Numerical modeling for CO2 storage with impurities associated with enhanced gas recovery in depleted gas reservoirs

Carbon capture and storage (CCS) in depleted gas reservoirs is an important strategy to mitigate the CO2 emissions, whereas the lack of financial incentives limits its application in large-scale. In order to reduce the costs and get potential financial benefits, CO2 with impurities (N-2 and O-2) were applied for CCS and CO2 storage with enhanced gas recovery (CSEGR). The impacts of the key properties of the depleted gas reservoir, including the gas recovery, reservoir temperature, residual water saturation, and the injection rate on the performance of CCS and CSEGR were analyzed systematically. The results showed that the CO2 storage capacity decreases proportionally to the impurity concentration. The reservoir with a temperature of 75 degrees C is favorable for the CO2 storage capacity compared with that of 114 degrees C. The impact of injection rate on the CO2 storage capacity is minor, whereas a high injection rate (10 kg/s) is advantageous for CSEGR, with a short project duration of 10.5 years compared with that of 20.1 years for the injection rage of 2.5 kg/s. The depleted gas reservoir with a primary gas recovery of 70% is favorable for CSEGR compared with that of 90%, while the order is reverse for CCS. It is suggested to produce the CH4 as possible before the operation of CCS and CSEGR. The N-2 and O-2 can be detected approximately 0.5 years before CO2 at the determined location, which can be regarded as a signal of potential CO2 leakage due to the chromatographic partitioning. In addition to the solubility and concentration of impurities would affect the partitioning, the residual water saturation is very crucial for the occurrence of significant chromatographic partitioning phenomenon.