NC Division of Air Quality
Estimate of Air Emissions from
Shale Gas Activities
in North Carolina
An estimate of potential emissions from
the development, production, processing and
transmission of natural gas from shale gas recovery
in North Carolina

September 2015

1

1 Market centers provide interconnections to other pipelines and provide short-term receipt/delivery balancing needs as well as other services that assist with gas transportation. They also provide some buyer/seller matching services and limited gas trading. (Natural Gas Market Centers: A 2008 Update, EIA, 2009)

Table of Contents

1Executive Summary

2Introduction

2.1Shale Gas Extraction

2.1.1Development

2.1.2Production, Processing and Transmission

2.2Pollutants of Concern

2.2.1Regulated Air Pollutants

2.2.2Other Unregulated Air Pollutants

3Key Assumptions

3.1North Carolina Shale Gas Formation Data and Assumptions

3.1.1Location of Shale Gas

3.1.2Number of Wells

3.1.3Potential Gas Recovery for a Single Well and Total Sub-Basin

3.1.4Annual Volume of Gas Produced and Development Timeframe

3.1.5Chemical Composition of NC Shale Gas

3.2Regulations

4Overall Emissions Estimation Methodology

4.1Emissions Calculations

4.2Uncertainties

5Summary of Estimated Air Emissions

6References

List of Appendices

Appendix ADevelopment Phase

Appendix BProduction Phase

Appendix CProcessing Phase

Appendix DGathering, Transmission and Distribution Phases

List of Tables

Table E-1.Summary of Criteria Air PollutantEmissions for Development, Production,
Processing, and Gathering/Transmission Activities

Table E-2. Summary of Key Hazardous Air PollutantEmissions for Development, Production,

Processing, and Gathering/Transmission Activities

Table 1.Classifications of Regulated Pollutants

Table 2.Sanford Sub-Basin Shale Annual Gas Production Estimate

Table 3.Chemical Composition of Sanford Sub-Basin Shale Gas Samples

Table 3a.Nation-Wide Average Gas Composition, in Volume Percent

Table 4. Summary of Criteria Air Pollutant Emissions for Development, Production, Processing, and Gathering/Transmission Activities

List of Acronyms

Acronym / Definition
AAL / Acceptable Ambient Level
BACT / Best Available Control Technology
bbl / Barrel
BTEX / Benzene, toluene, ethylbenzene, xylene
Btu / British thermal units
CAA / Clean Air Act
CAP / Criteria Air Pollutant
CenSARA / Central States Air Resource Agencies
cf / Cubic feet
CFR / Code of Federal Regulations
CH4 / Methane
CO / Carbon monoxide
CO2 / Carbon dioxide
CT / Combustion turbine
DAQ / North Carolina Division of Air Quality
DENR / North Carolina Department of Natural Resources
ft / Feet
FR / Federal Register
GHG / Greenhouse Gas
gal/MMcf / Gallons per million cubic feet
gal/yr / Gallons per year
g/hr / Gram per hour
g/hp-hr / Gram per horsepower-hour
g/mol / Gram per molecular weight
GVW / Gross vehicle weight
GVWR / Gross vehicle weight rating
H2S / Hydrogen sulfide
HAP / Hazardous Air Pollutant
hp / Horsepower
hp-hr / Horsepower hour
I/M / Inspection and maintenance
LDAR / Leak detection and repair
lb / Pound
lb/bbl / Pounds per barrel
lb/day / Pounds per day
lb/MMBtu / Pounds per million British thermal units
MACT / Maximum Achievable Control Technology
Mcf / 1000 cubic feet
MMbtu / Million British thermal units
MMcfg / Million cubic feet of gas
MMscf / Million standard cubic feet
MOBILE6 / Vehicle Emission Modeling Software Version 6
MOVES / Motor Vehicles Emission Simulator
MRI / Midwest Research Institute
NAAQS / National Ambient Air Quality Standard
NCGS / North Carolina Geological Society
NESHAP / National Emission Standards for Hazardous Air Pollutants
NGL / Natural gas liquid
NOx / Nitrogen oxides
NSPS / New Source Performance Standards
OSHA / Occupational Safety and Health Administration
NSR / New Source Review
PM / Particulate matter
PM2.5 / Particulate matterwith a diameter less than 2.5 microns
PM10 / Particulate matterwith a diameter less than 10 microns
ppm / Parts per million
REC / Reduced emissions completion (Green completion)
RICE / Reciprocating internal combustion engines
scf / Standard cubic feet
scf/hr / Standard cubic feet per hour
SCR / Selective catalytic reduction
SIP / State Implementation Plan
SL / Session Law
SO2 / Sulfur dioxide
TOC / Total organic carbon
tpy / Ton per year
US DOE / U.S. Department of Energy
US DOI / U.S. Department of the Interior
US EPA / U.S. Environmental Protection Agency
USGS / U. S.Geological Survey
VMT / Vehicle miles traveled
VOC / Volatile organic compounds

