1. Improving Area Source Oil and Gas Emissions Estimates
Hi, I’m Michael Ege, and I’ve worked at the Texas Commission on Environmental Quality for almost 19 years, with a focus on estimating oil and gas emissions for Texas for the last 5 years. Today I will be talking about improving area source oil and gas emission estimates by using basin-specific factors.
Michael Ege, Emissions Inventory Specialist
Air Quality Division
Texas Commission on Environmental Quality (TCEQ)
2017 International Emissions Inventory (EI) Conference
Aug. 17, 2017

2. Overview Background information
How area source emissions are estimated
Oil and gas emissions submitted for the National Emissions Inventory (NEI)
Texas oil and gas inventory milestones
Development of tools/calculators used to estimate oil and gas emissions
TCEQ Excel spreadsheet calculator
Central States Air Resource Agencies (CenSARA) Excel spreadsheet calculator
Environmental Protection Agency (EPA) Access database tool
Since I will be the first speaker in the oil and gas track at the EPA’s Emissions Inventory Conference in Baltimore in August, I will briefly go over some background information. I will describe how area source emissions are estimated, talk about how oil and gas emissions are submitted to the National Emissions Inventory (or NEI) every three years, and go over some Texas oil and gas milestones. Then I will talk about three tools or calculators that were developed to help estimate oil and gas emissions.

3. Overview (cont.)
Developing basin-specific equipment profiles and emission factors
Using survey data
Using point source data
Using EPA Greenhouse Gas Reporting Program (GHGRP) data
Example: Updated compressor engine equipment profiles developed using GHGRP data
In the second part of my presentation I will discuss developing basin-specific equipment profiles and factors, using three types of data: survey data, point source data, and EPA Greenhouse Gas Reporting Program data. Finally, I will give you an example of how I used GHGRP data to develop updated compressor engine equipment profiles for the entire country.

4. How Area Source Emissions Are Estimated
Emissions are estimated at the county-level
Activity
Surrogate county-level data that is representative of the source being estimated
Examples include: population, employment data, amount of fuel purchased, and number of oil and gas wells
Emission Factor (EF)
Generally, factors that are applied nation-wide
Example: combustion factors from AP-42
Emissions = Activity x EF
When I talk about area source emissions, I am talking about emissions from small industrial, commercial and residential sources, things like restaurants or hospitals or even the water heater in your home. It also includes oil and gas well sites that are not large enough to have to report annual point source emission inventories. The TCEQ estimates these emissions at the county-level, normally using the equation seen here, where emissions equal activity times emission factor. The activity is surrogate data that is representative of the source being estimated. Examples would include population, employment data, the amount of fuel purchased, and the number of oil and gas wells in a county. And the emission factors are in pounds of pollutant per unit of activity, such as pounds of VOC per person. Generally, the emission factors are applied nation-wide.

5. How Area Source Oil and Gas Emissions Are Estimated
For oil and gas sources, the equation is modified slightly:
Activity
Emission Factor (EF)
Equipment profile
Number of pieces of equipment per well
Operating parameters of equipment
Amount of controls on equipment
Goal: develop basin-specific equipment profiles to improve emission estimates
Emissions = Activity x EF x Equipment Profile
For oil and gas sources however, the equation is modified slightly. Usually we can’t go directly from the activity data and use the emission factor to estimate emissions. Instead, we need to add an equipment profile. So for example, when estimating heater emissions from oil and gas sites, we don’t know how many heaters there are, but we do know how many gas wells there are, and that becomes our activity data. Then to estimate heater emissions, we need an equipment profile of average number of heaters per well, plus the average number of hours these heaters operate, and their fuel consumption. And so our goal becomes to develop basin-specific equipment profiles to improve emission estimates. Where we once used nation-wide or state-wide profiles, we now use basin-specific profiles for many oil and gas sources.

