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Carbon storage presents prickly trade-offs

April 17, 2010

Not only are utilities grappling with how to pull carbon from their coal-fired emissions, but they also crave certainty about where to put the carbon.

In 2005, Duke Energy told the Indiana Utility Regulatory Commission that initial rock tests under Edwardsport in southwestern Indiana indicated a “good possibility” of significant potential for sequestration below its future generating plant.

That potential helped secure regulatory OK to proceed with the plant, said the Citizens Action Coalition. Even though sequestration was not factored into the plant’s price tag—now $2.4 billion—carbon capture and sequestration was always deemed a logical potential future complement. That’s because rather than burning pulverized coal, the plant will convert coal to artificial gas and burn the gas, resulting in fewer pollutants. The conversion process also provides for a more concentrated stream of carbon dioxide, helping simplify carbon capture.

But upon further geological testing, Duke last year revealed that the Edwardsport site actually isn’t suitable for sequestration. Duke sought IURC approval to tap ratepayers for $120 million to drill additional test wells about 50 miles northeast and west of the site, but later downgraded that request to $42 million.

“With the minimal information that is available about the deep subsurface in Indiana, there remains much to be done to determine where and at what scale the practice could be deployed within the state,” said John Rupp, senior research scientist at the Indiana Geological Survey.

There have been promising finds elsewhere in the Mount Simon sandstone formation that underlies parts of Indiana and surrounding states.

Last fall, 1,000 tons of carbon dioxide was injected into the formation about 3,500 feet beneath Duke’s East Bend power station in Rabbit Hash, Ky. Duke is a member of the Midwest Regional Carbon Sequestration Partnership, which conducted the test.

Though apparently successful, 11 groundwater wells at the site will be monitored over two years to make sure the carbon dioxide doesn’t migrate into drinking water.

That’s one of the concerns environmental groups have about sequestering carbon. Any commercial-scale sequestration likely would send carbon dispersing laterally for hundreds or thousands of square miles over the decades of a generating plant’s life. Containment requires confidence in the cap rock covering the sandstone that will be injected. Also, each of several wells to inject the carbon must be painstakingly constructed, including use of acid-resistant concrete seals, so as not to allow carbon to seep back up.

Even then, there are hazards that can’t be foreseen, including earthquake faults and the more than 70,000 oil and gas wells drilled in Indiana since the 1890s. Some of the wells, which mainly dot southwestern Indiana and the Trenton field of east-central Indiana, aren’t accounted for, and some go deeper than 3,000 feet.

Also, while Indiana had well-plugging standards as early as 1893, “many methods used to abandon wells prior to 1947 do not meet modern standards,” says the Indiana Department of Natural Resources.

That might not be an issue if carbon were injected deeper. For example, in Decatur, Ill., an 8,000-foot well was drilled to store carbon produced by an Archer Daniels Midland corn wet mill.•

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