### A-165 

# 3.5. Methodology for Estimating CH 4 

# and CO 2 

# Emissions from Petroleum Systems

The methodology for estimating CH 4

### and non-combustion CO 2 

### emissions from petroleum systems is based on the 1999 EPA draft report, Estimates of Methane Emissions from the U.S. Oil Industry (EPA 1999) and the study, Methane Emissions from the U.S. Petroleum Industry(EPA/GRI 1996). Sixty-four activities that emit CH 4 

### and thirty activities that emit non-combustion CO 2 

### from petroleum systems were examined from these reports. Most of the activities analyzed involve crude oil production field operations, which accounted for about 98 percent of total oil industry CH 4 

### emissions. Crude transportation and refining accounted for the remaining CH 4 

### emissions of less than one half and about one and a half percent, respectively. Non-combustion CO 2 

### emissions were analyzed for production operations and asphalt blowing in refining operations. Non-combustion CO 2 

### emissions from transportation operations are not included because they are negligible. The following steps were taken to estimate CH 4 

### and CO 2 

### emissions from petroleum systems.

Step 1: Determine Emission Factors for all Activities

The CH 4 

### emission factors for the majority of the activitie s for 1995 are taken from the 1999 EPA draft report, which contained the most recent and comprehensive determination of CH 4

### emission factors for the 64 CH 4 

### -emitting activities in the oil industry at that time. Emission factors for pneumatic devices in the production sector were recalculated in 2002 using emissions data in the EPA/GRI 1996c study. The gas engine emission factor is taken from the EPA/GRI 1996b study. The oil tank venting emission factor is taken from the API E&P Tank Calc weighted average for API gravity less than 45 API degrees with the distribution of gravities taken from a sample of production data from the HPDI database. Offshore emissions from shallow water and deep water oil platforms are taken from analysis of the Gulf-wide Offshore Activity Data System (GOADS) report (EPA 2005, BOEMRE 2004). The emission factors determined for 1995 were assumed to be representative of emissions from each sour ce type over the period 1990 through 2009. Therefore, the same emission factors are used for each year throughout this period.

The CO 2 

### emission factors were derived from the corresponding source CH 4 

### emission factors. The amount of CO 2 

### in the crude oil stream changes as it passes through various equipment in petroleum production operations. As a result, four distinct stages/streams with varying CO 2 

### contents exist. The four streams that are used to estimate the emissions factors are the associated gas stream separated from crude oil, hydrocarbons flashed out from crude oil (such as in storage tanks), whole crude oil itself when it leaks downstream, and gas emissions from offshore oil platforms. The standard approach used to estimate CO 2 

### emission factors was to use the existing CH 4 

### emissions factors and multiply them by a conversion factor, which is the ratio of CO 2 

### content to methane content for the particular stream. Ratios of CO 2 

### to CH 4 

### volume in emissions are presented in Table A- 5. The two ex ceptions are the emissions factor for storage tanks, which is estimated using API E&P Tank Calc simulation runs of tank em issions for crude oil of different gravities less than 45 API degrees; and the emissions factor for uncontrolled asphalt blowing, which is estimated using the data and methods provided by API (2009).

Step 2: Determine Activity Levels for Each Year Activity levels change from year to year. Some factors change in proportion to crude oil rates: production, transportation, refinery runs. Some change in proportion to th e number of facilities: oil wells, petroleum refineries. Some factors change proportional to both the rate and number of facilities. For most sources, activity levels found in the EPA/GRI 1996 for the 1995 base year are extrapolated to other years using publicly-available data sources. For the rema ining sources, the activity levels are obtained directly from publicly available data and are not extrapolated from the 1995 base year. For both sets of data, a determination was made on a case-by-case basis as to which measure of petroleum industry activity best reflects the change in annual activity. Publicly-reported data from the Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE), Energy Information Administration (EIA), American Petroleum Institute (API), the Oil & Gas Journal (O&GJ), the Inters tate Oil and Gas Compact Commission (IOGCC), and the U.S Army Corps of Engineers (USACE) were used to extrapolate the activity levels from the base year to each year between 1990 and 2009. Data used include total domestic crude oil production, number of domestic crude oil wells, total imports and exports of crude oil, total petroleum refinery crude runs , and number of oil-producing offshore platforms. The activity data for the total crude transported in the transportation sector is not available. In this case, all the crude oil that was transported was assumed to go to refineries. Therefore, the activity data for the refining sector was used also for the transportation sector. In the few cases where no data was located, oil industry data based on expert judgment was used. In the case of non-combustion CO 2 