6. Background Information
Area source emissions are submitted for the NEI every three years
Texas began estimating area source oil and gas emissions using well count and production activity data for the 2002 NEI
The current Texas oil and gas calculator was developed in 2010, for the 2008 NEI
Through the 2008 NEI, Texas was one of only a handful of states submitting area source oil and gas emissions for the NEI
Area source emissions are submitted by states to the EPA for the NEI every three years. Because of the number of oil and gas wells in Texas, and the importance of their emissions in SIP work, the TCEQ has been estimating area source oil and gas emissions for a long time. We began using well count and production activity data to estimate oil and gas emissions for the 2002 NEI. This was the first version of our TCEQ calculator. Our current calculator was developed in 2010, for the 2008 NEI. Through the 2008 NEI, Texas was one of only a handful of states that was submitting area source oil and gas emissions to EPA for the NEI.

7. Background Information (cont.)
Tools developed to help estimate oil and gas emissions
TCEQ Excel spreadsheet calculator
CenSARA Excel spreadsheet calculator
EPA Access database tool
For the 2014 NEI, Texas estimated oil and gas emissions for:
189,706 active oil wells
104,446 active gas wells
A large part of the reason why other states weren’t submitting area source oil and gas emissions for the NEI was due to a lack of resources and expertise. To help states with their estimates, tools were developed. It started first with our TCEQ Excel spreadsheet calculator, which was used as a starting point to develop a CenSARA Excel spreadsheet calculator. Then, the CenSARA calculator was expanded to become an EPA Access database tool. I’ll describe these three calculators/tools shortly. But to get an idea of the scope of oil and gas activity in Texas, you can see here how many active oil and gas wells there were for 2014, the last NEI year.

8. Here is a map that shows the oil and gas wells in Texas as of January 2017, courtesy of my co-worker Raj Nadkarni. You can see that there is oil and gas activity throughout the state, but the heaviest concentrations are grouped in distinct parts of the state. In a couple of slides, I will show you a map of the oil and gas basins in Texas, that will show how they match up with where the wells are.

9. TCEQ Oil and Gas Calculator
Developed by Eastern Research Group (ERG) in a 2010 TCEQ project, for the 2008 NEI
Set of two Excel spreadsheet calculators
By updating the activity data, Texas oil and gas inventories can be developed for different years by TCEQ staff
Initially state-level equipment profiles
A number of additional studies and projects have refined many equipment profiles and emission factors to the basin-level
As I mentioned previously, our TCEQ oil and gas calculator was developed by ERG in 2010, for the 2008 NEI. It is a set of two excel spreadsheet calculators, that allow TCEQ staff to develop Texas oil and gas inventories for different years by inputting well counts and production activity data. Initially it used mostly state-level equipment profiles, and we have done a number of studies and projects to refine the equipment profiles and emission factors to the basin-level.

10. Texas’ Oil and Gas Basins and Shale Plays
Here is a map that shows the oil and gas basins in Texas. There are the 7 traditional basins, plus we have broken the Eagle Ford Shale area out of the surrounding Western Gulf Basin because of the number of horizontal wells drilled in that shale area over the past few years.

11. CenSARA Oil and Gas Calculator
Based on the TCEQ calculator
Developed by Environ in a 2012 CenSARA project, for the 2011 NEI
Refined the equipment profiles and emission factors to the basin-level using survey data
Focused on CenSARA states other than Texas (however, includes some Texas coverage since a few basins cross from neighboring states into Texas)
For basins with no survey data, CenSARA average factors were developed
Similar to our TCEQ calculator, Environ developed a CenSARA calculator for the 2011 NEI. This calculator refined the equipment profiles and emission factors to the basin-level using survey data. This calculator was developed to help the other CenSARA states estimate their oil and gas emissions, and so the survey data focused on the other states. There was some Texas coverage however, since some basins cross from neighboring states into Texas. For basins with no survey data, CenSARA average factors were developed from the rest of the data.

