Analysis of CO ₂ leakage through ‘low-permeability’ faults from natural reservoirs in the Colorado Plateau, east-central Utah

Abstract

Abstract The numerous CO 2 reservoirs in the Colorado Plateau region of the United States are natural analogues for potential geological CO 2 sequestration repositories. To understand better the risk of leakage from reservoirs used for long-term underground CO 2 storage, we examine evidence for CO 2 migration along two normal faults that cut a reservoir in east-central Utah. CO 2 -charged springs, geysers, and a hydrocarbon seep are localized 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 CO 2 -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 geological and geochemical data are consistent with these faults being conduits for CO 2 moving to the surface. Consequently, the injection of CO 2 into faulted geological reservoirs, including faults with clay gouge, must be carefully designed and monitored to avoid slow seepage or fast rupture to the biosphere.