What lies beneath

The exploitation of massive Marcellus Shale natural-gas deposits in the Appalachian region of the northeastern U.S. sounds like a dream. With energy concerns at the top of the nation’s agenda, this natural-gas reservoir, located just several hundred miles from East Coast urban centers, has drilling companies pouring into the region. In Pennsylvania, where development is the most advanced, landowners are eagerly signing mineral-rights leases. But environmental groups and some industry insiders warn that local communities and state regulators could be blindsided by the environmental consequences of the gas boom.


TOM MURPHY
Each deep-drilling and hydraulic-fracturing operation, like the one shown here, has a multi-million-gallon thirst.

David Burnett, technical director of the Global Petroleum Research Institute at Texas A&M University, says that residents in central and northeastern Pennsylvania, and other prime areas for drilling the shale, should be braced for high-speed changes. During the past 7 years, exploitation of the Barnett Shale, a similar geological formation in Texas, “has turned Fort Worth into a boom town like Silver City, Nev., in its heyday,” he says. Burnett’s research aims to minimize the environmental consequences of gas and oil drilling.

Buried more than a mile beneath the surface, the Marcellus Shale’s vast amounts of natural gas have long tantalized geologists. Now, thanks to soaring natural-gas prices and improved drilling technologies—mainly hydraulic fracturing and horizontal drilling—an estimated 50 trillion cubic feet of gas could be recovered from the formation, according to Pennsylvania State University geoscientist Terry Engelder.

The technology involves vertically drilling a deep production well down to 5000 feet, and then directional drilling, or side tracking, the drill for the next 1000 feet so that the drill bit begins to move horizontally. The operators then drill horizontally for another 3000 feet. More than a million gallons of water and chemical additives as well as about half a ton of sand are injected into the well at high pressure, which then fractures the rock. Among the additives that have been used are guar gum, biocides, and diesel fuel, although the three major drilling service companies agreed to stop using diesel fuel in 2003. The water pumped out of the well contains the additives and brine that were trapped in the gas formation, along with metals, sulfides, and radioactive materials. The levels of metals and radioactivity are likely to be very low, Engelder says. Still, radioactive materials sometimes become concentrated on the drilling equipment.

A controversial 2004 U.S. EPA report rated the threat of hydraulic fracturing to drinking water as “minimal”. Thomas Rathbun of the Pennsylvania Department of Environmental Protection (PADEP) says that the state also estimates the threat to drinking water as minimal because the drinking-water aquifer is shallow. It lies more than 5000 feet above the Marcellus Shale. Pennsylvania regulations require companies to drill with air until they are below the aquifer, and then line the hole. As a result, the chances of fluids from hydraulic fracturing entering drinking water are slim.

But finding and disposing of the millions of gallons of water that hydraulic fracturing demands are two major problems. With hydraulic fracturing, “you aren’t even going to have a stream left,” Burnett says. Treating the fluids brought up from the well is also a problem. “The [brine] can’t go to a sewage treatment plant,” Burnett adds. “Those plants can’t handle a multi-million-gallon slug of salty water.”

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