A Note on the Valuation of Relative Permeability

Recently equations have been presented by Rose and Bruce and by Rose, showing how the relative permeability of a reservoir rock may be determinedfrom the capillary character of the rock. In particular, equations weredeveloped to show the relationship between capillary pressure and the effectivepermeability to the wetting phase in a poly-phase flow system. In measuring the flow of electric current through partially saturated coresamples, it has been observed that the electrical resistance usually is not asimple linear function of saturation. This fact indicates that the averagelength of path in the flow of electric current is not independent ofsaturation, but rather that the tortuosity of the path depends upon the averagesaturation to the conducting fluid as well as upon the characteristics of therock itself. Inasmuch as the flow of fluid and the flow of electric current inmany respects are analogous, it may be indicated further that the length ofpath for fluid also may not be independent of saturation. The above equation suggests including a correction for tortuosity whencalculating the relative permeability of a reservoir rock to a wetting phase.The correction factor may be obtained from the resistivity-saturationrelationship. It will be noted that the agreement between the calculated points and theobserved data is rather good. Further investigation of the above method forobtaining relative permeabilities may be merited. The writer acknowledges the permission of The Texas Co. to submit this note forpublication.