Energy & Resources
Coalbed Methane: The Future of U.S. Natural Gas?
Lisa M. Pinsker

Methane is a buzz word these days both in the energy community and on the Hill, where legislators are working to ensure the future security of energy resources in the United States. National demand for natural gas is increasing, with the resource now heating more than 50 percent of U.S. homes and fueling 95 percent of new power plants.

Speaking to congressional staffers at a briefing on Sept. 20, Rebecca Watson, assistant secretary for land and minerals management at the Department of the Interior, said that coalbed methane is the best source of energy to meet U.S. natural gas demand over the next five to six years. That projection was echoed at an energy and environment conference three days later held by the American Association of Petroleum Geologists (AAPG), where earth scientists referred to the new era of the "methane economy.

Hydraulic fracturing is necessary in order to extract natural gas from coalbeds. Shown here are fractures and cleats (joint systems along which the coal fractures) in a sample coal core. Photo courtesy of USGS.

Coalbed methane is the natural gas that lies trapped in coal seams at shallow depths. "It is different from other resources because it is both generated and stored within the coalbeds themselves. It also is an attractive resource because it occurs within coal, which is the most abundant fuel in the United States," said Patrick Leahy, associate director of geology for the U.S. Geological Survey, at the congressional briefing. Coal acts like a sponge, storing six times the volume of natural gas found in conventional reservoirs, Leahy explained.

Over the past 20 years, coalbed methane production has increased steadily due to its abundance and the relatively low cost of drilling at its shallow depths. As of 2000, coalbed methane accounted for 7 percent of the total U.S. natural gas production. Recent estimates put it at 9 percent of total U.S. natural gas production.

The San Juan Basin in Colorado is the world's most prolific coalbed play, but the Powder River Basin in Wyoming and Montana is the newest and most active coalbed play in the United States, Leahy said. Conservative estimates put about 700 trillion cubic feet of coalbed methane in place in the United States, of which 100 trillion cubic feet are economically recoverable with existing technology. Annual U.S. production now exceeds 1.25 trillion feet.

According to the National Energy Technology Laboratory's Strategic Center for Natural Gas, the year 2001 saw 7,000 wells in the Powder River Basin producing 700 million cubic feet per day.

A coalbed methane wellhead dots the Powder River Basin. Extending over southern Montana and northern Wyoming, the Powder River Basin is the newest and most active U.S. coalbed play. Currently, the Bureau of Land Management is reviewing all 5,100 gas leases in the Powder River Basin.

Indeed, Peter Stark, of IHS Energy Group in Denver, told those attending the AAPG conference that the Rocky Mountain states hold the most potential for future gas supplies. However, he stresses that much of the federal land is out of bounds for natural gas development, and that various regulations make an estimated 43 percent of Rocky Mountain gas unavailable for drilling.

Citing current political tensions between the United States and foreign interests, AAPG speakers stressed the importance of developing domestic resources to ensure energy security. For natural gas, the United States is relying more and more on imports from outside the continent. However, Stark pointed out, North America has ample resources, just not proper access to those resources, creating what he called an urgent situation for domestic natural gas production.
With the rising natural gas demand, Stark said that the country will need to reach a target of 162 trillion cubic feet of natural gas by the year 2020. To do that, he says, the United States needs to develop 12 analogs to the Powder River Basin. "Unless there is continuous and sustained drilling, coalbed methane could peak as early as 2006."