A Fabulous Step Forward (NewScientist)

Texas oil companies will soon be locking away carbon

• 07 April 2010 by Helen Knight
• Magazine issue 2754. Subscribe and get 4 free issues.
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THE industry most often accused of being responsible for the excess carbon dioxide in our atmosphere is, strange as it may seem, desperate to buy more of the stuff.

Oil companies are paying industrial plants and natural gas processing facilities to bottle their waste CO₂, and are then pumping it underground.

This is not an act of eco-altruism. The goal for the oil companies is to try and extract every last drop from ageing oilfields. But an incidental result is that the oil ends up with a smaller net carbon footprint than most, or even a negative one.

In a process known as enhanced oil recovery, water and compressed CO₂ are pumped into wells to flush out oil that cannot otherwise be brought to the surface. The CO₂ stays buried when production ends.

The gas is in short supply because the natural gas fields it is sourced from have limited capacity. So firms are looking to capture human-made CO₂instead, in an effort that parallels government-funded programmes to develop methods of carbon capture and storage (New Scientist, 12 December 2009, p 8).

Next month, Denbury Resources, based in Plano, Texas, will complete the first 400 kilometres of a pipeline to transport CO₂ from the Gulf coast to its Hastings oilfield near Houston, Texas. Exhaust CO₂ bought from a Dow Chemical ethylene oxide plant in Plaquemine, Louisiana, will start flowing down the pipeline next year.

Denbury will also buy waste CO₂ from a plant in Plaquemine which converts coal into the less polluting syngas, and four similar plants in the Midwest. Each tonne of CO₂ will cost around $10, depending on oil prices.

Company president Tracy Evans says Denbury plans to use CO₂ alone to flush out recalcitrant oil, rather than mixing it with water. "For every barrel of oil extracted, we replace it with an equivalent volume of CO₂," he says.

For every barrel of oil extracted, we replace it with an equivalent volume of carbon dioxide

By weight, though, more gas is pumped in than is released by burning the oil displaced. A barrel of oil emits around 0.4 tonnes of CO₂, but around 0.6 tonnes will be buried to get it out. "By the time enhanced recovery is uneconomical, we'll have sequestered 30 to 50 per cent more CO₂ than that barrel of oil will give off," Evans says.

Denbury is not alone in paying others not to pollute. Anadarko Petroleum in Wyoming plans to source 6 million tonnes of CO₂ from ExxonMobil's nearby LaBarge gas plant. Meanwhile, Occidental Petroleum, based in Los Angeles, is building a plant to treat and compress CO₂ from natural gas provided bySandridge Energy's plants in west Texas, due to come on stream this year.