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2010 ~.PR -7 PM 12: 46

TEXAS COMMISSION ON ENVIRONMENTAL QuAlflIn'filVISION

Bryan W. Shaw, Ph.D., Chairman

Buddy Garcia, Commissioner

Carlos Rubinstein, Commissioner

Mark R. Vickery, P.G., Executive Director

Protecting Texas by Reducing andPreventing Pollution

April 1,2010

Docket No. 2009-0801-SIP

Project No. 2009-018-SIP-NR

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Alfredo "AI" Armendariz, Ph.D., Regional Administrator

U.S. Environmental Protection Agency - Region 6

1445 Ross Avenue

Dallas, Texas 75202-2733

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Dear Dr. Armendariz:

On March 10,2010, the Texas Commission on Environinental Quality (Commission) adopted a revision to the

state implementation plan (SIP) for demonstration of reasonable further progress for the Houston-GalvestonBrazoria (HGB) 1997 eight-hour ozone nonattainment area.

The Commission adopted the HGB Reasonable Further Progress (RFP) SIP revision, demonstrating that the

RFP emissions reduction requirement will be met for the six-year period (2003-2008) beginning Janumy 1 ofthe

year following the year used for the baseline emissions inventory (2002) and all remaining three-year periods

after the first six-year period (2009-2011, 2012-2014, and 2015-2017) out to the area's attainment date (2019).

This SIP revision also sets the nitrogen oxides (NOx) and volatile organic compounds (VOC) motor vehicle

emissions budgets (MVEB) for transportation conformity purposes for the milestone years 2008, 2011, 2014,

2017, and 2018.

Enclosed are the proposed revision to the SIP, a public hearing certification, a complete record of the public

hearings, and the accompanying order. I look forward to your expeditious approval ofthis SIP revision.

Sincerely,

~~;dAtv- Bryan W. Shaw, Ph.D.

Chairman

BWS/ts

Enclosures

cc: The Honorable Rick Perry, Governor ofTexas

Mr. Toby Baker, Office ofBudget, Planning and Policy, Office ofthe Governor

.Mr. MarkR. Vickery, P.G., Executive Director, Texas Commission on Environmental Quality

P.O. Box 13087 Austin, Texas 78711-3087 512-239-1000 Internet address:www.tceq.state.tx.us

'.' " 'd
Texas Commission on Environmental Quality

Public Hearings

October 28 and 29. 2009

Concerning Revisions to the

HGB Eight-Hour Ozone Reasonable Further Progress SIP

Project No. 2009-018-SIP-NR
REVISION TO THE STATE IMPLEMENTATION PLAN FOR 

THE CONTROL OF OZONE AIR POLLUTION 

HOUSTON-GALVESTON-BRAZORIA 1997 EIGHT-HOUR 

OZONE STANDARD NONATTAINMENT AREA 

TCEQ 

TEXAS COMMISSION ON ENVIRONMENTAL QUALITY 

P.O. BOX 13087 

AUSTIN, TEXAS 78711-3087 

Houston-Galveston-Brazoria Reasonable Further Progress State 

Implementation Plan Revision for the1997 Eight-Hour Ozone Standard 

PROJECT NO. 2009-018-SIP-NR 

Adopted 

March 10, 2010 
HGB Reasonable Further Progress SIP Revision for the 1997 Eight-Hour Ozone Standard 

ix

LIST OF APPENDICES 

Appendix Appendix Name

Appendix 1 HGB Reasonable Further Progress Demonstration Calculations Spreadsheet 

Appendix 2 Development of Reasonable Further Progress Point Source Inventories 

Appendix 3 Development of Reasonable Further Progress Area Source Inventories 

Appendix 4 Development of Reasonable Further Progress Non-Road Mobile Source 

Emissions Inventories for Source Categories in the EPA’s NONROAD 2005 

Model 

Appendix 5 Development of Reasonable Further Progress Non-Road Mobile Source 

Emissions Inventories for Airports 

Appendix 6 Development of Reasonable Further Progress Non-Road Mobile Source 

Emissions Inventories for Locomotives 

Appendix 7 Development of Reasonable Further Progress Non-Road Mobile Source 

Emissions Inventories for Commercial Marine Vessels 

Appendix 8 Development of Reasonable Further Progress Non-Road Mobile Source 

Emissions Inventories for Drilling Rigs 

Appendix 9 Houston-Galveston-Brazoria 1997 Eight-Hour Ozone Nonattainment Area 

Reasonable Further Progress On-Road Mobile Source Emissions Inventories 
APPENDIX 8 

DEVELOPMENT OF REASONABLE FURTHER PROGRESS NON-ROAD MOBILE 

SOURCE EMISSIONS INVENTORIES FOR DRILLING RIGS 
Oilfield drilling rig diesel engines are included in the NONROAD model category “Other Oilfield 

Equipment” which includes various types of equipment. Due to the significant nature of the oil and gas 

exploration and production industry, the emissions inventory for diesel drilling rigs was selected to be 

included in a contract with Eastern Research Group, Inc. This appendix consists of portions of the report 

developed by ERG, entitled Emissions from Oil and Gas Production Facilities, relevant to the 

development of an inventory for drilling rig emissions. 
ERG No. 0227.00.001.001 

EMISSIONS FROM OIL AND GAS PRODUCTION FACILITIES 

DRAFT FINAL REPORT 

TCEQ Contract 582-7-84003 

Work Order No. 1 

Prepared for: 

Mr. Bertie Fernando, P.E. 

Texas Commission on Environmental Quality 

Air Quality Division 

Mail Code 206 

P.O. Box 13087 

Austin, Texas 78711-3087 

Prepared by: 

Eastern Research Group, Inc. 

1600 Perimeter Park Drive 

Suite 200 

Morrisville, North Carolina 27560 

August 21, 2007
TABLE OF CONTENTS 

Section Page

LIST OF TABLES......................................................................................................................... iii 

EXECUTIVE SUMMARY ........................................................................................................... vi 

1. INTRODUCTION ........................................................................................................... 1-1 

 1.1 Purpose and Objectives........................................................................................ 1-1 

 1.2 Report Organization............................................................................................. 1-2 

2. CHARACTERIZATION OF OIL AND GAS SOURCES INVENTORIED.................. 2-1 

 2.1 Definition of Oil and Gas Sources and SCCs ...................................................... 2-1 

 2.2 Emission and Activity Data Issues ...................................................................... 2-2 

 2.2.1 Onshore Exploration Sources .................................................................. 2-2 

 2.2.2 Onshore Production Sources.................................................................. 2-12 

 2.2.3 Offshore Production Sources ................................................................. 2-16 

3. SUMMARY OF 2005 BASE YEAR EMISSIONS......................................................... 3-1 

 3.1 Oil and Gas Emissions Summary ........................................................................ 3-1 

 3.2 Source Category Contributions by Pollutant ..................................................... 3-27 

 3.2.1 Carbon Monoxide Emissions................................................................. 3-27 

 3.2.2 Nitrogen Oxide Emissions ..................................................................... 3-27 

 3.2.3 Volatile Organic Compound Emissions................................................. 3-28 

 3.2.4 Sulfur Dioxide Emissions ...................................................................... 3-28 

 3.2.5 Particulate Matter Emissions ................................................................. 3-28 

 3.3 Comparison of Emissions by County ................................................................ 3-29 

 3.3.1 Onshore Exploration .............................................................................. 3-29 

 3.3.2 Onshore Production ............................................................................... 3-40 

 3.3.3 Offshore Production Sources ................................................................. 3-41 

 3.4 Comparison of Emissions by Attainment Status ............................................... 3-42 

i 
TABLE OF CONTENTS (Cont.) 

Section Page

4. EMISSION PROJECTIONS ........................................................................................... 4-1 

 4.1 Projections Methodology..................................................................................... 4-1 

 4.2 Summary of Oil and Gas Area Sources Projected Emissions.............................. 4-5 

5. REFERENCES ................................................................................................................ 5-1 

Appendix A – Documentation of Exploration Sources Emissions 

Appendix B – Documentation of Production Sources Emissions 

Appendix C – Documentation of Offshore Sources Emissions 

ii 
LIST OF TABLES 

Table Page

2-1a Identification of Source Categories Addressed in the Texas Oil and Gas Emission 

Inventory in the Onshore Exploration Grouping ............................................................. 2-3 

2-1b Identification of Source Categories Addressed in the Texas Oil and Gas Emission 

Inventory in the Onshore Production Grouping............................................................... 2-3 

2-1c Identification of Source Categories Addressed in the Texas Oil and Gas Emission 

Inventory in the Offshore Production Grouping.............................................................. 2-4 

2-2a Assignment of SCCs to Texas Oil and Gas Sources in the Onshore Exploration 

 Grouping .......................................................................................................................... 2-4 

2-2b Assignment of SCCs to Texas Oil and Gas Sources in the Onshore Production 

 Grouping .......................................................................................................................... 2-5 

2-2c Assignment of SCCs to Texas Oil and Gas Sources in the Offshore Production 

 Grouping .......................................................................................................................... 2-8 

3-1 Summary of Annual Statewide Criteria Pollutant Emissions.......................................... 3-2 

3-2 Summary of Ozone Season Daily (OSD) Statewide Criteria Pollutant Emissions ......... 3-4 

3-3 Summary of Oil and Gas Category Emission Contribution Rankings by Pollutant........ 3-6 

3-4a County-Level Annual and Ozone Season Daily (OSD) Criteria Pollutant Emissions 

 for Exploration Sources ................................................................................................... 3-8 

3-4b County-Level Annual and Ozone Season Daily (OSD) Criteria Pollutant Emissions 

 for Production Sources................................................................................................... 3-16 

3-4c County-Level Annual and Ozone Season Daily (OSD) Criteria Pollutant Emissions 

 for Offshore Platforms ................................................................................................... 3-24 

3-5 Combined County-Level Emission Estimates for All Sources Included 

 in the Inventory.............................................................................................................. 3-30 

3-6 Summary of Oil and Gas Area Source Emissions by Attainment Status ...................... 3-43 

4-1a Texas Counties in the Onshore-Gulf Coast EIA Region ................................................. 4-2 

4-1b Texas Counties in the Onshore-Southwest EIA Region.................................................. 4-3 

4-1c Texas Counties in the Onshore-Shallow EIA Region...................................................... 4-3 

4-1d Area-Blocks in the Offshore-Deep EIA Region .............................................................. 4-4 

4-2a Projected EIA Production ................................................................................................ 4-5 

4-2b Projected EIA Production (MMBtu)................................................................................ 4-5 

4-2c Final Projection Factors by EIA Region.......................................................................... 4-5 

iii 
LIST OF TABLES (Continued) 

Table Page

4-3a CO Projected Emissions by Location and Type .............................................................. 4-6 

4-3b NOx Projected Emissions by Location and Type............................................................. 4-6 

4-3c PM10 PRI Projected Emissions by Location and Type .................................................... 4-6 

4-3d PM2.5 PRI Projected Emissions by Location ................................................................... 4-7 

4-3e SO2 Projected Emissions by Location and Type ............................................................. 4-7 

4-3f VOC Projected Emissions by Location and Type ........................................................... 4-7 

iv 
LIST OF ACRONYMS 

Acronym Definition

API American Petroleum Institute 

CAPP Canadian Association of Petroleum Producers 

CBM Coal Bed Methane 

CERR Consolidated Emissions Reporting Rule 

CO Carbon Monoxide 

DOE U.S. Department of Energy 

EIA Energy Information Administration 

ERG Eastern Research Group 

GPA Gas Processors Association 

HARC Houston Advanced Research Center 

hp Horsepower 

H2S Hydrogen Sulfide 

MMBBL Million Barrels 

MMBTU Million British Thermal Units 

MMS Minerals Management Service 

MMscf Million Standard Cubic Feet 

Mscf Thousand Standard Cubic Feet 

MW Molecular Weight 

NEI National Emissions Inventory 

NH3 Ammonia 

NIF NEI Input Format 

NOx Nitrogen Oxides 

OFW Offshore Federal Waters 

OSW Offshore State Waters 

OE Onshore Exploration 

OP Onshore Production 

OSD Ozone Season Daily 

PM Particulate Matter 

PM10 PM with particle diameter less than 10 micrometers 

PM2.5 PM with particle diameter less than 2.5 micrometers 

SCC Source Classification Code 

scf Standard Cubic Feet 

SIP State Implementation Plan 

SO2 Sulfur Dioxide 

TCEQ Texas Commission on Environmental Quality 

TexAER Texas Air Emissions Repository 

THC Total Hydrocarbons 

TRC Texas Railroad Commission 

TXCO Texas Exploration Company 

US EPA United States Environmental Protection Agency 

VOC Volatile Organic Compounds 

WRAP Western Regional Air Partnership 

WYDEQ Wyoming Department of Environmental Quality 

v 
EXECUTIVE SUMMARY 

The purpose of this study was to compile a comprehensive emissions inventory for 

onshore and offshore oil and gas exploration and production facilities in Texas for the base year 

2005. The inventory was compiled for criteria pollutant emissions and ammonia (NH3) 

emissions as permissible with available emission factors. The emissions inventory will be used 

for general inventory compilation and tracking purposes, trends analysis, and potential control 

strategy development purposes. Related to this, the inventory will also potentially serve as 

improved input data to photochemical air quality dispersion modeling, emissions sensitivity 

analyses, State Implementation Plan (SIP), and rule development activities. 

This project addressed the development of an emissions inventory for oil and gas industry 

sources in Texas that have not been well characterized previously. The oil and gas exploration 

and production industry is a large and complex one with many different potential sources of air 

pollution. The larger sources such as refineries, bulk plants, and large transmission/distribution 

stations are generally well identified and typically treated as major point sources for inventory 

purposes. The Texas Commission on Environmental Quality (TCEQ) already has good quality 

inventories on these sources. The industry, however, contains many smaller and much more 

diffuse sources that occur in the course of exploring for oil and gas and bringing these products 

to the marketplace. Many of these sources fit the definition of being non-point or area sources, 

i.e., they have emissions below major source thresholds, they are large in number, and are 

geographically dispersed. Historically many of these area oil and gas sources have not been 

adequately inventoried. These “missing” source emissions, their identification and locations can 

be significant. 

The goals of this study were to identify the extent of the area oil and gas source 

categories, including defining new categories not previously identified, and to develop 

preliminary baseline emissions estimates for as many of the identified categories as possible 

using readily available data from studies completed in the last few years. The emissions 

estimates were developed using top-down, area source methods (i.e., the inventory was not 

intended to be on a source-by-source, bottom-up basis). This approach was taken to be 

consistent with the resources that are available for the project. The oil and gas industry in Texas 

is very large and diverse. Compiling an inventory on a point source basis for a state the size of 

Texas would be very resource intensive and costly. By applying these broader area source 

methods, preliminary emission estimates could be obtained that start to give some reference 

points for the level of emissions attributable to these previously uncharacterized sources. It also 

helps provide input on where effort should be placed in the future to refine and improve the data. 

The oil and gas source categories that were the focus of initial investigations included the 

following. Sources were organized into three groups – onshore exploration, onshore production, 

and offshore production. 

Exploration sources: 

• Drilling Rigs 

• Gas Well Completions 

• Oil Well Completions 

vi 
vii 

• Gas Well Pneumatic Devices 

• Oil Well Pneumatic Devices 

Production sources: 

• Wellheads 

• Compressor Engines 

• Dehydrators 

• Heater Treaters 

• Oil and Condensate Storage Tanks 

• Loading of Oil and Condensate for Transportation 

• Pump and Piping Component Fugitive Losses 

• Coal Bed Methane (CBM) Engines 

Offshore platforms: 

• Oil and Gas Platforms Operating in Texas State Waters (0-10 miles from shore) 

• Oil and Gas Platforms Operating in Federal Waters (>10-25 miles from shore) 

These are the source types included in the emissions inventory. In some cases, these source 

categories have multiple emission sources associated with them. For example, for Drill Rigs, 

emission estimates were assembled for drill rig power engines and for mud degassing operations. 

