From the Associated Press (Dan Elliott) via CBS Denver:
Fewer than 5 percent of the region’s water wells that were checked for methane pollution had been tainted by oil and gas leaks, according to a study released Monday in the Proceedings of the National Academy of Science.
About 18 percent had methane that came from coal seams that underlie the area, the researchers said.
The other wells either had methane that couldn’t be definitively traced or had no detectable methane at all…
“I think it’s important for people to realize that being able to light your tap water on fire in many cases is a natural occurrence,” said Owen Sherwood, lead author of the study and a research associate at the University of Colorado.
“However, accidents do happen, leaks do happen,” he said.
The study looked only at the Denver-Julesburg Basin, an energy-rich formation in northeastern Colorado. The findings don’t necessarily apply to other formations because of differences in geology, drilling history and regulation, Sherwood said.
The $12 million study was funded by the National Science Foundation and got no money from the energy industry, Sherwood said.
Sherwood and five other researchers reviewed public records from the Colorado Oil and Gas Conservation Commission, the state’s energy regulator, from 1988 to 2014.
The records showed that 924 individual water wells were tested for methane after residents complained about pollution. Of those wells, 593 had detectable levels of methane, including 169 with methane that could be traced to coal beds and 42 with methane that could be traced to oil and gas production.
Researchers can distinguish between the two because they have distinct chemical footprints, Sherwood said. Methane from oil and gas production is also mixed with ethane, propane and butane, he said.
If the study couldn’t determine the source of the methane, it was usually because regulators hadn’t finished their investigation at the time the researchers retrieved the data in 2014, or because the case was so old that the available technology couldn’t identify the source.
Regardless of the source, the methane gets into water wells by first infiltrating an aquifer, a natural underground water reservoir, Sherwood said. It’s then drawn up into the well.
Researchers were able to trace groundwater methane pollution to a leak in a specific oil or gas well in 11 instances. In each case, the culprit was the surface casing — the lining inside the upper part of the well bore — in an older petroleum well drilled under now-obsolete rules, Sherwood said.
In all 11 instances, the well casing was too shallow by current standards for new wells. Six of those wells also had leaks in the casings.
The current rules, adopted in the mid-1990s, require the surface casing to extend 50 feet below the deepest aquifer in some areas. In the Denver-Julesburg Basin, that can be as deep as 1,200 feet, Sherwood said.
In none of those 11 instances could the leak be attributed to hydraulic fracturing, Sherwood said. Hydraulic fracturing, or fracking, injects water, sand and chemicals into a well bore to break open underground formations and release oil and gas.
In 2010, drilling companies began high-volume fracking, injecting the fluids perhaps 20 times at different locations in the same well, compared with three or four times under previous practice, Sherwood said.
But the number of documented incidents of water wells polluted by methane from oil and gas production each year didn’t change, he said.
“It’s relatively rare, a rate of about two cases a year” since 2000, Sherwood said.
Rob Jackson, an earth sciences professor at Stanford University who wasn’t involved in the research, said he thinks the study is sound, although he said a potential weakness is whether water sampling techniques were consistent over the years covered.
“I still like what they’ve done,” he said. The study highlights the importance of oil and gas well casing, he said.
From InsideClimateNews.org (Neela Banerjee):
The study, published in the Proceedings of the National Academy of Sciences on Monday, is the latest to pinpoint the sources and pathways of methane reported in residential drinking water near drilling sites, a concern to many communities as the fracking boom has spread across the country.
Environmental activists have asserted that fracking opens fissures underground along which methane, the main ingredient in natural gas, migrates from fossil fuel reservoirs into aquifers. Industry has maintained that residents’ water already contained methane before oil and gas activity began.
The Colorado study builds on several others published in the last few years, examining water from Texas to Pennsylvania. They all indicate methane can bleed from oil and gas wells if the metal casings inside the wellbore are not cemented completely or sealed deep enough underground.
“The bottom line here is that industry has denied any stray gas contamination: that whenever we have methane in a well, it always preexisting,” said Avner Vengosh, professor of earth and ocean sciences at Duke University, who read the paper but was not involved in the study. “The merit of this is that it’s a different oil and gas basin, a different approach, and it’s saying that stray gas could happen.”
All 11 wells with barrier failure were drilled before 1993 and did not undergo high-volume fracking and horizontal drilling. Further, they were not subject to new regulations adopted by Colorado in 1993 that set more stringent standards for cement casings inside new oil and gas wells.
