Effect of N2 impurity on CO2-based cyclic solvent injection process in enhancing heavy oil recovery and CO2 storage

CO2-based CSI (CO2–CSI) process is an effective EOR technique for heavy oil reservoirs after primary production. However, the application of CO2–CSI in the field is limited by the massive requirement and cost of pure CO2. To address this limitation, the effect of N2 impurities on the CO2–CSI process is evaluated by experiments using a 1D sand pack model. The results illustrated that the oil recovery significantly decreases when the N2 content surpasses 17.2 % because of the low solubility of N2 content in the oil phase and the lower viscosity reduction effect. Additionally, the N2 impurity component in the reservoir displaces some of the pore volume available for CO2 storage, but the CO2 storage ratio, the CO2 storage amount out of the consumption amount, is similar to that of the pure CO2–CSI process. An economic analysis is conducted for the material cost of each unit oil production in cases with different N2 impurities. The results indicate that the material cost follows a pattern of initially declining and then rising along with the increase of N2 content. In this study, the optimal N2 content in CO2 for the CSI process is approximately 17 %, considering its high CO2 storage ratio, high oil recovery factor, and low material costs compared to other N2 purity schemes. The findings of this study provide valuable insights for optimizing the solvent components in the CO2–CSI process, contributing to the economic and sustainable development of heavy oil resources and considerable CO2 storage.