Squaring the Circle: CO2 Sequestration and EOR

There is a large and increasing body of opinion that sees the use of depleted North Sea reservoirs as ideal for CO2 sequestration, but the lack of ongoing projects suggests that operators see the process as unproven and uneconomic. Can this circle be squared so the apparent synergy between the need to sequester CO2 and its ability technically to increase oil reserves is exploited? Jon Gibbins (j.gibbins@imperial.ac.uk), a Senior Lecturer in the Mechanical Engineering Department at Imperial College , London with research interests in fossil fuel power generation and its role in energy policy, gives a personal opinion.

Gaining public support for carbon capture and storage (CCS) from coal power stations as the only direct alternative to nuclear power and a more flexible complement to renewables than nuclear is probably the key to complementary development of CO2 sequestration technology and North Sea EOR. The Royal Commission on Environmental Pollution's Report: Energy - The Changing Climate (http://www.rcep.org.uk/newenergy.html) identified a possible future requirement for "baseload plants: either nuclear or fossil fuel with carbon dioxide recovery and disposal" (and a definite need for separate " fossil fuel plants to back up intermittent renewables capacity" and "meeting peak electricity demand") and noted that:

"If renewables and demand reduction cannot be brought forward on the scale required, and if capture and isolation of carbon dioxide proves unsafe or prohibitively expensive, the case for building new nuclear stations will be strengthened."

In fact CCS is more than an alternative to nuclear power, since CCS plants have much greater flexibility. Integrated gasifier combined cycle (IGCC) plants with CO2 capture can also supply hydrogen (e.g. http://www.jacobsconsultancy.com/publications.asp?type=pres ). Existing pulverised coal power stations are inherently flexible in their output and when upgraded for CCS can have the additional benefit of 100 MW of pumped storage power generation for peak load capacity for every 400 MW of baseload near-zero-emission capacity [1], complementing intermittent renewables such as wind power. Media debates that fail explicitly to identify the role of CCS (and hence possibly EOR) as an alternative to nuclear power (e.g. http://www.guardian.co.uk/uk_news/story/0,3604,1035996,00.html) and a better complement for renewables are unlikely to leave the public with a balanced view.

Progressive Energy's Design for 460 MW IGCC Power Station ( http://www.valleys-energy.co.uk/english/home.html )

It may appear to be unfortunate that the returns and risks for North Sea CO2 EOR schemes have apparently not matched other investment opportunities in the oil industry and so require additional support, but it is likely that schemes undertaken primarily for EOR would not also maximise the potential benefits of carbon sequestration and so not make the best use of a finite geological resource. The most obvious way in which EOR might not automatically optimise CCS is in the amount of CO2 sequestered - EOR schemes will normally be designed to minimise the consumption of CO2, which represents a cost, rather than maximise consumption as required for CCS. Less obvious disadvantages may occur if EOR requirements alone were to determine the rate at which CO2 is supplied. Power stations in CCS schemes will best be able to complement variable renewable generation sources if the CO2 supply can be varied over timescales varying from a few hours, to meet daily peak power demands, to perhaps months to compensate for seasonal variations in renewables generation and fossil fuel mix. It must be possible to balance the value of flexible power generation against possible restrictions on additional oil production to maximise the combined overall project returns.

Combining EOR with CO2 storage in aquifers and other geological structures is an obvious way to maximise the returns on offshore CO2 supply infrastructure investments in the longer term - this may also make the start date for EOR schemes less critical. In the shorter term aquifer or gas field storage would also help to maintain optimum CO2 injection rates for EOR while still allowing flexibility in overall CO2 supply to meet daily or seasonal variation in power output. Gaining public understanding and support for CCS will, however, be critical in establishing the necessary international consensus required to modify conventions on waste disposal under the sea bed to allow CO2 storage other than EOR. In this context, it is worth noting that if deliberate release of CO2 into the water column in any form is not explicitly excluded then this may outweigh all the other benefits of CCS in public debates.

Finally, it must be recognised that the underlying 'market' for CCS is still very limited and will remain so until such time as global agreements are in place to make significant cuts in CO2 emissions. Key parties to such an agreement are the USA , China and India , all countries with large coal reserves and minimal access to gas supplies for the fuel switching that has taken place in Europe . This makes it almost certain that the development and acceptance of CCS will be an essential prerequisite for a successful conclusion to the very difficult negotiations that will be required. In the local context of EOR in the North Sea , the challenge is to develop and demonstrate a future capability for CCS and to maximise the amount of oil recovered without taking an inappropriately large share of the zero-emission electricity market at too early a stage.

CCS has the potential for large amounts of near-zero emission generation, so care has to be taken that it is not expanded so rapidly that it seriously hampers the development of other new energy sources such as renewables and energy conservation (there is probably also a benefit in saving CO2 capacity for future use when CO2 'prices' are likely to be higher). Conversely, if other new energy projects are pursued entirely to the exclusion of CCS a valuable flexible complement to renewables will not be available, leaving inflexible baseload nuclear plants as the only option to meet any future generation shortfall and hence probably a more restricted scope for deployment of renewables. Public support is essential, in synergy with revenues from enhanced oil production, for the best utilisation of what is both a collection of oil company assets and a strategic UK geological resource.

Reference

1. Gibbins, J., Crane, R. and Cooper, P., "Integration of absorber system with steam cycle for energy, exergy, economic and economic risk optimisation", Report on 4th Workshop, International Test Network for CO2 Capture (5th October 2002, Kyoto, Japan) IEA GHG Report Number PH4/13, November 2002.

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