Dependency of Seismic Compressional Wave Velocity and Attenuation on Temperature and Liquid-steam Phase Transition

The temperature dependence measurements showed that P-wave velocities decrease with increasing temperature in a systematic way that generally fits the predictions of the Gassmann relationship, implying that liquid characteristics, with modifications that allow for the presence of bubbles and micro-fracturing, account for much of the seismic velocity changes. The Q factor (inverse of attenuation) is affected by temperature through the viscosity of liquids and the formation of bubbles and thermal micro-fracturing. In the phase transition measurement, P-wave velocities did not increase immediately with a pore pressure decrease but with some retardation at the liquid-steam phase transition. Relative P-wave amplitudes did not decrease immediately with a pore pressure decrease but with some retardation at the liquid-steam phase transition. Our results show two distinctive observations during the temperature-dependent and the liquid-steam transition experiments: 1) A lower P-wave velocity and a higher attenuation are most likely an indication of rocks saturated with a high temperature liquid and subject to some thermal fracturing process that is responsible for the generation of patchy saturation due to bubbles; 2) A higher velocity and higher attenuation are more likely an indication of rocks saturated with liquid that is subject to a liquid-steam transition or a steam phase.