Unexpectedly large effects of partial oil-brine saturation on the elastic wave velocities of Berea sandstone

摘要

Velocities of elastic waves measured in the subsurface generally involve saturations of multiple phases. This is commonly modeled by fluid substitution using an effective fluid modulus determined. In order to address the applicability of this approach we measure the ultrasonic velocities of a Berea sandstone core partially saturated with brine and crude oil through drainage. The measurements show decreases in compressional velocity and consequently bulk modulus far exceeding the values expected from general fluid substitution. We propose the variations to be caused by the presence of kaolinite in the pores of the sandstone.