### emission sources, the activity factors remain the same as for CH 4 

### emission sources.

### A-166 Inventory of U.S. Greenhous e Gas Emissions and Sinks: 1990-2009 Step 3: Estimate Methane and Carbon Dioxide Emissions for Each Activity for Each Year

Annual CH 4

### emissions from each of the 64 petroleum system activities and CO 2 

### emissions from the 30 petroleum system activities were estimated by multiplying the activity data for each year by the corresponding emission factor. These annual emissions for each activity were then summed to estimate the total annual CH 4

### and CO 2 

### emissions, respectively. Table A- 140 provides the CO2 content in natural gas for equipment in different crude streams to estimate CO2 emission factors using CH4 emission

### factors. Table A-136, Table A-137, Table A-138, and Table A-141 pr ovide 2009 activity factors, emission factors, and emission estimates and Table A-139 and Table A-142 provide a summary of emission estimates for the years 1990, 1995, 2000, and 2005 through 2009. Table A- 140 provides the CO 2 

### content in natural gas for equipment in different crude streams to estimate CO 2 

### emission factors using CH 4 

### emission factors.

Table A-136: 2009 CH 4 

### Emissions from Petroleum Prod uction Field Operations

Activity/Equipment 2009 EPA Inventory Values
Emission Factor Activity Factor Emissions (Bcf/yr) Emissions (Gg/yr) Vented Emissions 67.625 1,300

Oil Tanks 7.39 scf of CH 4/bbl crude 1,490 MMbbl/yr (non stripper wells) 11.016 211.8

Pneumatic Devices, High Bleed 330 scfd CH 4/device 139,797 No. of high-bleed devices 16.859 324.2

Pneumatic Devices, Low Bleed 52 scfd CH 4/device 259,624 No. of low-bleed devices 4.928 94.76

Chemical Injection Pumps 248 scfd CH 4/pump 28,166 No. of pumps 2.550 49.04 Vessel Blowdowns 78 scfy CH 4/vessel 182,451 No. of vessels 0.014 0.274 Compressor Blowdowns 3,775 scf/yr of CH 4/compressor 2,473 No. of compressors 0.009 0.179 Compressor Starts 8,443 scf/yr. of CH 4/compressor 2,473 No. of compressors 0.021 0.401 Stripper wells 2,345 scf/yr of CH 4/stripper well 317,230 No. of stripper wells vented 0.744 14.31

Well Completion Venting 733 scf/completion 11,804 Oil well completions 0.009 0.166 Well Workovers 96 scf CH 4 /workover 39,450 Oil well workovers 0.004 0.073 Pipeline Pigging 2.40 scfd of CH 4 /pig station 0 No. of crude pig stations - -
Offshore Platforms, Shallow water

Oil, fugitive, vented and combusted 54,795 scfd CH 4/platform 1,441 No. of shallow water oil platforms 28.823 554.3

Offshore Platforms, Deepwater oil,

fugitive, vented and combusted 260,274 scfd CH 4/platform 28 No. of deep water oil platforms 2.649 50.93

Fugitive Emissions 2.539 49

Oil Wellheads (heavy crude) 0.13 scfd/well 14,718 No. of hvy. crude wells 0.001 0.013 Oil Wellheads (light crude) 16.6 scfd/well 194,052 No. of lt. crude wells 1.178 22.65 Separators (heavy crude) 0.15 scfd CH 4/separator 10,740 No. of hvy. crude seps. 0.001 0.012 Separators (light crude) 14 scfd CH 4/separator 97,745 No. of lt. crude seps. 0.494 9.504 Heater/Treaters (light crude) 19 scfd CH 4/heater 73,966 No. of heater treaters 0.518 9.965 Headers (heavy crude) 1 0.08 scfd CH 4/header 13,721 No. of hvy. crude hdrs. 0.000 0.007 Headers (light crude) 11 scfd CH 4/header 42,536 No. of lt. crude hdrs. 0.169 3.241 Floating Roof Tanks 338,306 scf CH 4 /floating roof tank/yr. 24 No. of floating roof tanks 0.008 0.159

Compressors 100 scfd CH 4/compressor 2,473 No. of compressors 0.090 1.736 Large Compressors 16,360 scfd CH 4/compressor 0 No. of large comprs.

