Effect of reservoir temperature and water driving pressure on dynamic behavior of geothermal reservoirs under production loads

The safe and efficient development of geothermal energy is a key driver of the energy revolution and environmental governance in this century. To understand the effect of water driving pressure on drilling safety and hydraulic fracturing efficiency during the development of geothermal energy under varying reservoir temperatures, dynamic compression tests were conducted on granite samples subjected to thermal treatment (25, 100, 200, 300, 400 and 600 °C) and subsequent forced water absorption (0, 4, 8, 12 MPa) using a split Hopkinson pressure bar system. The results indicate that a higher water driving pressure exacerbates the deterioration of dynamic compressive strength with increasing temperature, while it enhances the rate dependence of dynamic compressive strength, except at 600 °C. The dynamic increase factor (DIF) of dynamic compressive strength vs. strain rate is determined by both temperature and water driving pressure. A prediction model for the deterioration of dynamic compressive strength considering reservoir temperature and water driving pressure is proposed for geothermal reservoirs. While the splitting failure of samples remains unchanged, crack density increases with increasing temperature and water driving pressure, exhibiting multiscale failure cracks parallel to the loading direction. The structure effective strength model, the wing-crack propagation model, the effect of pore water pressure on dynamic stress intensity factor, and the dynamic response of forced absorbed water can collectively reveal the response mechanisms of dynamic strength. Based on the experimental findings, implications for safe and productive geothermal energy development are discussed, with particular attention to the effect of drilling fluid leakage on wellbore stability and the impact of residual fracturing fluid after backflow on repeated fracturing. This study has important reference value for understanding dynamic wellbore stability under drilling disturbance loads and for the design of repeated dynamic hydraulic fracturing schemes in geothermal energy development.