SPE ABSTRACT SUBMISSION

TITLE: Determining the value of residual gas saturation from production data in volumetric gas reservoirs.

OBJECTIVE/SCOPE

To develop a simple mathematical model that uses simple field and laboratory parameters to determine residual gas saturation.

METHODS PROCEDURES, APPROACH

The approach is based upon simple manipulation of the real gas equation to arrive at a straight-line equation with a slope value containing residual gas saturation Sgr along with other easily known parameters, restricted to volumetric gas reservoirs only. A simple plot of density of gas vs. the ratio of pressure and deviation factor (P/Z) calculated at different intervals would lead to a straight line.

RESULTS, OBSERVATIONS AND CONCLUSION

A residual gas saturation value comparable to that derived from core analysis and/or well-log data is obtained. Since the method assumes constant hydrocarbon pore volume (HCPV), it arrives at satisfactory results only in the case of volumetric gas reservoirs. This very fact may also be used as an additional diagnostic tool to determine the presence/absence of a water drive since then the data points obtained would not lie in a straight line implying absence of 100% depletion drive, and hence may facilitate modification of reserves based on material balance.

Although the method may require few years of field data when applied to new discoveries but can be readily applied to gas reservoirs having a few years of history.

The method will provide the engineer with an additional residual gas saturation value which may be useful especially in cases where the log and core data are not available or if available, are not comparable to each other.