Carbon Capture and Storage

[MAVI]

Carbon Capture and Storage

Carbon dioxide capture and storage (CCS) is the process of capturing carbon dioxide (CO2) from emission sources such as power stations or industrial facilities, transporting it, and storing it so that it is prevented from entering the atmosphere. CCS is generally taken to mean geological storage, that is, injecting CO2 into deep underground formations. This storage option is the most technologically advanced, offers large, long term storage capacity and minimal environmental impact. Other CO2 storage options are also being considered, including:

• ocean storage (injecting CO2 into the deep ocean)
• mineralisation (locking CO2 into minerals)
• commercial use (e.g. the food and chemical industries recycling emitted CO2 rather than using natural sources of CO2)
• biological sequestration (extracting CO2 from the atmosphere through planting forests).

Some of these may provide additional or niche opportunities for reducing CO2 emissions to the atmosphere.
Geological storage

Geological storage of carbon dioxide occurs when CO2 is injected into deep underground geological formations and is permanently trapped there through several natural mechanisms.
The CO2 is first transported (usually by pipeline) to a well characterised storage site. There it is injected as a supercritical fluid (which means it is dense and liquid-like) through an injection well into the target reservoir formation, generally at a depth of 800m or more. A reservoir rock could be a sandstone, in which the CO2 is stored in the microscopic pore spaces between individual sand grains. The CO2 becomes trapped in the deep underground formation through:

• the physical impediment of the impermeable cap rock (for example, a mudstone)
• dissolution into the saline brine already in the formation
• precipitating as minerals in the formation, and
• as tiny blobs of liquid-like CO2 within pore spaces.

Options for geological storage of CO2 include injection and storage into depleted oil and gas fields, deep saline formations, unmineable coal seams, and the use of CO2 for enhanced oil recovery (EOR) and enhanced coal bed methane recovery (ECBM). Deep saline formations are generally considered to have the greatest potential for CO2 storage, however, depleted oil and gas fields offer early opportunities for application of this technology. Less developed storage options, which may provide niche opportunities, include storage in basalts, shales, and hydrates beneath the sea floor.
Injection and geological storage of CO2 is an established process, especially in the oil and gas industry, and is already occurring at a commercial scale through several projects worldwide, including at Statoil’s Sleipner and Snohvit fields in the North and Barents Seas respectively, BP’s In Salah Project in Algeria, and the enhanced oil recovery project at the Weyburn and Midale fields in Canada. In addition, over 30 million tonnes of CO2 are injected each year for enhanced oil recovery in the USA.