Original synthetic study
The same rock volume with three different fluid volume bases
One reservoir gas amount can be described as reservoir cubic feet, reservoir barrels or standard cubic feet. Numerical differences between those volumes are not differences in gas inventory.
By PetroCalcHub Team · Updated October 24, 2026 · Free to read and use
Define one amount before changing its units
This study fixes a reservoir gas volume and Bg. It converts reservoir cubic feet to reservoir barrels geometrically, then converts the gas amount to standard cubic feet using Bg.
The barrel conversion changes units at the same reservoir state. The standard-volume conversion changes the reference state used to express the amount.
Keep unit conversion and PVT conversion apart
A petroleum barrel contains 5.614583333 ft³. Bg in reservoir ft³/scf must be converted if the reservoir numerator is switched to barrels.
Using a barrel numerator with a cubic-foot Bg creates a factor-of-5.6146 error. A spreadsheet can hide this if every column is labelled simply volume.
Check both calculation paths
Compute standard volume directly from reservoir cubic feet, then repeat using reservoir barrels and the converted Bg. The two answers must agree.
The study uses a fixed synthetic Bg. It does not simulate separator shrinkage, composition changes or a new standard state.
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 volume (ft³) = 1000. Reservoir volume (bbl): 178.107607; Standard gas volume (scf): 200000.
- Reservoir volume (bbl)
Worked example
One gas amount through two conversion paths
Bg = 0.005 reservoir ft³/scf. One petroleum barrel = 5.614583333 ft³.
Relation and unit basis
Vres,bbl = Vres,ft³/5.614583333; Vstd = Vres,ft³/0.005
Converted Bg is 0.005/5.614583333 reservoir bbl/scf. Both paths preserve the same gas amount.
1. Define the baseline
Reservoir volume (ft³) = 1000
Bg = 0.005 reservoir ft³/scf. One petroleum barrel = 5.614583333 ft³.
2. Select the relation
Vres,bbl = Vres,ft³/5.614583333; Vstd = Vres,ft³/0.005
Converted Bg is 0.005/5.614583333 reservoir bbl/scf. Both paths preserve the same gas amount.
3. Substitute the values
1,000/5.614583333 = 178.107607 reservoir bbl; /[0.005/5.614583333] = 200,000 scf
Retain intermediate precision. The displayed values are rounded only after evaluation.
4. Read the result
Reservoir volume (bbl) = 178.107607; Standard gas volume (scf) = 200000
Different numbers describe one gas amount; state conversion and geometric unit conversion are separate operations.
Result and interpretation
Reservoir volume (bbl) = 178.107607; Standard gas volume (scf) = 200000
Different numbers describe one gas amount; state conversion and geometric unit conversion are separate operations.
The three columns are different representations of the same amount. Compare direct and converted paths.
Study data and reproduction
Original synthetic teaching calculation. Equations and fixed controls are stated here; these are not field measurements.
| Reservoir volume (ft³) | Reservoir volume (bbl) | Standard gas volume (scf) |
|---|---|---|
| 10 | 1.781076 | 2,000 |
| 100 | 17.81076 | 20,000 |
| 1,000 | 178.1076 | 200,000 |
| 10,000 | 1,781.076 | 2,000,000 |
| 100,000 | 17,810.76 | 2.0000e+7 |
Scroll the table to see all columns. The highlighted row is the worked baseline. Downloads retain full numerical precision.
Test your understanding
Work through the question before revealing its answer. Use the stated assumptions and include units in every numerical step.
1. Can reservoir barrels be added directly to standard cubic feet?
Show the worked answer
No. They are different units and state bases; convert both to one explicitly defined basis first.
2. Reproduce the baseline Reservoir volume (bbl) without rounding intermediate values.
Show the worked answer
1,000/5.614583333 = 178.107607 reservoir bbl; /[0.005/5.614583333] = 200,000 scf. Reservoir volume (bbl) = 178.107607. Different numbers describe one gas amount; state conversion and geometric unit conversion are separate operations.
3. Compare the first and last recorded scenarios. Which input changes?
Show the worked answer
Reservoir volume (ft³) changes from 10 to 100000. Other controls remain as stated in the premise. Reservoir volume (bbl) changes from 1.78107607 to 17810.7607.
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. Converted Bg is 0.005/5.614583333 reservoir bbl/scf. Both paths preserve the same gas amount. Different numbers describe one gas amount; state conversion and geometric unit conversion are separate operations.
Before using the result
- Label state and volume unit together.
- Convert Bg with its numerator.
- Verify two equivalent conversion paths.
Different numbers describe one gas amount; state conversion and geometric unit conversion are separate operations.
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.