# 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 twenty-nine

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 97.8 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 two 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 activit ies 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 1996 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 average for API gravity less than 44 API degrees. Offshore emissions from shallow water and deep water oil platforms are taken from analysis of the Gulfwide Offshore Activity Data System (GOADS) report (EPA 2005, MMS 2004). The emission factors determined for 1995 were assumed to be representative of emissions from each so urce type over the period 1990 through 2008. 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 variou s 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, a nd 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 emissions for crude oil of different gravities less than 44 API degrees; and the emissions factor for uncontrolled asphalt blowing, which is estimated using the data and methods provided by API (2004).

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 the 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 remain ing 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 Minerals Management Service (MMS), Energy Information Administration (EIA), American Petroleum Institute (API), the Oil & Gas Journal (O&GJ), the Interstate Oil and Gas Compact Commission (IOGCC), and the U.S Army Corps of Engineers (UCACE) were used to extrapolate the activity levels from the base year to each year between 1990 and 2008. 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-158 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008

### 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- 134, Table A- 135, Table A- 136, and Table A- 139 provide 2008 activity factors, emission factors, and emission estimates and Table A- 137 and Table A- 140 provide a summary of emission estimates for the years 1990 through 2008.

Table A- 134: 2008 CH 4 

### Emissions from Petroleum Prod uction Field Operations

Activity/Equipment Emission

Factor Units Activity

Factor Units Emissions (Bcf/yr) Emissions (Gg/yr)

Vented Emissions 63.977 1,230

Oil Tanks

Pneumatic Devices, High Bleed 5.28 scf of CH 4 /bbl crude

330 scfd CH 4 /device 1,326 MMbbl/yr (non stripper wells)

138,471 No. of high-bleed devices 7.001

16.70 134.6

321.1

Pneumatic Devices, Low Bleed 52 scfd CH 4 /device 257,160 No. of low-bleed devices 4.881 93.86
Chemical Injection Pumps 248 scfd CH 4 /pump 28,113 No. of pumps 2.545 48.95

Vessel Blowdowns 78 scfy CH 4 /vessel 180,628 No. of vessels 0.014 0.271
Compressor Blowdowns 3,775 scf/yr of CH 4 /compressor 2,444 No. of compressors 0.009 0.177
Compressor Starts 8,443 scf/yr. of CH 4 /compressor 2,444 No. of compressors 0.021 0.397
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 17,929 Oil well completions 0.013 0.253

Well Workovers 96 scf CH 4 /workover 39,375 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 Offshore Platforms, Deepwater oil,

fugitive, vented and combusted 54,795 scfd CH 4 /platform

260,274 scfd CH 4 /platform 1,479 No. of shallow water oil platforms

26 No. of deep water oil platforms 29.58

2.470 568.8

47.50

Fugitive Emissions 2.516 48

Oil Wellheads (heavy crude) 0.13 scfd/well 14,648 No. of hvy. crude wells 0.001 0.013 Oil Wellheads (light crude) 16.6 scfd/well 193,123 No. of lt. crude wells 1.172 22.54 Separators (heavy crude) 0.15 scfd CH 4 /separator 10,643 No. of hvy. crude seps. 0.001 0.011 Separators (light crude) 14 scfd CH 4 /separator 96,859 No. of lt. crude seps. 0.490 9.418 Heater/Treaters (light crude) 19 scfd CH 4 /heater 73,127 No. of heater treaters 0.512 9.852 Headers (heavy crude) 1 0.08 scfd CH 4 /header 13,695 No. of hvy. crude hdrs. 0.000 0.007 Headers (light crude) 11 scfd CH 4 /header 42,455 No. of lt. crude hdrs. 0.168 3.235
Floating Roof Tanks

Compressors 338,306 scf CH 4 /floating roof tank/yr.

100 scfd CH 4 /compressor 24 No. of floating roof tanks

2,444 No. of compressors 0.008

0.089 0.159

1.715
Large Compressors 16,360 scfd CH 4 /compressor 0 No. of large comprs.

- - Sales Areas 41 scf CH 4 /loading 1,505,384 Loadings/year 0.061 1.174
Pipelines

Well Drilling NE scfd of CH 4 /mile of pipeline

NE scfd of CH 4 /oil well drilled 11,694 Miles of gathering line

19,864 No. of oil wells drilled NE

NE NE

NE
Battery Pumps 0.24 scfd of CH 4 /pump 157,500 No. of battery pumps 0.014 0.265

Combustion Emissions 3.748 72.07

Gas Engines 0.24 scf CH 4 /HP-hr 15,396 MMHP-hr 3.695 71.06

Heaters 0.52 scf CH 4 /bbl 1,807 MMbbl/yr 0.001 0.018 Well Drilling 2,453 scf CH 4 /well drilled 19,864 Oil wells drilled 0.049 0.937

Flares 20 scf CH 4 /Mcf flared 154,014 Mcf flared/yr 0.003 0.059 Process Upset Emissions 0.171 3.284

