3.1 Storage in saline formations

Saline formations that are suitable for CO2 storage are subsurface salt-water reservoirs overlain by relatively impervious sealing formations that effectively allow the CO2 to be trapped permanently. Often the formations are sufficiently deep (usually over 800 metres) that the pressure in them is high enough to maintain the injected CO2 in a very dense super-critical state. When CO2 is in such a state, it is immiscible in water. The CO2 is permanently stored in the formation by one or more of mechanisms, such as stratigraphic, structural, hydrodynamic and geochemical trapping mechanisms. These are described in the IPCC's "Special Report on Carbon Dioxide Capture and Storage" [26].

A feature of storage in saline formations, including those in South-East Asia, is that data on their reservoir characteristics is limited. This is typically because few wells have been drilled into them and seismic surveys have not targeted the subsurface structures. Very often the properties of saline formations have to be inferred from oil and gas reservoirs in the same sedimentary basins.