Integrated Framework for Assessing Impacts of CO₂ Leakage on Groundwater Quality and Monitoring-Network Efficiency: Case Study at a CO₂ Enhanced Oil Recovery Site

This study presents a combined use of site characterization, laboratory experiments, single-well push–pull tests (PPTs), and reactive transport modeling to assess potential impacts of CO₂ leakage on groundwater quality and leakage-detection ability of a groundwater monitoring network (GMN) in a potable aquifer at a CO₂ enhanced oil recovery (CO₂ EOR) site. Site characterization indicates that failures of plugged and abandoned wells are possible CO₂ leakage pathways. Groundwater chemistry in the shallow aquifer is dominated mainly by silicate mineral weathering, and no CO₂ leakage signals have been detected in the shallow aquifer. Results of the laboratory experiments and the field test show no obvious damage to groundwater chemistry should CO₂ leakage occur and further were confirmed with a regional-scale reactive transport model (RSRTM) that was built upon the batch experiments and validated with the single-well PPT. Results of the RSRTM indicate that dissolved CO₂ as an indicator for CO₂ leakage detection works better than dissolved inorganic carbon, pH, and alkalinity at the CO₂ EOR site. The detection ability of a GMN was assessed with monitoring efficiency, depending on various factors, including the natural hydraulic gradient, the leakage rate, the number of monitoring wells, the aquifer heterogeneity, and the time for a CO₂ plume traveling to the monitoring well.