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PVT Short Course for Cairo UniversitySPE Student Chapter
Ahmed Muaz
Khalda Petroleum Company
April 23, 2011
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Contents
Why Study PVT?
Objectives of PVT Analysis
Types of Reservoir Fluids
Differentiation Between the Different Types
of
Reservoir Fluids
Fluid Sampling
Laboratory Experiments
PVT Reports
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Why Study PVT?
Transport
.Sep
Gas
StockTank
Oil
.Diff Flow Regime
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Objectives of PVT Analysis
Need to understand PVT analysis for:
Determination of reservoir fluid type
Knowledge of physical properties of reservoir fluids
Match an EOS to the measured data
Creation of PVT models
Ultimate recoveries of different components
Amounts and composition of liquids left behind
Determination of well stream composition
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Objectives of PVT Analysis Cont.
Completion design
Separator/NGL plant specifications
Product values Vs. time
Prediction compositional gradient
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The Five Reservoir Fluids
Black Volatile Retrograde Wet Dry
Oil Oil Gas Gas Gas
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Reservoir Fluid Type Identification
Analyzing a representative sample in the lab
Production data
1.Initial GOR
2.API
3.Oil color
4.C7+
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Black Oil
An initial GOR, 1750 SCF/STB or less
A 45 API initial stock tank oil gravity or less
A dark color of stock tank oil
C7+ > 20 mole %
Initial Bo of 2 res bbl/STB or less
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Black Oil Phase Diagram
T h e in itia l re se rvo ir
( & )con d ition s P T are
m u ch lo w e r th a n
th e critica l
co n d itio n s
T h e h e a vy m o le cu le s
co n ce n tra tio n is
h ig h
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Volatile Oil
An initial GOR, 1750 SCF/STB or greater
A 51.2 API initial stock tank oil gravity
A medium orange stock tank oil color
C7+ concentration between 19 and 22 mole %
Bo 2.0 res bbl/STB or greater
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Volatile Oil Phase Diagram
The initial reservoir
conditions (P&T)
are close to the
critical conditions
Have fewer heavy
molecules than
black oil
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Retrograde Gas Condensate
An initial GOR > 3200 SCF/STB
API > 45 initial stock tank oil gravity
A light stock tank oil color
C7+ concentration
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Retrograde Gas Phase Diagram
The initial reservoir
conditions (P&T) arehigher than thecritical conditions
Have fewer heavy
molecules thanvolatile oils
The overallcomposition of the
reservoir fluidbecomes heavier asthe lighter gas isproduced and theheavier condensate
remains behind
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Wet Gas
An initial GOR > 15,000 SCF/STB
API up to 70 initial stock tank oil gravity
Water white of tank oil color
C7+ concentration
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Wet Gas Phase Diagram
Reservoir
Temperature aboveCricondentherm(pressure path notenter phaseenvelope)
The reservoir fluid isgas throughout thelife of the reservoir
The separatorcondition is twophases
Gravity of stock tankliquid same as
retrograde gas
Temperature
% Liquid
2
1
ressure pathn reservoir
e t g as
Criticalpoint
Bubble
point
line
Separator
150
Dewp
oint
line
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Dry Gas
An initial GOR > 1000,000 SCF/STB
Almost no liquid
C7+ concentration < 0.7 mole %
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Dry Gas Phase Diagram
Primarily methane and
some intermediates
The reservoir fluid isgas throughout thelife of the reservoir
No liquids formedeither in reservoir orat surface
Temperature
% Liquid
2
1
ressure pathn reservoir
r y g as
Separator
Dewp
o in t
l in e
150
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R e t r o g r a d ee t r o g r a d eR e g i o ne g i o n
w o P h a s e R e g io nwo P h a s e R e g i o nTemperatureTemperature
Pressur
e
Pressur
e
I LI L G A Slack Oil Volatile Critical Critical Gas Wet
Oil Oil Gas
Cricondenterm
ew PointLociubblePointLoci
r it ic al P oi ntricondenbar
A
B
C
eservoir Fluids Phase DiagramWindow
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C7+ & GOR for Reservoir Fluids
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Classification
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Composition of Reservoir Fluids
Differences Between Black and
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Differences Between Black andVolatile Oil
Black Oil
The evolved gas is a dry gas.
The solution gases remain gas phase in the
reservoir, tubulars and separator.
As reservoir pressure decreases, the gas leaving
solution, becomes richer in intermediate
components.
API gradually decreases during the reservoir life.
Phase Diagram of Black Oil and
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Phase Diagram of Black Oil andAssociated Gas
Production Processes for a Black
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Production Processes for a BlackOil
Differences Between Black and
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Differences Between Black andVolatile Oil
Volatile Oil
The evolved gas is a retrograde gas.
