Deep Saline Formations
Deep Saline Formations, or deep saltwater reservoirs, are rocks with porous spaces that are filled with brine. They exist nearly world-wide and have great potential for CO2 storage. The most suitable reservoirs are those at depths greater than 800m as at this depth CO2 will behave more like a liquid than a gas, enabling much more to be stored. Carbon dioxide may remain buoyant for hundreds, if not thousands of years until it slowly dissolves in the brine, eventually sinking deeper into the reservoir. While in the supercritical state the buoyant forces push the CO2 upward. Therefore, an impermeable cap-rock over the storage site is necessary to ensure that the CO2 remains underground. The geology of deep saline formations is not as well characterized compared to that of oil and gas fields. However, saline reservoirs have been used as buffer stores for natural gas, which supports the belief that CO2 could be stored safely in carefully selected sites. More research will be needed for these reservoirs to become viable options.
A commercial project in the North Sea currently injects CO2 into an offshore deep saline formation.
This project, at the Sleipner West gas field, has been operating since 1996. Approximately one million tons of carbon dioxide is injected underground for storage annually. Another more recent project by EPRI in collaboration with the DOE and American Electric Power will demonstrate integrated CCS by combining two types of solvent-based carbon capture technologies with deep saline injection. CO2 will be injected into different kinds of typical U.S. underground formations as part of a comprehensive monitoring and measuring study to identify location and movement of injected underground CO2. The project is to be completed by 2014.