Analysis of CO₂ leakage through "low-permeability" faults from natural reservoirs in the Colorado Plateau, southern Utah

Abstract

The numerous CO2 reservoirs in the Colorado Plateau region of the United States are natural analogues for potential geologic CO2 sequestration repositories. To better understand the risk of leakage from reservoirs used for long-term underground CO2 storage, we examine evidence for CO2 migration along two normal faults from a reservoir in east-central Utah. CO2 -charged springs, geysers, and a hydrocarbon seep are localised along these faults. These include natural springs that have been active for long periods of time, and springs that were induced by recent drilling. The CO2 -charged spring waters have deposited travertine mounds and carbonate veins. The faults cut siltstones, shales, and sandstones and the fault rocks are fine-grained, clay-rich gouge, generally thought to be barriers to fluid flow. The geologic and geochemical data are consistent with these faults being conduits for CO2 to the surface. Consequently, the injection of CO2 into faulted geologic reservoirs, including faults with clay gouge, must be carefully designed and monitored to avoid slow seepage or fast rupture to the biosphere