Investigation on the time-dependent characterization of stimulation behaviors for the shale under fracturing fluid invading

In order to understand the time-dependent characteristics of stimulation behaviors during hydraulic fracturing, the self-developed hydraulic fracturing monitoring system under triaxial loading was employed to investigate the cracks' propagation under shale-fluid coupling process. The results reveal that with different duration of fracturing fluid invasion, the pressurization rate of fluid pressure and breakdown pressure (BP) value are obviously varied, and the tensile crack is the dominant crack type, the amounts of shear cracks change accordingly, as well as the failure mode's evolution includes radial split, oblique shear, and combination of oblique shear and radial split. Moreover, the stress regime evolution rules around the cracks are obtained based on the Mohr-Coulomb criterion. This investigation will provide theoretical support for the fracturing's implement in the field, also can be as the laboratory evidence for the interpretation of microseism induced by long-term hydraulic fracturing.