April 2015
Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2013: Revision to Well Counts
Data
Overview of Well Counts in the GHG Inventory
A significant number of emission sources in the natural gas and petroleum systems source categories of the Inventory
rely on well counts as a key data input for emissions calculations. Some source calculations use well counts data as the
only activity data input (e.g., calculations for fugitives from wells); some source calculations use well counts to calculate
the counts of other equipment in a given year (e.g., calculations for pneumatic devices which use the number of
pneumatic devices per well and well counts); and some source calculations use well counts to calculate other inputs
(e.g., dehydrator vent calculations use well counts, number of dehydrators per well, and the amount of throughput per
dehydrator). The well count populations historically used in the Inventory are presented in Table 1. Note that the
associated gas well counts currently in the natural gas systems portion of the Inventory are a subset of oil wells, which
are the primary well population used in the petroleum systems portion of the Inventory.
Table 1. Well Populations and Use in the 2014 Inventory for Natural Gas and Petroleum Systems
Well Population
Well Population
Description
Inventory Emission Sources Estimated Using Well Population Data as
Inputs to Calculations
Natural Gas Systems
Associated Gas
Wells
Oil wells that also
produce gas
Fugitive
o Field Separation Equipment - Meters/Piping
Non-Associated
Gas Wells
Natural gas wells
Fugitive
o Non-Associated Gas Wells
o Field Separation Equipment - Heaters, Separators, Dehydrators,
Meters/Piping
o Gathering Compressor-Small and Large Reciprocating Compressors, Large
Reciprocating Stations, Pipeline Leaks
Vented and Combusted
o Gas Well Completions without Hydraulic Fracturing
o Well Drilling
o Normal Operations - Pneumatic Device Vents, Chemical Injection Pumps,
Kimray Pumps, Dehydrator Vents
o Compressor Exhaust for Gas Engines
o Well Workovers - Gas Wells without Hydraulic Fracturing, Gas Wells with
Liquids Unloading
o Blowdowns-Vessel Blowdowns, Pipeline Blowdowns, Compressor
Blowdowns, Compressor Starts
o Upsets - Pressure Relief Valves, Mishaps
Gas Wells with
Hydraulic
Fracturing
Gas Wells with
Hydraulic
Fracturing (cont.)
Natural gas wells
that were
completed using
hydraulic
fracturing
Natural gas wells
that were
completed using
Fugitive
o Gas Wells with Hydraulic Fracturing
o Field Separation Equipment - Heaters, Separators, Dehydrators,
Meter/Piping
o Gathering Compressor-Small and Large Reciprocating Compressors, Large
Reciprocating Stations, Pipeline Leaks
Vented and Combusted
o Gas Well Completions without Hydraulic Fracturing
o Gas Well Completions with Hydraulic Fracturing
o Well Drilling
o Normal Operations - Pneumatic Device Vents, Chemical Injection Pumps,
Kimray Pumps, Dehydrator Vents
o Well Workovers - Gas Wells without Hydraulic Fracturing, Gas Wells with
Hydraulic Fracturing
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April 2015
Table 1. Well Populations and Use in the 2014 Inventory for Natural Gas and Petroleum Systems
Well Population
Well Population
Description
Inventory Emission Sources Estimated Using Well Population Data as
Inputs to Calculations
hydraulic
fracturing
o Blowdowns-Vessel Blowdowns, Pipeline Blowdowns, Compressor
Blowdowns, Compressor Starts
o Upsets - Pressure Relief Valves, Mishaps
Petroleum Systems
Oil Wells
Oil wells
Fugitive
o Oil Wellheads (Heavy Crude)
o Oil Wellheads (Light Crude)
o Separators (Heavy Crude)
o Separators (Light Crude)
o Heater/Treaters (Light Crude)
o Compressors
o Headers (Heavy Crude)
o Headers (Light Crude)
o Battery Pumps
Vented
o Pneumatic Devices, High Bleed
o Pneumatic Devices, Low Bleed
o Vessel Blowdowns
o Compressor Blowdowns
o Compressor Starts
o Well Workovers
Combusted
o Gas Engines
Stripper Wells
Oil wells that
produce less than
10 bbl/day
Fugitive
o Oil Wellheads (Heavy Crude)
o Oil Wellheads (Light Crude)
Vented
o Oil Tanks
o Stripper Wells
Combusted
o Flares
Approach for 2012 and Previous Inventories
Data sources for well counts in the natural gas and petroleum systems portions of the Inventory have changed over
time. For 2012 and previous Inventories, the well counts data came from the following publically available sources:
Natural gas systems:
Associated gas wells:
¦ 1990 to 2004 data: API Basic Petroleum Book Table 12 - Section III - Producing Oil Wells in the