1Executive Summary

North Carolina has a shale formation in the Sanford Sub-basin (Lee, Chatham and Moore counties)which isreported to contain natural gasthat is recoverable for commercial purposes. In 2011, The North Carolina General Assembly directed the Department of Environment and Natural Resources (DENR) to study oil and gas exploration in the State and the use of newer horizontal drilling and hydraulic fracturing techniques (Session Law (S.L.) 2011-276). The results of the DENR study were published in a 2012report.1 In 2012, the General Assembly enacted legislation (S.L. 2012-143) which established a regulatory program for the management of oil and gas exploration and development activities, parts of which were amended in S.L. 2015-1. The legislation also required DENR to assess the (1) emissions from oil and gas exploration and development activities, including impact of truck traffic, (2) adequacy of the State’s air toxics program, and (3) potential impact of the emissions on ozone levels. In 2014 the General Assembly passed additional legislation authorizing the issuance of permits for oil and gas exploration, development, and production activities (S. L. 2014-4). This report documents DENR’s evaluation of air pollutant emission levels from shale gas activities as mandated in S.L. 2012-143 and 2015-1.

The first step to assessing the impact to air quality is to develop an emissions inventory from various activities associated with shale gas extraction. This involves identifying the potential sources of air emissions from each operational phase. Air emissions from each source can be estimated using various published emissions factors along with the expected amount of use or activity of each source. The emissions factors and activity data used to estimate emissions in this report are based on data obtained from shale gas development and production facilities located outside of North Carolina

Since drilling for natural gas has not begun,there is still much uncertainty as to where and how the development may occur, how much gas may be extracted, and the requirements to bring the gas to an end user. As the shale gas industry moves closer to actual drilling of wells and more information is obtained on the expected activities, the air emissions estimates presented here will be revisited to reflect actual conditions

The results presented here are the product of an exhaustive review of available reference materials to develop the best emissions estimate for North Carolina. In addition, this report has been peer reviewed by the following air quality personnel that have direct experience in this subject matter:

1

Revised Sept 2015

Mark Gibbs

Air Quality Division,

Oklahoma Dept. of Environmental Quality

Ona Papageorgiou, P.E.

Bureau of Air Quality Planning, Division of Air Resources,

New York State Dept. of Environmental Conservation

Allen Robinson, Ph.D.

Dept. Head,

MechanicalEngineering

Carnegie Mellon University

1

Revised Sept 2015

The data and assumptions associated with the shale gas formation that were used to estimate air emissions are listed below. This information primarily comes from the “North Carolina Oil and Gas Study”1conducted under Session Law 2011-276. Additional information was provided by Dr. Ken Taylor, Geological Survey Section Manager of the DENR Energy Mineral and Land Resources Division.

Key Assumptions:

  1. Well Drilling and Gas Recovery
  2. Gas recovery occurs in the Sanford Sub‐basin (59,000 acres)
  3. Cumulative gas produced by the field is 773 billion cubic feet (Bcf)
  4. Well spacing of 160 acres, total of 368 wells drilled
  5. Four wells drilled per pad, total of 92 pads
  6. Year of maximum activity is Year 6 per DENR’s Dr. Ken Taylor
  7. 121 new wells drilled and 247 producing wells in Year 6
  8. total produced gas is 151,605 million cubic feet (MMcf)in Year 6
  9. each well recovers 2,115 MMcf of raw gas over a 20 year life
  10. Composition of gas recovered is based on national average
  11. Daily emissions are assigned as annual emissions divided by 365
  1. Development Phase
  2. 40 CFR Part 60 New Source Performance Standards and 40 CFR Part 63 and National Emission Standards for Hazardous Air Pollutants regulatory criteria apply
  3. Directional horizontal drilling and fracturing is employed
  4. Non-road engines are used for drilling and pumping activities
  5. Average drilling time is 200 hours per well
  6. Each pad contains 4 wells
  7. No electrification of drilling pads
  8. Reduced Emissions Completion (Green Completions) is employed to control flowback emissions per 40 CFR 60 Subpart OOOO.
  1. Production Phase
  2. 40 CFR Part 60 New Source Performance Standards and 40 CFR Part 63 and National Emission Standards for Hazardous Air Pollutants regulatory criteria apply
  3. Peak production estimate of 151,605 MMcf/yr gas, from 247 gas producing wells
  4. Four gas producing wells per well pad
  5. One dehydrator/reboiler and wellhead compressor engine per well pad
  6. No recoverable condensate is present in the raw gas
  7. All processes are uncontrolled
  1. Processing Phase
  1. A single gas processing plant is assumed to be required in the Sanford Sub-basin
  2. Regulated as a stationary source requiring an air permit and subject to all applicable state and Federal rules
  3. Peak production of 151,605 MMcf/yr
  4. Condensate recovery is not required
  5. Acid gas removal unit required for hydrogen sulfide (H2S) removal
  1. Gathering / Transmission Phase
  2. 40 CFR Part 60 New Source Performance Standards and 40 CFR Part 63 and National Emission Standards for Hazardous Air Pollutants regulatory criteria will be met
  3. Total volume of gas leaving the processing plant is piped to one location
  4. One transmission compressor station, requiring an air permit,is located in the Sanford Sub-basin

