The underground sequestration of carbon dioxide: containment by chemical reactions in the deep geosphere

This paper is part of the special publication No.157, Chemical containment of waste in the geosphere (eds: R.Metcalfe and C.A. Rochelle). Anthropogenic emissions of carbon dioxide (CO 2) have been linked to increasing levels in the atmosphere and to potential global climate change. The capture of CO 2 from large point sources, followed by its sequestration as a supercritical fluid into the deep geosphere, is one potential method for reducing such emissions without a drastic change in our energy-producing technologies. Once emplaced underground, geochemical and hydrogeological processes will act to ‘trap’ the CO 2 as dissolved species and in carbonate minerals. Although dry supercritical CO 2 appears to cause little reaction with the host rocks, once dissolved in water mineral dissolution and precipitation reactions can result. From a geochemical standpoint, sandstones appear to be preferable to carbonates for sequestration operations because fluid-mineral reactions within them have a better capacity for pH buffering. However, individual host lithologies will vary in structure, mineralogy and hydrogeology, and individual sequestration operations will have to take account of local geological, fluid chemical and hydrogeological conditions. This paper summarizes some of the recent laboratory experimental, natural analogue and computer modelling approaches directed at understanding reactions involved in the chemical containment of CO 2.