United States by State (2005)
¦ 2005 to 2010 data: World Oil Magazine Outlook 2011: Producing Oil Wells
Non-associated gas wells:
¦ 1990 to 2003 data: U.S. DOE/EIA Annual Number of Producing Gas Wells1
¦ 2004 to 2010 data: World Oil Magazine Outlook 2011: Producing Gas Wells
Gas wells with hydraulic fracturing:
¦ CBM wells in KS: Kansas Geological Survey All Wells
1 "Number of Producing Gas Wells." Energy Information Administration, U.S. Department of Energy. Available online at
http://www.eia.gov/dnav/ng/ng_prod_wells_sl_a.htm
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April 2015
¦ CBM wells in OK: Oklahoma Geological Survey Coalbed Methane Completions
¦ CBM wells in MT: Montana Department of Natural Resources and Conservation, Board of Oil and
Gas Live Data Access
¦ CBM wells in CO: Colorado State Oil and Gas Conservation Commission Coalbed Methane Wells
¦ CBM wells in WY: Wyoming Oil and Gas Conservation Commission Coalbed Production
¦ CBM wells in UT: Utah Department of Natural Resources, Division of Oil, Gas and Mining Well
Information Search
¦ Barnett shale wells in TX: Texas Railroad Commission Newark, East (Barnett Shale) Well Count
Petroleum systems:
Oil wells: EIA Annual Energy Review Table 5.2. Crude Oil Production and Oil Well Productivity2
Stripper wells:
¦ 1990 to 1992 data: API Basic Petroleum Data Book Section III Table 14 (2002)
¦ 1993 to 2010 data: Interstate Oil and Gas Compact Commission Marginal Wells: Fuel for Economic
Growth, Table 7.1 (2008)
Approach for 2013 (estimates for 1990-2011) and 2014 Inventories (estimates for 1990-2012)
As part of EPA's updates for the natural gas systems portion of the 2013 and 2014 Inventories, EPA revised the well
counts for each category using Drillinglnfo's U.S. well data. Updating the well count data source allowed for a more
transparent, consistent, and reproducible methodology for obtaining well counts as follows:
Associated gas wells are defined as those wells in the Drillinglnfo dataset that:
EPA classified as primarily producing "oil" or "oil and gas" based on the production type description and
that had non-zero natural gas; and
Had non-zero hydrocarbon liquids production.
Non-associated gas wells are defined as those wells in the Drillinglnfo dataset that:
EPA classified as "gas" producing and had non-zero gas production; or
EPA classified as "oil" or "oil and gas" producing and had zero liquids production, but non-zero natural
gas production.
Gas wells with hydraulic fracturing are defined as a subset of the non-associated gas wells that:
Were horizontally drilled; and/or
Located in an unconventional formation (i.e., shale, tight sands, or coalbed), as identified using a
crosswalk developed by EIA.
EPA did not make any changes to the well counts data sources in the petroleum systems portion of the 2013 or 2014
Inventories.
EPA has previously investigated differences between non-associated gas well counts from the previous activity data
sources (EIA and World Oil Magazine) compared to the current methodology which relies on Drillinglnfo data. In general,
Drillinglnfo counts are lower than those generated by the previous methodology. EIA counts of active gas wells exclude
wells producing both crude oil and natural gas3whereas the current Drillinglnfo methodology results in some co-
producing wells being included in the non-associated gas well counts. Therefore, based on available documentation, the
underlying reasons for differences in the previous gas well counts compared to those generated by the current
methodology is unclear. EPA has previously performed state-level count comparisons and taken steps to refine the
2 "Annual Energy Review." Energy Information Administration, U.S. Department of Energy. Available online at
http://www.eia.gov/totalenergy/data/annual/index.cfm
3 Annual Energy Review 2011. Energy Information Administration, U.S. Department of Energy. Available online at
http://www.eia.gov/totalenergy/data/annual/pdf/aer.pdf
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April 2015
Drillinglnfo processing methodology to resolve significant discrepancies (e.g., Drillinglnfo collects production data on a
well pad level in certain states; therefore, EPA refined the data processing methodology to account for single production
records representing multiple active wells). Table 2 below shows well counts for key comparison years from both
previous (2012 Inventory) and the most recent (2014 Inventory) methodology.
