Quantification of Methane and Volatile Organic Compound Emissions from Oil and Natural Gas Production in the Uintah Basin

Advancements in unconventional oil and natural gas extraction techniques have dramatically increased both production and emissions of natural gas nationally and in Utah's Uintah Basin during the last decade. Natural gas has been proposed as a more climate friendly source of energy compared to coal, but emissions of methane as natural gas is produced, processed, and transported to consuming facilities can reduce or potentially negate climate benefits. The Uintah Basin has become an area of particular interest after a study by Karion et al. (2013) reported methane emissions from the entire basin of 6 – 12 % of production, significantly higher than rates derived from national-scale inventories of emissions from the oil and natural gas sectors. In addition to methane, natural gas and oil production in the Uintah Basin emits large quantities of volatile organic compounds (VOC) that have led to numerous severe wintertime ozone episodes in recent years. Of particular interest to this study are the aromatic compounds benzene, toluene, and xylene, which are air toxics and potent ozone precursors. Additionally, VOC can serve as marker species to identify emission sources of methane.

The University of Wyoming Mobile Laboratory, equipped with a Picarro Cavity Ring-Down Spectrometer to measure methane and an Ionicon PTR-TOF-MS to measure VOC, made direct measurements of emissions from well pads and pipeline leaks in the Uintah Basin during the 2015 Joint Air and Ground Uintah basin Air emissions Reconciliation (JAGUAR) field campaign. The EPA Other Test Method (OTM) 33a was used to quantify atmospheric emissions of methane and VOC from 31 well pads. Fluxes are determined in OTM 33a via rapid wind and concentration measurements that are used to model average emissions from a source as a Gaussian plume. To determine the potential contribution of well pad emissions to basin-wide VOC and methane emissions, mass-weighted averages are calculated. Well pads are found to constitute a significant fraction of basin-wide methane and VOC emissions. In addition, the variation of methane to VOC ratios from a single well pad is examined.