The evolved retrograde gases release a large
amount of. condensate at surface conditions.
Often over one half of the stock tank liquid produced
during the reservoirs life.
API steadily increases with time.
Phase Diagram of Volatile Oil and
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Phase Diagram of Volatile Oil andAssociated Gas
Production Processes for a Volatile
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Production Processes for a VolatileOil
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Analysis and Prediction Tool
Black Oil Mbal
Assume free gas in the reservoir remains gas in the
separator
Treat a multi component black oil mixture as a two-
component mixture: gas and oil
Volatile Oil Mbal
Treat mixture as a multi-component mixture
Total composition of the production stream is known
Effect of Using Black Oil Mbal for
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Effect of Using Black Oil Mbal forVolatile Oil
Differentiation between Volatile and
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Differentiation between Volatile andRetrograde
A G O R o f 3 2 0 0
/S C F S TB is a g oo d
-cu t o ff
.A va lu e o f 1 2 5 m o le
% +of C7 is a
u se fu l d iv id in g lin e
Differences between Volatile Oil
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Differences between Volatile Oiland Retrograde Gas
Retrograde Gas GOR increases with time as condensate dropout
API increases with time
Compositional Mbal should be used in reservoircalculations
Conventional gas Mbal can be used above dew point
Also, it can be used below dew point if two phase Z-
factors are used
Differences between Retrograde
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Differences between Retrogradeand Wet Gas
A n in itia l G O R o f
, /1 5 0 0 0 S C F S T B
ca n b e a cu to ff
%A va lu e o f 4 m o le
o r le ss ca n b e
u se fu l d iv id in g lin e
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of
Reservoir Fluids
R i Fl id S li
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Reservoir Fluid Sampling
Open Hole Sampling:
RFT, small sample volume and often contaminated
MDT, allows controlled drawdown and multiple
sample chambers
Optical MDT, allows to identify the type of fluid
being sampled
Cased Hole Sampling:
Surface Sampling
Subsurface Sampling
f b f li
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Surface & Subsurface Sampling
W ll C di i i d i S li
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Well Conditioning during Sampling
Small perforation is preferable
Limiting drawdown
Large tubing diameter in case of high rates
Better well cleaning
Stable production
No liquid slugging
Small amount of produced fluid prior to sampling
L b T
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Laboratory Tests
Primary tests
Routine laboratory tests
Special laboratory PVT tests
P i T t
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Primary Tests
API
Gas specific gravity
Separator gas composition
GOR
Routine Laboratory Tests
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Routine Laboratory Tests
Constant-Composition Expansion - CCE
Differential Liberation
Constant-Volume Depletion CVD
Separator Test
Constant Composition Expansion -
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Constant Composition Expansion CCE Test
The test is conducted for the purposes of
determining:
Saturation pressure (bubble-point or dew-point
pressure)
Isothermal compressibility coefficients of the single-
phase fluid in excess of saturation pressure
Compressibility factors of the gas phase
Total hydrocarbon volume as a function of pressure
CCE T t P d
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CCE Test Procedures
GasLiquid
Hg
SecondStep
Liquid
Hg
LiquidLiquid
Hg
FirstStep
Hg
ThirdStep
Hg
FourthStep
Liquid
GasVtLiquid
Vt
LiquidVtVt LiquidVt
pb
CCE Test Data
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CCE Test Data
Diff ti l Lib ti T t
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Differential Liberation Test
The experimental data obtained from the test
include:
Amount of gas in solution as a function of pressure
The shrinkage in the oil volume as a function of
pressure
Properties of the evolved gas including the
composition of the liberated gas, the gascompressibility factor, and the gas specific gravity
Density of the remaining oil as a function of
pressure
erent a erat on xpans on est
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Vo Liquid
Hg
Gas
Hg
Liquid
Gas
First step
Hg
Liquid
GasLiquid
Hg
Vo
Gas
Vo
Hg
Liquid
pb
erent a erat on xpans on estProcedures
Differential Liberation Test Data
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Differential Liberation Test Data
Separator Test Procedures
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Separator Test Procedures
LiquidHg
Liquid
Stocktank
Gas
Gas
Liquid
Se
pa
ra
tor
Hg
pb
resbbl
STB
resbbl
STBBob =
scf
scf
Rsb =scfSTB
Separator Test Data
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Separator Test Data
CVD Test Procedures
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CVD Test Procedures
Constant Volume Depletion CVD
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Co s a o u e ep e o CTest
PVT Reports
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PVT Reports
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Thank You