Vasquez-Beggs Solution Gas-Oil Ratio Calculator
Enter pressure, reservoir temperature, oil API gravity, gas specific gravity, and the Vasquez-Beggs coefficient set for the applicable API range. The output is solution gas-oil ratio in scf/STB.
Calculation context and source notes
The Vasquez-Beggs correlation estimates solution gas-oil ratio from pressure, temperature, oil API gravity, gas specific gravity, and the coefficient set selected for the oil-gravity range.
Use the correlation for black-oil PVT screening when laboratory differential-liberation data or a calibrated PVT model are unavailable. Select the API-gravity coefficient range deliberately and compare the estimate with regional fluid data whenever possible.
Solves for
R_s (SCF/STB)
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Formula, variables, and default calculation
Reproducible default result
With the default values shown below, the calculation returns R_s = 569.164106 SCF/STB. Defaults demonstrate the implementation; they are not recommended field values.
2500
180
35
0.8
0.0178
1.187
23.931
Input definitions
p
psiPressure
T
°FReservoir Temperature
API
APIOil API Gravity
gamma_g
fractionGas Specific Gravity
C_rs1
dimensionlessVasquez-Beggs C1 Coefficient (0.0178 if API > 30; 0.0362 if API <= 30)
C_rs2
dimensionlessVasquez-Beggs C2 Coefficient (1.1870 if API > 30; 1.0937 if API <= 30)
C_rs3
dimensionlessVasquez-Beggs C3 Coefficient (23.931 if API > 30; 25.724 if API <= 30)
Output definitions
R_s
Solution Gas-Oil Ratio
p
Pressure
gamma_g
Gas Specific Gravity
Engineering use, assumptions, and limits
Use the correlation for black-oil PVT screening when laboratory differential-liberation data or a calibrated PVT model are unavailable. Select the API-gravity coefficient range deliberately and compare the estimate with regional fluid data whenever possible.
Assumptions
- Pressure, temperature, API gravity, and gas specific gravity use the field-unit basis of the published correlation.
- The input condition is within the black-oil behavior represented by the correlation.
- The coefficient set matches the selected oil API-gravity range.
Limitations
- An empirical correlation is not a substitute for representative laboratory PVT data.
- Accuracy can degrade for fluids and conditions outside the data range used to develop the correlation.
Common mistakes
- Using gauge pressure where the implementation or comparison requires absolute pressure.
- Selecting the wrong API-gravity coefficient set.
- Using separator gas gravity without applying the source correlation's gas-gravity basis or correction.
Source and record status
Source metadata identifies the relationship implemented by the calculator. Check the cited edition, unit basis, and scope against the engineering case before operational use.
Vasquez and Beggs 1980 oil PVT correlations, as summarized in IHS Harmony / WellTest documentation and PIPESIM fluid-property documentation.
Open source reference