Capture and Reinjection of CO2 in a Saline Aquifer at the Sleipner Field and the Future Potential of this Technology
Mr Tore A. Torp, project leader at Statoil, presented the CO2 injection project in Sleipner. His intervention was followed by an overview of the future potential of this technique in Europe by Mr Niels Christensen, representative from the European Network for Research in Geo-Energy Association.
CO2 CAPTURE AND REINJECTION AT THE SLEIPNER FIELD
In the Sleipner gas field in the North Sea, the natural gas contains 9% of CO2, which must be reduced to 2,5% before export. The extracted 1 million tonnes CO2 per year would, if released to the atmosphere, have increased Norway's CO2 emissions by nearly 3%. In order to help meet national emissions targets - and avoid high CO2 taxes - Statoil decided to adopt an aquifer storage strategy for Sleipner, starting in 1996.
The CO2 is absorbed in an amine contact tower at a pressure of 100 bars. The amine is then stripped for CO2 in another tower. The module for the CO2 extraction process weighs 8200 tonnes - the heaviest module ever lifted offshore -, measures 50x20x35 metres and costs over 350 million ECU. Capture of CO2 from the smoke stack of gas turbines is not done on Sleipner (it would require larger facilities not well suited for offshore installations and will cost far more than the CO2 capture from a pressurised natural gas). The CO2 extracted on Sleipner is injected into a deep saline aquifer, called "Utsira Sand", some 1000 metres below the sea through a separate injection well. This sand is not connected to the hydrocarbon reservoirs at 3500 metres.
It is the first time that CO2 is injected into an aquifer for environmental reasons. The project will provide valuable information on the feasibility of this technology. To learn the maximum of this ongoing "pilot project", Statoil, and its license partners Elf, Exxon and Norsk Hydro, has invited interested parties to run a 3 years monitoring and verification project.
A further demonstration, called "SACS", is now being organised by Statoil (as co-ordinator), BP, Norsk Hydro, Mobil, Saga Petroleum and Vattenfall. Application has been submitted to EU/Thermie for 40% support to a 5 million ECU project over 3 years. National authorities in Denmark, The Netherlands, Norway and United Kingdom have committed support, both in funding as well as help in data collection. France might also join. Seven scientific institutions from these countries will be responsible for research on the project.
Key objectives are to verify how good various present geological and reservoir methods and models are for monitoring and predicting CO2 behaviour in a salt water formation. Indeed, models and methods developed for oil, gas and water may not all work adequately for CO2 without adjustments. Energy companies, scientific institutions and national authorities will therefore co-operate to study how CO2 should be injected in underground saline aquifers in an efficient and safe way. The overall goal is to agree on a "best practice" for future use of this technology.
The intercontinental interest is increasing, and International Energy Agency (IEA) Greenhouse Gas R&D Programme, based in Cheltenham, UK has supported the formation of the "SACS" project, and is now active to ensure co-ordination and co-operation with activities world wide; in Australia, Canada, Japan and USA.
EUROPEAN PERSPECTIVES FOR CO2 STORAGE
Approximately 2/3 of the energy used in the EU comes from oil and gas. The majority of this is used for power generation and transport. According to the European Commission, this situation is unlikely to change drastically over the next 20-30 years. If anything, the relative importance of oil, and especially gas, may increase slightly, while renewable energy sources may grow to cover 10% of the energy needs, unless major technology breakthroughs occur. Against this background and in a business as usual scenario, the EU target of a 8% reduction in 6 greenhouse gases - of which CO2 will represent a major element - between 2008 and 2012 relative to 1990 might prove difficult to achieve.
A possible scenario for a carbon free society could be using fossil fuels as energy source and electricity and hydrogen as energy carriers. International political circumstances and the energy markets will decide if, how fast and to what degree such a vision could become a reality. For the industry, it is necessary to explore the technical and economic possibilities. Its judgement today is that there are no major technological obstacles stopping this scenario from being developed, but there are still economic barriers. These barriers may be overcome by new technologies or a shift in the economic boundary conditions in a post-Kyoto world.
CO2 can be captured in various conditions:
• From the flue gas of conventional power stations: a fairly expensive - but technically feasible - method. (It should be noted that storing the smoke stack without primarily separating the CO2 would even be more expensive. Indeed, beside CO2, the smoke stack consists of water and nitrogen. The latter needs to be compressed before being stored which is a very expensive process requiring a lot of pumping.)
• When using natural gas as fuel, it is possible to separate CO2 prior to combustion of the resulting hydrogen. This process is well known in petroleum refineries, and its use in power generation is being seriously considered.
The transport sector is another major contributor to CO2 emissions. The need for this sector is, notably, to switch to non-emission fuel types such as electricity or hydrogen. Hydrocarbon-based power plants with CO2 storage could provide both types of fuel.
The total storage potential in deep subsurface sediments within the EU & Norway is very high. Preliminary assessment indicate European storage capacity in onshore closed structures (old oil and gas fields plus confined deep saline aquifers) to be sufficient to contain all CO2 emissions from thermal power generation for at least 25 years. The total storage potential, including all deep saline aquifers (onshore and offshore, confined and open) and hydrocarbon fields, would be sufficient for about 800 years.
Preliminary studies indicate, that electricity can be generated from hydrocarbon-based power plants with subsequent CO2 storage, at an additional production cost of 40-80%. This would result in an electricity cost of 7-9.4 ECU cents/kWh, as compared to cost of 7-8 ECU cents/kWh for electricity generated from wind turbines. Consequently, the cost of CO2 emission avoidance would be 27-64 ECU/tonne. In comparison, CO2 emission taxes are 44 ECU/tonne for the Norwegian offshore, and 7-15 ECU/ tonne onshore Denmark. Estimates made by IEA indicate that capture will take 3/4 of the cost, while transport and reinjection will take 1/4 of the total extra cost.
Finally, it was concluded that further research and technological development within storage of CO2 in the subsurface was needed as part of the long-term policy making of the EU to reach the CO2 reduction targets.