Emission estimates were constructed for each source at the county level. Both annual 

and ozone season daily emission estimates were calculated. Much of the activity data used to 

develop the emission estimates came from records maintained by the Texas Railroad 

Commission (TRC). The 2005 base year emission estimates were also projected to future years. 

Projection years included 2010, 2015, and 2020. A procedure involving the use of U.S 

Department of Energy (DOE), Energy Information Administration (EIA) oil and gas production 

growth estimates for the Texas region was used to perform the projections. 

For emissions of nitrogen oxides (NOx), onshore drilling rig engine and compressor 

engine sources were found to contribute the greatest amounts to statewide area source emissions. 

These two categories were responsible for roughly 95% of statewide emissions from oil and gas 

area sources. The largest sources of volatile organic compounds (VOC), comprising 62.4% of 

the state area sources total, were found to be onshore production glycol dehydrators (26.9%), 

onshore condensate storage tanks (22.9%), and onshore gas production wellheads (12.6%). 

Sulfur dioxide (SO2) emissions were dominated by onshore drill rig engines (97.4%). Similarly 

for carbon monoxide (CO), the largest oil and gas area sources were onshore production 

compressor engines (70.5%), onshore drill rig engines (21.8%), offshore platform compressor 

engines (3.6%), and onshore production gas well completions (1.7%). Emissions of particulate 

matter (PM), PM10 and PM2.5, were found to be dominated by onshore production drill rig 

engines (53.8% for PM10 and 53.3% for PM2.5) and onshore compressor engines (42.5% for 

PM10 and 43% for PM2.5). The final 2005 emission estimates were put into National Emissions 

Inventory (NEI) Input Format (NIF) to facilitate reporting to EPA under Consolidated Emissions 

Reporting Rule (CERR) requirements. 
1.0 INTRODUCTION 

1.1 Purpose and Objectives 

The purpose of this study is to compile a comprehensive emissions inventory for 

onshore oil and gas exploration and production facilities in Texas and for offshore 

production platforms (within 25 miles of the Texas coast) for the base year 2005. The list 

of onshore oil and gas sources addressed in the study, as defined in the Work Order, is as 

follows. 

Exploration sources including: 

• Drilling Rigs 

- diesel engines 

- degassing of drilling muds 

• Gas Well Completions 

- flaring 

- venting 

• Oil Well Completions 

- flaring 

- venting 

• Gas Well Pneumatic Devices 

• Oil Well Pneumatic Devices 

Production sources including: 

• Wellheads 

• Compressor Engines 

• Dehydrators 

• Heater Treaters 

• Oil and Condensate Storage Tanks 

• Loading of Oil and Condensate for Transportation 

• Pump and Piping Component Fugitive Losses 

• Coal Bed Methane (CBM) Pump Engines 

Offshore oil and gas production platforms were inventoried in both state waters off the 

coast, which spans from shore out to a distance of 10 miles, and in federal waters out to a 

distance of 25 miles (basically the band between 10 and 25 miles). The inventory was 

compiled for both criteria pollutant emissions and ammonia emissions. 

This study primarily pertains to the development of an emissions inventory for oil 

and gas industry sources in Texas that have not been well characterized previously. The 

oil and gas exploration and production industry is a large and complex one in Texas with 

many different potential sources of air pollution. The larger sources in the state such as 

refineries, bulk plants, and large transmission/distribution stations are generally well 

identified and typically treated as major point sources for inventory purposes. The TCEQ 

already has good quality inventories on these sources. The industry though contains 

many smaller and much more diffuse sources that occur in the course of exploring for oil 

8 
and gas and bringing these products to the marketplace. Many of these sources fit the 

definition of being non-point or area sources, i.e., they have emissions below major 

sources thresholds, they are large in number, and are geographically dispersed. 

Historically, many of these area oil and gas sources have not been adequately identified 

and inventoried. Identifying, locating, and quantifying these “missing” source emissions 

is a significant task. 

The goals of this study are to identify the extent of these area oil and gas source 

categories, including defining new categories not previously inventoried, and to develop 

preliminary baseline emissions estimates for 2005 for as many of the identified categories 

as possible using currently available data (i.e., time and resources for extensive surveys 

and/or new source testing are not available). Studies within the last three years by 

TCEQ, the Houston Advanced Research Center (HARC), and the Western Regional 

Partnership (WRAP) have produced data and methods that can be applied for the 

purposes of this inventory (HARC, 2005; HARC, 2006a; HARC, 2006b; WRAP, 2005). 

The emissions estimates were developed using top-down, area source methods (i.e., the 

inventory was not estimated on a source-by-source, bottom-up basis). Compiling an 

inventory on a point source basis would be very resource intensive and take much more 

calendar time than was available for this study. By applying broader area source 

methods, preliminary emission estimates can be obtained that start to give some reference 

points for the level of emissions attributable to these previously uncharacterized sources. 

It also helps provide input on where effort should be placed in the future to refine and 

improve the data. The study results will be used for general inventory compilation and 

tracking purposes, trends analysis, and potential control strategy development purposes. 

