Air Toxics and Other Volatile Organic Compound Emissions from Unconventional Oil and Gas Development

Unconventional oil and natural gas (UONG) exploration and production have grown rapidly and are expected to increase further in the United States and internationally. Direct measurements of key air pollutant emissions from UONG are limited, especially during drilling and completion (hydraulic fracturing and flowback) of new wells. Knowledge of emission rates (ERs) of air toxics and other air pollutants from these activities is urgently needed to inform public policy. To address this key knowledge gap, we use a tracer ratio method to quantify pad-level, activity-specific [drilling, hydraulic fracturing (frocking), flowback, and production] ERs of 46 VOCs in the Denver-Julesburg (D-J, a mixed oil and gas play) and Piceance (primarily natural gas) basins in Colorado. Large differences in ERs of individual VOCs were observed across operation types, across facilities conducting the same operation type, and over time during a single operation. ERs of benzene and most VOCs were highest in both basins during flowback, when injected frocking fluids and produced water flow to the surface. ERs from production are much lower, an important result given the significant difference in the duration of activity (days to weeks for flowback vs decades for production). Frocking ERs of light alkanes and benzene were higher in the Piceance Basin than in the D-J Basin. Findings from this study provide important new information that can be used to evaluate potential health hazards and other air quality impacts of unconventional oil and gas activities in Colorado's two major oil and gas production basins.