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Calculate the properties of petroleum reservoir fluids with a reliable, simple PVT calculator. Use the Vazquez-Beggs total formation volume factor calculator.

Total Formation Volume Factor

Vazquez-Beggs (1980)
First-stage separator gas specific gravity
Stock-tank oil specific gravity
Solution gas-oil ratio at bubble point pressure

N.B. The total (two-phase) formation volume factor equation is used along with the Dranchuk-Abou-Kassem (DAK) (1975) correlation for the gas formation volume factor and the Vazquez-Beggs (1980) correlation for oil formation volume factor.

Want more details? Discover Vazquez-Beggs (1980) correlations.

Fluid Property Behavior

Total Formation Volume Factor

In this section, I would like to make sure that you can easily describe the behavior of the total (two-phase) formation volume factor property at any reservoir pressures, whether the pressure is less than or greater than the oil bubble point pressure. Therefore, I will give you brief technical notes by answering three questions.
The behavior of total or two-phase formation volume factor at pressures above and below the bubble point pressure
Behavior of the total FVF versus pressure
Why does the total formation volume factor increase as the pressure decreases in the reservoir?
At pressures greater than bubble point pressure, the total (two-phase) formation volume factor increases gently as the reservoir pressure decreases. That behavior occurs because the oil phase, holding the maximum amount of gas in solution, expands gently due to the pressure decrease. When the pressure decreases below the bubble point pressure, the total (two-phase) formation volume factor increases rapidly.​ That’s because more gas is liberating from the liquid phase, making the whole system expanded rapidly. Actually, almost all the black oil properties respond differently to the decrease in reservoir pressure.
What are the black oil PVT properties that are affecting the value estimated for the total formation volume factor?
The total formation volume factor is strongly dependent on the values estimated for the solution gas-oil ratio, the oil formation volume factor, and the gas formation volume factor.
What are the black oil PVT properties that depend on the value estimated for the total formation volume factor?
Actually, all other black oil PVT properties are independent of the value estimated for the total formation volume factor.

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Gas Z Compressibility Factor
Gas Formation Volume Factor
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