Table E-1 provides a summary of annual and daily emissions estimates for criteria air pollutants. Based on the assumptions applied, it is estimated that NOx emissions in the Lee County area would increase 3.7 tons per day (tpd). The emissions contribution from mobile sources are estimated to represent about 15 percent of the total NOx emissions. The emissions of VOC are estimated to increase by 2.9 tpd with the majority of those emissions expected to occur during the production phase.

Table E-1. Summary of Criteria Air PollutantEmissions fromShale Gas Activities

Estimated Annual Emissions (tpy)
Criteria Air Pollutants
Phase / NOX
(tpy) / VOC
(tpy) / CO
(tpy) / SO2
(tpy) / PM10z
(tpy) / PM2.5
(tpy)
Development - mobile source contribution / 213 / 28 / 195 / 0.2 / 6 / 5
Development - nonmobile source contribution / 287 / 882 / 215 / 0 / 4 / 4
Production / 287 / 882 / 215 / 0 / 4 / 4
Processing / 146 / 59 / 34 / 6.7 / 5.2E-02 / 5.2E-02
Gathering / Transmission / 176 / 65 / 93 / 0.4 / 2 / 2
YR 6 Annual Emissions Increase with Shale Gas / 1,344 / 1,075 / 658 / 8 / 205 / 205
Sanford Sub-basin Annual Emissions w/o Shale Gas / 1,944 / 1,274 / 12,720 / 43 / 62 / 370
Total Annual Emissions with Shale Gas / 3,288 / 2,349 / 13,377 / 51 / 268 / 575
% Emissions Increase / 69% / 84% / 5% / 20% / 330% / 55%
Estimated Daily Emissions (tpd)
Criteria Air Pollutants
Phase / NOX
(tpd) / VOC
(tpd) / CO
(tpd) / SO2
(tpd) / PM10z
(tpd) / PM2.5
(tpd)
Development - mobile source contribution / 0.6 / 0.1 / 0.5 / 5.4E-04 / 1.5E-02 / 1.5E-02
Development - nonmobile source contribution / 1.4 / 0.1 / 0.3 / 2.5E-03 / 5.3E-01 / 5.3E-01
Production / 0.8 / 2.4 / 0.6 / 7.0E-04 / 1.1E-02 / 1.1E-02
Processing / 0.4 / 0.2 / 0.1 / 1.8E-02 / 1.4E-04 / 1.4E-04
Gathering / Transmission / 0.5 / 0.2 / 0.3 / 9.9E-04 / 5.5E-03 / 5.5E-03
YR 6 Daily Emissions Increase with Shale Gas / 3.7 / 2.9 / 1.8 / 2.3E-02 / 0.6 / 0.6

Table E-2 provides a summary of annual and daily emissions estimates for hazardous air pollutants (HAP). The emissions of formaldehyde and benzene are estimated to increase the most at 0.00 and 0.079 tpd respectively. The emissions of acetaldehyde and xylene are estimated to increase by 0.024 tpd each. The increase in the HAP emissions occur predominantly during the processing and gathering/transmissions phases.

Table E-2. Summary of Key Hazardous Air PollutantEmissions fromShale Gas Activities

The remaining sections in this documentdetail the basic concepts of shale gas extraction, the air pollutants of concern, North Carolina’s geological information and estimated gas production, and the overall methodology used and uncertainties within the estimates. The four appendices further explain the emission estimates for the development, production, processing, and transmission phases of shale gas extraction.

2Introduction

2.1Shale Gas Extraction

The natural gas found in the Sanford Sub-basin comes from the sedimentation of clay mixed with organic matter.1 Over time, the sediments becamelow permeability shale rock formations that do not allow the gas to move freely. Therefore, conventional techniques for developing natural gas wells cannot be used in these formations. Newer drilling techniques offer the ability to substantially increase the yield of natural gas from a well, making it more economically viable for shale gas formations.2 These new techniques include horizontal drilling and hydraulic fracturing. A more detailed discussion of horizontal drilling and hydraulic fracturing can be found in the 2012 DENR study report.

