The arguments in favor of using more natural gas and less coal and petroleum are, at least at first glance, straightforward. Coal-fired plants generate about 50 percent of the electricity used in the United States, but they produce 82 percent of the power industry’s carbon dioxide emissions. Burning natural gas produces roughly half as much carbon dioxide as coal. What’s more, plenty of existing gas-fired power plants already have excess capacity, since they are generally used as backup to coal plants at times of peak electricity demand.
It’s also easy, from a technological perspective, to substitute natural gas for gasoline or diesel fuel in cars and trucks. Unfortunately, this wouldn’t reduce greenhouse-gas emissions nearly as much as replacing coal in power production. A natural-gas car emits about 25 percent less carbon dioxide than a gasoline-powered vehicle, but since transportation accounts for only about a third of U.S. greenhouse-gas emissions, even switching over all the country’s vehicles to natural gas would reduce overall emissions by just 8 percent. Still, using natural gas in a portion of the nation’s fleet vehicles, such as buses and taxis, would be relatively simple and could help reduce dependence on imported petroleum.
In mid-August, the Energy Future Coalition and the Center for American Progress, an influential Washington group with close ties to the Obama administration, released a paper called “Natural Gas: A Bridge Fuel for the 21st Century.” The timing of the report was triggered by the recent shale-gas findings and the desire to make natural gas a part of the discussion as Congress debates an energy bill. Proposed provisions in that bill, such as a cap-and-trade program that would effectively put a price on carbon dioxide emissions, could create a strong and growing market for this fuel. Once the carbon price reaches $20 to $30 a ton, says the Energy Future Coalition’s Detchon, “it would be economically advantageous for utilities to switch to gas from coal.” Detchon also favors a “low-carbon” mandate, which would require utilities to use natural gas for a certain percentage of their electricity production, and incentives for power producers to close down their oldest and dirtiest coal-fired plants.
Such policy changes are critical to encouraging further drilling in shale-gas deposits, says Jeff Ventura, the COO of Range. Prices for natural gas peaked at $13 per thousand cubic feet (MCF) last year, but oversupply and lackluster demand depressed them to around $3 per MCF this summer, the lowest level since December 2001. As a result, drilling slowed down, almost reaching a standstill in many regions of the country (though drilling in the Marcellus has actually increased). A “reasonable price” of around $6 to $8 per MCF, Ventura says, would enable drilling companies to more fully exploit shale gas. Getting back to that price will require not only an economic recovery but also policies that increase demand by influencing power generators to shift to natural gas. “That is something that could happen immediately,” he says. “More power generation from natural gas would have an immediate impact.”
Drilling for shale gas could also provide a less obvious environmental benefit, if research begun by the Stanford geophysicist Zoback is successful. Fossil-fuel power plants, whether they use coal or natural gas, will eventually need to capture and sequester their carbon dioxide emissions. That means finding a safe, economical way to store carbon dioxide so that it cannot leak out. Zoback believes that shale deposits might provide one solution.
Zoback is testing the feasibility of a process that could trap carbon dioxide in depleted natural-gas wells–and wring additional productivity from them at the same time. It is thought that at least some of the methane in the shale is adsorbed to the sediments: the gas molecules form a thin film that adheres to the surface of the organic material and clay in the deposits. Preliminary tests have shown, however, that carbon dioxide binds to these materials more strongly than methane does. Carbon dioxide pumped into wells that have grown less productive, Zoback believes, could displace the adsorbed methane, which would then flow out of the shale and into the well. If it works, the process would free extra natural gas in these wells while confining the carbon dioxide securely underground.