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Old gas and oil wells used to store natural gas

Monday, March 22, 1999

By Don Hopey, Post-Gazette Staff Writer

A spaghetti tangle of silver and gray pipes a couple of football fields long crowns a hill off Route 22 in Westmoreland County. It's the pump station for the largest of Pennsylvania's 64 underground natural gas storage fields.

 
Transmission lines carry natural gas at the Oakford Natural Gas storage facility in Delmont. (V.W.H. Campbell Jr., Post-Gazette) 

Think of it as the tip of an iceberg.

Running underground from the pumps of CNG Transmission Corporation's Oakford facility are 120 miles of pipes connecting 300 wells along a north-south axis 13 miles long. The wells tap into two deep layers of sandstone used to store 120 billion cubic feet of natural gas.

Think of it as geologic recycling.

Oakford, just 25 miles from downtown Pittsburgh, and all of the storage facilities use strata of sandstone or limestone, between 700 and 7,800 feet deep, that once held natural gas and oil before wells were drilled in the first half of this century and the gas and oil pumped out.

The most porous and permeable of those natural geological reservoirs now are reused to store natural gas pumped from Texas, the Gulf of Mexico and the Midwest. The gas is needed to supply the energy needs of people, industries and utilities in New England, the Northeast and the Mid-Atlantic region.

"The Oakford Station was started after World War II to meet increased demand, as industry was picking up and a lot more homes were switching from heating oil to natural gas," said Robert Fulton, a CNG Transmission spokesman.

"The pipelines from the South couldn't always meet peak demands, especially in the winter heating season, so the gas industry needed to find storage sites close to those markets."

At least as important as Pennsylvania's geographic position is its geology. The state's old, depleted gas fields are natural storage tanks.

"The companies look for geologic closure, natural features that close the containers," said Thomas Flaherty, permit chief for the state Department of Environmental Protection's Bureau of Oil and Gas Management in Pittsburgh.

Some of those features are structural - occurring where rock layers have been folded over geologic time and adjacent faults trap the natural gas in a fold. Some closures are stratigraphic, containing the natural gas in a convex lens-shaped rock layer capped by impermeable rock.

Also important is high "deliverablity," said John Harper, a geologist with the state Department of Conservation and Natural Resources. That means the gas must be able to flow into and back out of the sandstone or limestone layer.

"The ideal rock has good porosity - that's space between the grains of sand," Harper said. "Think of it like a jar filled with marbles. You can still pour water into that jar because there's space between the marbles.

"It also must have good permeability. That means the spaces must be interconnected."

Underground natural gas storage was first done successfully by National Fuel Gas in Welland, Ontario, in 1915. The next year the company opened the Zoar Field in western New York, a storage field that's still active.

The first storage site in Pennsylvania was the Queen field in Forest County. It opened in 1920 and remains in use. The newest storage field is North Summit in Fayette County, which opened in 1992.

Pennsylvania not only has some of the oldest and biggest underground storage fields in the nation, it also has the two most highly pressurized storage fields. The Greenlick and Leidy fields in Potter and Clinton counties are naturally pressurized at 4,200 pounds per square inch and 4,240 pounds per square inch, which makes storage harder but extraction during periods of demand much easier.

Both use famous old gas fields in the Oriskany sand, a tightly packed sandstone stratum that was a saltwater beach during the time of the dinosaurs. The sandstone was capped by a layer of dense Onondaga limestone, which has little porosity, trapping methane gas formed by decaying organic materials in the sandstone.

The area gained fame in the 1950s when the first natural gas wells were drilled, setting off a wild land rush. The combination of high pressure gas deposits and indiscriminate drilling caused numerous blowouts and some spectacular well fires. Red Adair, who gained fame as an oil well fireman in Texas and later snuffed oil fires in Kuwait after the Gulf War, got his start in the north central Pennsylvania gas fields.

Storage fields are generally established away from populated areas in rural environs, but aren't considered especially dangerous - the "DANGER: NO SMOKING" signs inside Oakford's front gate notwithstanding.

"We're more concerned with old producing wells than with storage fields. I don't know of any storage operator that doesn't keep its wells in good repair," Harper said. "They're so well regulated and engineered that the possibility of a problem or contamination of ground water is infinitesimal."

Paul Kucsma, Bureau of Oil and Gas Management compliance chief in Meadville, said the last failures in the state's northern tier counties occurred in the 1970s, when steel well casings cracked or corroded and gas escaped from the well bore. It migrated through porous rock layers near the surface before coming up in a stream and several homes.

"We're really not aware of any substantial gas loss from wells up here," Kucsma said. "We do regular inspections and companies have to report problem wells."

By 1960, there were 217 natural gas storage pools in the United States with a combined capacity of 2.8 trillion cubic feet. Today, there are nearly 400 with a total capacity of 8 trillion cubic feet. Much of the recent expansion has come in West Virginia and New York.

One recent attempt to establish a new storage field in the state is noteworthy because it proposed using salt deposits in Tioga County, below an existing CNG storage field. CNG has challenged that proposal and it remains under review.

The Oakford storage field can hold up to 101 billion cubic feet of natural gas in the 1,400 foot deep Murrysville sand stratum, and 21 billion cubic feet in another sand layer, the Fifth sand.

A $40 million expansion that will be completed in November will bump storage capacity up another 10 billion cubic feet.

The Pennsylvania storage fields promise to become more valuable as coal-fired electric utilities convert to cleaner natural gas.

Don Raikes, CNG Transmission marketing director, said utilities began switching to natural gas 10 years ago, spurred by more stringent federal air quality standards. Aging coal-fired plants would require millions of dollars in capital improvements to meet those standards.

"We have a number of utility customers now," he said, "and have a number of ongoing discussions with more customers interested in using natural gas for electricity production. We're seeing significant interest in New England and throughout the Mid-Atlantic states."



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