The three basic stages in the life of a gas well are development, production and reclamation.

Development refers to all activities associated with preparing for the extraction of natural gas including building infrastructure, transporting equipmentto the well sites, drilling, fracturingand completing the wells. Production begins immediately after development and includes all activities to extract, process, and transport the gas to an end user. After the well has reached its useful life, reclamation begins and the well is plugged and the land is reclaimed for other uses. Each of these stages has uniqueactivities, equipment and timeframes associated with them.

This report focuses on the development,production, processing, and transmission phasesand their associated emissions of air pollutants. These phases are discussed at a higher level in the following sections. Figure 1 outlines the different activities that are part of the shale gas phases. For a detailed discussion of all activities, sources, and air emission estimates from these phases, refer to the appendices at the end of the report.

Figure 1. Generalized Schematic of Shale Gas Phases

Phase / Activity or Equipment / Reference Section
1 / Development / Site preparation (land clearing, unpaved roads, truck trips, truck idling), well drilling and completion (drilling, drilling mud degassing, hydraulic fracturing, green well completion) / Appendix A
2 / Production / Blowdown, glycol dehydrator, reboiler, pneumatic controllers, heaters, equipment leaks, produced water tanks / Appendix B
3 / Processing / Acid gas removal (sweetening), compressor engines, glycol dehydrator, reboiler, liquid removal / Appendix C
4 / Gathering, transmission and distribution / Compressor engines (gathering, booster and high pressure), pipeline leaks / Appendix D

2.1.1Development

The development of shale gas wells includes a variety of activities andpotential air emission sources. For a given well, these activities do not occur simultaneously. Each activity has multiple sources of air emissions. Air emissions from well development activities are directly proportional to the number of wells being constructed and the depth to which the wells are drilled.

The development phase includes the following basic activities:

1)site preparation

2)transportation of equipment, supplies, and waste

3)drilling of the well, and

4)hydraulic fracturing of the well.

Site preparation includes all activities associated with constructing roads, well pads, pipelines, and other infrastructure that may be required to develop the wells and produce natural gas.

Drilling and fracturing equipment must be transported to the well pad as well as all supplies including water. Transportation may be provided through a variety of means including rail, short haul and long haul trucks, and cargo vans. Drilling and fracturing requiresapproximately two to four million gallons of water.2 It may be pumped from local water wells to the well pad or it may be transported longer distances via tanker trucks. Wastewater and other waste materials must also be transported and disposed of offsite. Wastewater may be transported long distances and even across state lines to approved disposal sites.

New directional drilling technology makes it possible to capture larger amounts of gas. This technique involves drilling a well vertically several thousand feet into the shale formation, then turning the drill horizontally to extend the well thousands of feet through the formation.2 Drilling of a well may occur from several days to several weeks and employs large diesel engines on portable drill rigs to power the drill.

Hydraulic fracturing increasesthe flow of natural gas from shale or other impermeable rock formations.2 The process involves perforating the well then injecting fracturing fluid under high pressure to fracture the shale or rock. The fractures allow natural gas to flow up through the well. Large diesel powered pumps are required to pressurize the fluid in the well bore for fracturing. This activity occurs over several days to over a week.

After the fracturing has taken place, a certain amount of the fracturing fluid flows back out of the well. This process is called “flowback”.2 As discussed above, the flowback water must be collected and stored on site until it is transported and disposed of off site. “Well completion” refers to the beginning of the flowback period until the well is shut in or until the gas from the well flows continuously to a gathering line or storage container. Large amounts of gas are also released during the flowback process. Historically, this gas was vented or flared. Newer federal rules require capturing the gas emitted during flowback for use or sale; unless the well is identified as a low pressure well, which are exempt from green completion requirements.11

2.1.2Production, Processing and Transmission

After the well development process is complete, the well moves into the production, processing and transmission phases. The air pollution emissions from production are primarily a function of the amount of gas processed annually and the distance it must travel.

Production can be broken up into the following phases that occur simultaneously;

1) production,

2) processing, and

3) gathering, transmission and distribution.

The first phase occurs at the wellhead where the gas is extracted from the well. Depending on the pressure of the gas exiting the well, a gas compressor may be required to increase the gas pressure to allow for adequate flow.2 Some of the gas processing occurs here because the raw gas contains natural gas liquids, water vapor, and other contaminates such as the particulatesthat must be removed from the gas stream prior to piping.