Problems with natural gas well construction appears to be the primary cause of drinking water contamination from shale-gas extraction, according to a new study published today by researchers from five universities.
The study did not find evidence of methane gas migrating from deep underground into residential drinking wells, an indication that neither the drilling nor “fracking” process caused contamination from those deep underground areas. But the study also left open the possibility that pressures from drilling or fracking could be contributing to or causing well casing failures closer to the surface.
“Future work should evaluate whether the large volumes of water and high pressures required for horizontal drilling and hydraulic fracturing influence well integrity,” said the study, published in the Proceedings of the National Academy of Sciences. “In our opinion, optimizing well integrity is a critical, feasible, and cost-effective way to reduce problems with drinking water contamination and to alleviate public concerns accompanying shale-gas extraction.”
The study, which examined methane leakage at wells in the Barnett Shale in North Texas and the Marcellus Shale in Pennsylvania, builds on the continuing review of the impacts of the rush of natural gas production in places like Northern West Virginia, where Marcellus drilling and production has boomed.
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In their push for more natural gas, drilling operators are increasingly using a combination of vertical drilling and hydraulic fracturing, or “fracking,” a process that shoots vast amounts of water, sand and chemicals deep underground to break apart rock and release the gas. West Virginia political leaders are hoping this practice expands as gas companies seek to tap into the vast reserves in the Marcellus Shale, a formation that stretches from 95,000 square miles from southern New York and into eastern Ohio.
In a peer-reviewed paper, the scientists from Duke University, Ohio State University, Stanford University, Dartmouth College and the University of Rochester used certain gas and hydrocarbon tracers to analyze the gas content of more than 130 drinking water wells in Texas and Pennsylvania.
They found eight clusters of wells — seven in Pennsylvania and one in Texas — with contamination, including increased levels of natural gas from both the Marcellus Shale in Pennsylvania and from shallower, intermediate layers in both states. In four of those clusters, the team found that methane from drill sites escaped into drinking water wells from shallower depths through faulty or insufficient rings of cement surrounding a gas well’s shaft. In three clusters, the tests suggest the methane leaked through faulty well casings. In one cluster, it was linked to an underground well failure.
“Our data clearly show that the contamination in these clusters stems from well-integrity problems such as poor casing and cementing,” said Thomas H. Darrah, assistant professor of earth science at Ohio State, who led the study while he was a research scientist at Duke.
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