The results can also serve as improved input data to photochemical air quality dispersion 

modeling, emissions sensitivity analyses, SIP planning, and possible rule development 

activities. 

For planning purposes, the 2005 base year estimates were projected to future 

years 2010, 2015, and 2020. Also, the final base year inventory estimates were provided 

in National Emissions Inventory (NEI) Input Format (NIF) for the purposes of submittal 

to EPA in order to comply with Consolidated Emissions Reporting Rule (CERR) 

requirements, and to facilitate entry of the data into the state’s TexAER (Texas Air 

Emissions Repository) database. 

1.2 Report Organization 

Section 2.0 of this report more thoroughly identifies the oil and gas source 

categories addressed in the emissions inventory and describes how each emission source 

is being treated in terms of the inventory development. The emissions aspects of each 

category are described, along with an identification of the pollutants being inventoried for 

each. Each emission source is assigned a Source Classification Code (SCC) for tracking 

purposes and a table of all SCCs is presented. Section 2.0 provides explanations of any 

assumptions or manipulations that had to be made to source categories to facilitate the 

development of area source emission estimates. 

9 
The summary results of the 2005 emissions inventory development process are 

presented in Section 3.0. Summary emissions tables are provided on a statewide and 

county level basis for both annual and ozone season daily (OSD) emissions. The 

emissions estimates are described in terms of known uncertainties and weaknesses, and 

suggestions for possible improvements are provided. Discussion and analysis is also 

provided to compare and contrast how sources rank relative to each other for each 

pollutant. Emissions are also presented to show geographic concentrations by county. 

Section 4.0 presents information and data on the projection of the 2005 base year 

estimates to three future years (2010, 2015, and 2020). The data and methods used to 

construct projection techniques are described and statewide and county level emission 

estimate are provided for all three projection years. Section 5.0 contains reference 

citations for the report. 

The full documentation and detailed county level 2005 emissions estimates data 

for each inventoried source category are provided in Appendices A, B, and C. The 

appendices address the onshore exploration, onshore production, and offshore production 

source groupings, respectively. Each appendix discussion provides full and transparent 

documentation on how each category’s estimates were derived, the procedures and 

assumptions used, and the input emission factor and activity data applied to determine all 

emission estimates. 

10 
2.0 CHARACTERIZATION OF OIL AND GAS SOURCES INVENTORIED 

2.1 Definition of Oil and Gas Sources and SCCs 

The majority of the list of onshore oil and gas exploration and production source 

categories addressed in this project was taken from a Western Regional Air Partnership 

(WRAP) study on area source oil and gas emissions (WRAP, 2005). In the WRAP study, 

volatile organic compounds (VOC), nitrogen oxides (NOx), carbon monoxide (CO), and 

sulfur dioxide (SO2) emission estimates were generated for several non-point oil and gas 

sources in 14 states of the WRAP region (note: not all applicable pollutants were 

estimated for every source). Many of these same sources are prevalent in Texas. Other 

oil and gas emissions sources were specified by TCEQ and in oil and gas industry data 

produced by the Minerals Management Service (MMS) for offshore oil and gas platforms 

in Texas state waters and federal waters (MMS, 2004; TCEQ, 2007b). The TCEQ 

provided information on the names and location coordinates for over 200 oil and gas 

platforms located within 25 miles of the Texas coastline. The MMS information 

characterizes emissions from 16 platform emission unit types (e.g., boiler, engines, 

turbines, amine units, glycol dehydrators, fugitives) at the equipment level for base year 

2005. Currently, base year 2005 estimates are being finalized; however, MMS has 

provided authorization for TCEQ to use these draft data for the purposes of this project, 

provided the data are marked as draft and are not released, cited, quoted, or otherwise 

used outside of TCEQ until such time as MMS publishes the data as final. 

In this project, the oil and gas source categories have been divided into three 

major groups: onshore exploration sources, onshore production sources, and offshore 

production platforms. For exploration and production, depending on the definition of the 

operations used, there is clearly some potential for overlap occurring between some 

emission sources, i.e., a source such as completion venting could be considered 

exploration or production. For the purposes of this project and this memorandum, 

exploration, production, and offshore sources are defined as follows. 

Exploration sources include: 

• Drilling Rigs 

• Gas Well Completions 

• Oil Well Completions 

• Gas Well Pneumatic Devices 

• Oil Well Pneumatic Devices 

Production sources include: 

• Wellheads 

• Compressor Engines 

• Dehydrators 

• Heater Treaters 

• Oil and Condensate Storage Tanks 

• Loading of Oil and Condensate for Transportation 

11 
• Pump and Piping Component Fugitive Losses 

• Coal Bed Methane Pump Engines 

Offshore stationary sources include: 

• Oil and Gas Platforms Operating in Texas State Waters (sources 0-10 

miles from shore) 

• Oil and Gas Platforms Operating in Federal Waters (sources >10-25 miles 

from shore) 

Emission totals in Section 3.0 are presented according to these groupings. 

Table 2-1 (a, b, and c) provides a summary of the source categories evaluated in 

the emissions inventory (according to their grouping), the specific operations or processes 

that generate air emissions, and an identification of the pollutants associated with each 

source. Table 2-2 (organized as a, b, and c for the three groupings) further delineates 

these source category types into specific emission processes, and presents SCCs for each 

individual emissions process. For onshore exploration and production sources, most of 

the SCC assignments originate as new codes proposed by TCEQ (TCEQ, 2007a) or 

codes proposed by ERG as a result of assessing all of the emission processes included in 

the inventory. The offshore SCC assignments are a combination of ones on the official 

EPA list and ones proposed by ERG. 

