49 10 log( ) 3.73 10
CO CO g
N N g
H S H S g
y
y
y
µ γ
µ γ
µ γ
− −
− −
− −
∆ = × × + × ∆ = × × + ×
∆ = × × + ×
2 2 21 1uc CO N H S µ µ µ µ µ = + ∆ + ∆ + ∆
Dempsey’s Correlation for Gas
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e psey s Co e at o o GasViscosity Ratio
2 3
0 1 2 3
1
2 3
4 5 6 7
2 2 3
8 9 10 11
3 2 3
12 13 14 15
ln g
pr pr pr pr
pr pr pr pr
pr pr pr pr
pr pr pr pr
T a a p a p a p
T a a p a p a p
T a a p a p a p
T a a p a p a p
µ
µ
= + + + +
+ + + +
+ + + +
+ + +
3/18/2013 57Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
a0 = −2.46211820 a1 = 2.970547414a2 = −2.86264054 (10−1)a3 = 8.05420522 (10−3)a4 = 2.80860949a5 = −3.49803305
a6 = 3.60373020 (10−1)a7 = −1.044324 (10−2)a8 = −7.93385648 (10−1)a9 = 1.39643306a10 = −1.49144925 (10−1)a11 = 4.41015512 (10−3)
a12 = 8.39387178 (10−2)a13 = −1.86408848 (10−1)a14 = 2.03367881 (10−2)a15 = −6.09579263 (10−4)
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Exercise 4
A gas well is producing at a rate of 15,000 ft3/dayfrom a gas reservoir at an average pressure of 2,000psia and a temperature of 120°F. The specificgravity is 0.72.
Calculate the vicosity of the gas mixture using bothgraphical and analytical methods.
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Properties of Crude Oil
3/18/2013 59Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
Oil density and gravity
Gas solubility
Bubble-point pressure
Oil formation volume factor
Isothermal compressibility coefficient of
undersaturated crude oils
Oil viscosity
These fluid properties are usually determined by laboratoryexperiments. When such experiments are not available,empirical correlations are used
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Crude Oil Density
3/18/2013 60Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
The crude oil density is defined as the mass of aunit volume of the crude oil at a specifiedpressure and temperature.
3 (lb/ft )oo
o
m
V ρ =
d l
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Crude Oil Gravity
3/18/2013 61Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
The specific gravity of a crude oil is defined as theratio of the density of the oil to that of water.
oAPI is usually used to reprensent the gravity ofthe crude oil as follow
3; 62.4 (lb/ft )oo ww
ρ γ ρ
ρ = =
141.5 -131.5o
o
API γ
=
The API gravity of crude oils
usually ranges from 47° API forthe lighter crude oils to 10° APIfor the heavier crude oils.
l k il d l
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Black Oil Model
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G S l bili R
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Gas Solubility Rs
3/18/2013 63Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
Rs is defined as the number of standard cubic feetof gas dissolved in one stock-tank barrel of crudeoil at certain pressure and temperature.
The solubility of a natural gas in a crude oil is a
strong function of the pressure, temperature, APIgravity, and gas gravity.
