Study Targets Methane Leaks Between Underground Wells
Hydraulic fracturing can form cracks that can connect new shale gas wells to nearby abandoned wells, possibly allowing methane to leak into the atmosphere or aquifers underground, according to a University of Vermont study published this week.
The study is one of the latest efforts to answer an elusive question: How do fracked oil and gas wells leak methane and other hydrocarbons into underground aquifers and into the atmosphere?
This map shows all of the natural gas wells that have been drilled in western New York east and southwest of the city of Buffalo.
Credit: U.S. Energy Information Administration Energy Mapping System
James Montague, the study’s lead author and a University of Vermont Ph.D. student, said the study focuses on how methane can leak from one well to another.
Though the study found that the chances of methane getting into the environment through cracks like these are no greater than 3.45 percent in New York State, Montague said the research shows that fracking operations often occur amid a larger network of gas wells that may be connected deep underground, facilitating methane leaks.
Leaking methane is one of the biggest climate threats posed by shale oil and gas development using hydraulic fracturing. Methane, which has about 35 times the power to warm the atmosphere as carbon dioxide over the span of a century, is one of the largest short-term drivers of climate change.
Previous research has shown that shale gas drilling and production may leak a large but not fully known amount of methane into the atmosphere, possibly up to 1,000 times more methane than previously thought. The U.S. Environmental Protection Agency has proposed rules to curb methane emissions from oil and gas wells and pipelines, seeking to slash emission from the oil and gas industry by up to 45 percent below 2012 levels over the next decade.
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Abandoned gas wells in the Marcellus shale in Pennsylvania have been found to leak methane, but nobody knows yet how many wells leak and how much methane they’re emitting.
Montague studied Marcellus shale wells in New York, calculating the probability that tiny rock fractures created by the hydraulic fracturing process would eventually intersect the underground borehole of an abandoned gas well or cracks connected to it.
Fracking is the high-pressure underground injection of millions of gallons of water, chemicals and sand, cracking rocks containing hydrocarbons to release crude oil and natural gas into a well. High volume hydraulic fracturing — fracking using more than 300,000 gallons of water — was banned in New York State in June because of its possible threats to public health, the environment and the climate.
“When they frack, they drill a hole vertically down and they induce it to go horizontally for a period of some distance. Water pressure induces fractures in the rock, and those fractures then provide potential conduits for both the fracking fluid and any methane that might be available in the rock that might flow along those fractures,” study co-author George Pinder, a University of Vermont professor of engineering and mathematics, said.
“There’s a certain probability that if you put a fracking well in any particular location, that in the process of doing the fracking operation you’re going to create conduits from the fracking activity to pre-existing abandoned wells,” he said.
In their published results, Pinder and Montague calculated that the probability of that happening in New York is between zero and 3.45 percent. But Pinder said the study may underestimate the probability that a fracked well could intersect an older well.
A natural gas well in Upstate New York.
Credit: Andy Arthur/flickr
Pinder said he and Montague originally assumed that fracking would crack rocks within a square quarter mile of a new well site, but the paper’s peer reviewers said that figure was too big. Since the paper was published, however, Pinder said he received new information from an industry expert, who said fractures could extend outward from a wellbore by several miles, increasing the probability that methane could leak into a nearby well by up to a factor of 10.
“It could be as high as 30 percent,” Pinder said.
Should new wells be fracked in New York, the University of Vermont researchers recommend that the operations occur away from abandoned wells to prevent methane leaks.
Some scientists unaffiliated with the study said they question its significance.
Cornell University environmental engineering professor Anthony Ingraffea, whose research has focused on methane leaks from Marcellus shale gas wells, said the study’s published results are consistent with other studies in other regions.
“It addresses a problem that I don’t think is a major problem,” he said. “Is inter-well communication going to substantially increase methane emissions currently not accounted for in the EPA methane inventory? The preliminary answer is no, because there aren’t many communications predicted.”
Other problems with natural gas development pose bigger climate threats, such as large methane leaks from gas compressor stations and pipelines, Ingraffea said.
Lawrence Cathles, an earth and atmospheric sciences professor at Cornell University, said the study is a first step at assessing risk from inter-well methane communication.
But, he said, an abandoned well within close range of a fracked well may not necessarily lead to methane moving between the two for any number of reasons. Scientists still have a lot to learn about how conduits form between wells deep under ground.
“We need to be careful of abandoned wells, and the authors make a nice contribution to assessing their risk, but they do not raise any risks about which the industry is not fully aware,” Cathles said.
William Kappel, a U.S. Geological Survey hydrologist based in Ithaca, N.Y., said it’s up to individual oil and gas drillers to find abandoned wells near new shale gas wells they intend to frack in order to prevent the new well from leaking into old ones.
Editor's Note: This story was updated Oct. 22 to include comments from Lawrence Cathles.
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