CNX reports suspected cause of Utica Shale well problem
CNX Resources Corp. said a problem with the casing in its compromised Utica Shale well in Westmoreland County was the likely root of high pressure gas that flooded nearby shallower wells two weeks ago.
The Cecil-based company told investors that the problem at its Shaw 1G well in Westmoreland County occurred about a mile underground.
It’s still early in the investigation, the company cautioned in its annual report filed on Thursday, “but based on the information we have at this time, we believe the issue is isolated to this well and was caused by a casing integrity issue that occurred at a depth below approximately 5,200 feet, allowing gas traveling up the wellbore to escape at that point.”
At that depth, according to the well record filed with the state, there were two pipes in the ground, one a 9.6-inch diameter steel casing and inside of it a 5.5inch diameter production casing.
The narrower pipe, which is the conduit for the gas to travel up the wellbore, was cemented to the wider one at that depth. But the cement stopped a few hundred feet above that. Operators
are not required to cement the production pipe all the way to the surface.
When the gas escaped from the wellbore at that depth, it made its way to nine vertical wells, drilled to a depth between 3,700 feet and 3,900 feet, according to the DEP.
Those were the ones that the company was flaring to relieve the pressure as it worked to “kill” its problematic well. When that was accomplished late on Monday by pumping heavy mud into the wellbore below the 5,200 foot mark, the pressures at the impacted shallow wells began to drop.
By Friday evening, only four of the nine were still flaring. The others had returned to an acceptable pressure, CNX said.
CNX spokesperson Brian Aiello said the conventional wells continue to be monitored “on a 24 hour basis.”
The company is also “actively testing private (water) wells” in the impacted area, he said. There are at least four such drinking water wells within 3,000 feet of the Shaw pad, according to the company’s permit documents.
Casing failures — which could mean a breach in the pipe, the cement, or both — are not thought to be common in Appalachia, although their frequency isn’t a well-known metric.
A number of academic studies from earlier in the decade used DEP violation records to calculate the rate of shale gas wells with problems in their casing integrity. The estimates varied from less than 1 percent of wells to more than 6 percent.
State regulators strengthened casing and cementing requirements in 2011 after poorly built barriers failed in several early Marcellus Shale wells and contaminated water supplies with natural gas. They also required operators to do quarterly well integrity checks and report that data to the state.
It’s not clear what will happen to the Shaw 1G well — whether CNX will opt to remediate and refrack it or plug it permanently.
The three other wells on the same pad remain suspended, Mr. Aiello said. One of those was being completed at the same time as the Shaw 1G, while the other two were drilled but not yet fracked.
DEP spokeswoman Lauren Fraley said the DEP has asked CNX for additional data on the wells and for the company’s plan going forward. The documents have been coming in regularly, she noted, with more expected over the weekend.
As far as resuming activity on the pad, neither CNX nor the DEP could provide a timeline.
“I think we want to just see everything before we give our OK,” Ms. Fraley said.