Colorado study finds methane contamination water wells due to leaks, not fracking
DENVER -- Methane contamination of Colorado water wells from nearby oil and gas development is likely due to faulty oil and gas well completions rather than hydraulic fracturing, according to a new study of aquifer contamination in the state.
The study, published in the Proceedings of the National Academy of Sciences, is the latest to pinpoint the sources and pathways of methane reported in residential drinking water near drilling sites (pnas.org/content/early/2016/07/05/1523267113.full). Two of the study authors are affiliated with the University of Colorado in Boulder and one with California State Polytechnical University in Pomona.
A news report by Inside Climate News cites environmental activists, who assert that fracking opens fissures underground along which methane migrates from fossil fuel reservoirs into aquifers. The oil and gas Industry, however, maintains that residential water already contained methane before oil and gas activity began.
The study authors used an archive of geochemical data collected from 1988 to 2014 to determine the sources and occurrence of groundwater methane in the Denver-Julesburg Basin of northeastern Colorado. This 60,000-km2 region has a 60-year-long history of hydraulic fracturing, with horizontal drilling and high-volume hydraulic fracturing beginning in 2010. Of 924 sampled water wells in the basin, dissolved methane was detected in 593 wells at depths of 20–190 m.
Based on carbon and hydrogen stable isotopes and gas molecular ratios, most of this methane was microbially generated, likely within shallow coal seams. A total of 42 water wells contained thermogenic stray gas originating from underlying oil and gas producing formations. Inadequate surface casing and leaks in production casing and wellhead seals in older, vertical oil and gas wells were identified as stray gas migration pathways.
The rate of oil and gas wellbore failure was estimated as 0.06% of the 54,000 oil and gas wells in the basin (lower estimate) to 0.15% of the 20,700 wells in the area where stray gas contamination occurred (upper estimate) and has remained steady at about two cases per year since 2001
According to the authors, these results show that wellbore barrier failure, not high-volume hydraulic fracturing in horizontal wells, is the main cause of thermogenic stray gas migration in this oil and gas-producing basin.