Joule-Thomson Cooling During CO2 Injection into Depleted Gas Reservoirs: Coupled Wellbore-Reservoir Simulations

Joule-Thomson (JT) cooling during CO2 injection poses significant thermal and operational challenges in depleted reservoirs. This study performs fully coupled wellbore-reservoir simulations to investigate transient thermal-hydraulic behavior during CO2 injection and to explicitly compare depleted gas and brine-filled reservoir conditions. Results show that depleted reservoirs experience pronounced JT cooling, with near-wellbore temperatures dropping to approximately 13 °C within the early injection stage. The cooling front propagates rapidly during the initial period and then transitions to a diffusion-controlled regime, with the 38 °C isotherm following a logarithmic radial expansion trend. A high-density liquid CO2 zone forms near the wellbore due to combined pressure buildup and cooling effects. In contrast, the brine-filled reservoir exhibits smaller temperature reductions and smoother pressure evolution, owing to its higher initial formation pressure. Parametric analysis indicates that injection rate strongly influences the intensity of transient cooling, with higher rates amplifying the early-stage temperature decline. Increasing the injection temperature mitigates but does not eliminate JT cooling under low reservoir pressure conditions. These findings highlight the dominant role of the thermodynamic state of the initial reservoir in governing injection-induced cooling and define operational strategies to maintain thermal integrity during CO2 storage in depleted gas reservoirs.