Abstract

One of the most important parameters in estimating recovery factor for a water drive gas reservoir is residual gas saturation. However, very limited references have examined this topic.

The objective of this paper is to find a correlation between residual gas saturation and recovery factor of a gas reservoir under bottom water-drive using a finite difference simulator. The reservoir model used in this study is a 2-D radial, 2-phase water-gas flow. The generated model was validated with a published analytical method for cumulative water influx and initial gas in place calculation.

A sensitivity analysis was then conducted by applying several different values of residual gas saturation to the reservoir model input. The values of the residual gas saturation vary between 0.28 and 0.38. The simulations were run until specified recovery factors corresponding to certain reservoir abandonment pressures. Performance of the reservoir pressure with respect to cumulative production was plotted for difference values of residual gas saturation. Hence, the resultant reservoir abandonment pressures can be correlated with the residual gas saturation data and recovery factors.

The correlation obtained is visually presented in a chart of residual gas saturation versus abandonment pressure for different values of recovery factor. The result also shows that the recovery factors decrease when the residual gas saturation increases for a certain reservoir abandonment pressure. The relationship is not linear, and validates as well as broadens the very limited available literatures.