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Natural gas and chemicals may be seeping through compromised barriers in northeastern Colorado oil and gas wells, according to a federal study, but state regulators and other researchers caution that analysis may overstate the problem.

In sampling 2,573 wells in the Greater Wattenberg, the area roughly from Greeley to just north of Denver, the study found natural gas outside the protective barrier in 96% of the wells and benzene and other chemicals in almost all the 580 wells where water samples were taken.

The likely causes, the study said, are compromised steel casings or cement seals.

“We don’t have to speculate anymore about sources,” Joe Ryan, a study co-author and professor of environmental engineering at the University of Colorado, said in a statement. “This shows that many oil and gas wells could indeed be sources for contamination.”

The study was led by the Pittsburgh-based National Energy Technology Laboratory, NETL, in collaboration with CU, Johns Hopkins University in Baltimore, and Dalhousie University in Nova Scotia, Canada.

However, the Colorado Oil and Gas Conservation Commission staff and researchers at the Colorado School of Mines, who have also examined the issue of well integrity, say that the findings conflict with data from the larger Denver-Julesburg Basin, which includes the Wattenberg.

“The samplings are a subset of all the wells in the DJ Basin, not an entirety,” Megan Castle, a commission spokeswoman, said in an email response to Sun questions. “The findings of this subset of wells are not indicative of all DJ Basin wells.”

Wells began being drilled in the region in the 1970s and there are nearly 50,000 in the DJ Basin.

A 2018 study funded by the National Science Foundation, done by Colorado School of Mines researchers and some of the researchers on the NETL analysis, found a high risk of failure among wells drilled before 1980, but the risk declined in newer wells.

“It seems they are coming up with some universal findings, and that does not make sense in light of the results they had back then when we were part of that NSF study,” said Jennifer Miskimins, head of the Mines petroleum engineering department, who was not involved in either study.

Greg Lackey, an NETL researcher and lead author, said the study is a departure point for more research. “We want to understand if gas is migrating through cement or casing or whether it is migrating from lower strata.”

The analysis did not take the age of the wells into account. “That’s something for further study,” Lackey said.

The NETL analysis used data from gas and water samples collected by Colorado oil and gas operators and the COGCC in the space between the protective steel casing and cement seals and the outermost pipe.

An oil or gas well has a series of pipes within pipes. The innermost pipe, the production casing, carries the oil and gas to the surface, Between the producing casing and the outermost pipe is a protective steel casing and cement seals.

The protective steel and cement are set through any underground areas with freshwater aquifers to safeguard drinking water.

The COGCC requires oil and gas companies to periodically test for leaked gas, oil and water in the outer pipe. The results are kept in a publicly available database — the only one of its kind in the U.S.

The NETL researchers analyzed data for wells up to 2020.

“The wells in this study set were all identified for potentially having issues and therefore were sampled,” the COGCC’s Castle said. “Many of the wells indicated in this analysis are now plugged and abandoned.”

Through the sampling program the commission has identified operators with wells that may be problematic and they are asked to submit plans to bring those wells into compliance, Castle said.

The 2018 NSF study looked at 17,948 Wattenberg wells, 93% of which were producing oil and gas. This included 15,723 vertical or directionally drilled wells and 973 of the newer, deeper horizontal wells.

The study zeroed in on a set 787 wells in the southern end of the Wattenberg drilled on average before 1983 as the highest risk for barrier failures — with wells drilled in the 1970s having a 60% risk of failure.

Although these wells met the state regulations at the time of their completion, the study said their surface casing did not reach to the Fox-Hills aquifer, which is deeper in this area of the Wattenberg, and had inadequate production-casing-cement tops over oil and gas bearing zones.

“The assessment confirms that although natural-gas migration occurring in poorly constructed wellbores is infrequent, it can happen, and the migration risk is determined by the well-construction standards,” the study said.

The standards for drilling, completing and monitoring a well have been upgraded in the state several times since those 787 wells went into operation. The most recent revision in 2020 requires additional steel casing and cement to protect groundwater and for every well to be tested every year.

“Colorado’s regulations are the most stringent in the nation, and they call for this type of monitoring and reporting,” said Dan Haley, president of the Colorado Oil and Gas Association, an industry trade group. “When issues are identified, operators work with the state to mitigate and remediate any potential concerns.”

Still, environmental groups say the studies and ones conducted in other states, such as a Pennsylvania study by Cornell University Emeritus Professor Anthony Ingraffea, show there is a risk of well failures that need surveillance.

The group 350 Colorado has asked the COGCC to implement a comprehensive well-monitoring program including monitoring plugged and abandoned wells.

“We know from consultation with expert Tony Ingraffea that cement degrades over time, but our recommendations to the COGCC have gone unanswered,” Heidi Leathwood, the environmental organization’s climate policy analyst said.

Special to The Colorado Sun Twitter: @bymarkjaffe More by Mark Jaffe

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