Damage characteristics of shale with different bedding inclinations under high-pressure water jet impact after thermal treatment

Water jet-assisted rock breaking is a conventional method for shale gas extraction. However, the complex conditions of deep shale reservoirs, including elevated temperatures and intricate stratification, obscure the rock-breaking mechanisms of jets. Therefore, this study conducted high-pressure water jet impact experiments on shale with five bedding angles (0°, 30°, 45°, 60°, and 90°) and four temperatures (room temperature, 100, 150, and 200 °C). Computed tomography (CT) and three-dimensional reconstruction techniques were used to analyze the damage characteristics. Results indicate that increased temperature significantly enhances rock-breaking efficiency. The crack volume fraction at 200 °C increased by 146.44 times compared to 25 °C. The new crack area exhibited a sharp increase from 100 to 150 °C compared to the slow increase rate before and after this temperature range, indicating the presence of a threshold temperature for effective fragmentation by jet impact. Damage showed significant anisotropy, with crack depth increasing with bedding angle and a through crack emerged at 90°, while the new crack area peaked at 45°. The jet rock-breaking efficiency index (JREI) was introduced which integrates crack volume, area, and depth to characterize the fragmentation efficiency at different temperatures and bedding conditions. These findings could provide a theoretical basis for enhancing the fragmentation of deep shale.