Note: This article is a sidebar to one of this issue's feature stories, "Colliding forces."
Understanding methane-gas drilling isn't easy. Here are some basics about what might be underground in a Western backyard.
Conventional wells extract methane gas from sandstone 1,000 to 20,000 feet below the surface. Sitting in zucchini-shaped air pockets in the rock, the gas is under pressure, a lot like air inside a balloon: It wants to escape its high-pressure confines and get into the lower-pressure area outside. When a steel pipe, encased in concrete, is drilled into the gas pocket, the methane moves naturally into the well pipe and up to the surface. Ninety percent of wells are conventional. In the Rocky Mountains, they're used in southwest and central Wyoming, eastern Montana, northeast North Dakota, both the Western Slope and the northern Front Range of Colorado, and southeastern New Mexico, near Roswell and Artesia.
Coal-bed methane wells extract methane gas from coal 2,500 to 5,500 feet below the surface. Methane gas sits in the cracks of the coal layer and is bound to the rock by water pressure. In order to release the gas, pumpjacks, generally 15 feet tall, suck out groundwater, decreasing the pressure and allowing the gas to escape up the well. Drilling for coalbed methane, a relatively new technology, is only 10 years old. Coalbed methane is tapped in the Four Corners region of northern New Mexico and southwest Colorado, Price, Utah, the Powder River Basin, Wyo., southeastern Montana, and the Raton Basin in southeastern Colorado and northeastern New Mexico.
If the concrete cracks around the steel pipe, methane gas seeps into the ground and rivers. Methane-saturated soils sap nutrients in the ground, killing crops and trees, even suffocating rodents in their burrows. Aquifers can become contaminated with methane and water wells can fill with gas. Some scientists say that methane wells have a higher rate of "seeps" than conventional wells because they are generally drilled closer to the surface.
If a well is drilled incorrectly, other types of gas can escape into the air. In some parts of the Animas River Basin in southwestern Colorado, the smell of rotten eggs pervades the air because hydrogen sulfide has followed the methane gas out of the ground. In other parts of the Rocky Mountains, people have reported seeps of benzene and carbon dioxide.
Many farmers and ranchers pump well water from the same coalbed methane layer that is drilled for gas. As water is pumped out of the rock to release the gas, domestic well water can be depleted and fill with methane. Gas can escape into homes, creating fire danger (HCN, 3/15/99: Oil wells in my backyard?).
Pumpjacks used for coalbed methane wells are noisy - one woman in northern New Mexico says it's as if a plane is taking off outside your bedroom window. Some pumpjacks run 24 hours a day for weeks at a time.
As the pumpjack sucks water out, oxygen fills the empty pockets and can ignite or exacerbate an underground coal fire. Currently, two underground coal fires are burning on the Southern Ute reservation, south of Durango, Colo.
Directional wells grab gas from all types of rock formations. Instead of drilling one hole straight down into one formation, the pipe reaches down for a few hundred feet and then angles to reach multiple gas pockets. Landowners say directional wells decrease the amount of wells needed to access multiple gas pockets, but engineers warn that directional drilling can cause the same problems as conventional and coalbed methane wells. Oil and gas companies say that the angled pipe is more likely to get stuck in the ground. When this happens, gas companies have to drill a new hole, doubling the cost of the well. Directional drilling, used in Alaska and off the Gulf of Mexico, isn't used anywhere in the Rocky Mountains.