Modeling the Geochemical Impact of an Injection of CO_2 and Associated Reactive Impurities ( SO_2 and O_2 ) into a Saline Reservoir

Carbon dioxide storage in deep geological structures is a strategic technology to mitigate climate change and to promote green development. However, despite continuous efforts to develop cost-effective capture processes to clean the CO_2 stream before transportation and injection, traces of accessory gases cannot be entirely removed. Consequently, before any injection of these gas mixtures, the impact of impurities on the geochemical reactivity of the system must be evaluated. This paper describes numerical simulations done with TOUGHREACT that focus on the chemical reactivity of deep reservoir rock impacted by an injection of CO_2 and associated reactive impurities (mainly SO_2 and O_2) . A simplified two-dimensional radial geo-model of the near-wellbore domain of a saline reservoir enabled us to predict its global geochemical behavior. Two CO_2:SO_2 ratios were studied. The results show the high reactivity of the near-well zone when ancillary gases ( SO_2 and O_2) are co-injected with CO_2 , which leads to the dissolution of carbonates and the precipitation of sulfate minerals. Major reactions occur in the reservoir formation, whereas clays in the caprock are only slightly affected by the injection of CO_2 and associated reactive impurities.