An examination of geologic carbon sequestration policies in the context of leakage potential

Carbon dioxide (CO₂) injected into geologic reservoirs for long-term sequestration, or the brine it displaces, may leak through natural or manmade pathways. Using a leakage estimation model, we simulated fluid leakage from a storage reservoir and its migration into overlying formations. The results are discussed in the context of policies that seek to assure long-term sequestration and protect groundwater. This work is based on a case study of CO₂ injection into the Mt. Simon sandstone in the Michigan sedimentary basin, for which we constructed a simplified hydrologic representation of the geologic formations. The simulation results show that (1) CO₂ leakage can reach an aquifer containing potable water, but numerous intervening stratigraphic traps limit the rate to be orders of magnitude less than the rate of leakage from the storage reservoir; (2) U.S. Department of Energy guidelines for storage permanence allow for more leakage from larger injection projects than for smaller ones; (3) well leakage permeability is the most important variable in determining leakage processes and substantial leakage requires that numerous wells leaking with the anomalously high permeability of 10^-10m²; and (4) leakage can reduce the U.S. Environmental Protection Agency's Area of Review.