Engineering Aspects of Geological Sequestration of Carbon Dioxide

Abstract Injection into geological formations is a technical option for decreasing carbon dioxide emissions to the atmosphere. Several key factors influence the performance and long-term integrity of injection into deep saline formations. Accurate representations of the physical properties of carbon dioxide have compiled and use to determine the theoretical storage density at typical sub-surface conditions, and the amount of energy that would be expended in injecting the carbon dioxide (whether pure or mixed with other gases), leading to an estimate of the net reduction of emissions. Detailed computer simulations indicate that the distribution of the injected carbon dioxide is initially dominated by gravity segregation, relative permeability effects and the permeability anisotropy of the saline formation. Post-injection, important effects occur which are not taken into account in conventional petroleum reservoir simulation. Convective mixing is predicted to occur, which greatly accelerates the dissolution of carbon dioxide in the saline formation water. This unusual phenomenon arises from the increase in the density of brine when saturated with carbon dioxide. Complete dissolution of the injected carbon dioxide is predicted to occur over hundreds to thousands of years, depending significantly on the vertical permeability of the formation and the geometry of the top seal. Reactions between the carbonated water and the formation also increase the rate of dissolution. If the chosen site is not a structural trap but a gently dipping regionally extensive formation, then the carbon dioxide can migrate up to tens of kilometres from the injection site, depending on the angle of dip and the horizontal permeability. However, convection and dissolution can still keep the carbon dioxide confined. This theoretical analysis has been developed as part of the Australian Petroleum CRC's GEODISC program, and is being used to assess the suitability of proposed sites for carbon dioxide sequestration.