- - Sales Areas 41 scf CH 4 /loading 1,630,377 Loadings/year 0.066 1.271 Pipelines NE scfd of CH 4 /mile of pipeline 11,249 Miles of gathering line NE NE

Well Drilling NE scfd of CH 4 /oil well drilled 13,255 No. of oil wells drilled NE NE

Battery Pumps 0.24 scfd of CH 4 /pump 157,800 No. of battery pumps 0.014 0.266 Combustion Emissions 4.7926 92.22

Gas Engines 0.24 scf CH 4 /HP-hr 15,577 MMHP-hr 3.739 71.89 Heaters 0.52 scf CH 4 /bbl 1956.8 MMbbl/yr 1.020 19.61 Well Drilling 2,453 scf CH 4 /well drilled 13,255 Oil wells drilled 0.033 0.625

### A-167 Activity/Equipment 2009 EPA Inventory Values
Emission Factor Activity Factor Emissions (Bcf/yr) Emissions (Gg/yr) Flares 20 scf CH 4 /Mcf flared 242,355 Mcf flared/yr 0.005 0.932 Process Upset Emissions 0.116 2.233

Pressure Relief Valves 35 scf/yr/PR valve 163,449 No. of PR valves 0.006 0.109 Well Blowouts Onshore 2.5 MMscf/blowout 44.2 No. of blowouts/yr 0.110 2.124
Total 75.08 1,444

- Zero Emissions

1 Emissions are not actually 0, but too smal l to show at this level of precision. NE: Not estimated for lack of data



### Table A-137: 2009 CH 4 

### Emissions from Petroleum Transportation

Activity/Equipment Emission Factor Units Activity Factor Units Emissions (Bcf/yr) Emissions (Gg/yr) Vented Emissions 0.209 4.024

Tanks 0.021 scf CH 4/yr/bbl of crude delivered to refineries 5,233 MMbbl crude feed/yr 0.108 2.073 Truck Loading 0.520 scf CH 4/yr/bbl of crude transported by truck 67.8 MMbbl trans. by truck 0.035 0.678 Marine Loading 2.544 scf CH 4/1000 gal. crude marine loadings 19,609,664 1,000 gal./yr loaded 0.050 0.959 Rail Loading 0.520 scf CH 4/yr/bbl of crude transported by rail 4.2 MMbbl Crude by rail/yr 0.002 0.042 Pump Station

Maintenance 1 36.80 scf CH 4/station/yr 496 No. of pump stations 0.000 0.000 Pipeline Pigging 39 scfd of CH 4/pig station 992 No. of pig stations 0.014 0.271 Fugitive Emissions 0.050 0.958

Pump Stations 25 scf CH 4/mile/yr. 49,585 No. of miles of crude p/l 0.001 0.024

Pipelines NE scf CH 4/bbl crude transported by pipeline 6,431 MMbbl crude piped NE NE

Floating Roof Tanks 58,965 scf CH 4/floating roof tank/yr. 824 No. of floating roof tanks 0.049 0.934

Combustion Emissions NE NE

Pump Engine Drivers 0.24 scf CH 4/hp-hr NE No. of hp-hrs NE NE Heaters 0.521 scf CH 4/bbl burned NE No. of bbl Burned NE NE Total 0.259 4.982

1 Emissions are not actually 0, but too smal l to show at this level of precision. NE: Not estimated for lack of data



### Table A-138: 2009 CH 4 

### Emissions from Petroleum Refining

Activity/Equipment 2009 EPA Inventory Values
Emission Factor Activity Factor Emissions (Bcf/yr) Emissions (Gg/yr) Vented Emissions 1.065 20.48 Tanks 20.6 scf CH 4/Mbbl 1,839 Mbbl/calendar day heavy crude feed 0.014 0.266 System Blowdowns 137 scf CH 4/Mbbl 14,336 Mbbl/calendar day refinery feed 0.716 13.77 Asphalt Blowing 2,555 scf CH 4/Mbbl 359 Mbbl/calendar day production 0.335 6.445 Fugitive Emissions 0.088 1.702 Fuel Gas System 439 Mscf CH 4 /refinery/yr 150 Refineries 0.066 1.266 Floating Roof Tanks 1 587 scf CH 4/floating roof tank/yr. 767 No. of floating roof tanks 0.000 0.009 Wastewater Treating 1.88 scf CH 4/Mbbl 14,336 Mbbl/calendar day refinery feed 0.010 0.189 Cooling Towers 2.36 scf CH 4/Mbbl 14,336 Mbbl/calendar day refinery feed 0.012 0.237 Combustion Emissions 0.090 1.723 Atmospheric Distillation 3.61 scf CH 4/Mbbl 14,659 Mbbl/calendar day refinery feed 0.019 0.371 Vacuum Distillation 3.61 scf CH 4/Mbbl 6,503 Mbbl/calendar day feed 0.009 0.165