Pressure Relief Valves 35 scf/yr/PR valve 150,918 No. of PR valves 0.005 0.101

Well Blowouts Onshore 2.5 MMscf/blowout 66.2 No. of blowouts/yr 0.166 3.183

Total 70.41 1,354

- Zero Emissions

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

NE: Not estimated for lack of data



### A-159

### Table A- 135: 2008 CH 4 

### Emissions from Petroleum Transportation

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

Vented Emissions 0.215 4.139

Tanks 0.021 scf CH 4 /yr/bbl of crude delivered to refineries 5,361 MMbbl crude feed/yr 0.110 2.124 Truck Loading 0.520 scf CH 4 /yr/bbl of crude transported by truck 69.3 MMbbl trans. by truck 0.036 0.693 Marine Loading 2.544 scf CH 4 /1000 gal. crude marine loadings 20,508,086 1,000 gal./yr loaded 0.052 1.003 Rail Loading 0.520 scf CH 4 /yr/bbl of crude transported by rail 4.3 MMbbl. Crude by rail/yr 0.002 0.043 Pump Station Maintenance 1 36.80 scf CH 4 /station/yr 502 No. of pump stations 0.000 0.000 Pipeline Pigging 39 scfd of CH 4 /pig station 1,004 No. of pig stations 0.014 0.275 Fugitive Emissions 0.050 0.959

Pump Stations 25 scf CH 4 /mile/yr. 50,214 No. of miles of crude p/l 0.001 0.024 Pipelines NE scf CH 4 /bbl crude transported by pipeline 6,858 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 0.265 5.097

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

NE: Not estimated for lack of data



### Table A- 136: 2008 CH 4 

### Emissions from Petroleum Refining

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

Vented Emissions 1.131 21.75

Tanks 20.6 scf CH 4 /Mbbl 1,885 Mbbl/cd heavy crude feed 0.014 0.273 System Blowdowns 137 scf CH 4 /Mbbl 14,688 Mbbl/cd refinery feed 0.733 14.11 Asphalt Blowing 2,555 scf CH 4 /Mbbl 411 Mbbl/cd production 0.383 7.370 Fugitive Emissions 0.089 1.712

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 14,688 Mbbl/cd refinery feed 0.010 0.194 Cooling Towers 2.36 scf CH 4 /Mbbl 14,688 Mbbl/cd refinery feed 0.013 0.243

Combustion Emissions 0.091 1.712 Atmospheric Distillation 3.61 scf CH 4 /Mbbl 15,027 Mbbl/cd refinery feed 0.020 0.381

Vacuum Distillation 3.61 scf CH 4 /Mbbl 6,585 Mbbl/cd feed 0.009 0.167 Thermal Operations 6.01 scf CH 4 /Mbbl 2,103 Mbbl/cd feed 0.005 0.089 Catalytic Cracking 5.17 scf CH 4 /Mbbl 4,934 Mbbl/cd feed 0.009 0.179 Catalytic Reforming 7.22 scf CH 4 /Mbbl 3,006 Mbbl/cd feed 0.008 0.152 Catalytic Hydrocracking 7.22 scf CH 4 /Mbbl 1,359 Mbbl/cd feed 0.004 0.069 Hydrorefining 2.17 scf CH 4 /Mbbl 2,097 Mbbl/cd feed 0.002 0.032 Hydrotreating 6.50 scf CH 4 /Mbbl 9,619 Mbbl/cd feed 0.023 0.439 Alkylation/Polymerization 12.6 scf CH 4 /Mbbl 1,053 Mbbl/cd feed 0.005 0.093

Aromatics/Isomeration 1.80 scf CH 4 /Mbbl 1,003 Mbbl/cd feed 0.001 0.013 Lube Oil Processing 0.00 scf CH 4 /Mbbl 163 Mbbl/cd feed 0.000 0.000 Engines 0.006 scf CH 4 /hp-hr 1,143 MMhp-hr/yr 0.007 0.125

Flares 0.189 scf CH 4 /Mbbl 14,688 Mbbl/cd refinery feed 0.001 0.019

Total 1.311 25.22

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



### Table A- 137: Summary of CH 4 

### Emissions from Petroleum Systems (Gg)

Activity 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Production Field Operations 1,581 1,593 1,552 1,514 1,506 1,492 1,490 1,481 1,469 1,427 1,406 1,403 1,388 1,355 1,334 1,312 1,311 1,340 1,354 Pneumatic device venting 489 498 482 472 469 463 462 461 452 437 428 425 424 412 408 397 396 398 415 Tank venting 179 179 173 166 162 161 161 165 163 153 153 154 150 149 142 134 134 137 135 Combustion & process upsets 88 90 86 84 83 82 82 83 80 77 76 75 75 73 72 71 71 72 75 Misc. venting & fugitives 799 799 786 768 767 762 759 747 748 735 726 726 716 699 691 690 693 714 707
Wellhead fugitives 26 26 24 24 25 25 25 26 26 24 22 22 23 22 21 19 17 20 23 Crude Oil Transportation 7 6 6 6 6 6 6 6 6 6 5 5 5 5 5 5 5 5 5
Refining 25 24 24 25 25 26 26 27 27 27 28 27 27 27 28 28 28 27 25

