Reservoir EngineeringPVT and Rock-Fluid Properties
API Gravity Formula
API Gravity calculates api gravity for pvt and rock-fluid properties workflows in reservoir engineering.
How engineers use this formula
Use this formula when the listed inputs (SG_o) 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, API equals 34.970588 dimensionless.
SG_odimensionless
0.85
Inputs
SG_o
dimensionlessSpecific Gravity of Oil Phase
Outputs
API
dimensionless
API Gravity
SG_o
dimensionless
Specific Gravity of Oil Phase (rearranged)
Source and review
reviewedU.S. Bureau of Mines. (1921). Definition and calculation of API gravity.
Source