Greenhouse Gas Storage - Basics
Greenhouse Gas Storage and Carbon Capture and Storage
Greenhouse gas storage is the storage component of the Carbon Capture and Storage (CCS). As a geological agency, Geoscience Australia does not deal with the capture process with research into the capture process in Australia being led by the CSIRO. However, as geoscientists, our expertise is utilised to locate and characterise suitable deeply buried formations in which the captured carbon dioxide (CO2) can be stored.
We prefer to use the term greenhouse gas when talking about storage of these compounds because, although CO2 is the major gas which will be stored, in some cases small amounts of another very potent greenhouse gas, methane (CH4), may be stored along with the CO2 in cases where it is uneconomic to separate the two gases.
What is CCS?
Capture of CO2 and its geological storage (geosequestration), also known as carbon capture and storage, or CCS, is the process of capturing 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. The 'S' in 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. The range of CO2 storage options being considered are:
- geological storage
- 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)
- soil sequestration (biochar)
Some of these may provide additional or niche opportunities for reducing CO2 emissions to the atmosphere.
How does geological storage work?
Geological storage of CO2 occurs when it 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 at a depth of 800 metres 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 (e.g., a mudstone)
- dissolution into the saline brine already in the formation
- precipitating as minerals in the formation, and
- retention as tiny blobs of dense (supercritical) CO2 within pore spaces.
Options for geological storage of CO2 include injection and storage into depleted oil and gas fields, deep saline formations and unmineable coal seams. It can be used also 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, although 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 and shales.
Injection and geological storage of CO2 is an established process, especially in the oil and gas industry, and is occurring already at a commercial scale through several projects worldwide, including at Statoil’s Sleipner and Snohvit fields in the North Sea and Barents Sea respectively, BP’s In Salah Project in Algeria and the enhanced oil recovery project at the Weyburn and Midale fields in Canada. In addition, more than 30 million tonnes of CO2 is injected each year for enhanced oil recovery in the USA.
Geoscience Australia's work in researching and identifying suitable sites for geological storage of CO2 will ensure Australia continues to be a leader in the development of this technology.
Projects undertaken in the 2010-11 financial year include: