Assessment of Trapping Mechanisms of CO2 Sequestration and Optimization of Key Process Parameters in a Deep Saline Aquifer Using Reservoir Simulation and Response Surface Methodology

Deep saline aquifers are perhaps one of the most ubiquitous sites available for CO2 sequestration. In this study, a compositional reservoir simulator was used to evaluate the effects of various CO2 trapping mechanisms in a saline aquifer which includes structural, solubility and mineral trapping. CO2 was injected at a rate of 4000 m3/day at the bottom of the aquifer for 50 years. The results indicate that structural trapping dominated for initial 3 years, after which the maximum gas saturation and pressure was reached. During solubility trapping, the gas saturation decreased by more than 70% of the maximum saturation. Mineral trapping decreased saturation further by another 10%. In another approach, the effect of wastewater injection following injection of CO2 was evaluated. The numerical simulations show reduction in both the amount of mobile CO2 and its upward migration. Among the different trapping mechanisms, solubility trapping is found to be the most vital one. Multivariate analysis and optimization of the responses, viz. average gas saturation and average pressure rise, were carried out using response surface methodology. Optimized results were obtained for efficient CO2 sequestration with lesser mobile CO2 and pressure rise at lower values of injection rate (1000 m3/day), injection time (50 years), vertical-to-horizontal permeability ratio, Kv/Kh (0.016), and residual gas saturation (0.4).