Improving Injectivity of CO2 in Saline Aquifers Through Chemical Additives

Summary A key metric for Carbon Capture and Storage (CCS) projects is the rate of injection of supercritical CO2 (sCO2) into the subsurface and maximizing injectivity will be important for success. The sCO2 injection rate into saline aquifers is limited by formation permeability and residual water saturation held in place by capillary pressure. The objective of this work is to explore the application of additives to lower the capillary pressure and the water saturation in the near wellbore region and thereby increase the relative permeability to sCO2. The intended benefit will be the ability to inject CO2 at higher rates while maintaining injection pressure below the desired level/fracture gradient or injecting at reduced pressures for the same rate. Screening tests identified several types of additives (Nonionic/Cationic/Anionic/Amphoteric) that reduced brine-CO2 IFT by a factor of 10 from 20-40 mN/m to 2-4 mN/m at 1000-2000 psi and modified contact angle between CO2, brine and sandstone and dolomite cores from 20-25 degrees with 2% KCl alone to 30-40 degrees with additives at 1000 to 2000 psi. In brine displacement tests in 100 md cores, the best additives when used in a concentration range of 0.1% to 0.2% decreased the water saturation by 10-30% and reduced the displacement pressures by ∼50% over the control, resulting in proportional increase of the relative permeability to sCO2. Well model results show that doubling the relative permeability in the near wellbore region can increase the CO2 injectivity by ∼20%. Recommendations on treatment volumes and procedures for candidate injection wells are provided. The approach presented here can provide a low-cost option to increase injectivity and other benefits including compensating for injection well downtime, providing higher injection rates in lower permeability rocks, and reducing injection pressures for safer and more cost-efficient operations.