12. EPA Oil and Gas Tool Based on the CenSARA calculator
Developed by ERG in 2013 for the 2011 NEI
An Access Database tool
Used by EPA to estimate emissions for states that don’t submit their own estimates
Initially populated with basin-specific factors from CenSARA and TCEQ projects
For other basins, populated with the CenSARA average factors as a default
This led to EPA’s oil and gas tool. Developed by ERG in 2013 for the 2011 NEI, it is an Access database instead of an Excel spreadsheet due to the amount of data involved since it estimates emissions for the entire country. This tool is provided to states to help them estimate their state’s emissions if they don’t have better data or tools available, but it is also used by EPA to estimate emissions for states that do not submit their own estimates. It was initially populated with basin-specific factors from CenSARA and TCEQ projects, and with CenSARA average factors as a default for other basins.

13. EPA Oil and Gas Tool (cont.)
EPA encourages states to review the default factors, and to update the tool with state-specific factors
Several states and regional organizations have provided area-specific updates
For the 2014 NEI, ERG updated the tool with some basin-specific equipment profiles based on GHGRP data:
Storage tank controls
Pneumatic device counts
Heater equipment profiles
Compressor engine factors
Continue to look for ways to update factors
EPA encourages states to review the default factors, and to update the tool with state-specific factors. And several states (including Texas) as well as regional organizations have provided state-specific updates to the tool. For the 2014 NEI, a big update that was done was ERG updated the tool using GHGRP data for several source types listed here. EPA and states continue to look for ways to update the factors in the EPA tool.

14. Developing Basin-Specific Equipment Profiles and Emission Factors
To develop basin-specific factors, you need representative data
Three common types of data used for oil and gas sources:
Survey data
Point source data
GHGRP data
This brings me to the second half of my presentation, where I will talk about developing basin-specific equipment profiles and emission factors. To develop these factors, you need a source of representative data. For Texas, three common types of data that we have used include survey data, point source data, and GHGRP data.

15. Developing Basin-Specific Factors using Survey Data
Obtain data directly from oil and gas operators through surveys
Pros
State-specific (and often basin-specific, or even county-specific)
Represents actual real-world conditions
Cons
Time and cost intensive
Difficult to get a high response rate
Data can become outdated
Question of whether there is enough data to be representative
First I’ll talk about using survey data. Survey data is data obtained directly from oil and gas operators. This has been the method used most often in the past for Texas’ for the largest sources of oil and gas emissions. The pros of using survey data are that they are state-specific (and often area-specific), and the data represents actual real-world conditions. However, it takes a lot of time to do a survey, and they can cost a lot of money to conduct. It is also difficult to get a high response rate, and in the fast-moving oil and gas world, the data can become outdated. Finally, it is hard to know how much data is enough to be considered representative.

16. Examples of Texas Studies: Factors Developed from Survey Data
2014 Statewide Drilling Rig Emissions Inventory with Updated Trends Inventories (July 2015)
Specified Oil and Gas Well Activities Emissions Inventory Update (August 2014)
Hydraulic fracturing pump engines
Mud degassing
Upstream Oil and Gas Heaters and Boilers (August 2013)
Here I’ve listed some of our TCEQ studies that have used survey data to develop basin-specific factors. Most recently, we updated our drilling rig factors to account for the change in drilling rig fleet characteristics due to the increase in horizontal drilling in shale areas. We’ve also looked at hydraulic fracturing pump engines, mud degassing, and heaters.

17. Examples of Texas Studies: Factors Developed from Survey Data (cont.)
Condensate Tank Oil and Gas Activities (October 2012)
Pneumatic Device surveys (2011 and 2012)
Barnett Shale Special Inventory (2011)
Compressor engines
Piping component fugitives
Characterization of Oil and Gas Production Equipment and Develop a Methodology to Estimate Statewide Emissions (Nov. 2010)
There is also a condensate storage tank project that developed basin-specific factors, plus a couple of projects done in-house by TCEQ staff: a pair of pneumatic device surveys, and the Barnett Shale Special Inventory, which we’ve used to improve compressor engines and piping component fugitives. And here’s the project that started it all, the project that developed our TCEQ calculator.

