Evaluation of the High-Speed Centrifuge Technique for Determining Capillary Pressure at Low Wetting-Phase Saturations

Abstract

ABSTRACTRecent experimental studies of the high-speed centrifuge technique have indicated that the method, if properly used, yields results which are in accordance with other methods. These studies have also shown that the concept of an irreducible wetting phase saturation is not valid. In the present paper work is reported in which these previously presented results are extended to both higher and lower capillary pressures. Air/liquid data have been obtained with n-decane as the wetting phase and are compared with new data (as well as with the previously reported data) for the air/brine system. The study involved 242 days of centrifugation and utilized 10 different Berea plug samples and 5 different high permeability plug samples taken from a producing reservoir.The linear relationship between log Pc and log <Sw> (or log Sw, as observed in previous work) was confirmed for Berea samples over the average saturation range from about 30 percent down to 10 percent. For lower average saturations, the saturation data are not sufficiently precise either to (1) demonstrate conclusively the persistence of this relationship, or (2) prove the breakdown of the Hassler boundary condition. For three of the five producing reservoir samples, it was found that two different linear segments characterized the log Pc versus log <Sw> relationship, with a rather sharp transition occurring in the 30 to 40 percent average saturation range.