Hydrogen sulfide high at 53 wells, Noble says

Noble Energy is reporting dangerous levels of hydrogen sulfide gas have been measured at least once at dozens of its wells not just in Garfield County, but Weld County as well.

The company says 21 of its wells in the Piceance Basin have had levels at or above 100 parts per million on at least one occasion, as have 32 wells in the Grover oil and gas field in Weld County.

Short-term exposures at such levels can cause several health problems, and exposures lasting hours can cause death. But Noble Energy says safety protocols are in place to protect workers.

Noble Energy reported its findings as part of a response to allegations by state regulators that it failed to comply with requirements to report hydrogen sulfide gas encountered at oil and gas sites in the two counties.

Noble Energy also reported lower levels of hydrogen sulfide   at eight of its wells in Mesa County, several miles south of Parachute. Noble Energy spokesman Stephen Flaherty said gas chromatograph tests at those sites all found levels less than two parts per million. The highest reading for any of those wells was 50 ppm, using a less accurate test designed simply to confirm the presence of the gas for the sake of workers, he said.

Bureau of Land Management spokesman David Boyd said that when Noble Energy has experienced hydrogen sulfide at federal well pads in the Piceance, it hasn’t been in the natural gas itself, but in liquids at the sites, and it has been associated with some wells on a pad but not others. That suggests it was introduced, he said.

Noble Energy says insufficient data exists to know for sure.

Hydrogen sulfide is uncommon in the Piceance Basin and the Grover field. Stuart Ellsworth, the Colorado Oil and Gas Conservation Commission engineering manager, believes it was introduced into Noble Energy’s Grover wells, but because Noble recently bought wells there from another company, “I can’t really say that Noble’s operating procedures are what caused that.”

Noble Energy says that between 2009 and 2011, only two gas chromatograph readings have been at 100 ppm or higher in any of its Piceance wells.

Noble Energy has been using biocides and other methods to try to reduce hydrogen sulfide levels. Ellsworth said those efforts appear to be working. In 2009, about half of Noble Energy’s Piceance test results showed levels of the gas to be less than 10 ppm; this year 95 percent of wells are that low, Ellsworth said.

That supports Ellsworth’s belief that Noble’s operations somehow introduced hydrogen sulfide, such as through water used during drilling or hydraulic fracturing. If it were naturally present in natural gas formations, its levels probably would remain constant, he said.


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