PVT symbols units and calculation practice pack
PetroCalcHub · Original synthetic teaching exercise · 2026-10-24

Practice PVT state labels, gravity definitions, absolute scales and formation-volume-factor directions before combining properties in a petroleum calculation.

Reservoir T = 600 °R and Z = 0.85; standard T = 520 °R, P = 14.7 psia, Z = 1. Reservoir pressure varies.

1. Which quantity changes when only a volume unit is changed: gas amount or its numerical representation?

Working: ________________________________________________


2. Reproduce the baseline Bg (reservoir ft³/scf) without rounding intermediate values.

Working: ________________________________________________


3. Compare the first and last recorded scenarios. Which input changes?

Working: ________________________________________________


4. What would be needed to apply this example to a different physical system?

Working: ________________________________________________


5. Convert 85.3 psig to psia for an assumed local atmosphere of 14.7 psia.

Working: ________________________________________________


6. Convert 1,500 reservoir bbl to STB at Bo = 1.25 reservoir bbl/STB.

Working: ________________________________________________


ANSWER KEY

1. Only the numerical representation changes. A state conversion must also preserve the same amount under its specified model.
2. Bg = 0.85 × 600 × 14.7/(3,000 × 520) = 0.00480576923 ft³/scf; reciprocal = 208.083233 scf/ft³. Bg (reservoir ft³/scf) = 0.00480576923. Both state definitions are part of the factor; changing standards changes the explicit ratio.
3. Reservoir pressure (psia) changes from 500 to 5000. Other controls remain as stated in the premise. Bg (reservoir ft³/scf) changes from 0.0288346154 to 0.00288346154.
4. Replace the synthetic controls with compatible documented inputs and check the relation's assumptions. Bg in reservoir ft³/scf when both volumes use cubic feet. This explicit state ratio differs slightly from rounded field coefficients. Both state definitions are part of the factor; changing standards changes the explicit ratio.
5. 100.0 psia. Gas-state equations require absolute pressure.
6. 1,500/1.25 = 1,200 STB. The state conversion is distinct from a geometric bbl-to-ft³ conversion.

Method: Original synthetic teaching calculation. Equations and fixed controls are stated here; these are not field measurements.
Sources:
Harmony: oil correlations and coefficient branches: https://www.ihsenergy.ca/support/documentation_ca/Harmony/content/html_files/reference_material/calculations_and_correlations/oil_correlations.htm
NIST SP 811: pressure, temperature and volume conversions: https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9