Revised Approach for 2015 Inventory
Table 2 below presents well count activity data for select years from the 2012, 2014, and 2015 Inventories. EPA solicited
feedback from expert reviewers4 and public reviewers on three options for revising the well count methodology for
natural gas and petroleum systems. Option 1 used the existing Inventory methodology to identify wells in natural gas
systems (including associated gas wells), and expanded the methodology to also develop petroleum systems counts (i.e.,
oil well counts). Option 2 greatly simplified the existing Inventory methodology in the interest of easier reproducibility;
the ratio of gas to oil production ("gas-to-oil ratio" or GOR) based on Drillinglnfo data was used to assign wells to either
the natural gas or the petroleum systems source categories, and there would be no sub-population of "associated gas"
wells within natural gas systems. Option 3 expanded on Option 2 to treat oil wells with significant gas production
differently than primarily gas-producing or oil-producing wells (as they are expected to have emissions somewhere
between the two populations)and therefore included a population of "associated gas" wells, similar to the current
Inventory and Option 1.
Feedback from reviewers indicated that Option 1 provided the least transparency of the overall methodology. Reviewers
generally favored continuing to establish associated gas wells as a distinct population. Based on analysis of the options
and taking into consideration feedback from expert reviewers, EPA has implemented the Option 3 approach in the
public review draft of the 2015 Inventory. Information on the other options considered can be found in Appendix B to
this memo.
In Option 3 (the option implemented in the 2015 Inventory), all wells in the Drillinglnfo database that report gas and/or
liquids production in a given year are classified as either "Gas Wells" or "Oil Wells," and an oil well sub-population is
defined as "Associated Gas Wells," all based solely on GOR. Detailed steps to produce well counts by this option are:
1. For each well, in each calendar year, calculate GOR using actual gas and hydrocarbon liquids production data
collected by Drillinglnfo. Note, this approach does not take into account any production classification
information reported by the operator, and includes all hydrocarbon liquids (including condensate) production in
the GOR denominator.
2. Apply a GOR threshold to classify wells as "Gas Wells" or "Oil Wells." Based on expert review feedback, EPA used
GOR >100 mcf/bbl wells to define gas wells and GOR <100 mcf/bbl to define oil wells. A GOR threshold of 100
mcf/bbl is employed by states including Texas, Alaska, and Pennsylvania to define gas wells versus oil wells.
3. Apply a GOR threshold to identify a sub-population of "Oil Wells" that produce substantial amounts of gas and
should be classified as "Associated Gas." In the 2015 Inventory, any well within the oil wells population
established above that also produces gas is classified as an associated gas well in the Inventory.
4. Estimate emissions from existing emission sources and calculation methodologies for natural gas and petroleum
systems.
Reviewers suggested that the threshold selected overestimates the population of associated gas wells. EPA plans to
investigate alternative thresholds such as a GOR greater than 6 Mcf/bbl for associated gas wells for the 2016 Inventory.
4 Every year, the Inventory undergoes an expert review period during which a first draft of the document is sent to a select list of
technical experts outside of EPA. The purpose of the Expert Review is to encourage feedback on the methodological and data
sources used in the current Inventory, especially for sources which have experienced any changes since the previous Inventory. This
memorandum references feedback from 2015 Inventory expert reviewers.
