MODELING AND MAPPING THE AREA OF POTENTIAL IMPACT ASSOCIATED WITH CO2 INJECTION WELLS

The EPA Underground Injection Program (UIC) geological carbon sequestration rule requires applicants to model and map an area of review (AoR) about the CO₂ injection well(s). The AoR focuses the geological and geographical survey for compromises to the sealing layers, such as from fractures or abandoned wells, which might provide migration pathways for CO₂ or displaced native brines and threaten the quality of Underground Sources of Drinking Water (USDWs). Therefore, the mapping of the AoR may be based on the projection of subsurface zones of potential and endangering influence. Given that supercritical phase CO₂ is less dense than the saline fluids in the receiving zone, it is important for the sealing layer(s) to physically contain the buoyant CO₂, especially during the lifetime of the injection. The sealing layer is also expected to contain the saline fluids displaced by the injection of CO₂. It is not pressure influence that contributes to endangerment, but the critical threshold pressure that could support upward flow of saline fluids from the injection zone to the USDW through a hypothetical unplugged well. Permit applicants are required to use computational (meaning numerical) models to map the maximum extent of separate phase CO₂ and the threshold pressure front. This research project is evaluating simpler area of potential impact (AoPI) tools for regulators to evaluate the complex numerical models associated with the permit applications. The AoPI tools are based on semi-analytic solutions for modeling and mapping the zone of pressure influence, the threshold pressure front, and the CO₂ front. The AoPI tools support conceptual model testing, and their computational efficiency allows for probabilistic uncertainty analysis. Comparisons to the TOUGH2 numerical model support the testing and verification of definitions of critical pressure. Products from the research will be web and desktop-based GIS tools for the modeling and mapping the AoPI based on the projection of the outer envelope containing maximum extent threshold pressure and CO₂ fronts. The research and development team includes support from Lawrence Berkeley National Lab, Princeton University, S.S. Papadopulos and Associates, and RTI International.