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BLACK OIL
BASIC WORKFLOW
FLUID EQUATIONS
Reservoir Fluid Fundamentals
Richard Henry [email protected]
Abstract A collection of equations used during basic workflows on black‐oil fluids.
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Contents Solution Gas‐Oil Ratio ................................................................................................................................... 2
SI Conversions ........................................................................................................................................... 2
Output ................................................................................................................................................... 2
Input ...................................................................................................................................................... 2
Formation Volume Factor ............................................................................................................................. 2
SI Conversions ........................................................................................................................................... 3
Output ................................................................................................................................................... 3
Input ...................................................................................................................................................... 3
Viscosity ........................................................................................................................................................ 3
SI Conversions ........................................................................................................................................... 4
Output ................................................................................................................................................... 4
Input ...................................................................................................................................................... 4
Density .......................................................................................................................................................... 4
Bubble Point Pressure ................................................................................................................................... 5
SI Conversions ........................................................................................................................................... 5
Output ................................................................................................................................................... 5
Input ...................................................................................................................................................... 5
Compressibility .............................................................................................................................................. 5
Macros .......................................................................................................................................................... 6
Reservoir Fluid Fundamentals ═════════════════════════════════════════════════════════════════════════
© PetroSkills, LLC. All rights reserved._____________________________________________________________________________________________
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Solution Gas‐Oil Ratio
𝑅 𝑎 𝛾 𝑝 𝑒
Equation 1: Vazquez & Beggs solution gas‐oil ratio correlation
Where: Oilfield
.Rs solution gas‐oil ratio [scf/stb]
.γg primary separator gas gravity (= gas component) [1/air]
.γAPI stock‐tank oil gravity ( = oil component) [oAPI]
.p pressure of interest [psia]
.T temperature of interest [oF]
.a00‐>a04 are constants
Constant γAPI ≤ 30 Value Constant γAPI > 30 Value
a00 3.62000E‐02 a00 1.78000E‐02
a01 1.09370E+00 a01 1.18700E+00
a02 2.57240E+01 a02 2.39310E+01
a03 459.68 a03 459.68
SI Conversions
Output
R𝑠msm
Rscfstb
5.61458
Input
p psia p kPa 0.145037738
T ℉ T K 9 5 459.68
Formation Volume Factor
𝐵 1 𝑎 𝑅 𝑇𝛾𝛾
𝑎 𝑎 𝑅
Equation 2: Vazquez & Beggs saturated oil formation volume factor correlation
Where: Oilfield
.Bob Saturated oil formation volume factor [bbl/stb]
.Rs solution gas‐oil ratio [scf/stb]
.γg primary separator gas gravity ( = gas component) [1/air]
.γo stock‐tank oil gravity ( = oil component) [1/wtr]
.T temperature of interest [oF]
Reservoir Fluid Fundamentals ═════════════════════════════════════════════════════════════════════════
