EVALUATION OF WATER SATURATION FOR SHALY RESERVOIRS

摘要

A method for determining effective water saturation of a shaly reservoir is described herein. For the purpose, an initial estimation of water saturation of the shaly reservoir is made. Subsequently, a spontaneous potential log is recorded in a borehole 106 drilled with a saline drilling mud 202 for continuous in-situ estimation of a membrane potential across the shaly reservoir. The saline drilling mud 202 includes an electrolyte such that the recorded SP log is substantially equal to a membrane potential log. The recorded SP log is normalized to compensate for the clay volume, and the normalized SP log along with the initial water saturation is used to determine effective water saturation of the shaly reservoir. The method compensates for internal structure and physical and chemical properties of the reservoir, thereby providing a realistic estimation of the effective water saturation of the shaly reservoir.