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Standing Oil PVT & Formation Volume Factor Calculator

Crude oil expands downhole as dissolved natural gas dissolves into the liquid phase under reservoir pressure and temperature.

Operating bubble-point or reservoir pressure in gauge psi.

Downhole formation temperature in degrees Fahrenheit.

Surface stock-tank oil API gravity (e.g. 35° API for light crude).

Specific gravity of dissolved solution gas relative to air.

Calculated Result
1.3410 bbl/STB

Oil Formation Volume Factor (Bo)

Solution Gas-Oil Ratio (Rs)

584.7 scf/STB

Stock Tank Oil Specific Gravity

0.850 (Water=1.0)

In-Situ Reservoir Oil Density

7.83 lb/ft³

Reservoir Shrinkage Factor (1/Bo)

0.7457 STB/bbl

Calculation Breakdown

  1. Solution GOR Correlation (Rs)Rs = γg · [(P/18.2 + 1.4) · 10^(0.0125·API - 0.00091·T)]^1.2048 = 584.7 scf/STB
  2. Standing Oil FVF Formulation (Bo)Bo = 0.9759 + 0.000120 · [Rs·(γg/γo)^0.5 + 1.25·T]^1.2 = 1.3410 bbl/STB
  3. Volumetric Reservoir Balance1 STB at surface expands to 1.3410 reservoir barrels at downhole conditions

What Is the Standing Oil PVT & Formation Volume Factor Calculator?

The oil formation volume factor (Bo) represents the volume in reservoir barrels (res bbl) occupied by one stock-tank barrel (STB) of oil plus its dissolved solution gas at reservoir conditions.

Because gas dissolves in crude oil under pressure, Bo is always greater than 1.0 (typically 1.1 to 1.7 bbl/STB).

How Does the Standing Oil PVT & Formation Volume Factor Calculator Work?

Standing correlated hundreds of PVT cell measurements from California crude oils to formulate empirical power-law relations for Rs and Bo as functions of API gravity, gas gravity, pressure, and temperature.

Standing Oil PVT & Formation Volume Factor Calculator Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

R_s = γ_g · [ (P/18.2 + 1.4) · 10^(0.0125·API - 0.00091·T) ]^1.2048, B_o = 0.9759 + 0.00012 · [ R_s·(γ_g/γ_o)^0.5 + 1.25·T ]^1.2

Standing empirical correlations relating dissolved gas-oil ratio and oil swelling to pressure, temperature, and fluid gravities.

How to Use the Standing Oil PVT & Formation Volume Factor Calculator

  1. Input the reservoir pressure and temperature.
  2. Enter the stock-tank API gravity and separator gas specific gravity.
  3. Use the resulting Bo and Rs for material balance and reserves estimation.

Step-by-Step Example Calculation

35° API Crude at 2500 psig and 200°F

Input Values:

reservoirPressurePsig:2500
reservoirTempDegF:200
oilApiGravity:35
gasSpecificGravity:0.75
Worked Steps: Predicts Bo ≈ 1.35 bbl/STB and dissolved GOR for typical light crude.

Understanding Your Result

Bo indicates crude swelling; when oil is produced to the surface and gas escapes, oil shrinks by the factor 1/Bo.

Rs represents the volume of gas (scf) dissolved in each barrel of stock-tank oil.

Factors That Affect the Result

  • Pressure: Higher pressure increases gas solubility (Rs), which expands Bo up to the bubble point.
  • Temperature: Thermal expansion further increases Bo.
  • Crude API gravity: Lighter oils dissolve substantially more gas than heavy crudes.

When Should You Use This Calculator?

  • Preliminary reservoir screening prior to full laboratory PVT fluid analysis.
  • Converting surface tank production into downhole reservoir volume replacement.

Assumptions & Limitations

  • Applicable at or below the bubble point pressure Pb.

Frequently Asked Questions

Calculation Accuracy & Reference Note

Typically accurate within ±3% to ±5% of laboratory PVT flash vaporization tests.

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