Reservoir EngineeringPVT and Rock-Fluid Properties
Fraction of the Total Solution Gas Retained in the Reservoir as Free Gas Formula
Fraction of the Total Solution Gas Retained in the Reservoir as Free Gas calculates fraction of solution gas retained as free gas for pvt and rock-fluid properties workflows in reservoir engineering.
How engineers use this formula
Use this formula when the listed inputs (N_p, R_p, N, R_si, R_s) are known and the assumptions behind the cited pvt and rock-fluid properties relationship match the engineering case being checked.
Assumptions
- Input values are representative for the well, reservoir, fluid, or equipment case being evaluated.
- The declared units match the field-unit constants used in the formula.
- The cited formula applies to the selected petroleum engineering workflow.
Limitations
- The calculation does not replace a full engineering model or operating procedure.
- Accuracy depends on the source correlation, assumptions, input quality, and unit consistency.
Common mistakes
- Mixing unit systems without converting the inputs.
- Using default example values as field recommendations.
- Applying the formula outside the source assumptions.
Default example
Using the default inputs, alpha_g equals 0.4 fraction.
N_pSTB
500000
R_pscf/STB
900
NSTB
1000000
R_siscf/STB
1000
R_sscf/STB
500
Inputs
N_p
STBCumulative Oil Production
R_p
scf/STBProduced Gas-Oil Ratio
N
STBInitial Oil in Place
R_si
scf/STBInitial Solution Gas-Oil Ratio
R_s
scf/STBGas Solubility
Outputs
alpha_g
fraction
Fraction of Solution Gas Retained as Free Gas
Source and review
reviewedAhmed, T., McKinney, P.D. 2005. Advanced Reservoir Engineering, Gulf Publishing of Elsevier, Chapter: 4, Page: 314.
Source