Saturday, October 17, 2009

natural gas changes the energy map?

Technology Review | Vast amounts of the clean-burning fossil fuel have been discovered in shale deposits, setting off a gas rush. But how it will affect our energy use is still uncertain.

The first sign that there's something unusual about the flat black rocks strewn across the shore of Lake Erie comes when Gary Lash smashes two of them together. They break easily and fall into shards that give off the faint odor of hydrocarbons, similar to the smell of kerosene. But for Lash, a geologist and professor at nearby SUNY Fredonia, smashing the rocks is a simple trick designed to catch the attention of a visitor. The black outcroppings that protrude from the nearby bluff onto the narrow beach are what really interest him.

To Lash's expert eyes, the wide band of black shale, which runs roughly parallel to the beach, reveals hundreds of millions of years of geological history. The shale formed more than 350 million years ago when organic muck settled at the bottom of the shallow sea that covered much of what is now the eastern United States; it was once buried more than two kilometers underground but has gradually risen to the surface. Now, the exposed rock shows telltale patterns of breaks and splits. "We've demonstrated that these fractures could only have formed as a result of the generation of hydrocarbons," says Lash.

This formation is the edge of vast deposits of black shale that stretch under tens of millions of acres below western New York, much of western and northern Pennsylvania, and parts of Ohio, West Virginia, Maryland, and Kentucky. The oldest and deepest layer is called the Marcellus shale, and if geologists like Lash are correct, it holds enough natural gas to help change the way the United States uses energy for decades to come.

Experts now believe that the country has far more natural gas at its disposal than anyone thought three or four years ago. The revised estimates are largely due to advanced drilling techniques that make it economically feasible to extract the fuel from shale. And while the Marcellus is the most recently discovered and possibly the largest shale-gas deposit, others are scattered throughout the country. The U.S. consumes about 23 trillion cubic feet (TCF) of natural gas a year, according to the Department of Energy's Energy Information Agency (EIA). The Potential Gas Committee (PGC), an organization headquartered at the Colorado School of Mines, put the country's potential natural-gas resources at 1,836 TCF in a biennial assessment released in June. That's 39 percent higher than its estimate of two years earlier. Add to that the 238 TCF that the EIA has calculated in "proved reserves" (the gas that can be produced given existing economic conditions) and the PGC pegs the future supply at 2,074 TCF. In other words, there is enough natural gas to supply the country for 90 years at current consumption rates. Even if we used natural gas to totally replace coal in generating electricity, domestic supplies would last for 50 years.