Total 1,613 1,624 1,582 1,545 1,537 1,524 1,521 1,513 1,501 1,460 1,439 1,435 1,420 1,387 1,367 1,344 1,344 1,372 1,384



### A-160 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008

### Table A- 138: 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- 139: 2008 CO 2 

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

Activity/Equipment Emission

Factor Units Activity

Factor Units Emissions (Bcf/yr) Emissions (Gg/yr)

Vented Emissions 5.393 285.2

Oil Tanks

Pneumatic Devices, High Bleed 3.53 scf of CO 2 /bbl crude

6.704 scfd CO 2 /device 1,326 MMbbl/yr (non stripper wells)

138,471 No. of high-bleed devices 4.678

0.339 247.4

17.92
Pneumatic Devices, Low Bleed 1.055 scfd CO 2 /device 257,160 No. of low-bleed devices 0.099 5.238 Chemical Injection Pumps 5.033 scfd CO 2 /pump 28,113 No. of pumps 0.052 2.731

Vessel Blowdowns 1 1.583 scfy CO 2 /vessel 180,628 No. of vessels 0.000 0.015 Compressor Blowdowns 1 77 scf/yr of CO 2 /compressor 2,444 No. of compressors 0.000 0.010 Compressor Starts 1 171 scf/yr. of CO 2 /compressor 2,444 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 0.798 Well Completion Venting 1 14.87 scf/completion 17,929 Oil well completions 0.000 0.014

Well Workovers 1 1.95 scf CO 2 /workover 39,375 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 Offshore Platforms, Deepwater oil,

fugitive, vented and combusted 358 scfd CO 2 /platform

1,701 scfd CO 2 /platform 1,479 No. of shallow water oil platforms

26 No. of deep water oil platforms 0.193

0.016 10.22

0.854

Fugitive Emissions 0.052 2.738

Oil Wellheads (heavy crude) 1 0.003 scfd/well 14,648 No. of hvy. crude wells 0.000 0.001 Oil Wellheads (light crude) 0.337 scfd/well 193,123 No. of lt. crude wells 0.024 1.258 Separators (heavy crude) 1 0.003 scfd CO 2 /separator 10,643 No. of hvy. crude seps. 0.000 0.001 Separators (light crude) 0.281 scfd CO 2 /separator 96,859 No. of lt. crude seps. 0.010 0.526 Heater/Treaters (light crude) 0.319 scfd CO 2 /heater 73,127 No. of heater treaters 0.009 0.450 Headers (heavy crude) 1 0.002 scfd CO 2 /header 13,695 No. of hvy. crude hdrs. 0.000 0.000 Headers (light crude) 0.220 scfd CO 2 /header 42,455 No. of lt. crude hdrs. 0.003 0.181
Floating Roof Tanks 1

Compressors 17,490 scf CO 2 /floating roof tank/yr.

2.029 scfd CO 2 /compressor 24 No. of floating roof tanks

2,444 No. of compressors 0.000

0.002 0.023

0.096
Large Compressors 332 scfd CO 2 /compressor 0 No. of large comprs. 0.000 0.000

Sales Areas 2.096 scf CO 2 /loading 1,505,384 Loadings/year 0.003 0.167
Pipelines

Well Drilling NE scfd of CO 2 /mile of pipeline

NE scfd of CO 2 /oil well drilled 11,694 Miles of gathering line

19,864 No. of oil wells drilled NE

NE NE

NE
Battery Pumps 0.012 scfd of CO 2 /pump 157,500 No. of battery pumps 0.001 0.038

Process Upset Emissions 0.004 0.192

Pressure Relief Valves 1 1.794 scf/yr/PR valve 150,918 No. of PR valves 0.000 0.014

Well Blowouts Onshore 0.051 MMscf/blowout 66 No. of blowouts/yr 0.003 0.178
Refining Emissions 3.111 164.5
Asphalt Blowing 2 20,736 scf CO 2 /Mbbl 411 Mbbl/cd production 3.111 164.5

Total 8.559 453.1

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

2 Asphalt Blowing emissions are the only sign ificant 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 doubl e counting with fossil fuel combustion



### A-161

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

### Emissions from Petroleum Systems (Gg)

Activity 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Production Field

Operations Pneumatic device venting Tank venting Misc. venting & fugitives Wellhead fugitives Refining

A

sphalt Blowing 376

27

328

18

1

180 377

28

330

18

1

172 365

27

319

18

1

168 350

26

304

18

1

180 342

26

297

18

1

181 341

26

296

18

1

187 341

26

296

17

1

184 348

26

303

17

1

194 343

25

299

17

1

199 325

24

282

17

1

202 323

24

281

17

1

211 325

24

283

17

1

194 318

24

276

16

1

197 314

23

273

16

1

199 302

23

262

16

1

204 285

22

246

16

1

205 285

22

246

16

1

203 292

22

252

16

1

182 288

23

247

16

1

165

Total 555 549 533 530 523 528 525 542 543 527 534 519 515 512 505 490 488 474 453



### A-162 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008