Both compressional and shear wave velocities were measured in water- filled Berea sandstone as a function of pore pressure under a constant confining pressure of 200 bar. A t 145.5OC, compressional velocity increased from steam-saturated (low pore pressure) to water- saturated (high pore pressure) rock, whereas shear wave velocity decreased. Furthermore, a velocity minimum, attenuation and dispersions occur at water-steam transition for compressional wave. Results at 198?C show that both compressional and shear velocities decrease from steam saturated to waters at u rated rock, and a small velocity minimum is observed for compressional waves, but no attenuation nor dispersion occur. At both temperatures, the V/V ratio and Poisson's ratio increased from steam-saturated to water- PS saturated rock. The results are reasonably compatible with the mechanical effects of mixing steam and water in the pore space near the phase transition, and may be applicable to insitu geothermal field evaluation.

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