© PetroSkills, LLC. All rights reserved._____________________________________________________________________________________________
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.a00‐>a03 are constants
Constant γAPI ≤ 30 Value Constant γAPI > 30 Value
a00 4.67700E‐04 a00 4.67000E‐04
a01 1.75100E‐05 a01 1.10000E‐05
a02 ‐1.81100E‐08 a02 1.33700E‐09
SI Conversions
Output
Bmsm
Bbblstb
1
Input
Rscfstb
R𝑠msm
5.61458
Viscosity
𝜇 𝑋 𝜇
𝑋 𝑎 𝑅 𝑎
𝑋 𝑎 𝑅 𝑎
Equation 3: Beggs & Robinson live oil viscosity correlation
Where: Oilfield
.μob saturated oil viscosity [cP]
.μod dead oil viscosity [cP]
.Rs solution gas‐oil ratio [scf/stb]
.a00‐>a08 are constants, X2‐>X3 are intermediate variables
𝜇 10 1
𝑋 10
Equation 4: Beggs & Robinson dead oil viscosity correlation
Where: Oilfield
.μod dead oil viscosity [cP]
.γAPI stock‐tank oil gravity ( = oil component) [oAPI]
.T temperature of interest [oF]
.a00‐>a08 are constants, X1 is an intermediate variable
Reservoir Fluid Fundamentals ═════════════════════════════════════════════════════════════════════════
© PetroSkills, LLC. All rights reserved._____________________________________________________________________________________________
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Constant Value Constant Value
a00 ‐1.16300E+00 a05 ‐5.15000E‐01
a01 3.30324E+00 a06 5.44000E+00
a02 ‐2.02300E‐02 a07 1.50000E+02
a03 1.07150E+01 a08 ‐3.38000E‐01
a04 1.00000E+02
SI Conversions
Output
μ mPa. s μ cP 1
Input
Rscfstb
R𝑠msm
5.61458
T ℉ T K 9 5 459.68
Density
𝜌𝜌 𝛾 𝑀 𝛾
𝑅𝑎
𝑝𝑅 𝑎 𝑇
𝐵
Equation 5: Live oil density from theory
Where: Oilfield SI
.ρob saturated oil density [lb/cuft] [kg/m3]
.Bo Formation volume factor [bbl/stb] [m3/sm3]
.Rs Solution gas‐oil ratio [scf/stb] [sm3/sm3]
.γo stock tank oil specific gravity [1/wtr] [1/wtr]
.γg surface gas specific gravity [1/air] [1/air]
.psc standard pressure [psia] [kPa]
.Tsc standard temperature [oF] [oC]
.ρwsc water density at standard conditions [lb/cuft] [kg/m3]
.Mwair apparent molecular mass of air [lb/mol] [g/mol]
R universal gas constant [psia.cuft]/[mol.oR] [J/mol/K]
a00 gas‐oil ratio conversion constant 5.61458 [scf/stb] 1 [sm3/sm3]
a01 relative to absolute temperature conversion 459.68 [oR] 273.15 [K]
Reservoir Fluid Fundamentals ═════════════════════════════════════════════════════════════════════════
© PetroSkills, LLC. All rights reserved._____________________________________________________________________________________________
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Bubble Point Pressure
𝑝 𝑎𝑅𝛾
𝑒
𝑋 𝑎𝛾
𝑇 𝑎
Equation 6: Vazquez & Beggs bubble point pressure correlation
Where: Oilfield
.pb pressure of interest [psia]
.Rs solution gas‐oil ratio [scf/stb]
.γg primary separator gas gravity (= gas component) [1/air]
.γAPI stock‐tank oil gravity ( = oil component) [oAPI]
.T temperature of interest [oF]
.a00‐>a03 are constants, X0 is an intermediate variable
SI Conversions
Output
p kPa p psi 0.145037738
Input
Rscfstb
R𝑠msm
5.61458
T ℉ T K 9 5 459.68
Constant γAPI ≤ 30 Value Constant γAPI > 30 Value
a00 1/3.62000E‐02 a00 1/1.78000E‐02
a01 1/1.09370E+00 a01 1/1.18700E+00
a02 ‐2.57240E+01 a02 ‐2.39310E+01
a03 459.68 a03 459.68
Compressibility
𝑐1
𝐵𝜕𝐵𝜕𝑝
Equation 7: Under‐saturated oil compressibility
𝑐1
𝐵𝜕𝐵𝜕𝑝
𝐵𝜕𝑅𝜕𝑝
Equation 8: Saturated oil compressibility
Reservoir Fluid Fundamentals ═════════════════════════════════════════════════════════════════════════
© PetroSkills, LLC. All rights reserved._____________________________________________________________________________________________
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Where: Oilfield SI
.co oil compressibility [1/psi] [1/kPa]
.Bo oil formation volume factor [cuft/scf] [m3/sm3]
.Bg gas formation volume factor [cuft/scf] [m3/sm3]
.Rs solution gas‐oil ratio [scf/scf] [sm3/sm3]
.P pressure of interest [psia] [kPa]
.T temperature of interest [oF] [K]
Macros Name Purpose Qualifier Units Source Date Module
vasq_Pb Bubble Point Pressure
Oil, Black [psia] Vazquez & Beggs 1980 Oil
vasq_Bob Formation Volume Factor
Bubble Point [bbl/stb] Vazquez & Beggs 1980 Oil
vasq_Rsb Solution Gas‐Oil Ratio
Bubble Point [scf/stb] Vazquez & Beggs 1980 Oil
begg_Uob Viscosity, Dynamic Oil, Saturated [cP] Beggs & Robinson
1975 Viscous
begg_Uod Viscosity, Dynamic Oil, Dead [cP] Beggs & Robinson
1975 Viscous
Reservoir Fluid Fundamentals ═════════════════════════════════════════════════════════════════════════
© PetroSkills, LLC. All rights reserved._____________________________________________________________________________________________
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