Quantification of volatile organic compound emissions from unconventional oil and gas development

Collett, Jeffrey1 ; Zhang, Weixin1 ; Pan, Da1 ; Ku, I-Ting1 ; Zhou, Yong1

Published May 23, 2024; Updated Sep 16, 2024 on Dryad. https://doi.org/10.5061/dryad.g1jwstqzs

Abstract

Oil and gas (O&G) development in the U.S. has accelerated in the past two decades, aided by unconventional extraction techniques including hydraulic fracturing and horizontal drilling. Potential environmental and health impacts of volatile organic compounds (VOCs) originating from O&G activities in populated regions have raised concerns. In Broomfield, Colorado, six new O&G well pads were approved for development in 2017 and an air monitoring program was established in October 2018 to collect weekly and plume-triggered air samples. This study addresses the limited existing knowledge of activity-specific VOC emission rates from unconventional O&G development (UOGD), utilizing these observations and dispersion model simulations through emission inversion methods. Emissions are characterized from well drilling, hydraulic fracturing, coiled tubing/millout, flowback, and production operations.

Substantial variations in average VOC emission rates, determined using weekly canister observations, are observed across different UOGD phases. Drilling and coiled tubing/millout operations exhibit the highest VOC emission rates, attributed to hydrocarbon release from shale formations and drilling mud. In contrast, hydraulic fracturing gives lower emission rates, consistent with injection of fluids into the well, minimizing the probability of subsurface hydrocarbon emissions. Diesel-powered engines are identified as the primary ethyne sources during hydraulic fracturing. Production was characterized by lower VOC emission rates than pre-production phases but remains an important emission category due to its long duration (decades). Internal variations of emission rates within each phase highlight the complexity of factors and activities influencing emission rates, including, for example, vertical vs. horizontal drilling and periodic maintenance activities. VOC emission rates associated with drilling mud volatilization and hydraulic fracturing suggest that previously published emission estimates (EPA (2022), and Hecobian et al. (2019)) underestimate VOC emission rates during these activities. Significantly lower emission rates during flowback compared to previous work (Hecobian et al., 2019) reveal how improved management practices, including tankless, closed-loop fluid handling systems have effectively reduced what used to be a dominant source of pre-production VOC emissions. Plume-triggered samples, capturing transient high-concentration plumes, reveal short-term VOC emission rates approximately ten times higher for drilling and flowback than determined from weekly samples. In the case of flowback, short-term emission pulses have been linked to periodic emptying of sand canisters used to trap fracking sand emerging from previously fracked wells.

README: Quantification of Volatile Organic Compound Emissions from Unconventional Oil and Gas Development

https://doi.org/10.5061/dryad.g1jwstqzs

Versioning

Version 2 (September 2024): In this version, the AERMOD simulations for weekly canister samples use WRF-observation hybrid wind direction as input.
Version 1 (May 2024): In this version, the AERMOD simulations for weekly canister samples use WRF wind direction as input.

Overview

This dataset contains comprehensive data on emission rates and concentrations of volatile organic compounds (VOCs) during various operations of unconventional oil and gas development (UOGD) in Broomfield, Colorado, spanning from 2019 to 2022. It comprises both observed concentration from weekly and plume-triggered canister samples and simulations from the AERMOD dispersion model.

Data files and description

This dataset contains the following data:

Emission rates based on weekly canister samples for 51 individual VOCs during drilling, hydraulic fracturing, coiled tubing/millout, production tubing installation, flowback, and production operations of UOGD from six large well pads developed in Broomfield, Colorado between 2019 and 2022. These six well pads are Livingston (LS), Northwest A (NWA), Northwest B (NWB), United (UT), Interchange A (ICA), and Interchange B (ICB).
The observed concentrations of 51 individual VOCs from weekly average canister samples collected at ten monitoring sites in Broomfield between 2019 and 2022. The ten monitoring sites are Commons (COM), Interchange 01 (ICT01), Interchange 02 (ICT02), Interchange 03 (ICT03), Livingston 01 (LS01), Livingston 02 (LS02), Northwest Parkway 02 (NWP02), Northwest Parkway 03 (NWP03), United 01 (UT01), and United 02 (UT02).
AERMOD dispersion model simulated weekly average concentrations at each monitoring site (receptor) from each well pad (source) with a unit emission rate (1 g/s). The simulations correspond with the sampling time of weekly average canisters.
Emission rates based on plume-triggered canister samples for 51 individual VOCs during drilling, coiled tubing/millout, and flowback operations in Broomfield, Colorado between 2020 and 2022.
The observed concentrations and extrapolated 1-hour concentrations of 51 individual VOCs from 54 plume-triggered canisters. Among the 54 canisters, 34, 6, and 14 samples were collected during drilling, coiled tubing/millout, and flowback operations, respectively.
AERMOD simulated hourly concentrations for the 54 plume-triggered samples using wind rotation method. In this simulation, sources and receptors correspond with the emission well pads and sampling sites of each triggered sample.
The operational timelines of six large well pads in Broomfield, Colorado.

