Standing vs Vasquez-Beggs PVT Comparison

Calculation sequence

1. Use absolute pressure and a measured bubble point. The saturated Rs comparison stops at or below that bubble point; it is not an undersaturated-oil extrapolation.
2. This comparison uses the full Standing inversion with (p/18.2 + 1.4) and exponent 1/0.83. That differs from the simplified p/18 form retained in the historical standalone reference.
3. Vasquez-Beggs coefficients switch at API > 30: (0.0178, 1.187, 23.931); at API <= 30: (0.0362, 1.0937, 25.724). Both curves are shown in scf/STB so their spread can be inspected.

Worked check

At 2,500 psia, 180 F, 35 API and gas gravity 0.8, full Standing returns 651.478793 scf/STB and Vasquez-Beggs returns 569.164106 scf/STB. These are predictions, not laboratory measurements. Keeping the pressure interval below the measured 3,000-psia bubble point prevents saturated curves being extrapolated into an undersaturated region. Changing API from 30 to 31 intentionally switches the coefficient family.

Synthetic examples for reproducibility, not measured field results.

Assumptions and limitations

• Correlation agreement is not validation. Select or calibrate against measured PVT data; this tool does not rank accuracy or replace a laboratory study.
• The input envelope is a conservative overlap of the cited development ranges, not a guarantee of fluid applicability. Standing was developed for California oils.
• Gas gravity must be supplied on the appropriate separator/correlation basis. No separator correction is calculated; composition effects and volatile oils are outside this comparison.

Sources and maintenance

Published by PetroCalcHub Team. Implementation and source checks: 2026-10-10. This does not claim independent expert review.

• IHS Harmony: oil correlations, coefficients and limits
• NIST SP 811: pressure and temperature unit conversions

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