###### Abstract  
Injecting high-pressure fluid into a reservoir rock mass will change the mechanical properties of the rock; the strength and safety of a shale well wall are also extremely critical. In order to investigate the law of variation in water-sensitive shale strength during fracturing, an experimental study on the mechanical properties of shale under high confining pressure and water-rock coupling was carried out. Taking water-sensitive shale rock as the research object, the effects of high confining pressure and water content on the mechanical properties, residual strength, and macroscopic and microscopic failure modes of shale were analyzed. The test results show that the stress-strain curve of the shale gradually shortened with the decrease in the water content in the stage of void compaction and plastic yield, and the peak of the stress-strain curve was continuously enhanced. The water content and the peak intensity exhibited a negative linear correlation. The elastic modulus and water content showed an exponentially decreasing distribution. However, as the water content increased, the decreasing rate became slower, the softening coefficient increased, and the plastic deformation increased. The research results provide basic load parameters for the strength and safety of the casing of an oil layer under fracturing conditions. s +
Footnote †: journal: applied sciences  
wellbore stability of shale has been effectively solved. [PERSON] et al. [4] studied the influence of shale characteristics on compressibility. They found that the factors affecting the compressibility of shale are complex, depending on petrological characteristics, confining pressure conditions, and differences in ground stress, and the fracturing effect is related to the selection of a fracturing fluid system and construction parameters. [PERSON] et al. [5] compared three kinds of borehole stability analysis methods, namely, pure mechanics, seepage force coupling, and chemical coupling, according to the differences in the composition and structure of hard and brittle shale. Four kinds of mechanical instability mechanisms of hard and brittle shale have been studied. [PERSON], [PERSON], et al. [6; 7] used a triaxial rock mechanic testing machine to conduct a triaxial test of mud shale. According to the test, a static elastic modulus, cohesion, an internal friction angle, Poisson's ratio, and compressive strength characteristic parameters were obtained; mechanical analysis was carried out on shale well walls; and safety windows of drilling fluid density, including collapse pressure and rupture pressure, were obtained. [PERSON] et al. [8] explored the borehole instability mechanism of layered mud shale and studied the borehole stability prediction model of layered mud shale formation considering the presence of drilling fluid under a real three-way stress state. Ignoring the influence of intermediate principal stress, it is impossible to reasonably predict the possibility of the collapse of the layered shale formation. The seepage of drilling fluid filtrate along the bedding surface will reduce the cohesion and internal friction angle of the bedding surface. The improved analysis model of the wellbore stability of the layered shale formation can truly reflect the state of the in situ stress and the mechanical properties of the wellbore rock. [PERSON] et al. [9] comprehensively analyzed shale fracture characteristics and factors influencing UCS. The sliding of micro-fractures, the generation and expansion of new micro-fractures, and the collapse of pores will affect the deformation mechanism of the inelastic section of the uniaxial loading curve of shale. The uniaxial compressive fracture of mud shale is tensile or shear. The shear fracture can easily occur in the part with low stiffness and a weak consolidation degree, and the tensile fractures can occur in the part with high stiffness and a strong consolidation degree. [PERSON] et al.