Study on the characteristics of crack initiation in deep dense shale containing circular hole under varying stress conditions

Abstract

The evolution of cracks in shale directly affects the efficient production of shale gas. However, there is a lack of research on the characteristics of crack initiation in deep dense shale under different stress conditions. In this work, considering the different combinations of confining pressure and bedding plane inclination angle (α), biaxial mechanical loading experiments were conducted on shale containing circular holes. The research results indicate that the confining pressure and inclination angle of the bedding planes significantly influence the failure patterns of shale containing circular holes. The instability of shale containing circular holes can be classified into five types: tensile failure along the bedding planes, tensile failure through the bedding planes, shear slip along the bedding planes, shear failure through the bedding planes, and block instability failure. Furthermore, the evolution of strain and stress fields around the circular holes was found to be the fundamental cause of variations in the initiation characteristics and locations of shale cracks. The crack initiation criterion for shale containing circular hole was established, providing a new method for evaluating the trajectory of shale hole wall fractures. This study holds significant importance for evaluating the evolution and stability of fracture networks within shale reservoirs.

Keywords

shale gas / deep dense shale / crack initiate characteristics / failure modes

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Central South University