Volatile Oil
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Phase diagram
For a volatile oil, the shape of the phase envelope has contorted some, rotating counter-clockwise as compared to the black oil.
The reservoir temperature (point 1) is much closer to the critical point, and that the quality lines are no longer evenly spaced. As pressure drop below the bubble point, a modest decrease in pressure translates into a large change in gas evolution.
Characteristics
| Reservoir state | liquid |
| Initial GOR | between 2000 and 3300 scf/STB |
| Producing GOR | increases when reservoir pressure drops below bubble point |
| Initial STO (McCain) | greater than 40oAPI, and increasing as Pres falls below bubble point |
| Color | usually brown, orange, or slightly green |
| Bo at bubble point | greater than 2.0 rb/STB |
| C7+ Mole Fraction | between 12.5% and 20% (+/- 2) |
| Other | produced gas is normally a retrograde gas |