Fracture propagation of deflagration fracturing in deep shale multi-branch wells

Based on the finite element-discrete element numerical method, a numerical model of fracture propagation in deflagration fracturing was established by considering the impact of stress wave, quasi-static pressure of explosive gas, and reflection of stress wave. The model was validated against the results of physical experiments. Taking the shale reservoirs of Silurian Longmaxi Formation in Luzhou area of the Sichuan Basin as an example, the effects of in-situ stress difference, natural fracture parameters, branch wellbore spacing, delay detonation time, and angle between branch wellbore and main wellbore on fracture propagation were identified. The results show that the fracture propagation morphology in deflagration fracturing is less affected by the in-situ stress difference when it is 5–15 MPa, and the tendency of fracture intersection between branch wellbores is significantly weakened when the in-situ stress difference reaches 20 MPa. The increase of natural fracture length promotes the fracture propagation along the natural fracture direction, while the increase of volumetric natural fracture density and angle limits the fracture propagation area and reduces the probability of fracture intersection between branch wells. The larger the branch wellbore spacing, the less probability of the fracture intersection between branch wells, allowing for the fracture propagation in multiple directions. Increasing the delay detonation time decreases the fracture spacing between branch wellbores. When the angle between the branch wellbore and the main wellbore is 45° and 90°, there is a tendency of fracture intersection between branch wellbores.