18. Developing Basin-Specific Factors using Point Source Data
Review data submitted by oil and gas operators
Point source EI supporting documentation
Permit supporting documentation
Pros
Large amount of data available for some basins
Low (or no) cost
Cons
Can be time intensive, especially if the data is not in electronic format
Reporting threshold: is data representative of area sources, or just the larger sources?
The next source of data that can be used to develop basin-specific factors is point source data. This is data submitted by oil and gas operators such as supporting documentation included with annual point source EI’s and with permit applications. The pros of point source data are that there is a good amount of data available for many basins, and you can access it at little or no cost, assuming the supporting documentation is stored onsite somewhere at your agency. The cons are that it can be time intensive gathering the data, especially if you are having to review paper forms and hand enter the data into a spreadsheet. Also, since you are dealing with larger major sources, there is a question or whether the data is representative of area sources.

19. Examples of Texas Factors Developed from Point Source Data
Natural gas speciation and Volatile Organic Compound (VOC) content
Derived from Glycol Dehydrator calculations
Used the “wet stream” gas analyses to develop basin-specific speciation profiles
These profiles are used for gas well piping fugitives, pneumatic devices, and mud degassing emissions estimates
Condensate storage tank VOC emission factors and control factors
Data taken from sample calculations
Used to supplement survey data
Here are two examples of how point source data has been used to improve Texas’ oil and gas estimates. First, a natural gas speciation profile was developed for each basin, using information from glycol dehydrator calculations. The “wet stream” gas analyses were used to develop the basin-specific speciation profiles, and these are applied to gas well piping fugitives, pneumatic devices, and mud degassing emission estimates. And condensate storage tank data taken from point source emission inventory sample calculations was used to supplement the survey data in the condensate storage tank project mentioned a couple of slides ago.

20. Developing Basin-Specific Factors using GHGRP data
Review data submitted by oil and gas operators to the EPA GHGRP under Subpart W
Pros
Large amount of data available for many basins
Mandatory reporting results in good response rate
Data is current (2016 data will be available soon)
Data is available for free on EPA’s Envirofacts website
Cons
Reporting threshold: is data representative of all sources in a basin, or just the larger sources?
Shale areas are not broken out and may skew the data
One of the newest sources of data available to use has been EPA GHGRP data. This is data submitted by oil and gas operators to the EPA under Subpart W reporting. Because this program requires mandatory reporting, there is a large amount of data available for many basins. The data is also current and continues to be updated each year (with 2016 data available soon), and the data is available for free on EPA’s Envirofacts website. The negatives are that there is a question of whether the data is representative. The GHGRP has a reporting threshold of 25,000 metric tons of carbon dioxide equivalent per basin, so for some smaller basins only the larger companies are reporting data. Also, the data is reported at the traditional basin-level, and shale areas are not broken out. Since a large portion of recent activity has been from horizontal wells drilled in shale areas, and these wells typically have much higher production than vertical wells, this may skew the data for some basins. And I will give an example of this in a couple of slides.

21. Examples of Basin-Specific Factors developed from GHGRP data
ERG-developed factors for the EPA tool
Storage tank controls
Pneumatic device counts
Heater equipment profiles
Number of compressor engines per gas well
TCEQ-developed factors
Storage tank controls (survey data supplemented by GHGRP data)
Compressor engine horsepower (hp) sizes
Still, because the GHGRP is a new source of data, and because there is a lot of data available, several updated factors have been developed from this data in the past year or two. For the EPA tool for example, ERG developed updated basin-specific factors for storage tank controls, number of pneumatic devices per well, heater equipment profiles, and number of compressor engines per gas well. And I have also used the GHGRP data, first to supplement our survey data on amount of storage tank controls, and then to complement ERG’s compressor engine update, I developed updated compressor engine horsepower sizes.

22. Updated Compressor Engine Profiles developed using GHGRP data
Two types of basin-specific factors were developed:
Number of compressors per gas well
Average compressor engine hp sizes
GHGRP data is available from EPA’s Envirofacts website at:
Oil and gas data is available under Subpart W “Petroleum and Natural Gas Systems”
Now I’m going to go over how GHGRP data was used to develop these updated compressor engine profiles. Here’s a link to the EPA’s Envirofacts website. And on that site, the oil and gas data is available under the Subpart W link, which covers Petroleum and Natural Gas Systems.

