“It’s a complex job in horizontal wells, many with horizontal bores running up to three miles long,” Ingraffea points out. Those bores are fracked in 500-foot sections. “Each time you re-pressurize the well bore for a frack job, it puts the cement at risk,” says Ingraffea. The industry already knows frequently stressed cement has a higher failure rate.
Ingraffea would like to see regulations require cement logs. After completing a cement job, drillers lower a device into the well bore that sends images of the cement. That way drillers should catch tiny cracks that might allow gas migration, Ingraffea explains. “But it doesn’t take much dis-bonding between the cement and the casing to provide a pathway for methane molecules.”
Tens of thousands of slickwater hydraulically fractured wells have been drilled into Barnett shale and Fayetteville shale and now Marcellus shale, Ingraffea pointed out. The EPA needs to demand data on cement reliability of these wells, not vertical wells drilled a decade or more ago.
Another problem is aging. Over the years cement shrinks and cracks, and casings corrode, says Ingraffea. This raises a number of questions about well integrity during re-fracking.
That is evidence that the industry is under reporting failure and the EPA is not investigating. As I said the wells are multiply fracked over their lifetime. There is industry data built up over years showing the progressive failure rates of well casing with time. It reaches about 100% after 30yrs. This data is available but a little bit more difficult to track down.
Edited by Br Cornelius, 15 September 2012 - 07:57 AM.