Perilous Pathways: How Drilling Near An Abandoned Well Produced a Methane Geyser

Perilous Pathways: How Drilling Near An Abandoned Well Produced a Methane Geyser by Scott Detrow, October 9, 2012, NPR State Impact 
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.

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. Shell’s Guin­don well, located  a few thou­sand feet from the old But­ters well, was lined with more than 1,200 sacks of cement, along with four lay­ers of cas­ing rang­ing from 13 3/8 inches to 4 1/2 inches in diameter. Most of the time, this cas­ing pre­vents the shal­low gas from mov­ing to the sur­face. (That’s not always the case – just see StateIm­pact Pennsylvania’s report­ing on a methane leak in Brad­ford County.)

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. Bal­dasarre 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. Depend­ing on how old the aban­doned well is, the cas­ing can be leaky, rot­ten, or nonex­is­tent. Methane can eas­ily move into nat­ural faults and cracks, fol­low­ing a path toward the sur­face that can travel through aquifers. That’s likely how gas ended up bub­bling into a creek, out of a water well and up into the 30-foot geyser in Union Township. [Emphasis added]

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