Triaxial tests on weak planes damage of hard brittle shale of Longmaxi formation in South Sichuan Basin, China

In petroleum field, rock mechanical property is a significant parameter for design of drilling operation. Shale formation has high risk of wellbore instability during drilling. To reduce risk in drilling, more investigations on shale should be conducted. Therefore, in this paper, by using X-ray diffraction and electron microscope scanning test, the mineral composition and microstructure of brittle shale of Longmaxi formation have been analysed. Based on the triaxial compression tests, rock mechanical parameters in variable time have been discussed when shale is in the external force condition. In particular, considering shale failure along weak plane, changes in shale mechanical properties, like stress, strain, structure integrity and elastic parameters, have been analysed. This work offers comprehensive exploration on shale mechanical properties. Mechanical parameters of shale in this study can provide reference for engineering design, and more importantly, establish the foundation for investigation of rock damage in the future.