23. GHGRP Data: Number of Compressors per Gas Well
Data taken from table EF_W_EQUIP_LEAKS_ONSHORE
Number of gas wellheads
Number of compressors
Adjustment made by TCEQ: removed data points where no compressors were reported (but gas wellheads were reported)
GHGRP data is a subset of all oil and gas sources
However, there were more gas wellheads reported in the GHGRP data than were present in the EPA tool for 10 out of 36 basins
Appeared that some oil wellheads were mistakenly reported as gas wellheads
First, the number of compressor engines per gas well were originally developed by ERG, using data from this table, which is equipment leak data for onshore sites. Included are the number of gas wellheads and the number of compressor engines per basin. For Texas, I made one adjustment to this data. I removed the data points where an operator reported gas wellheads but no compressor engines. This seemed strange, and after doing additional research, it appeared that some companies mistakenly reported their oil wellheads as gas wellheads. Because of the reporting threshold, the GHGRP data is a subset of the overall data. But when I compared the number of gas wells in the EPA tool to the number of gas wells reported in the GHGRP, for 10 out of the 36 basins with data reported, the GHGRP data was higher.

24. GHGRP Data: Number of Compressors per Gas Well
For most basins in Texas, the adjustments were minor:
Basin
Compressors per gas wellhead original
Compressors per gas wellhead adjusted
220 - Gulf Coast Basin (LA TX)
0.111
0.112
260 - East Texas Basin
0.052
0.057
350 - South Oklahoma Folded Belt
0.381
360 - Anadarko Basin
0.156
400 - Ouachita Folded Belt
0.316
415 - Strawn Basin
0.247
0.248
420 - Fort Worth Syncline
0.182
425 - Bend Arch
1.047
430 - Permian Basin
0.050
0.051
National average
0.077
0.087
Luckily for Texas, this resulted in just minor adjustments for the 9 basins with GHGRP data. Where it did make a larger impact was the nation-wide average. This factor went up by almost 15%, and this factor was applied to the basins in Texas with no GHGRP data.

25. GHGRP Data: Average Compressor Engine hp Sizes
Data taken from three tables and merged using the GHGRP facility ID number
EF_W_COMBUST_LARGE_UNITS
Basin-wide fuel usage by compressor engines
Carbon dioxide (CO2) emissions
EF_W_RECIP_COMP_ONSHORE
Number of compressor engines in each basin
EF_W_INTRODUCTION_SUMM
GHGRP facility ID number
Basin associated with facility ID
To go along with the updated number of compressor engines per gas well, I also developed average compressor engine horsepower sizes. When ERG originally updated their factors, it resulted in compressor engine emission estimates going down by 2/3rds. Well, the question I had was, are there fewer compressor engines in the GHGRP data because the compressor engines have gotten larger (with higher horsepowers)? To calculate the compressor engines horsepowers, I took data from three different GHGRP tables listed here. The first table provided a basin-level fuel usage and carbon dioxide emissions, the second table provided the number of compressor engines in each basin, and the third table allowed me to match up the data in the first two tables with the associated basins using the GHGRP facility ID number.

26. GHGRP Data: Average Compressor Engine hp Sizes (cont.)
Important to do some quality assurance checks to ensure the data is reasonable
Estimated CO2 emissions (based on fuel usage and AP-42 emission factors) were compared to reported CO2 emissions
Two data points were 1000x too high
One data point was 1000x too low
Average hp size for each data point was estimated using default engine parameters
hp’s > 2500 appeared to be too high
hp’s < 25 appears to be too low
I performed some quality assurance checks on the data to make sure it was reasonable. First, I estimated carbon dioxide emissions using the reported fuel usage and AP-42 emission factors, and compared these estimated emissions to the reported emissions. As you can see, I found a few data points where it was obvious that the wrong units were used for the fuel usage. And then I estimated an average horsepower size for each data point using default engine parameters. Resulting horsepowers above 2500 horsepower and below 25 horsepower appeared to be incorrect based on my review of the Barnett Shale Special Inventory data.

