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Saturday, June 29, 2013

Scientific American magazine: "Methane in Pennsylvania Groundwater May Originate in Fracked Gas Wells"

"...the problem lies in poorly designed well casings"

"Scientists at Duke University detected elevated levels of methane, ethane and propane in groundwater samples near active fracking sites. The scientists conclude that the gasses come from the wells, not natural sources, but that the problem could be solved with better-designed casings. "We think there's a well-integrity problem in this part of the Marcellus,” says Robert Jackson, a professor at Duke and lead author on the paper describing the findings. "And well problems are relatively easily fixed. They’re especially easier to fix than if there's some fundamental problem with fracking."

Hydraulic fracturing—more commonly referred to as fracking—extracts natural gas reserves that are unreachable by conventional techniques. The process requires drilling wells thousands of meters down and then blasting them with a mix of water, sand and chemicals to induce fractures in the underlying rock. Gas seeps through these fractures and flows back up the well where it is captured. But if the wells aren’t properly sealed, then gas can leak into the groundwater. The wells are lined with metal casings that prevent extracted gas and contaminated water from leaching into the surrounding rock. To block gas from flowing up the outside of the well shaft, engineers pour cement around the outer casing to plug any gaps. If the cement or casing isn’t properly set, then gas from deep shale deposits can find its way in to shallow groundwater. If the casing ruptures, fracking chemicals can also enter the water supply."