A modeling and numerical simulation study of enhanced CO2 sequestration into deep saline formation: a strategy towards climate change mitigation

The net increase in anthropogenic carbon dioxide (CO2) emissions from fossil fuel combustion contributes significantly to the global warming and climate change. CO2 capture and storage (CCS) in geological formations, specifically in deep saline aquifers, is among the very promising strategies to control and mitigate emissions into the atmosphere. Injection of CO2 into a reservoir may result in the formation of pore pressure which can initiate cracks and trigger fault activities. CO2 may leak into the atmosphere and invade shallow groundwater sources. Release of CO2 into the atmosphere has enormous effects on the environment and significantly contributes to global climate change. Therefore, storage safety, injection efficiency, and monitoring remain crucially important considerations in CO2 injection. This study attempts to establish an optimal CO2 injection strategy that aims at enhancing CO2 storage with an increased safety at Ordos basin. Furthermore, it establishes the safety limits of CO2 plume migration from the central axis of the injection well. In the investigation, injection parameters such as injection rate and bottom hole pressure were analyzed. The CO2 plume migration analysis was performed, and migration limits were determined. Simulation results revealed that different formation layers have varying storage capacities and pressure withstanding ability. The site maximum storage rate goal of storing 100,000 t of CO2 per year was attained. It is advised to perform injection at the Majiagou layer due to sufficient storage capacity and greater depth of over 2400 m from the surface. This study recommends that an optimum CO2 sequestration strategy which does not result into excessive migration of injected CO2 plume and limit formation pressure buildup should be adopted. Therefore, deep underground storage at an average depth of above 2400 m is optimum, because it has an adequate storage space to accommodate the desired rate of 100,000 t/year. Besides, its geological settings favor storage safety in the event of significant uplift that may cause induced seismicity. Furthermore, it will also limit CO2 plume that may come into contact with shallow groundwater sources. Likewise, investing in low carbon and carbon-free energy technologies and enhancement of energy efficiency systems around the site is also recommended.