Permanent carbon dioxide storage in deep-sea sediments

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Abstract
Stabilizing the concentration of atmospheric CO 2 may require storing enormous quantities of captured anthropogenic CO 2 in near-permanent geologic reservoirs. Because of the subsurface temperature profile of terrestrial storage sites, CO 2 stored in these reservoirs is buoyant. As a result, a portion of the injected CO 2 can escape if the reservoir is not appropriately sealed. We show that injecting CO 2 into deep-sea sediments 2 resides in its liquid phase and can be denser than the overlying pore fluid, causing the injected CO 2 to be gravitationally stable. Additionally, CO 2 hydrate formation will impede the flow of CO 2 (l) and serve as a second cap on the system. The evolution of the CO 2 plume is described qualitatively from the injection to the formation of CO 2 hydrates and finally to the dilution of the CO 2 (aq) solution by diffusion. If calcareous sediments are chosen, then the dissolution of carbonate host rock by the CO 2 (aq) solution will slightly increase porosity, which may cause large increases in permeability. Karst formation, however, is unlikely because total dissolution is limited to only a few percent of the rock volume. The total CO 2 storage capacity within the 200-mile economic zone of the U.S. coastline is enormous, capable of storing thousands of years of current U.S. CO 2 emissions.