The Truth about Fracking: Fracturing a deep shale layer one time to release natural gas might pose little risk to drinking-water supplies, but doing so repeatedly could be problematic by Chris Mooney, October 19, 2011, Scientific American (November 2011 issue)
“I just wish the industry would stop playing the game of ‘fracking doesn’t cause the contamination.’ You’ve got to drill to frack. It’s a matter of semantics and definition that they’re hiding behind.”…“If you do a poor job of installing the well casing, you potentially open a pathway for the stuff to flow out,” explains ecologist and water resource expert Robert B. Jackson of Duke University’s Nicholas School of the Environment. Although many regulations govern well cementing and although industry has strived to improve its practices, the problem may not be fully fixable.
“A significant percentage of cement jobs will fail,” Ingraffea says. “It will always be that way. It just goes with the territory.” Contamination because of bad cementing has been a long-standing problem in traditional vertical wells, which were fracked at times, too. … Poor cementing accounts for a number of groundwater contamination cases from unconventional gas drilling—including the $1-million Chesapeake violation. “Methane migration is a problem in some areas. That’s absolutely correct,” Engelder says. … As the British Columbia Oil and Gas Commission warned operators, “Fracture propagation via large scale hydraulic fracturing operations has proven difficult to predict.” The agency added that fracture lengths might extend farther than anticipated because of weaknesses in the overlying rock layers. [Emphasis added]