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April 2015
Table 2. Previous Inventory Well Counts Compared to 2015 Inventory Well Counts
Well Population
Methodology
2000
2005
2010
2011
2012
2012. Natural Gas Systems Well Counts in 2012 Inventory (1990-2010)
Associated Gas Wells
1990 to 2004 data: API Basic Petroleum Book - Producing Oil Wells
2005 to 2010 data: World Oil Magazine - Producing Oil Wells
246,700
230,604
245,309
N/A
N/A
Non-Associated Gas Wells
1990 to 2003 data: U.S. DOE/EIA - Producing Gas Wells
2004 to 2010 data: World Oil Magazine - Producing Gas Wells
341,678
395,272
484,795
N/A
N/A
Hydraulically Fractured
From state oil and gas inventories of CBM and Barnett shale wells (TX only)
6,892
16,949
50,434
N/A
N/A
2014. Natural Gas Systems Well Counts in 2014 Inventory (1990-2012) ||
Non-Associated Gas Wells
'GAS' wells with > 0 gas production
'OIL' or 'O&G' wells with no liquids production and > 0 gas production
292,004
379,602
466,884
469,426
470,913
Hydraulically
Fractured
Subset of Non-Associated Gas Wells that were horizontally drilled or are in
coalbed, shale, or tight gas reservoirs (as classified using the EIA Crosswalk)
112,547
166,966
220,400
226,038
227,862
Associated Gas Wells
'OIL' or 'O&G' wells with > 0 liquids and gas production
295,188
286,514
310,310
316,065
323,392
2014. Petroleum Systems Well Counts in 2014 Inventory (1990-2012) ||
Oil Wells
From EIA
534,000
498,000
520,000
536,000
536,000a
Stripper Wells
From IOGCC; subset of Oil Wells
411,629
401,072
394,016
394,016
394,016
2014 Inventory Total Active Wells (Non-Associated Gas Wells + Oil Wells)
826,004
877,602
986,884
1,005,426
1,006,913
2015. Natural Gas and Petroleum Systems in 2015 Public Review Inventory (1990-2013) ||
Gas Wells
Wells with > 0 gas production and GOR > 100 MCF/bbl
296,905
378,264
461,036
467,113
464,447
Hydraulically
Fractured
Subset of Gas Wells that were horizontally drilled or are in coalbed, shale,
or tight gas reservoirs (as classified using the EIA Crosswalk)
123,532
180,461
242,023
247,557
248,305
Oil Wells
Wells with > 0 liquids production and GOR < 100 MCF/bbl
767,227
757,076
810,463
829,421
855,979
Associated Gas Wells
Subset of Oil Wells with > 0 gas production
400,930
400,270
441,305
450,971
472,817
Stripper Wells
From IOGCC; subset of Oil Wells
411,629
401,072
394,016
394,016
394,016
2015 Inventory Total Active Wells
1,064,132
1,145,491
1,228,263
1,234,340
1,231,674
a - EIA has not published 2012 final value. This number is ElA's 2011 estimate carried forward unchanged.
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February 2015
Appendix A:
Current Production Sector Methodology
This appendix further documents the current methodology for the production sector, which relies on
source-level emissions that are typically calculated by applying emission factors to either: (1) a well
count or well equipment population value; or (2) a throughput value. For many sources, the emission
calculation methodology may not use well counts as a direct input, but this appendix aims to identify
where there is a "trickle-down" impact of well counts on other activity data. For example, emissions
from small reciprocating compressors are calculated by applying an activity factor for the number of
reciprocating compressors per well to the annual number of non-associated gas wells, and then applying
an emission factor; so the "general basis" for this emission source lists "well count" in the table below
for this source.
Table A.l of this appendix is intended to facilitate contemplating how emission sources will be applied
to different well populations once Drillinglnfo data are used to develop all well populations. As shown in
Table 1 of this document, the current methodology only accounts for fugitive emissions from field
separation equipment as the incremental emissions generated by "Associated Gas" compared to "Oil"
wells. Stakeholder feedback may include reconsideration as to whether there are additional emission
sources currently calculated in the natural gas systems production sector of the Inventory that make
sense to apply to "Associated Gas Wells."
