Numerical experiment on damage and fracture of shale based on micro-scale

Correctly understanding the micro-scale fracture characteristics of the Lower Cambrian shale and the evolution law of acoustic emission signals are of great reference value in the study of shale mechanical characteristics, fracture mechanism and shale gas development and utilization. In this paper, based on digital image processing technology, the non-uniform characterization of quartz-filled shale is carried out, and a numerical model is established using the real rock fracture analysis system RFPA^2D-DIP to simulate the failure process of shale under different confining pressures. The test results show that under the micro-scale structure, the shale failure mode can be roughly summarized into three forms, namely inverted V shape(0,2 MPa), V shape(6 MPa) and inverted Z shape(10 MPa). Due to the irregular and non-uniform distribution of quartz mineral particles, the stress distribution has a significant difference in the shale micro-scale structure. When single-axis, the cumulative acoustic emission(AE) behaves as a “gentle-linear-gentle-stable” mode; when the confining pressure is 2 MPa, the cumulative AE behaves as a “gentle-nonlinear-surge-gentle-stable” mode; When the confining pressure is 6 MPa and 10 MPa, the cumulative AE behaves as a “slow-nonlinear-stable” mode. The research results provide important theoretical guidance for shale gas fracturing.