SEGJ Technical Conference

Changes in crack shape and degree of saturation estimated from P and S wave velocity changes during the water penetration into a stressed rock

Abstract We estimated crack characterizations such as the aspect ratio and the degree of water saturation and their changes during the water migration into a granitic rock subjected to the confining pressure and the differential stress. We applied the differential stress of 370 MPa under the confining pressure of 30 MPa. We injected water from the bottom end surface of the sample. The pressure of water injection was held constant at 25 MPa. During the water migration, P-and S-wave velocities of elastic waves that propagated along the paths parallel to the top and bottom surfaces of the sample were measured. We also measured strains of the sample surface and monitored acoustic emissions, AE. We estimated the aspect ratio and the degree of water saturation by applying the cracked solid model to the data on P and S wave velocities and the crack density. We found, the aspect ratio of dry cracks before the water injection was 1/400, during the water migration, the aspect ratio changed from 1/400 to 1/220, and degree of water saturation increased up to 0.7.