Study on anisotropic mechanics and acoustic emission response characteristics of layered shale under uniaxial compression.

Deep shale has obvious bedding structure, and its complex anisotropic mechanical characteristics bring challenges to the development of shale gas resources. In order to explore the effect of bedding on the mechanical properties and failure modes of shale. This paper takes the Longmaxi Formation shale in Changning, Sichuan Province as the research object, uniaxial compression tests were conducted on shale with different bedding angles, and acoustic emission (AE) signals were monitored during the loading process. The anisotropic mechanical properties of shale under loading were analyzed, and a further comprehensive evaluation of shale brittleness characteristics and rock burst tendency was conducted. Additionally, the evolution law of statistical parameters of AE and the mechanism of rock fracture were explored. The results showed that: (1) The deformation and mechanical properties of shale containing laminations during uniaxial compression show strong anisotropic characteristics, showing significant dip angle effect. (2) The fracture morphology of shale under uniaxial loading was complex, mainly characterized by splitting tensile failure and shear tensile failure, showing a strong tendency towards rockburst. (3) The Rickman brittleness index of shale attains 45.59, manifesting strong brittleness properties that are conducive to reservoir fracturing transformation. (4) During the loading process, there is good consistency between the AE signal and the stress-strain curve. The evolution of shale AE parameters corresponds to the rock damage and failure process, and the distribution characteristics of AE spectrum RA-AF data can distinguish the type of stress-generated cracks, and it is found that the shale under uniaxial compression was dominated by shear damage on the whole, and the proportion of shear damage increases firstly and then decreases with the increase of bedding angle. The research results can provide theoretical reference and guidance for the optimization design of hydraulic fracturing and the control of drilling stability during deep shale gas exploitation.