CNX Resources say they think they know why a Utica well they were fracking in Westmoreland County, PA suddenly lost pressure as they were fracking it–with gas escaping into nearby conventional wells.
The reason for the loss of pressure and leaks into other wells had nothing to do with fracking itself. The problem is a faulty well casing.
CNX was fracking their Shaw 1G Utica well in Washington Township on Saturday, Jan. 26, when they detected “a strong drop in pressure” and stopped fracking (see CNX Hits Major Problem Fracking Utica Well Near SWPA Reservoir). Turns out the well was “communicating” (i.e. losing gas to) several nearby conventional wells.
At first it was thought there were four conventional wells affected, then the number went to seven, and then nine. CNX looked at all conventional wells within a two-mile radius of the Shaw well because it’s possible more wells were impacted.
CNX and the state Dept. of Environmental Protection (DEP) are still investigating how it could have happened–how fracking a single shale well could suddenly lose its gas/pressure to so many nearby conventional wells, all of which have had to be flared to relieve the pressure. The working theory is a bad well casing about a mile down.
What is well casing? It’s a series of metal pipes, one inside the other, with cement poured between them. Here’s a diagram from the Marcellus Shale Coalition, to give you a better idea of what it is:
The following video, a bit long at 6 minutes, does a good job of describing the casing process:
CNX said last week they believe bad casing about a mile down (in the “production casing”) is the cause:
On January 25, 2019, the Company experienced a subsurface pressure anomaly during hydraulic fracturing operations on its Shaw 1G Utica Shale well in Westmoreland County, Pennsylvania. The Company also observed pressure increases at several nearby shallow oil and gas wells not owned by CNX. CNX immediately suspended hydraulic fracturing operations on the pad. On February 5, 2019, CNX successfully remediated the Shaw 1G well to arrest the subsurface flow of gas. There were no injuries and no impact to the environment. While the Company is continuing to evaluate the cause of this incident, it appears that the pressure anomalies that the Company observed were caused by a casing integrity issue that occurred at a depth below approximately 5,200 feet, allowing gas traveling up the wellbore to escape into shallower formations. CNX believes this issue is isolated to this well. All hydraulic fracturing operations on the 4-well Shaw pad remain suspended while the Company continues to assess this incident. As a precaution, CNX will continue to monitor the Shaw 1G well and several nearby shallow oil and gas wells for a period of time. CNX is working in close coordination with the Municipal Authority of Westmoreland County and all appropriate state and local stakeholders to ensure the situation was and continues to be addressed in a safe and environmentally compliant manner. (1)
The Shaw well is located on Municipal Authority of Westmoreland County property, close to the 1,300-acre Beaver Run Reservoir which provides drinking water for some 130,000 people. Authorities have been testing the water frequently and there have been no impacts (so far).
CNX hired a well control team to “kill” the well, which means pumping it full of heavy mud, which happened last week.
The following media story contains a few more details, such as no decisions have yet been made about whether CNX will attempt to reopen the Shaw 1G well and complete it.
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 5.5-inch 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 okay,” Ms. Fraley said. (2)
(1) Securities and Exchange Commission (Feb 7, 2019) – CNX Resources Corporation – Form 10-K
(2) Pittsburgh (PA) Post-Gazette (Feb 9, 2019) – CNX reports suspected cause of Utica Shale well problem near Beaver Run Reservoir
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