Total has launched a pilot CO2 capture and sequestration project in the Lacq basin in southwestern France. The project, which leverages a technique considered among the most promising in the fight against climate change, calls for up to 150000 metric tonnes of CO2 to be injected into a depleted natural gas field at Rousse in the Pyrenees over a period of two years from the end of 2008.

Explaining his company’s strategy, president of exploration and production Christophe de Margerie said: “This project will demonstrate the role that CO2 capture and sequestration can play in reducing greenhouse gas emissions from industrial installations. It represents the first integrated CO2 capture system using oxy-fuel combustion combined with storage in a depleted hydrocarbon field.”

The first link in the chain is a steam production unit at the Lacq gas processing plant. Oxygen will be used for combustion rather than air to obtain a more concentrated CO2 stream that will be easier to capture. Once purified, the gas will be compressed and conveyed via pipeline to the depleted Rousse field, 30km from Lacq, where it will be injected through an existing well into a rock formation 4500metres under ground.

Following preliminary studies in 2006, the Rousse field was selected for its geological structure, which gave the best guarantee of sustainable storage. Total has just launched the engineering study phase. Gas injection is scheduled to begin in November 2008. The project, which will cost nearly E60million, is to be carried out in partnership with Air Liquide and in cooperation with the French Petroleum Institute (IFP), the French Bureau of Geological and Mining Research (BRGM) and others.

Over the past 10 years, Total has participated in several CO2 sequestration projects, notably in saline aquifers at North Sea oil production sites. The capture and sequestration of CO2 provides yet another way of reducing greenhouse gas emissions alongside programmes already deployed by the group to develop renewable energy sources, reduce flaring of associated gas and make production facilities more energy efficient.

Meanwhile, researchers from the University of Leicester and the British Geological Society (BGS) in the UK have proposed storing CO2 in huge underground reservoirs as a way of reducing emissions. They have even identified sites in Western Europe that would be suitable. Their research, published in the journal Planet Earth and with highlights on the Alpha-Galileo website, reveals that CO2 can be contained in cool geological aquifers or reservoirs, where it can remain harmlessly for many thousands of years.

PhD research student Ameena Camps is working with professor Mike Lovell at the University’s Department of Geology and with Chris Rochelle at BGS, investigating the storage of CO2.

Storing the gas in a solid form as a gas hydrate, or as a pool of liquid CO2 below a cap of hydrate cemented sediments, is believed to offer an alternative method of geological sequestration to the current practices of storage in warm, deep sediments in the North Sea.

Although gas hydrates were first discovered two centuries ago, the possible use of carbon dioxide hydrate as a means to help resolve problems of global climate change, and of naturally occurring methane hydrate as a future source of energy, have only recently been suggested (Fig.1).

Why bother with CO2 at all?

About one third of all CO2 emissions due to human activity come from fossil fuels used for generating electricity, with each power plant capable of emitting several million tonnes of CO2 annually. A variety of other industrial processes also emit large amounts of the gas, for example oil refineries, cement works, and iron and steel production. These emissions could be reduced substantially, without major changes to the basic process, by capturing and storing the CO2. Other sources of emissions, such as transport and domestic buildings, cannot be tackled in the same way because of the large number of small sources of CO2 involved.

Capturing CO2 can be applied to large point sources, such as large fossil fuel or biomass energy facilities, major CO2 emitting industries, natural gas production, synthetic fuel plants and fossil fuel-based hydrogen production plants. Broadly, three different types of technologies exist: post-combustion, pre-combustion, and oxyfuel combustion.

In post-combustion, the CO2 is removed after combustion of the fossil fuel â“ this is the scheme that would be applied to conventional power plants. Here, carbon dioxide is captured from flue gases at power stations â“ in the case of coal, this is sometimes known as ‘clean coal’. The technology is well understood and is currently used in niche markets.

The technology for pre-combustion is widely applied in fertiliser, chemical, gaseous fuels such as hydrogen and methane, and power production. In these cases, the fossil fuel is gasified and the resulting CO2 can be captured from a relatively pure exhaust stream.

An alternative method under development is chemical looping combustion. Chemical looping uses a metal oxide as a solid oxygen carrier. Metal oxide particles react with a solid, liquid or gaseous fuel in a fluidised bed combustor, producing solid metal particles and a mixture of carbon dioxide and water vapour.

The water vapour is condensed, leaving pure carbon dioxide that can be sequestered. The solid metal particles are circulated to another fluidised bed where they react with air, producing heat and regenerating metal oxide particles that are recirculated to the fluidised bed combustor.

Transportation

After capture, the CO2 must be transported to suitable storage sites. This is done by pipeline, which is generally the cheapest form of transport, by ship or by land transport when no pipelines are available. Both methods are currently used for transporting CO2 for other applications.

Having captured the CO2 it would need to be stored securely for hundreds or even thousands of years, in order to avoid it reaching the atmosphere. Major reservoirs, suitable for storage, have been identified under the earth's surface and in the oceans. Work to develop many of these options is in progress.

Underground storage of CO2 has taken place for many years as a consequence of injecting CO2 into oil fields to enhance recovery. CO2 is being deliberately stored in a saltwater reservoir under the North Sea for climate change reasons.

Sleipner is located in the North Sea where Norway’s Statoil strips carbon dioxide from natural gas with amine solvents and disposes of this carbon dioxide in a saline formation. The carbon dioxide is a waste product of the field’s natural gas production and the gas contains more (nine per cent CO2) than is allowed into the natural gas distribution network.

Storing it underground avoids this problem and saves Statoil hundreds of millions of euro in avoided carbon taxes. Sleipner stores about one million tonnes CO2 a year.

The Weyburn project started in 2000 and is located in an oil reservoir discovered in 1954 in Weyburn, Southeastern Saskatchewan, Canada. The CO2 for this project is captured at the Great Plains Coal Gasification plant in Beulah, North Dakota which has produced methane from coal for more than 30 years. At Weyburn, the CO2 will also be used for enhanced oil recovery with an injection rate of about 1.5 million tonnes per year.

The third site is In Salah, Algeria, and like Sleipner is a natural gas reservoir. The CO2 will be separated from the natural gas and re-injected into the subsurface at a rate of about 1.2million tonnes per year. The potential capacity for underground storage is large but not well documented.