scope:

SUMMARY AND CONCLUSIONS

The equations and conclusions presented in this report have grown out of a study initiated by the American Petroleum Institute's Subcommittee on Recovery Efficiency in 1956. The Subcommittee's assignment then and now was to study reservoir recovery processes based on actual performance of producing fields rather than on theory or laboratory data.

The study began as an effort to apply machine methods of analysis to updated data from the 103 reservoirs investigated by Craze and Buckley in 1945,¹ using multiple correlation analysis procedures described by Guthrie and Greenberger in 1955. This initial effort was later expanded to include collection and analysis of reservoir and recovery data on additional reservoirs.

Availability of advanced computers made it possible to apply more sophisticated techniques to arrive at statistically significant correlations between indicated recovery factors and the reservoir parameters.

The subcommittee collected data on 312 reservoirs which were weighted 1, 2, and 3 according to their reliability. This report deals with:

Oil reservoirs under a water drive mechanism, where invading bottom or edge water is the dominant displacing medium; and

Oil reservoirs under a solution gas drive mechanism (also referred to as depletion or internal gas drive) where the expansion of gas liberated from solution is the sole source of expulsion of the oil.

Not covered in this report are combinations of water drive and solution gas drive, gas cap drive, or gravity drainage which together comprised 30 to 40 percent of the case histories. Another 10 percent of all cases received could not be used for correlation purposes because of lack of adequate performance control or because pertinent data were missing.

¹See p. 27 for references.