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7/29/2019 04 Fluid Properties
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Copyright 2007, , All rights reserved
Fluid Properties
Basic Fluid Parameters Used in Reservoir Engineering
(Viscosity, Compressibility, Volume Factor, GOR, PhaseDiagrams)
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What is Petroleum?
Petroleum: a natural yellow-to-black liquid hydrocarbonfound at and beneath the earths surface,
Hydrocarbon: an organic compound made up of carbon and
hydrogen atoms.
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Crude Oils
Light CrudePalo Pinto Field
North Texas
Heavy CrudeHumble Oil FieldSouthwest Texas
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Crude Oils
Extra Heavy Oil(Orinoco Belt, Venezuela)
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Petroleum ProductsA Barrel of Crude Oil Provides:
Gasoline - 19.5 gallons
Fuel Oil - 9.2 gallons
Jet Fuel - 4.1 gallonsAsphalt - 2.3 gallonsKerosene - 0.2 gallonsLubricants - 0.5 gallonsPetrochemicals,other products - 6.2 gallons
One Barrel =42 gallons
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Hydrocarbon
Combination of C and H
CH
H
H
H
CH
H
H
C
H
H
H
CH
H
H
C
H
H
C
H
H
H
METHANE
ETHANE
PROPANE
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Other elements in Reservoir Fluids
Water (Salinity)
H2S
CO2 N2
Hg (Mercury)
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API Gravity
5.131API
5.141SG
or
5.131SG
5.141API
Where
SG: Specific Gravity
API: API Gravity (60degF)
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Viscosity ()
A measure of resistance to flow
Symbols: o, g, w
Units: cp Sources: Lab measurements, correlations
Range and typical values
0.25 to 10,000 cp, Black oil
0.5 to 1.0 cp, Water
0.012 to 0.035 cp, Gas
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Variation of Viscosity with Pressure
Pressure
Pb
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Fluid Compressibility (Co, Cg, Cw)
Fractional change in volume due to a unit change in pressure
Symbol: co, cg, cw
Units: psi-1, microsips (1 microsip = 1x10-6 psi-1)
Source: Lab measurements, correlations
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Oil Formation Volume Factor (Bo)
Pb
Oil at Surface
Gas at Surface
Oil in Place
SurfaceatVolumeOil
PlaceinVolumeOilBo
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Gas-Oil Ratio (GOR)
Pb
Oil at Surface
Gas at Surface
Oil in Place
SurfaceatVolumeOil
SurfaceatVolumeGasGOR
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Exercise
There is 1,000,000 bbls of recoverable oil in reservoir. If yourecover all of the oil to the surface, how much stock tankvolume of oil and gas (standard condition) you can obtain?
Assume: Bo = 1.2, GOR = 600, reservoir is saturated and nofree gas is drained.
If the oil price is $75/bbl and gas price is $10 /mscf, howmuch revenue can you get? (you do not have to considerproduction cost in this exercise).
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GOR is different from Gas in Solution (Rs)
GOR is the ratio of ALL the gas at surface and the oil atsurface, while Rs is the ratio of gas in solution in the oil in thereservoir
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GOR RsSurface
Reservoir
Bg
GWR
GOR
Rs
VoVg3
Vg2
Vg1
BoBw
o
ggg
V
3V2V1VGOR
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Gas-Oil Ratio(for Pr < Pb and no Free Gas Cap)
where:GOR Production gas oil ratio
Rs Gas in solution in oil
Bo and Bg Oil and gas volume factorsmo and mg Oil and gas viscosities
krg/kro Gas/oil-relative permeability-ratio
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Hydrocarbons Classification
BlackOil
VolatileOil
RetrogradeGas
WetGas
DryGas
InitialProducingGas/Liquid
Ratio, scf/STB
3200 > 15,000* 100,000*
Initial Stock-Tank Liquid
Gravity, API
< 45 > 40 > 40 Up to 70 NoLiquid
Color of Stock-
Tank Liquid
Dark Colored Lightly
Colored
Water
White
No
Liquid
*For Engineering Purposes
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Hydrocarbons Classification
BlackOil
VolatileOil
RetrogradeGas
WetGas
DryGas
PhaseChange inReservoir
Bubblepoint Bubblepoint Dewpoint NoPhase
Change
NoPhase
Change
HeptanesPlus, MolePercent
> 20% 20 to 12.5 < 12.5 < 4* < 0.8*
OilFormationVolume
Factor atBubblepoint
< 2.0 > 2.0 - - -
*For Engineering Purposes
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Hydrocarbon Behavior
(Single Component / Constant Temperature)
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Hydrocarbon Behavior
(Single Component / Constant Temperature)
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DIFFERENTIAL GAS LIBERATIONGas phase removal process in a hydrocarbon system, when gas is formed below the bubble point pressure.During the process the composition of the system continuously changes.
HYDROCARBON PVT PROPERTIES
PISTON
GASLIQUID
PISTON
LIQUIDLIQUID
LIQUID
PISTON
GASLIQUID
(B) GAS EXTRACTION (C) GAS EXTRACTION(A)
PRESSURE DECREASE
PISTON PISTON
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FLASH EXPANSIONGas is formed from the liquid when de pressure is reduced, keeping in contact with the crudeoil. The total composition of the system remains constant.