Colorado’s adoption of tougher well-construction standards does not reflect national practices, however. Because Congress banned national regulation of fracking under the 2005 Energy Policy Act, standards for water and air protection around oil and gas sites vary by state.
There are also no laws governing the kind of cement that should be used. The cement used to hold the casings in place has to be “competent,” said Dominic DiGiulio, a visiting scholar at Stanford University and retired scientist from the Environmental Protection Agency. Petroleum engineers who work for the drilling company test the cement in a well and determine whether the seal is durable. But not every well is tested.
Industry has resisted efforts to standardize testing of the cement bond in fracked wells. The Bureau of Land Management’s draft fracking rules, recently struck down by a federal appeals court, call for testing the cement in fracked wells. The oil and gas industry has argued that it would be prohibitively expensive, estimating that would cost 20 times greater than the federal government has estimated.
Ensuring the integrity of the wellbore casing and cement job “isn’t a technical issue but a financial issue,” DiGiulio said. “The petroleum industry knows this technology but it’s not done on every single well, and that gets down to cost.”
Here’s the release from the University of Colorado:
The rate of groundwater contamination due to natural gas leakage from oil and gas wells has remained largely unchanged in northeastern Colorado’s Denver-Julesburg Basin since 2001, according to a new University of Colorado Boulder study based on public records and historical data.
The results also suggest that microbially-generated methane, rather than high-volume hydraulic fracturing, is the primary source of dissolved methane present in the area’s groundwater. Old and faulty oil and gas wells contribute a smaller percentage, with the risk of groundwater contamination due to a leak estimated to be between 0.12 percent of all the water wells in the region to 4.5 percent of the water wells that were tested.
Oil and gas development — particularly the introduction of horizontal drilling and high-volume hydraulic fracking — has generated public concern in Colorado over potential groundwater contamination due to the possibility of leakage from oil and gas wells. When present, natural gas can turn drinking water flammable, a safety hazard observed in numerous historical cases.
The researchers sifted through over 25 years of publically-available historical information in order to determine the sources and occurrence rate of methane and other gases in groundwater. All of the data were sourced exclusively from open records maintained by the Colorado Oil and Gas Conservation Commission (COGCC), a regulatory division of the state’s Department of Natural Resources.
The study was funded entirely by the National Science Foundation’s AirWaterGas Sustainability Research Network, which is based in Boulder, Colorado.
“The ability to do this kind of far-reaching impact study using public domain data is key,” said Owen Sherwood, a research associate with the Institute for Arctic and Alpine Research (INSTAAR) at CU Boulder and lead author of the new research. “This study highlights the immense value of a large, continuously updated and publically accessible geochemical database maintained by a regulatory agency.”
In data dating back as far as 1988, dissolved methane was discovered in 523 of the 924 water wells sampled, a rate of about 64 percent. However, based on a geochemical analysis, the researchers determined that 95.5 percent of that methane was generated by naturally-occurring microbial processes, a result of proximity to shallow coal seams criss-crossing northeastern Colorado.
Aside from the microbial methane, oil and gas wells have been found to leak methane and other natural gases such as propane and butane due to faulty or unsuitably shallow surface casings. Older gas wells built as far back as the 1970s were typically cased to a depth of approximately 300 feet, leaving the state’s deepest water aquifers unprotected from potential gas leaks. Updated regulatory standards have since required that new wells be cased far deeper and a number of older wells are currently being repaired.
Between 2001 and 2014 (the last year of complete data), dissolved gas that could be directly linked to deep oil- and gas-bearing formations affected 42 water wells in 32 separate incident cases, a rate of about two cases per year. That rate did not change after the introduction of horizontal drilling and high-volume hydraulic fracturing in the state in 2010. Eleven of those cases could be linked to older, vertical wells drilled before 1993. The remaining 21 cases were either settled privately with the landowner, or remain unresolved due to lack of data.
“This study incorporates a tremendous amount of hard data, but also considers individual case narratives so that we can see what happened in each particular instance of natural gas contamination,” said Joseph Ryan, a professor in the Department of Civil, Environmental, and Architectural Engineering at CU Boulder and a co-author of the new study. “It’s important to remember the human impact of this issue across the state.”
The new research is believed to be the most comprehensive study to date on the prevalence and sources of groundwater methane in Colorado using only public data. Previous studies have sampled fewer oil and gas sites and/or relied on data provided by industry stakeholders.