Thermal-mechanical coupling in shale geothermal reservoirs: a framework for temperature-dependent seismic characterization

Reliable seismic characterization of geothermal reservoirs requires quantifying the effects of temperature on rock elastic properties. We investigate temperature-dependent seismic velocity evolution in shale through integrated laboratory ultrasonic measurements and finite-element modeling. The P- and S-wave velocities were measured on shale samples from China and the United States with diverse mineralogies over a temperature range from 20 °C to 200 °C, with numerical simulations extending the predictions to 300 °C. Results show a systematic decrease in P-wave velocity with increasing temperature. In contrast, S-wave velocity exhibits enhanced sensitivity to thermally induced micro-fracturing and pore-structure evolution, displaying a biphasic temperature response associated with the competing effects of thermoelastic softening and progressive microcrack development. Temperature-dependent rock-physics models incorporating evolving elastic moduli accurately reproduce the observed velocity trends. These findings establish a quantitative thermo-mechanical framework for interpreting seismic responses in shale-dominated geothermal systems and improve the reliability of seismic monitoring under high-temperature conditions.