Feasibility study of underground CO2 storage through Water Alternative Gas (WAG) operation: A case study in Southwestern Ontario

Geological CO2 storage (GCS) offers a promising, low-risk, long-term solution for carbon sequestration. This study assesses the feasibility of GCS water-alternating-gas (WAG) operations in a brine formation targeted for the Western Ontario GCS plan. The Cambrian strata shows potential for CO2 storage but faces challenges like limited lateral extension and geopolitical issues from plume migration. To mitigate these risks, a deep evaluation of CO2 trapping mechanisms is crucial. CO2 dissolution into brine provides secure storage by reducing the free plume. The proposed WAG operation promotes dissolution, using a vertical equilibrium model coupled with a black oil model to estimate CO2 trapping proportions during and post-injection. The Taguchi design of experiments investigates various WAG scenarios with minimal simulations, reducing numerical costs. Sensitivity analysis/ optimization of WAG parameters, including water extraction rate (WER), water injection rate (WIT), and CO2 injection time (CIT), ranked their effectiveness in CO2 dissolution. Optimal WAG operations can reduce the free plume by 49 % and increase the dissolution ratio from 0.26 to 0.52. CIT and WIT were found to be the most influential factors, contributing 42 % and 31 % to CO2 dissolution, and 43 % and 34 % to overall CO2 trapping, respectively, while WER exhibited a lower impact of 8-9%.