Page 1 of 5 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF

AIR AND RADIATION



### Petroleum and Natural Gas Systems (Subpart W) of the Greenhouse Gas Reporting

Rule

Docket: EPA-HQ-OAR-2009-0923

Title: Portable Combustion Emissions

Summary: This memo discusses how EPA evalua ted data on portable GHG emissions to

determine what portion of the GHG emissi ons from the onshore production petroleum

and natural gas industry segment are coming from portable equipment.Page 2 of 5 

### Portable Combustion Emissions

EPA received numerous comments from th e April 2010 proposal for 40 CFR Part 98 –

Subpart W Petroleum and Natural Gas Syst ems of the Greenhouse Gas Reporting Rule

on whether or not portable greenhouse gas ( GHG) emissions should be included as an

emissions source for the onshore production se gment. In response to those comments

received, EPA evaluated data on portable GHG emissions to determine what portion of

the GHG emissions from the onshore producti on petroleum and natural gas industry

segment are coming from portable equipment.

EPA determined that 45 percent of the CO 2 

### e emissions from the onshore production

segment originate from portable equipment combustion and process emission sources.

EPA based this finding on the process and co mbustion emissions from onshore petroleum

and natural gas sources fr om the U.S. Inventory 1 

### with corrections for under-estimated

sources (see Section 4.C and Appendix B of the Technical Support Document to final

subpart W in docket EPA-HQ-OAR-2009-0923) . EPA then made assumptions on

stationary and portable equipment base d on the Natural Gas STAR Program data 2 

### , further

collaboration with industrial partners in the Natural Gas STAR Program and on expert

opinion. With these analyses, subpart W covers 85% of the emissions (including

stationary combustion and pr ocess emissions) from the onshore petroleum and natural

gas production industry segment , from 3% of the onshore production owner-operator

companies only by including the portable eq uipment emissions in the rule. Excluding

portable equipment emissions would reduce th e coverage well below 55% of emissions

because many facilities (basins) do not have significant well liquid unloading emissions

(34% of total onshore production).

Portable Equipment Emission Sources

EPA reviewed emission sources in the 2006 U. S. Inventory and those estimated in the

Technical Support Document (TSD) to determine what emissions originate from

equipment that fits the defin ition of “portable equipment.” EPA determined that portable

equipment in the onshore production segment cer tainly includes all drilling rigs and

workover rigs. Therefore, all combustion from th ese equipment (17% of total) as well as

all process emissions associated with drilli ng and workover operations, primarily venting

gas hydraulic fracturing completions (8% of total) would be excluded without portable

equipment included. Furthermore, EPA has determined that most wellhead equipment

such as compressors, dehydrators and heater-t reaters are skid mount ed and thereby could

be considered portable. Indeed, EPA has learned that many owner-operators move

equipment such as glycol dehydrators that move from well to well when the production

rate from one well declines below producti on rate to operate effectively. Therefore,

considering that this type of wellhead equipm ent is portable, the sum from drilling rigs

and workovers, plus production gas fired compressor engines (17%), production gas

fueled dehydrators and heater-treaters (3%), and the total portable equipment contribution

1 EPA. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 – 2008 . April 2010, U.S. EPA #

430-R-10-006. <http://epa.gov/climatech ange/emissions/usinventoryreport.html>.

2 Onshore Production Basin Threshold Analysis EPA-HQ-OAR-2009-0923Page 3 of 5 

### to onshore production emissions is 45%. The wellhead equipment considered to be

portable by subpart W includes:

1) Petroleum Systems Compressors and Engines

2) Natural Gas Systems Compressors and Engines

3) Petroleum Heater-Treaters

4) Petroleum Drilling Rigs

5) Natural Gas Drilling and Workover Rigs and Unconventional Well Completion Vents

6) Dehydrator Reboilers

Appendix B in the TSD (docket EPA-HQ-OAR -2009-0923) discusses how the emissions

from these combustion sources were estim ated. Table 1 below shows the total and

reported process emissions from the onshor e production sector broken into U.S.

Inventory Natural Gas Systems emissions, U. S. Inventory Petroleum Systems emissions,

unconventional well completion and workover emissions, conventional well completions

and workover emissions, and well liquids unloa ding emissions. Table 2 shows the total

and reported combustion emissions from th e onshore production industry segment broken

into Natural Gas Systems engines, Petroleum Systems engines, petroleum heater-treaters

, natural gas drilling rigs, petroleum drilli ng rigs, and dehydrator reboilers, and other

natural gas and petroleum combustion emissions.

Portable Equipment Emissions

EPA summed the emissions from the sources selected above and determined the

emissions from portable equipment to be about 120 million tonnes CO 2 

### -equivalent or 45

percent of the 265 million tonnes CO 2 

### -equivalent for the entire onshore production

segment.Page 4 of 5Table 1. Onshore Production Process Emissions by Source Nationwide and Reported (tonnes CO2-equivalent)3.U.S. NationwideEmissions% of U.S.ProcessEmissions% of TotalEmissionsReportedEmissions% of ReportedProcessEmissions% of ReportedEmissionsU.S. Inventory Petroleum Systems13,577,1208% 5%9,945,2257% 4%U.S. Inventory Natural Gas Systems41,441,13325% 16%38,083,39225% 17%Unconventional Well Workoversand Completions21,008,00013% 8%20,492,62413% 9%Conventional Well Workovers andCompletions122,8160.1% 0.0%113,0420% 0%Well Unloading90,092,00054% 34%83,672,20555% 37%Total Process 166,300,327 100% 63%152,353,196100% 67%Total Emissions 265,115,434100%226,010,270100%Table 2. Onshore Production Combustion Emissions by Source Nationwide and Reported (tonnes CO2-equivalent)4.NationwideEmissions% of U.S.CombustionEmissions% of TotalEmissionsReportedEmissions% of ReportedCombustionEmissions% of ReportedEmissionsPetroleum Systems Engines10,768,28211% 4%7,887,75511% 3%Natural Gas Systems Engines33,618,69334% 13%30,894,76042% 14%Natural Gas Combustion Emissions7,203,3407% 3%6,619,6949% 3%Petroleum Combustion Emissions1,455,1241% 1%1,065,8771% 0.5%Petroleum Heater-TreaterCombustion Emissions378,6320.4% 0.1%277,3480.4% 0.1%Petroleum Drilling Emissions12,636,85613% 5%7,462,62310% 3%Natural Gas Drilling Emissions32,348,60733% 12%19,103,28526% 8%3Onshore Production Basin Threshold Analysis EPA-HQ-OAR-2009-09234Onshore Production Basin Threshold Analysis EPA-HQ-OAR-2009-0923Page 5 of 5Dehydrator Combustion Emissions93,3240.1% 0.04%85,7630.1% 0.04%Total Combustion Emissions 98,815,107 100% 33%73,657,074100% 33%Total Onshore Production Emissions 265,115,434100%226,010,270100%