Experimental and numerical investigation on the fracture behavior of deep anisotropic shale reservoir under in-situ temperature

Abstract

Deep resource extraction is of great importance in advancing shale gas development. To obtain the fracture behavior of deep anisotropic shale reservoirs under in-situ temperatures, a series of fracture experiment on the Longmaxi shale specimens with 5 bedding orientations after constructing in-situ temperatures of 25–200 °C was conducted, as well as corresponding extended finite element method (XFEM) simulation by ABAQUS. The results reveal that increasing in-situ temperature decreases the fracture toughness but increases the fracture toughness anisotropy. Bounded by 100 °C, the fracture toughness varying versus bedding orientation shows two categories. With increasing in-situ temperature, the acoustic emission (AE) activity of specimens with bedding orientations of 45° and 60° develops at lower load levels, showing rapid AE hit development starting at the 20% and 60% peak load at 200 °C. Fracture path in specimens with bedding orientations of 0°, 30° and 90° is roughly not impacted by increasing in-situ temperature, but that in specimens with bedding orientations of 45° and 60° is impacted obviously. XFEM models match well with the experimental observations and give deeper analyses on the interaction between the fracture propagation and bedding plane. Finally, potential applications of elevated in-situ temperatures on deep shale gas extraction were proposed.