ABSTRACT: In the process of drilling, completion and fracturing of shale gas reservoir, and a large amount of water interacts with shale. Water-shale interaction will inevitably lead to softening of shale mechanical properties. This paper takes the shale of Longmaxi formation in southern Sichuan as the research object. Firstly, the dynamic changes of microstructure and aperture size of sample 15-1 at different immersion time were analyzed by scanning electron microscope and nuclear magnetic resonance (NMR) experiments. Then implementing the CT scanning experiment to analyze the internal crack evolution process of sample 15-1 under different immersion times. Finally, the degradation laws of mechanical parameters such as stress-strain curve, peak intensity, elasticity modulus and Poisson's ratio of shale samples at different immersion time under different confining pressures are obtained. With the help of continuous damage mechanics and statistical theory, the rock damage constitutive model under hydration coupling is established, and the damage effect of shale mechanical properties degradation under hydration is revealed.

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