Natural Leaking CO2-Charged Systems as Analogs for Failed Geologic Storage Reservoirs
Contribution to Book
Carbon Dioxide Capture for Storage in Deep Geologic Formations - Results from the CO2 Capture Project
David C Thomas
Analysis of leaky CO2 reservoirs in the northern Paradox Basin, Utah has allowed us to develop a model for the shallow subsurface CO2 flow system. The results provide information on how CO2 migrates and reacts with groundwater and reservoir rocks in the subsurface, and what the effects on surface environments are when CO2 leaks to the surface. A series of shallow fluvial and eolian sandstone groundwater reservoirs are charged with CO2 derived mostly from clay-carbonate reactions in Paleozoic source rocks within the basin (depths greater than 1.5 km). The CO2-charged groundwater builds up in a north-plunging anticlinal trap with fault sealing on its southern margin. Top seal is provided by shale-rich formations, but fractures related to the fault damage zone provide conduits through the top seal. This geometry has resulted in a series of stacked reservoirs, and ultimately in escape of the natural CO2 into the atmosphere. The CO2 escapes through a series of springs and geysers along the faults, and through wellbores that have penetrated the reservoir. At the surface, rapid degassing of CO2-charged groundwater results in the formation of travertine mounds around active springs. The presence of deeply incised ancient mounds attests to the long lifespan of this leaky system. There is no evidence of adverse effects of this leakage on wildlife or humans, and the springs provide (somewhat saline) water for plants in this high desert environment. Studies on the effect of long-term leakage both in the subsurface and at the point of leakage to the surface provide data on factors that affect the safety and feasibility of future CO2 injection projects and should guide the design and implementation of geologic storage projects.
Shipton, Z.K., Evans, J.P., Dockrill B., Heath J., Williams A., Kirchner D. and Kolesar P.T. 2005. Natural leaking CO2-charged systems as analogs for failed geologic storage reservoirs. In: Thomas D. (Ed). Carbon Dioxide Capture for Storage in Deep Geologic Formations -Results from the CO2 Capture Project, Volume 2. Elsevier Science. 699-712.