Abstract
Hydraulic fracturing experiments were conducted by employing usual water injection and an urethane sleeve pressurized on a borehole. The results of experiments were compared in order to investigate effects of injected water. Fault-plane solutions of recorded AE (acoustic emission) elucidated that shear type microcracks are dominant in the both cases. However, while quick and large pressure drops with bursts of AE were observed by water injection, the pressure increased and decreased gradually with an almost constant rate of AE occurrence by pressurizing through the sleeve. This indicates that cracks extend longer and more rapidly by water injection than the case by pressurizing through the sleeve. In usual hydraulic fracturing, thus, injected water play a role to fracture and extend the crack tips. This effect obviously characterizes the mechanism of usual hydraulic fracturing.