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April 2015
Table A.l. Inventory Natural Gas and Petroleum Systems Onshore Production Emission Source and Activity Factor Bases
Activity Factor Basis
Emission Source
General Basis
Description
Calculation Comments
Natural Gas Systems - FUGITIVE
Gas Wells
Associated Gas Wells
N/A
Emissions are currently accounted for in the Petroleum
Systems Inventory
Non-Associated Gas Wells
Population Based -
Well Count
Annual number of non-associated gas wells without
hydraulic fracturing
Gas Wells with Hydraulic Fracturing
Population Based -
Well Count
Annual number of gas wells with hydraulic fracturing
| Field Separation Equipment ||
Heaters
Separators
Dehydrators
Population Based -
Well Count
Annual total number of non-associated gas wells (with
and without hydraulic fracturing)
Meters/Piping
Population Based -
Well Count
Annual total number of associated and non-associated
gas wells (with and without hydraulic fracturing)
| Gathering Compressors ||
Small Reciprocating Compressors
Population Based -
Well Count
Annual total number of non-associated gas wells (with
and without hydraulic fracturing)
Large Reciprocating Compressors
Large Reciprocating Stations
Population Based -
Pipeline Miles
Annual total gathering pipeline miles
Pipeline Leaks
Population Based -
Pipeline Miles
Annual total gathering pipeline miles
Population Based -
Well Count
Annual total number of non-associated gas wells (with
and without hydraulic fracturing)
Natural Gas Systems - VENTED AND COMBUSTED
Drilling, Well Completion, and Well Workover
Gas Well Completions without Hydraulic
Fracturing
Population Based -
Well Count
Annual percent of non-associated gas well count (with
and without hydraulic fracturing) per NEMS Region and
total
Ratio the annual value to 1992, which is the
basis for the emissions.
Gas Well Workovers without Hydraulic
Fracturing
Population Based -
Well Count
Annual number of non-associated gas wells without
hydraulic fracturing
Hydraulic Fracturing Completions and
Workovers
Population Based -
Event Count
Events counted in each control technology category
based on GHGRP data. See Annex for documentation of
extrapolation to cover time series beginning in 1990.
From GHGRP
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April 2015
Table A.l. Inventory Natural Gas and Petroleum Systems Onshore Production Emission Source and Activity Factor Bases
Activity Factor Basis
Emission Source
General Basis
Description
Calculation Comments
Well Drilling
Population Based -
Well Count
Annual number of gas wells drilled
From EIA
Population Based -
Well Count
Annual percent of non-associated gas well count (with
and without hydraulic fracturing) per NEMS Region
| Produced Water from Coal Bed Methane ||
Powder River
Production Based
Annual gallons of water produced for Powder River Basin
CBM wells
From Wyoming Oil and Gas Conservation
Commission
Black Warrior
Population Based -
Well Count
Annual number of producing CBM wells in Black Warrior
Basin
From Geological Survey of Alabama - State
Oil and Gas Board
| Normal Operations ||
Pneumatic Device Vents
Chemical Injection Pumps
Kimray Pumps
Dehydrator Vents
Population Based -
Well Count
Annual total number of non-associated gas wells (with
and without hydraulic fracturing)
| Condensate Tank Vents ||
Condensate Tanks without Control Devices
Condensate Tanks with Control Devices
Production Based
Annual condensate production
From EIA
| Compressor Exhaust Vented ||
Gas Engines
Population Based -
Well Count
Annual percent of total non-associated gas well count
(with and without hydraulic fracturing), excluding NE
NEMS Region
Ratio the annual value to 1992, which is the
basis for the emissions
Gas wells in NE NEMS Region are not driven
by low pressure gas from the well; only
applies to the other NEMS Regions
| Well Clean Ups ||
Well Clean Ups (LP Gas Wells) - Vent Using
Plungers
Well Clean Ups (LP Gas Wells) - Vent without
Using Plungers
Population Based -
Well Count
Annual total number of non-associated gas wells (with
and without hydraulic fracturing)
| Blowdowns ||
Vessel Blowdowns
Compressor Blowdowns
Compressor Starts
Population Based -
Well Count
Annual total number of non-associated gas wells (with
and without hydraulic fracturing)
Pipeline Blowdowns
Population Based -
Pipeline Miles
Annual total gathering pipeline miles
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April 2015
Table A.l. Inventory Natural Gas and Petroleum Systems Onshore Production Emission Source and Activity Factor Bases
Activity Factor Basis
Emission Source
General Basis
Description
Calculation Comments
Population Based -
Well Count
Annual total number of non-associated gas wells (with
and without hydraulic fracturing)
Upsets |
Pressure Relief Valves
Population Based -
Well Count
Annual percent of non-associated gas well count (with
and without hydraulic fracturing) per NEMS Region and
total
Ratio the annual value to 1992, which is the
basis for the emissions
Mishaps
Population Based -
Pipeline Miles
Annual total gathering pipeline miles
Population Based -
Well Count
Annual total number of non-associated gas wells (with
and without hydraulic fracturing)
(Petroleum Systems-VENTED |
Oil Tanks
Production Based
Annual oil production in the Lower 48
From EIA
Production Based
Average stripper well oil production
From Interstate Oil and Gas Compact
Commission
Population Based -
Well Count
Annual total number of stripper wells
From Interstate Oil and Gas Compact
Commission
Pneumatic Devices, High Bleed
Pneumatic Devices, Low Bleed
Vessel Blowdowns
Compressor Blowdowns
Population Based -
Well Count
Annual total number of producing oil wells
From EIA
Ratio the annual number of wells and
domestic production to the 1993 values,
which is the basis for the emissions.
