How can we transport and store CO2 safely and permanently?
Safe carbon dioxide (CO2) transport and long-term storage have been demonstrated by the oil and gas industries for more than 40 years. At the Sleipner offshore natural gas production platform operated by Norway’s Statoil, every year since 1996 more than one million tonnes of CO2 have been transported by pipeline and stored safely deep under the seabed.
CO2 transport
After CO2 is captured at a power plant or industrial location, it is transported to a suitable and safe storage site. The technologies available to transport CO2 are very similar to those used for many years in the natural gas industry. Unlike natural gas, CO2 is essentially a stable and inert substance.
The best way to transport CO2 depends on the quantity, terrain and transport distance required. Pipelines are a logical choice for large volumes over short, medium or long overland distances. Tanker trucks may be used for smaller volumes over short distances.
Geological CO2 storage
While there are a number of CO2 storage options, geological storage (also called geosequestration), offers the greatest potential.
Once captured from the coal-fired power plant, the CO2 is compressed to high pressure when it becomes essentially a liquid. The liquefied CO2 is transported to a carefully selected storage site where it is safely injected and stored deep underground.
These storage sites consist of layers of porous rock into which the liquefied CO2 is injected, overlain by a non-porous ‘cap’ rock that prevents the CO2 from escaping. Hydrocarbons such as oil and natural gas have been naturally trapped in porous underground sedimentary rocks for millions of years. The geosequestration process mimics this natural geological trapping process. Over time, the CO2 could be dissolved in the salty (non-drinkable) water formation and may also react chemically with the surrounding rock, converting it into stable carbonate minerals.
There are a number of geological storage options for CO2 and these fall into three main categories:
- saline water saturated rock formations
- depleted oil and gasfields
- unmineable
Saline water saturated rocks are underground formations of porous rock, such as sandstones, that are saturated with salty (non potable) water and covered by a layer of impermeable cap rock (such as shale or clay) which acts as a seal. Once injected into the formation, the CO2 dissolves into the saline water in the reservoir rock. CO2 storage in deep saline formations is expected to take place at depths below 800m. Saline formations have the largest storage potential globally and a number of CO2 storage demonstration projects are proving their effectiveness to maximise storage capacity and containment.
Depleted oil and gasfields have a proven ability to store hydrocarbons over millions of years, demonstrating very good reservoir characteristics. What’s more, CO2 injection is already widely used in the oil industry for from mature oilfields.
Coal seam storage involves injecting CO2 into deep unmineable coal seams, where it displaces other gases, such as methane. This displacement effect means that coal seam CO2 injection could be most effective as part of the commercial production of coal seam methane (also known as coal bed methane), an increasingly important and relatively new energy source. Learn more about coal seam methane
Storage monitoring
To ensure the safe storage of CO2, sites are carefully monitored both during and long after the CO2 is injected underground. Technologies and protocols for monitoring and verification that were originally developed by the oil, gas and waste storage industries are being used to track the CO2 migration within the porous rock formation and to ensure that the injected CO2 remains trapped in the reservoir.
Learn about carbon storage research in Australia on the CO2CRC Otway Project page.