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ROARING BRANCH, Pa. - The frack job was frozen.
Deep beneath an icy Tioga County farm last week, an effort to extract natural gas from the Marcellus Shale shuddered to a halt. The culprit was not the 14-degree weather, but an innocuous material more often associated with beaches: sand.
The procedure known as hydraulic fracturing, or "fracking," is designed to liberate gas locked in the shale by injecting pressurized fluid into a well to shatter the rock. But this frack job in north-central Pennsylvania was stalled: Sand contained in the frack fluid had clogged up the bore.
"These things happen," said Greg Carder, a contractor employed by East Resources Inc., of Warren, to frack the well.
Another contractor was summoned to dislodge the blockage. The one-day delay idled about 100 workers and the fleet of assembled machinery, adding tens of thousands of dollars to the well's $4 million price.
In the grand scheme of things, the clog amounted to a minor glitch in the high-tech construction of a modern natural gas well.
Far bigger and costlier obstacles loom for hydraulic fracturing.
As the Marcellus gas bonanza accelerates, the practice of fracking wells to stimulate production has come under fire. Officials in New York, worried that gas drilling threatens the city's watershed, have called for a ban. In northeastern Pennsylvania, Marcellus drilling is stalled because of opposition in the Delaware River basin.
U.S. Sen. Bob Casey (D., Pa.) has cosponsored legislation requiring federal regulation of fracking. "This legislation will ensure that hydraulic fracturing does not unnecessarily jeopardize our groundwater," he said.
The oil and gas industry says hydraulic fracturing is not a threat to groundwater supplies and is already closely monitored by state regulators. They say federal oversight would retard domestic gas exploration.
But Exxon Mobil Corp. was so concerned about the growing opposition that it included a clause that would allow it to back out of its $41 billion offer last month to buy natural gas producer XTO Energy Inc. if Congress made fracking illegal or "commercially impracticable."
Gas drillers say they have been hydraulically fracturing wells for more than six decades. Without fracking, "unconventional" shale plays such as the Marcellus would not be feasible.
"Over the years, our company has drilled thousands of wells, and every one of them is fracked," said Terrence M. Pegula, the chief executive officer of East Resources. "I can't believe we have to sit now and try to explain it."
Pegula acknowledged that the industry was unprepared for the attention hydraulic fracturing had attracted as the lucrative Marcellus efforts had expanded into areas unaccustomed to gas drilling. The Marcellus lies under much of Pennsylvania and parts of three other states.
"I think we have done an absolutely horrible job of defending ourselves against people who are criticizing a technique that has been used for 60 years," Pegula said.
Last month, East Resources agreed to donate $750,000 to the Susquehanna River Basin Commission to install a network of devices to remotely monitor water quality in the streams near wells. The monitors will alert regulators if any serious spills occur.
So confident is he that properly constructed gas wells will not leak, Pegula said, that he has ordered his company to begin installing water-monitoring wells next to all its drilling sites, to collect groundwater data before and after drilling.
"We're going to prove there's no effect on the aquifers," he said.
Much is at stake for Pegula, who grew up near Scranton and was a petroleum engineer in Texas. He founded East Resources 27 years ago in Warren County, focusing on the region where well-drilling has been part of the landscape since Edwin Drake struck oil in 1858 in Titusville.
East Resources is now one of the state's biggest producers, with 2,200 active oil and gas wells.
The Marcellus boom has catapulted the company into a bigger league. Last year, Pegula secured a $350 million investment from Kohlberg, Kravis, Roberts & Co., the New York private-equity firm, to help finance the development of its 650,000 Marcellus acres.
"We needed to jump into this with full force," Pegula said.
The scale of the investment is evident at this Tioga County location. Last week, tens of millions of dollars of equipment was packed onto the four-acre Fitch well site, named for the land's owner.
"This is a very sweet spot in the Marcellus," said Scott Blauvelt, East Resources' general manager for environmental, safety, and health issues. The shale formation is about 200 feet thick here and about 6,500 feet below the surface.
Unlike vertical wells that capture only a small part of the shale, horizontal wells are designed to turn laterally deep underground and follow the formation for great lengths. Gas drillers can drill several horizontal wells from one location and capture vast quantities of gas beneath an area as large as one square mile, rather than scattering dozens of vertical wells over the terrain.
But horizontal well sites are big. They must accommodate the machinery needed to pump millions of gallons of water and sand underground.
The Fitch 1H well, the first of six East Resources plans for this site, was drilled in August. As they advanced, the drillers installed progressively smaller steel casing into the hole. The narrowest of three pipes is about 4.5 inches in diameter.
State law requires the drillers to inject cement into the void between steel pipe and rock, to seal off the aquifer.
"The design and rules governing the construction are highly regulated," Blauvelt said. "The objective is to isolate the well bore from the groundwater source."
The Fitch well extends 11,000 feet underground, more than two miles. Last week, workers from Universal Well Services Inc., of Meadville, began hydraulically fracturing the final 4,500 feet in the Marcellus.
On the well pad, the contractors assembled a fleet of equipment: 50 trailers to store some of the three million gallons of water needed for the job. Most of the water was purchased from a local municipal supply. About a third was recycled from previous jobs.
As Blauvelt describes it, hydrofracking is essentially an effort to push sand into tiny fissures in the shale, allowing the gas to escape. The sand lodges in the cracks to prop the fissures open.
"The water is just a vehicle to transport the sand down the hole," he said. The company planned to use up to 5 million pounds of sand in the Fitch operation.
With 24 truck-mounted pumps, the slurry is injected under high pressure into the shale through holes in the steel casing. Sometimes, the wells "sand up," as the Fitch well did last week. The clog was dislodged by snaking a two-mile-long pipe into the well and blowing nitrogen into the hole.
A "slick-water" frack typically includes surfactants to keep the sand suspended, and polymer friction-reducers that speed the mixture. Biocides like bromine, a disinfectant used in hot tubs, may be added to prevent organisms from clogging the fissures.
"We don't want bacteria going down-hole and sliming things up," said Carder, an operations manager for Universal Well Services.
The industry downplays the environmental effects of the additives, saying they amount to less than 1 percent of the mixture. But a provision of the proposed federal legislation would require drillers to disclose the frack additives.
Industry geologists say the fluid that remains in the shale stays there. In the Marcellus, a mile of impermeable rock separates the shale from the aquifer. The big challenge is managing the fluid that flows back from the well when the fracturing is done.
Flowback brine is saltier than seawater, and the state Department of Environmental Protection requires the water to be treated before it can be disposed. But treatment is expensive, and the state is considering tighter rules to deal with the increasing volume of water.
"Every gallon that we use has to be accounted for," said Blauvelt, showing the elaborate spreadsheets the company must submit to regulators.
East Resources has six staff members whose job, he said, is to comply with water rules.
Contact staff writer Andrew Maykuth at 215-854-2947 or firstname.lastname@example.org.