2.2 Emission and Activity Data Issues 

This discussion further describes and clarifies the oil and gas emission sources 

included in the inventory. Factors affecting emissions are discussed and the rationales for 

using certain assumptions (related to source operation) for the purposes of the inventory 

are explained. General information is provided on how source emissions will be 

estimated. The detailed procedural description of the estimation processes and the 

accompanying input data and calculations are presented in Appendices A, B, and C. 

2.2.1 Onshore Exploration Sources

Drilling Rigs/Engines 

This category pertains to the engines used to generate power to run drilling rigs in 

the exploration field. These engines are assumed to be burning diesel fuel. Emission 

factors for diesel-fired engines operating drilling rigs were taken from AP-42 (US EPA, 

1996). Drilling rig engines were assumed to operate with a maximum horsepower (hp) 

greater than 600 hp (Engeser, 2004). For SO2 emissions, the weight percent of sulfur 

used in the diesel fuel (low sulfur fuel) is assumed to be 3400 ppmv or 0.34% by weight 

for every county in Texas (EPA, 2004b). It is possible that some counties in Texas may 

be using fuels with a lower or higher sulfur content. 

12 
Table 2-1a. Identification of Source Categories Addressed in the Texas Oil 

and Gas Emission Inventory in the Onshore Exploration Grouping 

Onshore Exploration 

Source Type Specific Emission Sources 

Potential 

Pollutantsa

Diesel engines to run electricity generators SO2, NOx, VOC, 

PM10, PM2.5, CO Drilling Rigs Drill mud degassing (open pits or storage 

tanks) VOC 

Emissions from flaring from the gas well 

completion phase CO, NOX, VOC 

Gas Well Completion Emissions from venting from the gas well 

completion phase VOC 

Emissions from flaring from the oil well 

completion phase 

CO, NOX, VOC, 

SO2 Oil Well Completion Emissions from venting from the oil well 

completion phase VOC 

Gas Well Pneumatic 

Devices 

Fugitive emissions from pneumatic devices 

used during gas well exploration and 

production 

VOC 

Oil Well Pneumatic 

Devices 

Fugitive emissions from pneumatic devices 

used during oil well exploration and 

production 

VOC 

a PM = Particulate Matter 

Table 2-2a. Assignment of SCCs to Texas Oil and Gas Sources 

in the Onshore Exploration Grouping 

Onshore Exploration Source 

Types and Emission Processes Proposed SCC SCC Description (abbreviated)a

Drilling Rigs 

- Diesel Engines 2310001200 ERG proposed SCC; Drilling Rig Engines 

using diesel fuel 

- Mud Degassing 2310001100 ERG proposed SCC; Mud Degassing Activities 

Gas Well Completion – Flaring 2310021701 ERG proposed SCC; Flaring during Gas Well 

Completions 

Gas Well Completion – Venting 2310021702 ERG proposed SCC; Venting during Gas Well 

Completions 

Oil Well Completion – Flaring 2310011701 ERG proposed SCC; Flaring during Oil Well 

Completions 

Oil Well Completion – Venting 2310011702 ERG proposed SCC; Venting during Oil Well 

Completions 

Gas Well Pneumatic Pumps 2310021401 ERG proposed SCC; Gas Well Pneumatic 

Pumps 

Oil Well Pneumatic Pumps 2310011401 ERG proposed SCC; Oil Well Pneumatic 

Pumps a

Unless otherwise noted, SCCs were obtained from EPA’s official SCC list (US EPA, 2004a). 

13 
All exploratory oil and gas drilling in Texas requires a permit. On the Texas 

Railroad Commission (TRC) website, a listing of year 2005 approved drilling permits 

was available, with the assumption being made that this would be typical for actual 

drilling activities that occurred in 2005. It is possible that drilling permits approved in 

2005, did not have actual drilling commence until 2006. Conversely, actual drilling may 

have taken place in 2005 under permit approvals made in 2004. An additional parameter 

retrieved for each approved permit is well depth. 

For most of the drilling permit data, the “spud date”, or the date in which drilling 

commenced, and the completed drilling date are included. Thus, actual number of 

drilling days can be calculated for each permit. Unfortunately, the effort required for 

obtaining this information for over 11,000 permits was time and resource prohibitive. As 

an alternative, representative drilling profiles were developed for each county and 

wellbore type (vertical, horizontal, directional, etc.) by obtaining the number of days 

drilled (from spud date and completed drilling date) for the permit with the maximum 

well depth. A total of 430 county-wellbore drilling profiles were developed and applied 

to over 11,000 permits. As expected, wellbore profiles that were “horizontal” took longer 

to drill significant depths when compared to “vertical” wellbores. Approximately 85% of 

identified drilling permits indicated the use of wellbore drilling. Using industry 

guidance, average horsepower ratings can be assigned for lightweight, intermediate, or 

heavyweight drilling operations (Engeser, 2004). These classifications are based on well 

depth. For example, lightweight rigs are generally used for well depths between 1,500 to 

2,000 meters (4,900 – 6,500 feet). The average horsepower for lightweight rigs is 650 

hp. Similar factors are available for intermediate and heavy weight rigs. Drilling 

operations are assumed to be 24-hours a day during the drilling period. Thus, total 

engine power output in terms of horsepower-hours (hp-hr) can be calculated for each 

permitted drilling operation, which in turn allows for the estimation of emissions.

