Simultaneous injection of wastewater and CO (sub 2) in a heterogeneous aquifer

One of the major obstacles to development, implementation, and deployment of carbon capture and storage (CCS) is cost. As a result, sustainably combining CCS with existing technologies to make CCS less costly or profitable is vital. We propose a CCS strategy in which captured anthropogenic carbon dioxide (CO2) and municipal wastewater are simultaneously injected into a confined saline aquifer. Numerical simulations of simultaneous injection of CO2 and wastewater into a confined saline aquifer were conducted under both isotropic and vertically heterogeneous conditions. The results of the simulations were quantified based on changes in mineral volume fractions and spatial distributions of gas saturation, pH, ionic species concentrations, and pressure, over an injection period of 50 years. Results from the simulation of CO2-wastewater injection (3214 tons/day each) into a carbonate saline aquifer predict very low gas saturations (0.4 maximum after 50 years) and enhancement of dissolved CO2 mass fraction as a result of the dissolution of CO2 into wastewater and resident brine. Transfer of supercritical CO2 to the dissolved phase reduces buoyancy effects and traps CO2 in a more stable phase, increasing storage efficiency. Vertical baffling as a result of vertical heterogeneity also increases sequestration efficiency from about 4% in the homogeneous case to 6% in the vertically heterogeneous case. A simulation of wastewater injection alone into the same saline aquifer predicts near-wellbore scaling from mineral precipitation. However, little or no mineral precipitation is simulated for the CO2-wastewater injection case because the CO2 causes reduction in pH near the wellbore, inhibiting mineral precipitation. These results suggest that co-injection of CO2 and wastewater in deep confined saline aquifers enhances CO2 storage efficiency and security and reduces scaling problems encountered during deep well injection of wastewater.