GAS
PISTON
LIQUID
LIQUID
PISTON
PISTON
LIQUID
GAS
PRESSURE DECREASE
LIQUID
PISTON
Pb
HYDROCARBON PVT PROPERTIES
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Typical PVT Data for Differential Vaporization of anUndersaturated Oil at Constant Temperature (305F)
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Five Reservoir Fluids
Black Oil
Volatile Oil
Retrograde Gas
Wet Gas
Dry Gas
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The Reservoir Fluid Type
Determined using the pressure-temperature phase diagram.
Requires knowledge of the reservoir to surface pressure-temperature path.
Estimated using field data with rules of thumb.
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Phase Diagram Typical Black Oil
Black Oil
Criticalpoint
Pressure,psia
Separator
Pressure pathin reservoir
Dewpoint line
% Liquid
Temperature, F
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Phase Diagram of a Typical Volatile Oil
Pressure
Temperature, F
Separator
% Liquid
Volatile oil
Pressure pathin reservoir
3
2
1 Criticalpoint
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Phase Diagram of a Typical Retrograde Gas
3
Separator
% Liquid
Pressure path
in reservoir1
2Retrograde gas
Critical point
Pressure
Temperature
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Phase Diagram of Typical Wet Gas
Pressur
e
Temperature
% Liquid
2
1
Pressure pathin reservoir
Wet gas
Criticalpoint
Separator
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Phase Diagram of Typical Dry Gas
Pressu
re
Temperature
% Liquid
2
1
Pressure path
in reservoir
Dry gas
Separator
Th Fi R i Fl id
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Black Oil
Criticalpoint
Pressure,psia
Separator
Pressure pathin reservoir
Dewpoint line
% Liquid
Temperature, F
Pressure
Retrograde Gas Wet Gas Dry Gas
The FiveReservoirFluids
Pressure
Temperature
Separator
% Liquid
Volatile oil
Pressure pathin reservoir
3
2
1Criticalpoint
3
Separator
% Liquid
Pressure pathin reservoir
1
2Retrograde gas
Critical
point
Temperature
Pressure
Temperature
% Liquid
2
1
Pressure pathin reservoir
Wet gas
Criticalpoint
Separator
Black Oil Volatile Oil
Pressure
Temperature
% Liquid
2
1
Pressure pathin reservoir
Dry gas
Separator
The Five Reservoir Fluids
Th G
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Three Gases
Dry gas - gas at surface is same as gas in reservoir
Wet gas - recombined surface gas and condensaterepresents gas in reservoir
Retrograde gas - recombined surface gas and condensaterepresents the gas in the reservoir but not the total reservoirfluid (retrograde condensate stays in reservoir)
C t f N t ll i P t l
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Components of Naturally occurring PetroleumFluids
Component Composition,mole percent
Hydrogen sulfide 4.91Carbon dioxide 11.01Nitrogen 0.51Methane 57.70
Ethane 7.22Propane 4.45i-Butane 0.96n-Butane 1.95i-Pentane 0.78n-Pentane 0.71
Hexanes 1.45Heptanes plus 8.35100.00
Properties of heptanes plusSpecific Gravity 0.807Molecular Weight 142 lb/lb mole
I iti l P d i GLR C l t With C7
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Initial Producing GLR Correlates With C7+
0
20000
40000
60000
80000
100000
0 10 20 30 40 50
Heptanes plus in reservoir fluid, mole %
Initialprodu
cing
ga
s/liquidratio,
scf/STB
Dewpoint gas
Bubblepoint oil
I iti l P d i GLR C l t With C7
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Initial Producing GLR Correlates With C7+
10
100
1000
10000
100000
1000000
0.1 1 10 100
Heptanes plus in reservoir fluid, mole %
Initialproduc
ing
gas
/liquidratio,scf/STB
Dewpoint gasBubblepoint oil
R t d G
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Retrograde Gas
2000
3000
4000
5000
10 11 12 13 14 15
Heptanes plus in reservoir fluid, mole %
Initialprodu
cing
ga
s/liquidratio,
scf/STB
Th G Wh t th diff ?
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Three Gases What are the differences?
