Experimental and numerical investigation on shale fracture behavior with different bedding properties

Abstract

Research on crack evolution mechanism and fracture behavior of bedding shale is of great significance for shale gas exploitation. The mechanical properties of shale, especially the strong anisotropy, have great influence on the nucleation and propagation of hydraulic fractures. To investigate the mechanical properties of bedding shale, the micro fracture process of Longmaxi shale under three-point bending load was observed using scanning electron microscope (SEM) equipped with a loading device, and the smooth joint model based on particle flow code (PFC2D) was established to simulate the effect of different bedding properties on shale fracture behavior. The results demonstrated that the mechanical properties of the weak bedding planes have significant effect on the fracture pattern, tensile strength, fracture toughness, crack initiation angle, crack propagation path, and complex fracture network generation. In addition, the evolution characteristics of microcracks were studied by fractal method. The results showed that fractal method can well quantitatively characterize the evolution process of microcracks in bedding shale.