Transport is the element in the CO2 chain which is considered to be the least technologically complex and the least cost-intensive.
As CO2 behaves differently under different pressures and temperatures, the transport must take place in a controlled manner, in part to ensure that the CO2 does not solidify, clogging pipes or equipment.
Transporting CO2 in ships is more complicated than transport in pipelines. In order to ensure maximum capacity in a shipload, the gas is liquefied using a combination of pressurisation and chilling.
In principle, transporting CO2 in pipelines is no different from transport of hydrocarbon gas. These are known technologies, and we can draw on many years of experience in building and operating major pipelines for transporting natural gas from the Norwegian Continental Shelf. The US has around 6,000 km of land-based CO2 transport pipelines currently in operation. However, there is little experience with transporting large volumes of CO2 through long pipelines offshore, but Statoil has operated a pipeline from Melkøya to Snøhvit since 2007.
CO2 can be stored in geological formations far below ground, or the seabed
Norway has extensive experience with geological storage of CO2 under the seabed in the North Sea. Statoil has stored CO2 from the Sleipner field since 1996, and from Snøhvit since 2007.
In Norway, the most relevant initial alternative is to store CO2 in porous, water-filled sandstone formations, so-called aquifers, on the continental shelf. When CO2 is injected, the water is forced out. Storage locations where the reservoir is capped by solid, impenetrable layers of clay are selected so as to prevent undesirable leakage.
Storing CO2 in abandoned oil and gas reservoirs is another possibility. Most of the world's current storage projects are combined with enhanced oil recovery (EOR). Put differently, the oil companies use CO2 to squeeze more oil out of mature fields.
Pressure increases deep below the earth's crust. At depths of approx. 800 metres below the sea surface, the pressure is high enough to keep the CO2 in liquid form. Therefore, all stored CO2 will be pumped down to this depth, or deeper.
Liquid CO2 takes up less space, and there is little danger of the gas seeping up to the surface.