Water saturation effects on elastic wave attenuation in porous rocks with aligned fractures

Elastic wave attenuation anisotropy in porous rocks with aligned fractures is of interest to seismic remote sensing of the Earth's structure and to hydrocarbon reservoir characterization in particular. We investigated the effect of partial water saturation on attenuation in fractured rocks in the laboratory by conducting ultrasonic pulse-echo measurements on synthetic, silica-cemented, sandstones with aligned penny-shaped voids (fracture density of 0.0298 +/- 0.0077), chosen to simulate the effect of natural fractures in the Earth according to theoretical models. Our results show, for the first time, contrasting variations in the attenuation (Q(-1)) of P and S waves with water saturation in samples with and without fractures. The observed Q(s)/Q(p) ratios are indicative of saturation state and the presence or absence of fractures, offering an important new possibility for remote fluid detection and characterization.