The impact of CO2 impurities on gas injection for enhanced oil recovery

CO 2 injection for enhanced oil recovery (CO 2 -EOR) is a proven technique for boosting oil recovery in mature reservoirs while enabling permanent CO 2 geo-storage, promoting decarbonization towards neutrality. However, CO 2 streams from fossil fuel plants often contain impurities, and their purification requires energy-intensive and costly processes. While certain impurities can improve EOR efficiency, others can reduce it. Determining the optimal CO 2 purity, therefore, involves balancing technical economic performances. We propose herein an integrated three-dimensional geo-modelling workflow for using compositional fluid simulation in porous media to quantify the effects of impurities (N 2 , O 2 , NO 2 , SO 2 , H 2 S, CO, and H 2 O) on CO 2 -EOR. We combine compositional numerical simulations with Monte Carlo simulations to assess a wide range of impurities and identify impurity mixtures from hard-to-abate fossil fuel plants that simultaneously have a good benefit-cost ratio considering CO 2 -EOR. Results show that the main impurities in the CO 2 stream from the exhaust of fossil fuel plants (i.e., N 2 and O 2 ) reduce the density of the injected stream (from 2.6% to 4.5%) and increase minimum miscibility pressure (from 23.3-28.0%), leading to lower oil recovery (by 3.9-6.5%) and reduced carbon storage capacity (by 1.5-9.2%). In contrast, NO 2 , SO 2 , H 2 S, and CO play a less impactful role and, thus, may be admissible at the injection within certain ranges. Economic analysis, under typical market conditions, indicates that reductions in carbon capture costs due to 20% reduction in purity can outweigh losses in oil and carbon credit revenues, resulting in a net positive benefit-cost ratio (∼20%). The proposed geo-modelling workflow can be used to identify impurity composition that maintains acceptable technical performance while substantially improving the overall CCUS value chain. This approach equips operators with quantitative guidance for relaxing purification specifications without compromising project viability, paving the way for faster deployment of CO 2 -EOR.