A variety of air toxics, ozone precursors, and methane are emitted from oil and gas production and from drilling and completion of unconventional oil and gas wells. Here we present the results of two studies of air emissions from drilling and completion of new wells in the Piceance Basin of western Colorado and from production activities and new well completions in the Denver-Julesburg (D-J) Basin on the Colorado Front Range. Each study made use of a tracer ratio method to quantify pad-level emissions. Acetylene was released at a controlled rate from the pad and measured downwind along with methane and a suite of 47 volatile organic compounds (VOCS). Methane and acetylene were measured using cavity ringdown spectrocopy and the VOCs were collected in canisters and analyzed by GC-FID. The acetylene concentration measured downwind of the site accounts for turbulent dilution in the emissions plume. The emission rates of methane and VOCs were quantified as the ratio of the background-corrected compound of interest to the background-corrected acetylene concentration multiplied by the acetylene emission rate. The highest emission rates of methane and many VOCs were found during flowback and during liquids offloading activities. Median activity emissions of methane ranged from a minimum of 0.051 g/s during fracking of new wells in the D-J to a maximum of 40 g/s during well flowback in the Piceance. Absolute methane emission rates from production sites in the D-J were observed to increase with production rate; on a relative basis most methane emissions fell below 0.8% of production. Median benzene emission rates from flowback were similar in the Piceance (0.062 g/s) and Front Range (0.069 g/s) and exceeded those from drilling, fracking, and production activities. AERMOD dispersion model simulations of annnual mean concentration increases of benzene around a hypothetical Front Range production site with a median benzene emission rate of 0.001 g/s were less than 0.1 ppbv at distances greater than 500 feet. Larger concentration increases are associated with higher emitting, shorter-term activities, especially flowback.

Emissions of air toxics, ozone precursors, and methane from production sites and new well drilling and completion activities in the Piceance and Denver-Julesburg basins of Colorado

253rd National Meeting (2017)

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