A CRITICAL ASSESSMENT OF CO2 INJECTION STRATEGIES IN SALINE AQUIFERS

The main concern in geological storage of CO2 is its long term retention. Development decisions such as number of injection wells, injection rates, placement of injection wells, and the need for water production/reinjection can have a profound impact on the long term storage. Several prototype reservoir geomodels were studied to determine the impact of injection strategy on CO2 retention, plume extension, and movement to top seal. Application There is an overwhelming evidence of increased level of green house gases such as CO2 in atmosphere with an urgent need to stabilize the atmospheric content by storage in geological formations. Several injection schemes were studied to assess the impact on formation pressure during injection, the amount sequestered and the extent of vertical migration. Results, Observations, and Conclusions Simulations were performed taking into account the hysteresis, dissolution in brine, and mineralization of CO2 to carbonate. Injection strategies included several well completions and configurations. Injection options included continuous CO2, water alternating CO2, simultaneous CO2 and water, and inject/stop/inject sequence. The total mass of injected CO2 was kept constant for comparison purposes. The assessment was based on the amount of mineralized, dissolved, and trapped CO2. The vertical migration of CO2 and the mobile CO2 at the top seal was also compared for these cases. The effect of each design on formation pressure during the injection was also evaluated. The results indicated that the injection strategy has great impacts on the total amount retained, vertical migration, and extent of the plume at the top seal. Significance of Subject Matter The development decisions of well placement/ completion, and injection rates need to be made specific to each candidate storage site to maximize dissolved and trapped CO2 for long term containment.