Description of the data and file structure

This dataset contains 204 CSV files in total, while 192 of them are in a ZIP file ("CSU_Broomfield_Weekly_Raw_Data.zip"). Missing values are represented as "NA" in all files.

Seven files provide emission rates of 51 individual VOCs for seven operations including (1) drilling using Gibson mud; (2) drilling using Neoflo mud; (3) hydraulic fracturing; (4) coiled tubing/millout; (5) production tubing installation; (6) flowback; and (7) production operations based on weekly canister samples. All units are in "g/s". The name of each file contains the operation type. Within each file, the 1st and 2nd columns provide the "Start Date" and "End Date" of each weekly sample (format: yyyy-mm-dd) and the 3rd to the 53rd columns are emission rates of 51 VOCs with the VOC names provided in the first row. These files are: "CSU_Broomfield_Weekly_VOC_Emission_Rate_Drilling_Gibson.csv", "CSU_Broomfield_Weekly_VOC_Emission_Rate_Drilling_Neoflo.csv", "CSU_Broomfield_Weekly_VOC_Emission_Rate_Hydraulic_Fracturing.csv", "CSU_Broomfield_Weekly_VOC_Emission_Rate_Coiled_Tubing.csv", "CSU_Broomfield_Weekly_VOC_Emission_Rate_Production_Tubing_Installation.csv", "CSU_Broomfield_Weekly_VOC_Emission_Rate_Flowback.csv", and "CSU_Broomfield_Weekly_VOC_Emission_Rate_Production.csv".
Three files provide emission rates of 51 individual VOCs for three operations including (1) drilling using Neoflo mud; (2) coiled tubing/millout; and (3) flowback operations based on plume-triggered samples. All units are in "g/s". The name of each file contains the operation type. Within each file, the 1st column provides the "Triggered Time" of each triggering event (format: yyyy-mm-dd hh:mm:ss) and the 2nd to the 52nd columns are the emission rates of 51 VOCs with the VOC names provided in the first row. These files are: "CSU_Broomfield_Triggered_VOC_Emission_Rate_Drilling_Neoflo.csv", "CSU_Broomfield_Triggered_VOC_Emission_Rate_Coiled_Tubing.csv", and "CSU_Broomfield_Triggered_VOC_Emission_Rate_Flowback.csv".
"CSU_Broomfield_Weekly_Raw_Data.zip": this contains 192 CSV files. One single file corresponds to one week's observed and simulated concentrations for 51 individual VOCs. All units are in "microgram per cubic meters (ug/m3)". The name of each file contains the weekly information. For example, "2019-7-5_2019-7-11_week-11.csv" is for the week of July 5 to July 11, 2019, and this is the eleventh week among 192 weeks. Within each file, the first column, "Stations", is the monitoring site. The 2nd to the 52nd columns are the concentrations of each VOCs from the weekly canisters collected at the 10 monitoring sites (e.g., column "obs_CH4" is the observed concentration of methane). The 53rd column is the AERMOD simulated weekly average concentrations from LS pad to 10 monitoring sites with a unit emission rate (1 g/s), while the 54th to 58th columns are the AERMOD simulations from NWA, NWB, ICA, ICB, and UT pads, respectively.
"CSU_Broomfield_Triggered_Samples_Raw_Data.csv": this contains the raw data for the 54 triggered samples. This file contains the operation type, sampling site, emission source, sampling start time, sampling end time, concentrations of 51 VOCs, 1-hour estimated concentrations of 51 VOCs, 1-hour average temperature, and AERMOD simulated concentration from the emission source to the receptor for each triggered sample. The second row presents the unit for each variable if applicable. The 6th to 56th columns are concentrations of 51 VOCs, which are the concentrations from the triggered samples directly. The 57th to 107th columns are 1-hour estimated concentrations for 51 VOCs.
"CSU_Broomfield_Wellpad_Operation_Timelines.csv": this contains the start date and end date for each operation of each well pad.

Sharing/Access information

Dr. Collett and his group are currently working on manuscripts based on this data.