Numerical simulation of a hidden fault at different stages of evolution in a carbon dioxide-enhanced saline water recovery site

CO2 geological storage combining with deep saline water (or brine) recovery (CO2-EWR), which is a novel geoengineering approach of CO2 geological utilization and storage, is presented to solve the dilemma between increasing carbon emissions and water scarcity in China. The major idea of CO2-EWR is to use the pressure buildup from CO2 injection to enhance the recovery of deep saline water. However, avoiding all the buried faults in the reservoir at CO2-EWR sites is impossible. Some faults may penetrate through the reservoir into the caprock and basement. Both the fault zone's architecture and the related permeability structure affect the fluid flow in the reservoir and fault zone. In this paper, we investigated the influences of faults at different stages of evolution on reservoir management and induced fault slippage. The results indicate that CO2 injection can effectively enhance the recovery of deep saline water when the fault zone acts as a conduit. In addition, the induced fault slippage can be significantly reduced when the production-injection ratio is appropriately controlled. However, when the fault zone acts as a barrier, CO2 injection can no longer enhance the recovery of deep saline water. The production of water may play a negative role in the stability of the fault. Moreover, surface uplift from fluid injection may cause the region above the fault to undergo a potentially serious tilt, which may be very harmful to infrastructures on the ground.