# Using Ambient Concentration Measurements to Quantify Volatile Organic Compound Emissions from Unconventional Oil and Gas Operations

## TL;DR

This study measures VOC emissions from unconventional oil and gas operations in Colorado, finding that drilling and coiled tubing operations emit the most pollutants.

## Contribution

The study introduces a new emission inversion method to quantify VOC emissions from specific unconventional oil and gas operations.

## Key findings

- Drilling with synthetic muds and coiled tubing operations have the highest median NMVOC emission rates of 2.8 g/s and 1.1 g/s.
- Flowback emissions of NMVOC and benzene are 96% and 98% lower than previously reported, due to improved management practices.
- The EPA's emission estimation tool underestimates VOC emissions from drilling mud volatilization and flowback completions.

## Abstract

Oil and gas (O&G)
development in the U.S. has accelerated in
the past two decades, aided by unconventional extraction techniques.
Potential environmental and health impacts of volatile organic compounds
(VOCs) originating from O&G activities have raised concerns, but
emission estimates remain highly uncertain. This study offers new
insights into operation-specific VOC emission rates during unconventional
O&G development (UOGD). We utilize dispersion model simulations
with a new emission inversion method to analyze four years (2019–2022)
of weekly air canister samples, measuring 48 VOCs at 10 monitoring
sites in Broomfield, Colorado, where several large multiwell pads
were drilled, completed, and entered production during the study period.
Emissions are characterized for well drilling, hydraulic fracturing,
coiled tubing/millout, flowback, and production operations. Drilling
using synthetic drilling muds and coiled tubing operations exhibit
the highest NMVOC emission rates, with median values of 2.8 g/s and
1.1 g/s, respectively. NMVOC and benzene emission rates during flowback
were 96% and 98% lower, respectively, than previously reported values,
highlighting the effectiveness of improved management practices in
reducing air pollutant emissions from what used to be often the most
significant emission source during UOGD. Our findings provide the
first report of VOC emissions from coiled tubing/millout operations
and show that the EPA’s nonpoint oil and gas emission estimation
tool underestimates VOC emissions from drilling mud volatilization
and flowback green completions.