27. GHGRP Data: Average Compressor Engine hp Sizes (cont.)
Basin-level compressor engine runtimes were taken from the EPA tool
Since 95% of the load factors were 0.75 or 0.76, a load factor of 0.75 was used to develop these hp sizes
The GHGRP data was not subdivided into lean-burn and rich-burn engines, so average hp sizes were developed
Using the hp size data from the EPA tool, the average hp sizes were ratioed to get updated lean-burn and rich-burn hp’s
After doing these QA checks and removing the outliers, I then took the basin-level compressor engine runtimes from the EPA tool. Using a load factor of 0.75 to simplify the calculations, I then back-calculated basin-level average horsepower sizes using the fuel usage and number of compressor engines. One downside to the GHGRP data was that the data was not sub-divided into lean-burn and rich-burn engines. But using the original horsepower data from the EPA tool, the average horsepower sizes from the GHGRP data were ratioed to get updated lean-burn and rich-burn horsepowers. As I expected, most of the average hp’s calculated were larger than the previous factors. For the nation-wide average, the hp’s were about 75% higher, resulting in emission estimates decreasing by about half instead of 2/3rds.

28. GHGRP Data: Things to Consider
The GHGRP data is reported at the basin- level for most source types
Shale areas are not broken out from the basins, and can sometimes skew the data
Some source types have data reported at the county-level, so it may be possible to develop separate factors for shale areas versus non-shale areas
Example: TCEQ performed an in-depth review of storage tank controls, and was able to develop control factors for the Eagle Ford Shale area
From using GHGRP data for a couple of projects, I have found there are a few things that need to be considered. As I noted previously, GHGRP data is reported at the basin-level, and the shale areas are not broken out from the encompassing basins, which can sometimes skew the data. Some source types have GHGRP data reported at the county-level, so it may be possible to develop separate factors for shale areas versus non-shale areas. An example of this is work I did to develop updated storage tank control factors. Here I was able to develop control factors for the Eagle Ford Shale area separate from the Western Gulf Basin it is in.

29. Storage Tanks Controls
Comparison between EPA tool and TCEQ calculator storage tank control factors:
* The EPA tool does not break the Eagle Ford Shale area out of the Western Gulf Basin
Oil storage tanks
EPA tool
% controls
TCEQ calculator % controls
Western Gulf Basin
81.1
31.9
Eagle Ford Shale area
81.1*
83.6
Here is a comparison of the control factors ERG developed (where they didn’t break out the Eagle Ford Shale counties from the rest of the Western Gulf Basin) and the control factors I developed. As you can see, the factors I developed for the Eagle Ford Shale area match up pretty well with the factors that ERG developed. However, for the rest of the Western Gulf Basin, I came up with much lower control factors. And this makes sense; the OOOO regulations cover new storage tanks constructed after 2012, and most of the new wells in the Western Gulf Basin are in the Eagle Ford Shale area. So those storage tanks are more likely to have controls on them versus the older tanks in the rest of the basin.
Condensate storage tanks
EPA tool
% controls
TCEQ calculator % controls
Western Gulf Basin
78.8
43.3
Eagle Ford Shale area
78.8*
70.5

30. Project Reports posted on the TCEQ website
Air Quality Research and Contract Reports can be found at:
Reports include:
Growth Factors for Area and Point Sources
2014 Statewide Drilling Rig Emissions Inventory with Updated Trends Inventories
Specified Oil and Gas Well Activities Emissions Inventory Update
Upstream Oil and Gas Heaters and Boilers
Condensate Tank Oil and Gas Activities
Emission Factor Determination for Produced Water Storage Tanks
So that concludes my presentation. I’ve included this slide which lists our Project Reports website, so you can look up any of our reports that might interest you.

31. Contact Information
Michael Ege
(512)
TCEQ area source Web page
And here is my contact information in case you think of any questions in the coming days. But if you have any questions now, I’ll be happy to answer them. Thanks!