Numerical Assessment of Impurities and Injection Parameters on the Safety, Trapping Efficiency and Economic Viability of CO2 Sequestration in Saline Aquifers

Abstract

Geological carbon sequestration in deep saline aquifers is a key strategy for meeting global climate targets. To support large-scale deployment, operators must evaluate storage sites based on safety, trapping efficiency, economic feasibility, and environmental considerations. This study presents an integrated decision framework for CO2 storage by performing 850 TOUGH+RGB simulations in the Utsira Formation, evaluating how injection design, fluid composition, and formation properties influence storage performance over a 2-year injection and 10-year post-injection period. A benchmark set of simulations first isolates the roles of impurities (N2, H2S) and bottom-hole injection temperature (BHIT). Results show that N2 is the dominant compositional control. A 10 mol% N2 fraction increases horizontal plume migration by 67 %, enhances dissolution trapping by 85 %, reduces residual trapping by 25 %, and decreases normalized storage capacity by 40 % at Sleipner-relevant conditions. In contrast, 10 mol% H2S has negligible impact on plume geometry and retains 93 % of pure CO2 capacity. BHIT variations mainly modify vertical redistribution and the balance between dissolution and residual trapping without compromising caprock integrity on their own. The extended simulation set, combined with neural-network surrogate models, identifies permeability, N2 content, and injection rate as key drivers of maximum pressure buildup and trapping partitioning. These physical insights are coupled with purification and storage cost functions yielding a total CCS cost that varies with residual impurity level. The resulting workflow quantifies when it is preferable to purify versus co-inject impurities, subject to economic, environmental, and regulatory constraints. Overall, the framework provides a practical screening tool for designing safe and efficient CO2 storage projects in saline aquifers.