14 
3.0 SUMMARY OF 2005 BASE YEAR EMISSIONS 

This section of the project report presents summarized results of the Texas area 

source oil and gas emission inventory development effort. Emission inventory estimates 

are presented on both statewide and county-specific bases according to the previously 

identified groupings of onshore exploration sources, onshore production sources, and 

offshore production sources (Section 3.1). In addition to presenting the inventory results, 

discussion is provided on the strengths and weaknesses of the inventory, inventory 

uncertainties, and possible improvements that can be made to the emission estimates. 

Section 3.2 describes how the various individual source categories compare and rank 

relative to each other for each of the estimated pollutants. 

Section 3.3 provides input on the level of emissions per county and what counties 

represent the largest share of statewide emissions. In Section 3.4, emissions are 

examined in terms of county attainment/nonattainment designations. The distribution of 

emissions by designation is presented. 

3.1 Oil and Gas Emissions Summary 

For the 2005 base year, emission estimates were prepared on both an annual and 

ozone season daily (OSD) basis. The specific details on how each category’s emissions 

were calculated can be found in Appendix A (for onshore exploration sources), Appendix 

B (for onshore production sources), and Appendix C (for offshore production sources). 

Any required derivations of activity or emission factor data are explained, and all data 

used for the derivations are shown. All applied equations are presented and discussed, 

and every variable, constant, and conversion factor used is defined and documented. 

Each source appendix section presents emission estimates (in tabular form) on an SCC 

basis for every applicable county in the state. All of these individual emissions data are 

summed to provide the tables in Section 3.0. Electronic Excel® spreadsheet files are 

provided along with this hard copy report that mimic all of the information in the 

documentation appendices. 

Table 3-1 presents a summary of annual statewide criteria pollutant emissions 

from individual area source oil and gas categories. Table 3-2 presents the same statewide 

information, but for emissions on an OSD basis as opposed to annual. The emissions 

data in Tables 3-1 and 3-2 are organized by the exploration, production, and offshore 

(divided into state and federal waters) groupings. As shown in Table 3-1, the largest 

amount of CO emissions (70.6%) comes from onshore production sources (primarily 

from natural gas compressor engines). Emissions of NOx are dominated by onshore 

exploration (54.2%) and onshore production sources (41.6%). Drill rig engines are the 

most significant NOx exploration category, while compressor engines are the major 

production-related NOx source. 

For VOC emissions, onshore production sources make up 85.1% of the total VOC 

and onshore exploration sources at 14.3%. The chief production sources contributing to 

VOC are glycol dehydrators (26.9%), condensate storage tanks (22.9%), and gas 

15 
16 

wellheads (12.6%). The onshore exploration grouping, namely drill rig engines, 

constitute 98.4% of SO2 emissions. Drill rig engines (onshore exploration) and 

compressor engines (onshore production) together are responsible for roughly 96.4% of 

PM (PM10 and PM2.5) emissions. The source category contributions are summarized by 

pollutant in Table 3-3. 

Table 3-1. Summary of Annual Statewide Criteria Pollutant Emissions 

Annual Emissions (tons/yr) 

Oil and Gas Emission Sources CO NOX PM10 PM2.5 SO2 VOC 

Onshore Exploration 

Drilling Rig Engines 27,442 119,647 1,998 1,954 13,697 3,183 

Mud Degassing -- -- -- -- -- 10,674 

Pneumatic Pumps-Gas Wells -- -- -- -- -- 73,474 

Pneumatic Pumps-Oil Wells -- -- -- -- -- 19,764 

Well Completions: Gas Wells 2,180 401 -- -- -- 19,764 

Well Completions: Oil Wells 74 14 -- -- 138 13,145 

Onshore Exploration Total 29,695 120,061 1,998 1,954 13,835 120,240 

Table 3-2. Summary of Ozone Season Daily (OSD) Statewide Criteria Pollutant 

Emissions 

Ozone Season Daily (tons/day) 

Oil and Gas Emission Sources CO NOX PM10 PM2.5 SO2 VOC 

Onshore Exploration 

Drilling Rig Engines 74.82 326.21 5.45 5.33 37.34 8.68 

Mud Degassing -- -- -- -- -- 29.10 

Pneumatic Pumps-Gas Wells -- -- -- -- -- 200.21 

Pneumatic Pumps-Oil Wells -- -- -- -- -- 182.12 

Well Completions: Gas Wells 5.94 1.09 -- -- -- 53.88 

Well Completions: Oil Wells 0.20 0.04 -- -- 0.38 35.81 

Onshore Exploration Total 80.96 327.33 5.45 5.33 37.72 327.88 

 
Table 3-3. Summary of Oil and Gas Category Emission Contribution Rankings by Pollu

