Study on distribution characteristics of shale triaxial compression acoustic emission energy under different confining pressures

The development of shale gas has always been restricted by low pressure, low porosity and low permeability. With the wide application of hydraulic fracturing technology in shale gas mining, the study of deformation and failure mechanism of shale under stress state is of great significance. In order to reveal the evolution mechanism of shale failure process, the author took the Luoreping Formation shale in Chongqing City as the research object, and carried out the conventional triaxial compression acoustic emission test on the rock samples collected under different confining pressure conditions, with the aim of recording the mechanical parameters and acoustic emission data about rock deformation and failure process. The critical model was used to quantitatively analyze the statistical distribution of acoustic emission energy of shale, and determine the critical characteristics and the critical power law distribution, and the maximum likelihood estimation method was used to determine the Power Rate Distribution Index. The test results show that the failure process of shale under triaxial compression can be divided into the calm stage, the failure stage, the post-peak stage and the stable stage; the probability density of acoustic emission energy of shale under different confining pressure follows the distribution law of non-scale power law and the critical exponents under three confining pressures are 1.34, 1.40 and 1.55 respectively; the critical components increase as the confining pressure increases; the existence of confining pressure limits the generation of cracks inside the rock, and reduces the "degree of chaos" inside the rock and weakening the deterioration of internal rock structure.