Influence of Circular Hole Diameter on Deformation and Failure of Longmaxi Shale

Shale gas exploitation usually requires drilling perforated wells with a circular shape. To explore the influence of circular hole diameter on shale deformation and failure, uniaxial compression tests were carried out on Longmaxi shale samples with a single prefabricated hole, combined with digital image correlation and wave velocity tests. Studies have shown that the wave velocity increases as the bedding angle increases while increasing slightly as the hole diameter decreases. The circular hole diameter has a significant effect on the uniaxial compressive strength of shale. As the diameter of the circular hole increases, the uniaxial compressive strength decreases. Large hole diameter (10 mm) and medium hole diameter (6 mm) are dominated by tensile failure, while a sample with a small hole diameter (2 mm) exhibits mixed tension and shear failure. Under uniaxial compression, the end of the specimen mainly undergoes shear failure.