### A-169 Activity/Equipment 2009 EPA Inventory Values
Emission Factor Activity Factor Emissions (Bcf/yr) Emissions (Gg/yr) fugitive, vented and combusted platforms Fugitive Emissions 0.052 2.776

Oil Wellheads (heavy crude) 1 0.003 scfd/well 14,718 No. of hvy. crude wells 0.000 0.001 Oil Wellheads (light crude) 0.337 scfd/well 194,052 No. of lt. crude wells 0.024 1.267 Separators (heavy crude) 1 0.003 scfd CO 2 /separator 10,740 No. of hvy. crude seps. 0.000 0.001 Separators (light crude) 0.281 scfd CO 2 /separator 97,745 No. of lt. crude seps. 0.010 0.531 Heater/Treaters (light crude) 0.319 scfd CO 2 /heater 73,966 No. of heater treaters 0.009 0.456 Headers (heavy crude) 1 0.002 scfd CO 2 /header 13,721 No. of hvy. crude hdrs. 0.000 0.000 Headers (light crude) 0.220 scfd CO 2 /header 42,536 No. of lt. crude hdrs. 0.003 0.181 Floating Roof Tanks 1 17,490 scf CO 2 /floating roof tank/yr. 24 No. of floating roof tanks 0.000 0.023

Compressors 2.029 scfd CO 2 /compressor 2,473 No. of compressors 0.002 0.097 Large Compressors 332 scfd CO 2 /compressor 0 No. of large comprs. 0.000 0.000 Sales Areas 2.096 scf CO 2 /loading 1,630,377 Loadings/year 0.003 0.181 Pipelines NE scfd of CO 2 /mile of pipeline 11,249 Miles of gathering line NE NE

Well Drilling NE scfd of CO 2 /oil well drilled 13,255 No. of oil wells drilled NE NE

Battery Pumps 0.012 scfd of CO 2 /pump 157,800 No. of battery pumps 0.001 0.038 Process Upset Emissions 0.003 0.134

Pressure Relief Valves 1 1.794 scf/yr/PR valve 163,499 No. of PR valves 0.000 0.016 Well Blowouts Onshore 0.051 MMscf/blowout 44 No. of blowouts/yr 0.002 0.119 Refining Emissions 2.720 144.2 Asphalt Blowing 2 20,736 scf CO 2 /Mbbl 359 Mbbl/calendar day production 2.720 144.2

Total 8.747 463.6

1 Emissions are not actually 0, but too smal l to show at this level of precision.

2 Asphalt Blowing emissions are the only significant vented emissions from the refining sector; other sources are too small to sh ow at this level of precision. NE: Not estimated for lack of data Energy use CO 2 emissions not estimated to avoid doublecounting with fossil fuel combustion



### Table A-142: Summary of CO 2 

### Emissions from Petroleum Systems (Gg) Activity 1990 1995 2000 2005 2006 2007 2008 2009 Production Field

Operations 376 341 323 285 285 292 288 319 Pneumatic device venting 27 26 24 22 22 22 23 23 Tank venting 328 296 281 246 246 252 247 278 Misc. venting & fugitives 18 18 17 16 16 16 16 16 Wellhead fugitives 1 1 1 111 1 1 Refining Asphalt Blowing 180 187 211 205 203 182 165 144 Total 555 528 534 490 488 474 453 463