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Standing’s Correlation for R
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Standing s Correlation for Rs
3/18/2013 65Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
( )
1.2048
1.4 1018.2
0.0125 0.0009 460
x
s g
p
R
x API T
γ
= + ×
= × − × −
Ch t i ti f R i R k
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Characteristics of Reservoir Rocks
3/18/2013 66Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
Porosity
Permeability
In-situ Saturation
P it
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pore bulk matrix
bulk bulk
V V V
V V φ −
= =
Porosity
3/18/2013 67Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
P it
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Porosity
Porosity depends on grain packing, NOT grain size
Rocks with different grain sizes can have the sameporosity
• Rhombohedral packing
• Pore space = 26 % of total volume• Cubic packing
• Pore space = 47 % of total volume
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Rock Matrix and Pore Space
Rock matrix Pore space
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P S Cl ifi ti
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Pore-Space Classification
Total porosity
Effective porosity
Total Pore Space
Bulk Volume
pore
t
bulk
V
V
φ = =
Interconnected Pore SpaceBulk Volume
eφ =
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bili
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Permeability is a property of the porous
medium and is a measure of the capacity of
the medium to transmit fluids
Permeability
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R l i P bili
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Relative permeability is defined as the ratio
of the effective permeability to a fluid at a
given saturation to the effective permeability
to that fluid at 100% saturation
Relative Permeability
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Darcy’s Law
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Darcy s Law
v: Velocity
q: Flow rate
A: Cross-section areak: Permeability
µ: Viscosity∆L: Length increment
∆p: Pressure drop
q
Direction of flow A
q k pv
A Lµ
∆≡ = − ×
∆
3/18/2013 76Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
Fluid Saturation
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Fluid Saturation
Fluid saturation is defined as the fraction of porevolume occupied by a given fluid
Phase saturations
Sw = water saturation
So = oil saturationSg = gas saturation
specific fluid
poreSaturation
V
V =
3/18/2013 77Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
I Sit S t ti
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In-Situ Saturation
Rock matrix Water Oil and/or gas
3/18/2013 78Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
Exercise 5
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Exercise 5
1. Pore volume occuppied by water
2. Pore volume occupied by hydrocarbon
3/18/2013 79Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
Given the following reservoir data:
Bulk Volume Vb
Porosity
Water saturation Sw
Calculate:
Reservoir Drive Mechanisms
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Reservoir Drive Mechanisms
Solution Gas Drive
Gas Cap Drive
Water Drive
Gravity drainage drive
Combination drive
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Reservoir Energy Sources
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Reservoir Energy Sources
Liberation, expansion of solution gas
Influx of aquifer water
Expansion of reservoir rock
Expansion of original reservoir fluids
Free gas
Connate water
Oil
Gravitational forces
Solution-Gas Drive in Oil Reservoirs
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Solution-Gas Drive in Oil Reservoirs
Oil
A. Original Condition
B. 50% Depleted
Oilproducing
wells
Oilproducing
wells
3/18/2013 82Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
Solution-Gas Drive in Oil ReservoirsF i f S d G C
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Formation of a Secondary Gas Cap
Wellbore
Secondarygas cap
3/18/2013 83Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
Gas Cap Drive in Oil Reservoirs
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Oil producing well
Oilzone
OilzoneGas cap
Gas-Cap Drive in Oil Reservoirs
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Water Drive in Oil Reservoirs
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Oil producing well
Water Water
Cross Section
Oil Zone
Edgewater Drive
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Water Drive in Oil Reservoirs
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Oil producing well
Cross Section
Oil Zone
Water
Bottomwater Drive
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Gravity Drainage Drive in OilR i
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Reservoirs
Oil
Oil
Oil
Point A
Point B
Point C
Gas
Gas
Gas
3/18/2013 87Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
Combination Drive in Oil Reservoirs
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Combination Drive in Oil Reservoirs
Water
Cross Section
Oil zone
Gas cap
3/18/2013 88Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
Pressure and Gas/Oil Ratio Trends
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Pressure and Gas/Oil Ratio Trends
0 20 40 60 80 100
100
80
60
40
20
0
Gas-cap drive
Water drive
Solution-gas drive
R
e s e r v o i r p r e
s s u r e ,
P e r c e n t o f o r
i g i n a l
Cumulative oil produced, percent of original oil in place
3/18/2013 89Mai Cao Lân – Faculty of Geology & Petroleum Engineering - HCMUT
Exercise 6
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Exercise 6
1. How can we identify different reservoir drive
mechanisms?
2. Rank in descending order typical reservoir drivemechanisms in terms of efficiency
3. How does knowledge about reservoir drive mechanisms
help us in designing an oil field development plan?