Failure characterization of Longmaxi shale under direct shear mode loadings

Experimental Study of Direct Shear Properties of Anisotropic Reservoir Shale

“…Shale is a typical transversely isotropic rock mass; its bedding structure is developed and its bedding strength is low [4,[17][18][19]. On one hand, during horizontal well drilling, shale formations around shale horizontal wells are more likely to shear and slide along the bedding plane, resulting in a significant increase in the risk of collapse and instability of horizontal wells [20,21]. On the other hand, in the process of hydraulic fracturing, shale bedding and natural fractures are the key to the formation of complex network fractures [22].…”

“…Both triaxial compression tests with different confining stresses and direct shear experiments with various normal stresses are usually adopted to explore the shear mechanical properties of reservoir shale [20]. Previous research shows that the triaxial compression test is difficult to use to analyze the propagation and evolution of a shear fracture in depth due to the uncertainty of the shear fracture plane and the randomness of the fracture initiation point.…”

“…Moreover, the loading path can be precisely controlled and experimental parameters are easily obtained in the direct shear experiment [25][26][27][28][29][30][31]. Hence, the direct shear experiment has been viewed as the preferred experimental method to understand the shear properties of reservoir shale [20][21][22]24,32,33]. In order to theoretically study the effect of shear mechanical properties for shale on the stability control of horizontal well drilling and the optimal design of hydraulic fracturing in shale gas reservoirs, many scholars have conducted direct shear experiments to characterize the shear mechanical properties of reservoir shale with different bedding orientations [20][21][22]24,32,33].…”

“…Hence, the direct shear experiment has been viewed as the preferred experimental method to understand the shear properties of reservoir shale [20][21][22]24,32,33]. In order to theoretically study the effect of shear mechanical properties for shale on the stability control of horizontal well drilling and the optimal design of hydraulic fracturing in shale gas reservoirs, many scholars have conducted direct shear experiments to characterize the shear mechanical properties of reservoir shale with different bedding orientations [20][21][22]24,32,33]. For example, Ma and Chen [21] conducted direct shear tests on cubic shale samples with side lengths of 50 mm.…”

“…The anisotropy of the peak shear strength of shale was controlled by the anisotropy of its shear failure mechanism. Lu et al [20] conducted a group of direct shear tests at the shear rate Energies 2024, 17,1977 3 of 19 of 0.0003 mm/s on cubic shale samples with a side length of 50 mm. It was found that for increasing the angle of the shear direction from 0 • to 30 • , 60 • , and 90 • with the shale bedding orientation (acute-angle shear mode, clockwise rotation along the shear direction to the bedding orientation with an acute angle, as shown in Figure 1b), the peak shear strength of shale increased first and then decreased.…”