VOC Concentration Increases Near Oil and Gas Well Drilling, Completion, and Production Operations

Growth in population and unconventional oil and gas development (UOGD) has increased the frequency of well pad development near residential neighborhoods in Colorado. Unfortunately, limited information is available about emissions of air toxics and other volatile organic compounds (VOCs) during UOGD operations, especially during well drilling and completions, leaving open questions regarding air quality impacts of these activities. Some detailed studies of VOC emissions during well development are also now approaching a decade old and may no longer reflect evolving UOGD practices. Increasing use of grid-powered electrified drill rigs, synthetic drilling muds, and closed-loop, tankless fluid handling systems, for example, have likely altered emissions in recent years. Here we report concentrations of VOCs at locations surrounding development of several new well pads in the Denver-Julesburg Basin (DJB). Measurements were made during drilling, hydraulic fracturing, millout, flowback and early production operations. VOCs were measured at multiple locations around the pads using integrated and plume-triggered canisters and online gas chromatography. We use these observations to assess potential acute and chronic exposure to air toxics for individuals living near UOGD operations and to constrain VOC emission rates during individual UOGD operations. These emission rates are compared to previously published values and used as inputs to the new TRACER pre-production emissions model that incorporates information about operational timelines and practices. The model is evaluated in terms of its ability, when combined with the AERMOD dispersion model, to accurately simulate neighborhood-scale air quality impacts during well drilling, hydraulic fracturing, flowback, and early production. Overall observations of studied DJB operations reveal that peak emissions are shifting from flowback operations to drilling and millout operations, that the composition of drilling emissions is increasingly dominated by C8-C10 alkanes attributed to degassing of synthetic drilling muds, and that emissions during early production cannot necessarily be assumed to be much lower than levels associated with well drilling and completions.