Tuesday, November 27, 2012

when new wells meet old wells

In February 1932, the United States was in the midst of the Great Depression. Franklin Roosevelt was plotting a run for the White House. And in northeast Pennsylvania, the Morris Run Coal Co. had just finished drilling a 5,385-foot-deep gas well on a farm owned by Mr. W.J. Butters.
Eighty years and four months later, the Butters well was tied to another incident — even though it had been inactive for generations. It played a key role in a methane gas leak that led to a 30-foot geyser of gas and water spraying out of the ground for more than a week.
Methane is an odorless, colorless gas that exists naturally below the surface. It isn't poisonous, but it's dangerous. When enough methane gathers in an enclosed space — a basement or a water well, for instance — it can trigger an explosion.
The gas didn't come from the Butters well, nor did it originate from the Marcellus Shale formation that three nearby Shell wells had recently tapped into. What most likely happened to cause the geyser in June, Shell and state regulators say, was something of a chain reaction. As Shell was drilling and then hydraulically fracturing its nearby well, the activity displaced shallow pockets of natural gas. The gas disturbed by Shell's drilling moved underground until it found its way to the Butters well, and then shot up to the surface.
Companies have been extracting oil and gas from Pennsylvania's subsurface since 1859, when Edwin Drake drilled the world's first commercial oil well. Over that 150-year period, as many as 300,000 wells have been drilled, an unknown number of them left behind as hidden holes in the ground. Nobody knows how many because most of those wells were drilled long before Pennsylvania required permits, record-keeping or any kind of regulation.
It's rare for a modern drilling operation to intersect with an abandoned well. But incidents like Shell's Tioga County geyser are a reminder of the dangers these many unplotted holes in the ground can cause when Marcellus or Utica Shale wells are drilled nearby.
New Well Meets Old Well
Fred Baldassare worked at Pennsylvania's Department of Environmental Protection for 25 years. He spent more than half his career investigating cases of methane migration, where gas from wells, coal mines, landfills or other sources broke loose and made its way to the surface.
Baldassare investigated more than 200 different episodes. Only a handful of them, he says — perhaps five or six — involved an active drilling site communicating with an abandoned oil or gas well. But when the new and old operations did intersect, Baldassare says, the results were often "dramatic."
When energy companies drill down to the Marcellus Shale, deep below the surface, their wells pass through several smaller, shallow gas formations. Drillers go to great lengths to seal off their gas wells, and Pennsylvania regulations require companies to bond their multiple layers of steel casing with top-grade cement. Most of the time, this casing prevents the shallow gas from moving to the surface.
But if an old, unplugged gas well has been drilled into the same formation already, the new activity can displace pockets of gas, through pressure changes and physical interaction. Baldassare explains, "that gas can move to the old well, because [the well] represents a low-pressure zone and a natural migration highway.
"Gas always wants to go from high pressure to low pressure," Baldassare continues. "That old well represents a low-pressure zone. Much like water wants to move downhill, gas wants to move to low-pressure zones." The lowest pressure is near the surface, so once the gas reaches an old well, it will shoot straight up.
And a new well doesn't need to be present to trigger this migration. Gas can migrate to the surface through these pathways on its own. The state has investigated dozens of cases where unknown wells have led to gas pooling in basements, water wells or other locations.
So it's critical for regulators and drillers to find these wells before it's too late. That's much easier said than done, though. In the decades since these wells have been drilled, towns have been built over top of them, vegetation has covered them up, and the physical signs of wells — metal casing and pipes — have been removed by scrap collectors. The result: Oftentimes, the first indication of a well's presence is a methane gas leak at the surface.
The best guess of both the state and the energy industry is that somewhere in the neighborhood of 325,000 wells have been drilled in Pennsylvania since Drake's. Of those, about 120,000 have state permits on file. "Just do the math," Gene Pine of Pennsylvania's Department of Environmental Protection says. "There's probably close to 200,000 wells that are largely or relatively unaccounted for in the commonwealth."
So finding old wells can require a good amount of forensic work. To find one, you can employ high-tech radar or use a musty antique survey map. Whatever method you choose, it's going to be a time-intensive effort.npr



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