Optimization of Integrated CO2-EOR and Post-EOR CO2 Storage: Maximizing Economic and Environmental Gains

Abstract Injecting anthropogenic carbon dioxide (CO2) into oil reservoirs for the dual purposes of Enhanced Oil Recovery (EOR) and carbon storage presents a promising method for slowing the rise of atmospheric CO2 levels. After the completion of a CO2-EOR project, operations can transition into a dedicated CO2 storage phase. While most previous studies have focused on CO2-EOR or dedicated CO2 storage in isolation, this paper addresses the optimization of an integrated approach that combines CO2-EOR with post-EOR CO2 storage to maximize both economic and environmental outcomes. A compositional simulation model associated with a San Andres reservoir in the Permian Basin was used. The CO2-EOR phase was simulated using two strategies: continuous CO2 injection and CO2-WAG (Water-Alternating-Gas injection), both followed by a post-production CO2 storage phase. The effectiveness of each CO2-EOR strategy, as well as the integrated approach of CO2-EOR followed by CO2 storage, was evaluated in terms of oil production and CO2 storage. Life Cycle Analysis (LCA) was conducted to assess environmental impacts by calculating net atmospheric CO2 emissions, while an economic model estimated the Net Present Value (NPV) of different scenarios, accounting for varying oil prices, CO2 acquisition costs, and carbon storage incentives. The two strategies showed differences in economic and environmental performance, which stem from distinct approaches to reservoir pressure management, water production dynamics, and CO2 injection volumes. CO2-WAG exhibited a higher oil production during the EOR phase but stored less CO2 compared to continuous CO2 injection, leading to greater net atmospheric CO2 emissions. From an economic standpoint, CO2-WAG was more profitable under low to moderate CO2 storage incentive scenarios. In contrast, continuous CO2 injection became the economically superior option at higher storage incentive levels, effectively aligning financial and environmental objectives. The post-EOR phase holds significant potential for CO2 storage and for reducing the emission intensity of the earlier EOR phase. The dedicated CO2 storage phase, when preceded by continuous CO2 injection, demonstrated superior CO2 storage capacity and achieved lower net atmospheric CO2 emissions. The absence of CO2 storage incentives during the EOR phase significantly increased the required incentives during the post-EOR phase to achieve a balance between economic and environmental goals in the integrated system. Storage efficiency, calculated as CO2 stored (adjusted for all upstream, gate-to-gate, and downstream emissions) per unit of oil produced, offers a standardized way to compare environmental performance across projects. Introducing tiered, performance-based incentive systems—where incentives are calibrated fairly based on storage efficiency—was shown to reduce the required incentive levels for both standalone CO2-EOR and the integrated CO2-EOR and post-EOR storage process. Optimal incentive structures were identified to maximize environmental benefits under varying oil prices and CO2 acquisition costs.