Monitoring above-zone temperature variations associated with CO2 and brine leakage from the storage aquifer

CO2 injection in saline aquifers induces temperature changes owing to processes such as Joule-Thompson cooling, endothermic water vaporization, and exothermic CO2 dissolution. CO2 leaking from the injection zone, in addition to initial temperature contrast due to the geothermal gradient, undergoes similar processes, causing temperature changes in the above zone. We used numerical simulation tools to evaluate temperature changes associated with CO2 leakage from the storage aquifer to an above-zone monitoring interval and to assess the monitorability of CO2 leakage on the basis of temperature data. We considered the impact of both CO2 and brine leakage on temperature response for three cases (1) a leaky well co-located with the injection well, (2) a leaky well at a distant from the injector, and (3) a leaky fault. We performed sensitivity analysis to determine key operational and reservoir parameters that control the temperature signal in the above zone. Throughout the analysis injection-zone parameters remain unchanged. Significant pressure drop upon leakage causes expansion of CO2 associated with Joule-Thompson cooling. However, brine may begin leaking before CO2 breakthrough at the leakage pathway, causing heating in the above zone.