Practice and answer pack
PVT symbols units and calculation practice pack
Practice PVT state labels, gravity definitions, absolute scales and formation-volume-factor directions before combining properties in a petroleum calculation.
By PetroCalcHub Team · Updated October 24, 2026 · Free to read and use
Create a symbols-and-units ledger
For every problem identify P, T, Z, Rs, Bo or Bg and write the required units. A dimensionless Z still needs a state and mixture; a formation volume factor still needs both volume bases.
The baseline derives Bg from explicit reservoir and standard states rather than relying on an unexplained field coefficient.
Solve the reverse mapping
After converting standard gas to reservoir volume, reverse the calculation and recover the starting amount. Do the same for reservoir oil and stock-tank oil using Bo.
The additional exercises distinguish gas gravity from API and gauge pressure from absolute pressure. They are definition checks as much as arithmetic checks.
State what the property model does
A correlation predicts a property under its selected assumptions. It is not automatically an EOS flash, a laboratory characterization or a production forecast.
Print the answer pack or reveal each solution after working it. The synthetic values make unit choices transparent without implying a particular fluid's measured PVT behavior.
Explore the example
Original synthetic teaching calculation. Equations and fixed controls are stated here; these are not field measurements.
Select one of 5 recorded scenarios. Intermediate states are not interpolated.
Reservoir pressure (psia) = 3000. Bg (reservoir ft³/scf): 0.00480576923; Expansion (scf/reservoir ft³): 208.083233.
- Bg (reservoir ft³/scf)
Worked example
Bg from two explicit absolute states
Reservoir T = 600 °R and Z = 0.85; standard T = 520 °R, P = 14.7 psia, Z = 1. Reservoir pressure varies.
Relation and unit basis
Bg = Zr Tr Ps/(Pr Zs Ts); expansion = 1/Bg
Bg in reservoir ft³/scf when both volumes use cubic feet. This explicit state ratio differs slightly from rounded field coefficients.
1. Define the baseline
Reservoir pressure (psia) = 3000
Reservoir T = 600 °R and Z = 0.85; standard T = 520 °R, P = 14.7 psia, Z = 1. Reservoir pressure varies.
2. Select the relation
Bg = Zr Tr Ps/(Pr Zs Ts); expansion = 1/Bg
Bg in reservoir ft³/scf when both volumes use cubic feet. This explicit state ratio differs slightly from rounded field coefficients.
3. Substitute the values
Bg = 0.85 × 600 × 14.7/(3,000 × 520) = 0.00480576923 ft³/scf; reciprocal = 208.083233 scf/ft³
Retain intermediate precision. The displayed values are rounded only after evaluation.
4. Read the result
Bg (reservoir ft³/scf) = 0.00480576923; Expansion (scf/reservoir ft³) = 208.083233
Both state definitions are part of the factor; changing standards changes the explicit ratio.
Result and interpretation
Bg (reservoir ft³/scf) = 0.00480576923; Expansion (scf/reservoir ft³) = 208.083233
Both state definitions are part of the factor; changing standards changes the explicit ratio.
Work the explicit state-ratio example first, then audit the direction and units of each additional conversion.
Exact scenario data
Original synthetic teaching calculation. Equations and fixed controls are stated here; these are not field measurements.
| Reservoir pressure (psia) | Bg (reservoir ft³/scf) | Expansion (scf/reservoir ft³) |
|---|---|---|
| 500 | 0.02883462 | 34.68054 |
| 1,000 | 0.01441731 | 69.36108 |
| 2,000 | 0.007208654 | 138.7222 |
| 3,000 | 0.004805769 | 208.0832 |
| 5,000 | 0.002883462 | 346.8054 |
Scroll the table to see all columns. The highlighted row is the worked baseline. Downloads retain full numerical precision.
Practice problems and answer key
Work through the question before revealing its answer. Use the stated assumptions and include units in every numerical step.
1. Which quantity changes when only a volume unit is changed: gas amount or its numerical representation?
Show the worked answer
Only the numerical representation changes. A state conversion must also preserve the same amount under its specified model.
2. Reproduce the baseline Bg (reservoir ft³/scf) without rounding intermediate values.
Show the worked answer
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. Compare the first and last recorded scenarios. Which input changes?
Show the worked answer
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. What would be needed to apply this example to a different physical system?
Show the worked answer
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. Convert 85.3 psig to psia for an assumed local atmosphere of 14.7 psia.
Show the worked answer
100.0 psia. Gas-state equations require absolute pressure.
6. Convert 1,500 reservoir bbl to STB at Bo = 1.25 reservoir bbl/STB.
Show the worked answer
1,500/1.25 = 1,200 STB. The state conversion is distinct from a geometric bbl-to-ft³ conversion.
Before using the result
- Use absolute scales where required.
- Keep state and unit labels together.
- Reverse-check volume-factor conversions.
Both state definitions are part of the factor; changing standards changes the explicit ratio.
Continue learning
Start with the broader workflow guide · Related method guide
Sources and method
The explanation and synthetic examples are original PetroCalcHub teaching material. The references below support the definitions and model context. They do not supply field validation for the synthetic scenarios.