Seismic Attenuation in Fluid-saturated Rock: Experimental Evidence of a Gas Dissolution-exsolution Mechanism
S.A. Chapman, N. Tisato, B. Quintal and K. Holliger
Event name: 77th EAGE Conference and Exhibition 2015
Session: Rock Physics - Applications and Case Studies
Publication date: 01 June 2015
Info: Extended abstract, PDF ( 1.5Mb )
Price: € 20
Laboratory measurements of seismic attenuation were performed on a synthetic rock sample using the forced oscillation method. Studying first the effect of partial water saturation, significant and frequency-dependent attenuation was only observed at near full water saturation and at low pore fluid pressures (≤0.6 MPa). Increasing the confining pressure and fluid pressure equally, thus keeping the effective stress unchanged, caused a significant decrease in attenuation. For fluid pressures >2.5 MPa attenuation was negligible and frequency independent. Additional measurements at different effective stresses showed that the mechanism responsible for the observed frequency-dependent attenuation is not sensitive to the effective stress. The physical mechanism that can potentially explain these results is wave-induced-gas-exsolution-dissolution (WIGED) occurring in response to fluid pressure variations, rather than wave-induced fluid flow (WIFF).