Potential Sources of Methane Based Upon Isotopic Analyses in the Center of Natural Gas Development in Garfield County, Colorado

The development of natural gas in Garfield County, Colorado involves the drilling and hydraulic-fracturing (fracing) of individual well bores to attain optimal gas production from tight gas-bearing formations.  The geologic formations from which the gas is produced are more than a mile beneath fresh water-bearing zones that serve as water supplies for domestic or agricultural purposes.  Water-quality concerns have driven the Colorado Oil and Gas Conservation Commission (COGCC) as well as operators to initiate water-quality monitoring programs.  Garfield County has seen a significant increase in the number of gas wells completed since 2001.  Concerns have been expressed that increased drilling and fracing have lead to potential increases in chloride and methane concentrations in groundwater.  Sampling of groundwater quality prior to 2001 was sparse and intermittent, resulting in an erroneous conclusion that concentrations of chloride and methane are increasing with time and increased drilling in the area. Similarly, interpretations have been made, based upon isotopic analyses, that all of the methane detected in shallow groundwater is derived from the Williams Fork Formation, the primary gas producing formation.  Since 2001, the natural gas companies have implemented voluntary groundwater quality sampling programs prior to and after the completion of wells to assess potential impacts.  A critical analysis of the isotopic data based upon mixing calculations and other sources of data indicate that methane detected in domestic wells did not result from rapid migration through boreholes from gas wells or through fracing-induced fractures.  The COGCC continues to require groundwater monitoring in sensitive portions of the basin, and operators continue to collect pre- and post-drilling water-quality samples surrounding their operations, providing ample opportunity to realize changes should they occur in the future.  Lastly, operators continue to implement stringent drilling and fracing protocols to prevent impacts to water quality.