Compressor Starts
Production Based
Annual domestic production
From EIA
Chemical Injection Pumps
Production Based
Annual domestic production
From EIA
Ratio the annual number of wells and
domestic production to the 1993 values,
which is the basis for the emissions.
Stripper Wells
Population Based -
Well Count
Annual total number of stripper wells
From Interstate Oil and Gas Compact
Commission
Well Completion Venting
Production Based -
Well Count
Annual total number of crude oil wells drilled
From EIA
Well Workovers
Production Based -
Well Count
Annual total number of producing oil wells
From EIA
[Petroleum Systems - FUGITIVE |
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April 2015
Table A.l. Inventory Natural Gas and Petroleum Systems Onshore Production Emission Source and Activity Factor Bases
Activity Factor Basis
Emission Source
General Basis
Description
Calculation Comments
Oil Wellheads (Heavy Crude)
Oil Wellheads (Light Crude)
Population Based -
Well Count
Annual total number of producing oil wells
From EIA
Population Based -
Well Count
Annual total number of stripper wells
From Interstate Oil and Gas Compact
Commission
Separators (Heavy Crude)
Separators (Light Crude)
Heater/Treaters (Light Crude)
Compressors
Population Based -
Well Count
Annual total number of producing oil wells
From EIA
Ratio the annual number of wells and
domestic production to the 1993 values,
which is the basis for the emissions.
Production Based
Annual domestic production
From EIA
Headers (Heavy Crude)
Headers (Light Crude)
Population Based -
Well Count
Annual total number of producing oil wells
From EIA
Floating Roof Tanks
From Industry Panel and Entropy Tank
Survey
Use the 1995 value for all years
Large Compressors
Use the 1995 value for all years
Sales Areas
Production Based
Annual domestic production
From EIA
Pipelines
Population Based -
Pipeline Miles
Total miles of gathering lines
From EIA
No EF for this source
Well Drilling
Population Based -
Well Count
Annual number of oil wells drilled
From EIA
No EF for this source
Battery Pumps
Population Based -
Well Count
Annual total number of producing oil wells
From EIA
(Petroleum Systems - COMBUSTED |
Gas Engines
Population Based -
Well Count
Annual total number of producing oil wells
From EIA
Ratio the annual number of wells and
domestic production to the 1993 values,
which is the basis for the emissions.
