A technique for trapping the greenhouse gas carbon dioxide deep underground could at the same be used to release the last fraction of natural gas liquids from ailing reservoirs, thus offsetting some of the environmental impact of burning fossil fuels. So says a paper to be published in the peer-reviewed International Journal of Oil, Gas and Coal Technology.

While so-called "fracking" as a method for extracting previously untapped fossil fuel reserves has been in the Sequestration and fuel reservess recently, there are alternatives to obtaining the remaining quantities of hydrocarbons from gas/condensate reservoirs, according to Kashy Aminian of West Virginia University in Morgantown, USA, and colleagues there and at Kuwait University in Safat.

Earlier experiments suggests that using carbon dioxide instead of nitrogen or methane to blast out the hydrocarbon stock from depleted reservoirs might be highly effective and have the added benefit of trapping, or sequestering the carbon dioxide underground.

Aminian and colleagues have calculated the economic benefits associated with the enhanced liquid recovery and demonstrated that the approach is technically and financially viable.

The team explains that the mixing of carbon dioxide with the condensate reservoir fluid results in a reduction of the saturation pressure, the liquid drop-out, and the compressibility factor, boosting recovery of useful hydrocarbon and allowing the carbon dioxide to be trapped within.

The team found that the process works well regardless of the characteristics of the reservoir or even the rate at which the carbon dioxide is injected into the reservoir, the amount that is recovered remains just as high.

Moreover, because of the compressibility of the carbon dioxide it is possible to squeeze out 1.5 to 2 times the volume of reservoir gas for the amount of carbon dioxide pumped in, there is also then the possibility of pumping in an additional 15% once as much reservoir liquid as can be retrieved has been extracted.