Zones of Endangering Influence Modeling and Mapping for CO2 Injection Wells

The EPA-proposed Underground Injection Program (UIC) geological sequestration rule for CO₂ injection requires applicants to model and map an Area of Review (AoR) about the injection well(s).  The AoR focuses the survey for compromises to the sealing layers, such as from fractures or abandoned wells, which might provide migration pathways for CO₂ or 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 (ZEI). 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 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 pressure that could support upward flow of saline fluids from the injection zone to the USDW through a hypothetical borehole.  We are investing in computational tools, based on semi-analytic and numerical solutions, for modeling and mapping the zone of pressure influence, the critical pressure, and the CO₂ front.  The semi-analytical solutions support simpler tools for conceptual model testing, and their computational efficiency allows for probabilistic uncertainty analysis.  Comparisons to the TOUGH2 numerical model allows for 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 ZEI based on the projection of the outer envelope containing critical 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.