Potential New Uses for Old Gas Fields: Sequestration of Carbon Dioxide

By

KNOX, P. R., and HOVORKA, S. D.

Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, The University of Texas at Austin, Austin, TX,

OLDENBURG, C. M.

Lawrence Berkeley National Laboratory, Berkeley, CA

Although the reality and significance of global warming remain controversial, advanced planning for all contingencies would be advantageous to operators. One approach under consideration by the U.S. Department of Energy and the international community that has the potential to reduce the rate of increase of atmospheric carbon dioxide (CO₂) concentrations is to capture CO₂ from industrial point sources and inject it into the subsurface (geologic sequestration). This approach is especially attractive in cases where sequestration provides economic benefits (lower overall costs), such as accelerated gas production, increased ultimate recoveries, and new revenue streams for mature reservoirs.

Carbon sequestration with enhanced gas recovery accelerates production in mature gas reservoirs because CO₂, which is denser than methane, settles at the gas-water interface and displaces remaining methane. Such displacement reenergizes the reservoir and increases ultimate recovery. Another approach, sequestration at the gas-oil contact, might accelerate production of a gas cap otherwise kept in place as pressure support for maximizing oil production. Both techniques are being evaluated through modeling of CO₂ and CH₄ flow and transport processes. Finally, mature gas reservoirs ready for abandonment but with infrastructure still in place represent a high-volume, low-cost sequestration option, especially when situated near a CO₂ source such as a fossil-fuel-burning power plant or chemical plant.

These sequestration options are particularly applicable in the Gulf Coast region, where many CO₂ sources lie near reservoirs. Further evaluation and increased operator interest could provide the U.S. with early sequestration approaches, if necessary, and breathe new life into Gulf Coast reservoirs.