### A-168 Inventory of U.S. Greenhous e Gas Emissions and Sinks: 1990-2009 Activity/Equipment 2009 EPA Inventory Values
Emission Factor Activity Factor Emissions (Bcf/yr) Emissions (Gg/yr) Thermal Operations 6.01 scf CH 4/Mbbl 2,034 Mbbl/calendar day feed 0.004 0.086 Catalytic Cracking 5.17 scf CH 4/Mbbl 4,694 Mbbl/calendar day feed 0.009 0.170 Catalytic Reforming 7.22 scf CH 4/Mbbl 2,970 Mbbl/calendar day feed 0.008 0.150 Catalytic Hydrocracking 7.22 scf CH 4/Mbbl 1,393 Mbbl/calendar day feed 0.004 0.071 Hydrorefining 2.17 scf CH 4/Mbbl 2,067 Mbbl/calendar day feed 0.002 0.031 Hydrotreating 6.50 scf CH 4/Mbbl 9,480 Mbbl/calendar day feed 0.022 0.432 Alkylation/Polymerization 12.6 scf CH 4/Mbbl 1,027 Mbbl/calendar day feed 0.005 0.091 Aromatics/Isomeration 1.80 scf CH 4/Mbbl 956 Mbbl/calendar day feed 0.001 0.012 Lube Oil Processing 0.00 scf CH 4/Mbbl 165 Mbbl/calendar day feed 0.000 0.000 Engines 0.006 scf CH 4/hp-hr 1,128 MMhp-hr/yr 0.006 0.124 Flares 0.189 scf CH 4/Mbbl 14,336 Mbbl/calendar day refinery feed 0.001 0.019 Total 1.243 23.90

1 Emissions are not actually 0, but too smal l to show at this level of precision.


### Table A-139: Summary of CH 4 

### Emissions from Petroleum Systems (Gg) Activity 1990 1995 2000 2005 2006 2007 2008 2009 Production Field

Operations 1,653 1,557 1,468 1,366 1,365 1,396 1,409 1,444 Pneumatic device venting 489 463 428 397 396 398 416 419 Tank venting 250 226 214 187 188 192 189 212 Combustion & process

upsets 88 82 76 71 71 72 75 94 Misc. venting & fugitives 799 762 727 691 693 714 707 696 Wellhead fugitives 26 25 22 19 17 20 23 23 Crude Oil Transportation 7 6 5 5 5 5 5 5 Refining 25 26 28 28 28 27 25 24 Total 1,685 1,589 1,501 1,398 1,398 1,427 1,439 1,473 Note: Totals may not sum due to independent rounding.


### Table A-140: Ratios of CO 2 

### to CH 4 

### Volume in Emissions from Petrol eum Production Field Operations Whole Crude, Post-Separator Associated Gas Tank Flash Gas Offshore

Ratio %CO 2 

### / %CH 4 

### 0.052 0.020 0.017 0.004



### Table A-141: 2009 CO 2 

### Emissions from Petroleum Production Fi eld Operations and Petroleum Refining

Activity/Equipment 2009 EPA Inventory Values
Emission Factor Activity Factor Emissions (Bcf/yr) Emissions (Gg/yr) Vented Emissions 5.972 316.5

Oil Tanks 3.53 scf of CO 2 /bbl crude 1,490 MMbbl/yr (non stripper wells) 5.256 278.6

Pneumatic Devices, High Bleed 6.704 scfd CO 2 /device 139,797 No. of high-bleed devices 0.342 18.13

Pneumatic Devices, Low Bleed 1.055 scfd CO 2 /device 259,624 No. of low-bleed devices 0.100 5.299 Chemical Injection Pumps 5.033 scfd CO 2 /pump 28,166 No. of pumps 0.052 2.742 Vessel Blowdowns 1 1.583 scfy CO 2 /vessel 182,451 No. of vessels 0.000 0.015 Compressor Blowdowns 1 77 scf/yr of CO 2 /compressor 2,473 No. of compressors 0.000 0.010 Compressor Starts 1 171 scf/yr. of CO 2 /compressor 2,473 No. of compressors 0.000 0.022 Stripper wells 48 scf/yr of CO 2 /stripper well 317,230 No. of stripper wells vented 0.015 0.800

Well Completion Venting 1 14.87 scf/completion 11,804 Oil well completions 0.000 0.009 Well Workovers 1 1.95 scf CO 2 /workover 39,450 Oil well workovers 0.000 0.004 Pipeline Pigging NE scfd of CO 2 /pig station NE No. of crude pig stations NE NE Offshore Platforms, Shallow water

Oil, fugitive, vented and combusted 358 scfd CO 2 /platform 1,441 No. of shallow water oil platforms 0.188 9.984

Offshore Platforms, Deepwater oil, 1,701 scfd CO 2 /platform 28 No. of deep water oil 0.017 0.917