Monitoring Carbon Dioxide Underground

Thursday, June 10 2010

A technique originally applied to monitor the flow of contaminants into shallow groundwater supplies has been repurposed by Lawrence Livermore National Laboratory researchers to monitor carbon dioxide pumped deep underground for storage.

Electric Resistance Tomography (ERT) has been installed to track where a plume of injected CO₂ moves underground at Cranfield Oilfield, an oil field near Natchez, MS. The site is part of the Southeast Regional Carbon Sequestration Partnership (SECARB), a project that eventually will test more than one million tons of CO₂ in underground formations.

At 10,000 feet, the ERT project at Cranfield is the deepest subsurface application of the method to date. ERT uses vertical electrode arrays, usually in a cross-well arrangement, to perform four-electrode measurements of changes in the spatial distribution of electrical resistance within a subsurface formation. Because the Cranfield site contains CO₂, which is five times as resistive as its surroundings, ERT showed that significant resistance changes occurred during plume growth and movement.

“We can image the CO₂ plume as the fluid is injected,” said geophysicist Charles Carrigan, the LLNL lead on the project. “What we’ve seen is a movement of the plume outward from the injection well into the geologic formation used for storage.”