Dry gas - gas at surface is same as gas in reservoir
Wet gas - recombined surface gas and condensate representsgas in reservoir
Retrograde gas - recombined surface gas and condensaterepresents the gas in the reservoir But not the total reservoirfluid (retrograde condensate stays in reservoir)
Fi ld Id tifi ti
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Field Identification
BlackOil
VolatileOil
RetrogradeGas
WetGas
DryGas
InitialProducingGas/Liquid
Ratio, scf/STB
3200 > 15,000* 100,000*
Initial Stock-Tank Liquid
Gravity, API
< 45 > 40 > 40 Up to 70 NoLiquid
Color of Stock-
Tank Liquid
Dark Colored Lightly
Colored
Water
White
No
Liquid
*For Engineering Purposes
L b t A l i
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Laboratory Analysis
BlackOil
VolatileOil
RetrogradeGas
WetGas
DryGas
PhaseChange inReservoir
Bubblepoint Bubblepoint Dewpoint NoPhase
Change
NoPhase
Change
HeptanesPlus, MolePercent
> 20% 20 to 12.5 < 12.5 < 4* < 0.8*
OilFormation
VolumeFactor atBubblepoint
< 2.0 > 2.0 - - -
*For Engineering Purposes
P i P d ti T d
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Primary Production Trends
GOR
GOR
GOR
GOR
GOR
Time Time Time
TimeTimeTimeTimeTime
TimeTime
No
liquid
No
liquid
DryGas
WetGas
RetrogradeGas
VolatileOil
BlackOil
API
API
API
API
API
E i
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Exercise
One of the wells in the Merit field, completed inDecember 1967 in the North Rodessa formation,originally produced 54API stock-tank liquid at a gas/oilratio of about 23,000 scf/STB. During July 1969, thewell produced 1987 STB of 58API liquid and 78,946Mscf of gas. By May 1972, the well was producingliquid at a rate of about 30 STB/d of 59API liquid and
gas at about 2,000 Mscf/d. What type of reservoir fluidis this well producing?
Plot of Exercise
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Plot of Exercise
00 12 24 36 48 60 72
50
5152
53
54
55
60
59
58
57
56
100000
90000
80000
70000
60000
50000
40000
30000
1000020000
Months since start of 1967
Producing
g
as/oilratio,s
cf/STB
Stock-tank
liqu
idgravity,API
Exercise Solution
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Exercise Solution
Retrograde Gas Condensate
Initial GLR over 3,200 scf/STB and producing gas-liquid ratioand stock tank oil gravity increasing with production, thus fluidis retrograde gas condensate
Initial GLR over 15,000 scf/STB, thus fluid can be treated aswet gas
GLR apparently started increasing immediately, indicating thatpi = pd and the possibility of an oil zone
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EMPIRICAL CORRELATIONS
HYDROCARBON PVT PROPERTIES
STANDING CORRELATION
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P 10 0.0125 o API 1.205
Rs = g x when P Pb18 10 0.00091 T
Bo = 0.972 + 0.00014 F 1.175
Rs: Gas in solution, SCF/STB;
Bo: Oil volumetric factor , Bbl/STB;
P: Pressure, psi;
T: Temperature F;
g: Gas Specific gravity (air = 1);o: Oil Specific gravity (water = 1) ;o API: Oil API Gravity
o: Oil density, lb/ft3
STANDING CORRELATION
gF = Rs + 1.25 To
0.6
Rs(Solution Gas, SCF/STB) and Bo (Oil volume factor, Bbl/STB) calculation
OIL DENSITY
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62.4 o + 0.0764 g Rs / 5.615
o = Bo
OIL DENSITY
Where o= Oil density, lb/ft3 @ P,T
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GAS VOLUMETRIC FACTOR, Bg
zT
Bg = 0.028269 (vol./vol.)P
The gas volumetric factor, Bg, can be determined using followingequation, which is derived from state equation (PV = znRT)
P: pressure, psia,
T: temperatureo
R (=o
F + 460)and z: supercompressibility factor.
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g= gSC / Bg ,
Gas density at P and T
Where gSC
= 0.0764 g
HYDROCARBON PVT PROPERTIES
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GAS
PISTON
LIQUID
LIQUID
PISTON
PISTON
LIQUID
GASLIQUID
PISTON
RESERVOIRCONDITION
Pr, Tr
BUBBLEPRESSURE
Pb
CONDITION AT A GIVENPOINT IN THE PIPE
P, T
STANDARDCONDITIONS
14.7 psi, 60oF
HOW TO DETERMINE FREE GAS AND CRUDE OIL VOLUME AT A GIVEN PRESURE AND
TEMPERATURE CONDITION
1 2 3 4
VgSC
Vo SC
GOR = Vg SC / Vo SC
Vg P,T
Vo P,T
Vo (P,T)= Bo x VoSC
Vg (P,T)= Bg X (GOR - Rs) x VoSC
P
T
LIQUID GAS
TWO PHASES
1
2
3
4
60o F
14.7 psi
HYDROCARBON PVT PROPERTIES
EXERCISE
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A well is producing 35 oAPI oil at a rate of 1000 STB/day, with a GOR of 500 SCF/STB.Gas specific gravity is 0.65 (air = 1).
1) Calculate the oil and gas flow rates in ft3/sec. in a point of the tubing where the pressureis 800 psi and the temperature is 140 oF.. Assume Z= 0.9.
Use empirical correlations for Bo, Bg, Rs Calculations
2) Calculate the oil and gas densities for the same conditions. Sol# Rs=152, F=307.9, Bo=1.089Bg=.0189
Qo(800psi, 140 F) = Bo x Qo(STB/day) ,AnsQ0=1089 bpdQg(800psi, 140 F) = BgxQo(STB/day)x(GOR Rs)
1 bbl = 5.615 ft3 y 1day=86400 sec
EXERCISEAPPLICATION OF FLUID PROPERTIES CALCULATIONS