Journal of Petroleum Geology, Vol.4, No.4, pp. 407-418, 1982

©Copyright 2000 Scientific Press, Ltd.

ESTIMATION OF IRREDUCIBLE WATER SATURATION AND EFFECTIVE PORE SIZE OF MUDSTONES

Hiromi Honda* and Kinji Magara**

*Exploration Dept., Japan Petroleum Exploration Co. Ltd. Seiwa-Ebisu Bldg. 2F. 1-18-14. Ebisu, Shibuya-ku. Tokyo. Japan.

**Bureau of Economic Geology. The University of Texas at Austin. Austin, Texas 78705, USA.

Abstract

A theoretical consideration of immobile water saturation in mudstone is made by means of a capillary model of a porous medium using the air and water absolute permeabilities of a sample. The calculated values of immobile water saturation of the Tertiary mudstones from Japan tend to support a generally-accepted concept; virtually all the water in mudstones is irreducible. Immobile or irreducible water saturation increases gradually with decrease of porosity of mudstones; 15% porosity is a critical value beyond which mudstones contain 100% immobile water in the pores.