Laboratory measurements of seismic attenuation in water-saturated porous borosilicate

Abstract

Laboratory measurements of seismic attenuation were performed on borosilicate samples using the forced oscillation method. First, we studied the effect of partial water-air saturation. Significant and frequency-dependent attenuation was only observed at nearly full water saturation and at low pore fluid pressures (≤0.5 MPa). A peak in attenuation, quantified by the inverse quality factor 1/Q, of 0.02 was observed at about 1.5 Hz. A similar experiment was performed for water-nitrogen saturation and, again, at low fluid pressures and near full water saturation, a peak in attenuation of 0.015 was observed at about 3 Hz. Increasing the confining stress and fluid pressure equally, and thus keeping the effective stress unchanged, resulted in negligible attenuation. An attenuation mechanism that can explain these results, possibly better than wave-induced fluid flow (WIFF) at the mesoscopic scale, is the dissolution and exsolution of microscopic gas bubbles in response to wave-induced fluid pressure variations.