In theory, many layers of steel and concrete in hydraulic fracturing wells are supposed to prevent leakage into surrounding rock. But Duke University researchers suspect wells in Pennsylvania leaked, allowing gasses to contaminate well water.
In theory, many layers of steel and concrete in hydraulic fracturing wells are supposed to prevent leakage into surrounding rock. But Duke University researchers suspect wells in Pennsylvania leaked, allowing gasses to contaminate well water. Image courtesy Marcellus Shale Coalition

This is Part II of a story about hydraulic fracturing and its effects on drinking water. You can read Part I here.

By Gabe Rivin

Duke University researchers had made an alarming discovery.

Natural-gas wells in northeast Pennsylvania appeared to be leaking into groundwater, saturating nearby residents’ drinking water with methane, ethane and propane.

Yet the researchers arrived at a surprising conclusion: Hydraulic fracturing, or “fracking,” the controversial process used to recover oil and natural gas, was not in itself to blame.

Instead, poorly built wells were the likely cause of these leaks, the researchers said. The real culprits were probably bad cement jobs and poorly installed casing.

As North Carolina prepares to issue its first-ever drilling permits, the researchers’ conclusion raises several concerns: whether the state’s proposed drilling rules will be stringent enough, and whether they will require that wells maintain high-enough structural integrity in order to protect groundwater.

In theory, many layers of steel and concrete in hydraulic fracturing wells are supposed to prevent leakage into surrounding rock. But Duke University researchers suspect wells in Pennsylvania leaked, allowing gasses to contaminate well water. Image courtesy Marcellus Shale Coalition

“[Pennsylvania] modified their rules several times,” said Kenneth Taylor, North Carolina’s state geologist. “They’ve learned lessons from mistakes that were made. And we had the advantage of coming in last and saying, ‘Hey, we can take advantage of all the new things everybody else has learned in constructing these things the best.’”

Taylor is a member of the Mining and Energy Commission, the group tasked to develop drilling and fracking regulations. He also sits on the MEC committee that developed rules for well construction, as well as those for “well stimulation,” the processes, including fracking, that produce gas and oil from shale.

The full MEC gave initial approval to the construction rules last September. Taylor’s committee finished its work, on Feb. 17, on the draft well-stimulation rules; the full MEC still needs to give initial approval to those rules.

Both sets of rules still face additional debate by the full MEC, as well as a round of public comments, before the General Assembly can approve both final rules, as well as the rest of the drilling rules. That approval will allow the state to issue its first wave of drilling permits.

According to Taylor, the draft rules ensure that gas wells will maintain their structural integrity.

Layers upon layers

“We require cementing from bottom to top on each of the sequences. So you don’t have just steel against rock,” Taylor said. In order to separate the gas well from the aquifer, North Carolina will also require that drillers install four levels of steel and five levels of cement, he said.

Charles Holbrook, who chairs that committee, echoed Taylor’s claims. The well-construction rules, he said, have strong requirements for casing and are based on recommendations by the American Petroleum Institute, the industry group that represents oil and gas industries.

“The casing is selected, with a large safety margin, to withstand any pressures expected to be encountered in the well,” he said. “And the cementing is designed around the same parameters.”

According to Holbrook, the cement’s quality will be tested before it is installed in the well. After it is installed, drillers will have to perform – and report to the state – a so-called cement bond log. This is an acoustic tool that sends vibrations through the well and measures how well cement has bonded to the casing.

If the cement fails to seal the well’s section that crosses aquifers, developers, under the state’s watch, will have to fix the cement or abandon the well. Additionally, if developers find any problems with the casing or cement they will have to immediately fix the defects and report to the state within 24 hours.

The Environmental Defense Fund’s David Kelly said that these and other requirements set a high standard for the structural integrity of wells.

“We’ve got strong rules proposed in North Carolina for how you actually drill the well, how you put the steel casing in and then how you cement the casing in place,” Kelly said. “The rules that North Carolina has proposed look strong.”

Under pressure

But strong construction rules won’t mean much unless they’re accompanied by strong rules for well stimulation, Kelly also said.

“Once you build that well the right way, it has to be operated in a way that it was designed to be operated,” he said. That means drillers will have to limit the pressures that build inside the well.

“If you build the well but then you exceed its tolerances in some way when you do your hydraulic-fracturing treatment, you can still compromise that well.”

Kelly, as a member of the diverse stakeholder group that advises Holbrook’s committee, recommended that the committee adopt a more conservative pressure limit within wells. The stakeholder group gave its endorsement to his recommendation.

But the MEC committee, when finishing its work on the draft well-stimulation rule, opted for the somewhat more tolerant limit on well pressure.

“We were disappointed in that,” Kelly said. But, he added, “I can’t say that that makes it a weaker rule,” he said.

Holbrook, like Kelly, lauded the rules’ requirements to monitor well pressure while fracking is underway.

“There will be more or less constant observation at the surface, checking for any leaks or anything escaping, whether it be gas or water,” he said.

Enforcing the drilling rules

Perhaps what’s most important is how the state will enforce the MEC’s rules.

According to Duke University geochemist Robert Jackson, it’s important to remember “the difference between the rules that are on the books and what’s actually done in the field.”

States need to ensure that well inspections are adequately staffed, and that “you have enough separation between the people doing drilling and the people watching over their shoulders,” Jackson said.

As currently written, the draft rules require that developers alert the N.C. Department of Environment and Natural Resources 48 hours before installing or cementing a well’s casings. This, the rule says, will allow the department staff to participate onsite as inspectors.

But the rules do not specifically require that DENR perform these inspections.

Walt Haven, the supervisor of DENR’s oil and gas program, maintains department staff will be onsite during major steps of the drilling process.

“We want to be out there for cement jobs in specific,” he said.

Haven added that – as has been the case with water wells – DENR can participate in inspections even without explicit approval in law or in regulations. If natural-gas developments proceed at a rapid clip though, the General Assembly might need to appropriate more funds for inspectors, he said.

In addition to its site inspections, DENR will be able to gather information from drillers’ reports, required within 30 days after wells are drilled and after the fracking is complete.

In the end though, even if the rules are strong, a gas well might spring a leak and present a threat to public health.

“You can never get to a place where all risk is eliminated,” said Kelly. “What we can try to do is provide the largest safety margin as possible.

“But we’re still going to need a robust inspection and enforcement program to go out and look at these wells, make sure they’re built the way they’re supposed to be built, that they’re operated the way they’re supposed to be operated and that well operators are abiding by the rules of their permits.”

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Gabe Rivin

Gabe is our former environmental health reporter from 2014-2016. He is a former editor of The Cooperative Business Journal, and a former reporter for Inside Washington Publishers, where he covered federal...