The In Salah gas project, a four-year old venture grouping energy majors Sonatrach of Algeria, BP of Britain and Statoil of Norway, is described by its managers as the world's first and largest onshore carbon capture and sequestration scheme.

Natural gas from the Krechba field, one of three In Salah fields currently in operation, has a carbon dioxide content of 9.1 percent, making it unmarketable in that form in Europe, where CO2 can be no higher than 0.3 percent.

"You can't sell gas with a high carbon content -- you have to take it out," said Michael Mossman of BP.

"And so we had a decision to make -- are we just going to vent it into the atmosphere or are we going to do something different?"

"Something different" at the Krechba facility, a bewildering warren of pipes and tanks, was the re-injection of the CO2 into aquifers that lie 1,850 metres (6,100 feet) beneath the surface, where according to project vice president Mohammed Keddamm it should stay forever under layers of shale, a rock that is impermeable to gas.

"There's no reason for the CO2 to migrate anywhere," he said. "There's no reason why it shouldn't stay there."

Either the CO2 is released into the atmosphere or it is captured and buried. There is no realistic third option, project officials contend.

In Salah managers say an estimated 800,000 tonnes of CO2 is being re-injected each year, equivalent to what 200,000 cars produce annually.

Over the anticipated 30-year life of project, about 20 million tonnes of carbon dioxide will be captured and sequestered deep in the earth.

The gas is purged of nearly all its CO2 by being pumped through a liquid amine solution. Amine is a chemical capable of detecting -- and separating -- CO2 from natural gas.

The natural gas is then transferred via pipeline to a collection point 530 kilometres (330 miles) away at Hassi R'Mel before being exported to Europe.

The sprawling In Salah project, which covers 3,000 square kilometres of the Sahara and is located 1,200 kilometres south of Algiers, must surely be among the most forbidding places on earth.

Project workers say the temperature in the summer can rise above 60 degrees Celsius (140 F) and fall below freezing in winter.

The site, often buffeted by violent sandstorms, is 200 kilometres from the nearest inhabited community and is realistically accessible only by air.

About 2,000 workers are on location, four weeks on duty, 12 hours a day and no weekends, and four weeks off.

There are some amenities, however -- a swimming pool, gym, a professional caterer and satellite television connection.

"We're in the middle of nowhere," said field operations manager Paul Andrews.

"If we want something we have to make it. We generate our own power, drill for water and deal with sewage."

About 4.0 billion dollars is to be invested in the project, with the CO2 capture and sequestration scheme costing just 100 million dollars.

But despite its cost effectiveness and technical feasibility, the In Salah model may not be universally applicable.

What is needed is a verifiably secure reservoir to contain the CO2, which may not be available elsewhere.

At the Krechba field, there are no worries on that score.

"We are sure about the integrity of the reservoir," said Keddam.

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