Carbon Dioxide Storage

CO2 storage is simply the process of taking captured CO2 and then placing in a location where it will not be in contact with the atmosphere for thousands of years. Storage of the CO2 in underground sites beneath a layer of impermeable rock (cap rock) which acts as a seal to prevent the CO2 from leaking out is the most popular option at present.

There are three main types of proposed underground storage sites:

• Depleted Oil and Gas Reservoirs

  CO2 can be pumped into the reservoirs to fill the empty spaces left by removal of hydrocarbons. The geology of these reservoirs is well understood and they have stored oil and gas for a long time making them good sites for CO2 storage.

• Deep Saline Aquifers

  CO2 can also be stored in deep salt water-saturated rock formations. These exist worldwide and have the potential to store large amounts of CO2. However the geology and effect of the CO2 on these aquifers is not yet well understood and more research is needed.

• Deep Unmineable Coal Seams

  CO2 can be stored in deep coal seams where it will be held in the pores on the surface of the coal and in fractures. This has the additional benefit of forcing methane from the coal beds which can be used as fuel.

Ocean Sequestration where CO2 is pumped into the bottom of deep oceans into cold and dense seawater has also been proposed. However, there are significantly more risks to this type of storage and it is not yet know if these can be overcome. Hence this method of storage is unlikely to be used in the short term.