99- www. energy- future. com 6.3- Understanding oil and gas already routinely stripped out from natural gas to improve the gas' heating value or to meet pipeline specifications. It's also cap-tured from industrial facilities to supply the food industry. The oil industry, meanwhile, has a profound understanding of oil and gas reservoirs and other geological formations; in fact, CO2 has been injected into oil res-ervoirs for decades to boost recovery of oil by flushing more of it out, notably in the US. And even some of the infrastructure is in place: there are over 3,500 kilometres of pipelines transporting more than 40 mil-lion tonnes a year of CO2 to support the US' enhanced oil- recovery business. And pipelines elsewhere that were formerly used to transport hydrocarbons from such reservoirs to refineries might be suitable for sending CO2 the other way - back to empty reservoirs. There's also plenty of space for storing the gas underground, which can be held in various geological formations ( see box). BP - which is working with Statoil and Algerian national oil company Sonatrach on a big CCS project linked to the In Salah gas de-velopment in the Algerian desert - has es-timated that old North Sea reservoirs could hold all the CO2 produced by European power stations over the next 60 years; oth-ers say they could accommodate consider-ably more. Just the aquifer of which Sleipner West is a small part has a thickness of 250 metres and has the potential to hold 600 bil-lion tonnes of CO2. At present, Statoil is stor-ing just 1 million tonnes a year there. But what about leakage? If the CO2 seeps back out into the atmosphere, then the benefits of storage would be lost. However, there can be few places better suited to storing CO2 securely than the sub-terranean chambers that managed to hold oil and gas securely for millions of years until man removed it. No- one can say the CO2 will never leak out into the atmos-phere, but Statoil estimates its North Sea site is highly unlikely to leak for several hundred years, by which time the human race should have created other solutions to the CO2 problem. The Intergovernmental Panel on Climate Change ( IPCC), the main global forum for collating scientific advice on climate change, says tests so far indi-cate that more than 99% of CO2 is likely to be retained in properly managed geological Where can the CO2 go? There are three main types of geological storage. The most attractive are existing oil and gas fields: their ability to hold gas in-definitely is already proved, the geology of producing fields is well defined and com-panies have experience of re- injecting gas through enhanced oil- recovery operations. Re- injecting CO2 can also defray the cost of CCS by boosting rates of recovery of oil and gas at mature oil fields. The second category is geological traps that do not contain hydrocarbons, but have similar characteristics to oil or gas bearing structures, or coal seams. The third possibil-ity is aquifers - deep saline reservoirs with no defined structural traps. Although less well understood than oil reservoirs, aquifers are an attractive long- term solution because of their large size. CO2 does not necessarily have to be stored underground. Alternatives under con-sideration include deep- ocean storage, in which CO2 is dissolved into seawater. Mineral sequestration above ground is an-other possibility, with CO2 exothermically re-acted with natural minerals to form stable carbonates. Another possibility would be to capture CO2 directly from the atmosphere with chemical solvents. ?? There can be few places better suited to storing CO2 securely than the subterranean chambers that managed to hold oil and gas securely for millions of years

100- www. world- petroleum. org 6.3- Understanding oil and gas structures after 100 years and that it could potentially be held there for thousands of years with little of it escaping. Can we afford it? Not everyone sees CCS as an appropriate solution to global warming problems: plenty of people have questioned whether CCS on a scale able to tackle climate change is fea-sible, either technologically or financially. While storage is comparatively straightfor-ward, the process of capture is complex and expensive. The IPCC estimated in a report on CCS in 2005 that building a power plant with carbon- capture technology would add 20- 40% to the cost of electricity production. The good news is that the cost of this tech-nology is likely to fall rapidly, as engineers understand more about it. Even environmental organisations that would prefer to see fossil fuel use reduced dramatically admit that this is not a practical proposition in the short term and are back-ing the use of CCS technology. NRDC, for example, wants the White House to make the fitting of CCS technology to all new coal plants compulsory. Some potential CCS investors are con-cerned that high- cost CCS projects - like other expensive, climate- oriented technol-ogies - may become lesser priorities for governments grappling with the more im-mediate problem of stopping the economic rot caused by the credit crunch of 2008. But many involved in the green- energy business say CCS could help move economies out of trouble, generating jobs and economic growth. Says BP's Hill: " The financial crisis is minuscule compared with the long- term challenges of climate change. CO2 stays in the atmosphere for 200- 300 years." Signs of serious action It is clear that governments are coming around to this view and are now taking the technology seriously as part of a basket of measures to limit global warming. President Barack Obama's US administration has brought a greener hue to its policies than its predecessor. Australia and China - like the US, countries with huge coal reserves - have been pushing ahead with programmes to develop and implement CCS schemes with government backing, while the North Sea of-fers ample room to handle European CO2. The UK said in April 2009 that all new coal-fired power stations in England and Wales must include CCS demonstration on at least 300 megawatts of their capacity and that de-velopers must agree to retrofit CCS across the whole plant once the technology is proved, if they are to get the go- ahead. The UK's first application of carbon cap-ture at a commercial coal- fired power sta-tion became operational at the end of May 2009 at the Longannet power station in Fife, Scotland. The 1 megawatt test unit, devel-oped by Aker Clean Carbon, is capable of processing 1,000 cubic metres an hour of exhaust gas, although the captured emis- The NRDC wants the US government to make the fitting of CCS technology to all new coal plants compulsory