CO Emissions 

Contributions 

NOx Emissions 

Contributions 

VOC Emissions 

Contributions 

PM10 Emissions 

Contributions 

PM2.5 Emissio

Contribution

Compressor Engines (OP) – 70.5% 

Drill Rig Engines (OE) – 54.1% 

Glycol Dehydrators (OP) – 26.9% 

Drill Rig Engines (OE) - 53.8% 

Drill Rig Engines (OE) - 53.3% 

Drill Rig Engines (OE) – 21.8% 

Compressor Engines (OP) – 41.2% 

Condensate Storage Tanks (OP) – 22.9% 

Compressor Engines (OP) – 42.5% 

Compressor Engi(OP) – 43% 

Gas Well Completions (OE) – 1.7% 

Natural Gas Turbines (OSW) – 1.5% 

Gas Wellheads (OP) – 12.6% 

Diesel Engines (OSW) – 1.9% 

Diesel Engines (OSW) – 1.9% 

All others - <1% each Compressor Engines (OFW) – 1.5% Crude Oil Storage Tanks (OP) – 9.1% All others - <1% each All others - <1% 

All others - <1% each 

Gas & Oil Well Pneumatic Devices (OE) – 8.7% 

Pump & Piping Fugitives (OP) – 5.1% Oil Wellheads (OP) – 4.1% Oil Loading (OP) – 3.2% Gas Well Completions (OE) – 2.4% Oil Well Completions (OE) – 1.6% Mud Degassing (OE) – 1.3% 

All others - <1% each 

17 
3.2 Source Category Contributions by Pollutant 

3.2.1 Carbon Monoxide Emissions

Total statewide emissions of CO for onshore exploration and production and offshore 

production sources are estimated to be 125,968 tons per year. The top contributor to this amount 

is natural gas compressor engines used for onshore production. Compressor engines were 

responsible for 70.5% of total CO emissions in the inventory. The next largest source after 

compressors was drill rig engines used in exploration, constituting 21.8% of the CO emissions. 

The next four largest CO contributors are offshore platforms-federal waters compressor engines 

(3.6%), gas well completions (1.7%), offshore platforms-state waters compressor engines 

(0.68%), and offshore platforms-state waters natural gas turbines (0.68%). These six categories 

generate nearly 99% of the CO statewide estimate from oil and gas area sources. 

3.2.2 Nitrogen Oxide Emissions

Similar to CO emissions, oil and gas area source NOx emissions are also dominated by 

onshore exploration drill rig engines and onshore production compressor engines. Total 

estimated NOx emissions for all oil and gas area sources included in this inventory are 221,357 

tons per year. Onshore exploration drill rig engines make up 54.1% of this amount, while 

onshore production compressor engines are responsible for 41.1%. The two categories combined 

generate over 95% of all estimated NOx emissions. The most significant of the remaining 

sources include offshore platforms-state waters natural gas turbines (1.5%), offshore platformsfederal waters compressor engines (1.5%), offshore platforms-state waters diesel engines 

(0.45%), onshore production heater treaters (0.44%), and offshore platforms-state waters 

compressor engines (0.38%). These seven categories constitute 99.4% of the NOx emissions 

estimated for oil and gas area sources statewide (including offshore sources). 

3.2.3 Volatile Organic Compound Emissions

Practically every source in the inventory emits VOC, some less than 1 ton a year, while 

others are estimated to release several hundred thousand tons per year. Total statewide VOC 

from the sources included in the inventory have been estimated at 841,295 tons per year. Five 

categories dominate this emissions total (80.2% of all VOC) – onshore production glycol 

dehydrators (26.9%), onshore production condensate storage tanks (22.9%), onshore production 

gas wellheads (12.6%), onshore production crude oil storage tanks (9.1%), and pneumatic 

devices associated with onshore production gas and oil wells (8.7%). Of the remaining VOC 

emissions sources, six are responsible for 17.5% of VOC emissions, making these 11 categories 

the source of nearly 98% of all oil and gas area sources VOC emissions. The six categories 

comprising the 17.5% of emissions consists of onshore production pump and piping fugitives 

(5.1%), onshore production oil wellheads (4.1%), onshore production oil loading (3.2%), 

onshore exploration gas well completions (2.4%), exploration oil well completions (1.6%), and 

onshore exploration mud degassing (1.3%). 

3.2.4 Sulfur Dioxide Emissions

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Estimated emissions of SO2 are clearly dominated by one source category – onshore 

exploration drill rig engines. This category is estimated to release 97.4% of the total SO2 

emissions from oil and gas area sources. The next largest source of SO2 is onshore exploration 

oil well completions at 138 tons per year or 0.98% of total emissions. Diesel engines and drill 

rig engines on offshore platforms-state waters are responsible for 0.56% and 0.44%, respectively, 

of total SO2 emissions. The remaining categories are estimated to be very minor SO2 emitters. 

3.2.5 Particulate Matter Emissions 

Contributions to PM10 and PM2.5 emissions track very consistently. Two categories 

dominate (over 96% of emissions) both PM10 and PM2.5 emissions – onshore exploration drill rig 

engines and onshore production natural gas compressor engines. The contributions to emissions 

are summarized as follows. 

PM10

 Drill Rig Engines – 53.8% of emissions 

 Compressor Engines – 42.5% of emissions 

PM2.5

 Drill Rig Engines – 53.3% of emissions 

 Compressor Engines – 43.0% of emissions 

The only other PM emissions category that is estimated to contribute at least 1% to total PM10 or 

PM2.5 emissions is diesel engines at offshore state waters platforms. This source category is 

responsible for approximately 1.9% of PM10 and PM2.5 emissions. All remaining PM10 and PM2.5 

categories are less than 1% contributors. 
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