Production Based
Annual domestic production
From EIA
Heaters
Production Based
Annual domestic production
From EIA
Well Drilling
Population Based -
Well Count
Annual number of oil wells drilled
From EIA
Flares
Production Based
Annual oil production in the Lower 48
From EIA
Production Based
Average stripper well oil production
From Interstate Oil and Gas Compact
Commission
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April 2015
Table A.l. Inventory Natural Gas and Petroleum Systems Onshore Production Emission Source and Activity Factor Bases
Activity Factor Basis
Emission Source
General Basis
Description
Calculation Comments
Population Based -
Well Count
Annual total number of stripper wells
From Interstate Oil and Gas Compact
Commission
[Petroleum Systems - PROCESS UPSETS ||
Pressure Relief Valves
Production Based
Annual domestic production
From EIA
Well Blowouts Onshore
Population Based -
Well Count
Annual number of oil wells drilled
From EIA
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April 2015
Appendix B:
Information on Options Considered
Table 2B.1 below presents well count activity data for select years from the 2012 and 2014 Inventories, as well as
example counts developed by three proposed approaches for the 2015 Inventory. Option 1 described below uses the
current Inventory methodology to identify wells in natural gas systems (including associated gas wells), and expands the
methodology to also develop petroleum systems counts (i.e., oil well counts). Option 2 described below greatly
simplifies the current Inventory methodology in the interest of easier reproducibility; the ratio of gas to oil production
("gas-to-oil ratio" or GOR) based on Drillinglnfo data is used to assign wells between the natural gas and petroleum
systems source categories, and there is no sub-population of "associated gas" wells within natural gas systems. Option 3
described below expands on Option 2 to acknowledge the idea that oil wells with significant gas production should be
treated differently than primarily gas-producing or oil-producing wells (as they are expected to have emissions
somewhere between the two populations)and therefore includes a population of "associated gas" wells, similar to the
current Inventory and Option 1.
The approaches considered are:
1. For each year, classify all active production wells in the Drill inglnfo database as "Non-associated Gas Wells," "Oil
Wells," and "Associated Gas Wells" (a sub-population of oil wells)starting with existing Inventory methodology
for natural gas systems.
a. Start with the OECA-processed version of the Drillinglnfo database, which includes a PROD_TYPE_CLASS
data field that EPA populates with the primary production type of each active oil and gas well (based on
information reported by the operator and/or assigned by the state). This PROD_TYPE_CLASS field is
populated with one of three values for each well: "GAS," "OIL," or "O&G."
b. Assume that all wells that are classified as "GAS" and produced gas in a given year are "Non-associated
Gas Wells" (and any amount of liquids produced is condensate). Assume that any wells classified as
"OIL" or "O&G" that produced gas but zero liquids in a given year are also "Non-associated Gas Wells."
c. Assume that all wells that are classified as "OIL" and produced liquids in a given year are "Oil Wells."
Assume that any wells classified as "GAS" or "O&G" that produced liquids but zero gas in a given year
are also "Oil Wells."
d. Choose and apply a GOR threshold to classify co-producing "O&G" wellsfor example, GOR > 100
mcf/bbl wells are "Non-associated Gas Wells" and GOR <100 mcf/bbl are "Oil Wells." Note: Table 2
shows counts according to a GOR threshold of 100 mcf/bbl, but other threshold values may be
considered.
e. Assume that any co-producing "OIL" or "O&G" wells are "Associated Gas Wells."
f. Estimate emissions from existing emission sources and methodology currently in the natural gas and
petroleum systems calculation spreadsheets.
2. For each year, classify all active production wells in the Drillinglnfo database as either "Gas Wells" or "Oil Wells"
based solely on GOR.
a. For each well, calculate GOR using actual gas and hydrocarbon liquids data reported by Drillinglnfo.
Note, this approach does not take into account any production classification information reported by
the operator, and includes all hydrocarbon liquids (including condensate) production in the GOR
denominator.
b. Choose and apply a GOR threshold to classify wells as "Gas Wells" or "Oil Wells"for example, GOR >
100 mcf/bbl wells are gas and GOR <100 mcf/bbl are oil. Note: Table 2 shows counts according to a GOR
threshold of 100 mcf/bbl, but other threshold values may be considered.
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April 2015
c. Estimate emissions from existing emission sources and methodology currently in the natural gas and
petroleum systems calculation spreadsheets, except that that "Gas Wells" will be treated as "Non-
associated Gas Wells" currently are, and "Associated Gas Wells" will no longer be a component of the
natural gas systems estimate.
3. For each year, classify all active production wells in the Drillinglnfo database as either "Gas Wells" or "Oil Wells/'
then define an oil well sub-population as "Associated Gas Wells/' all based solely on GOR.
a. Follow Option 2 steps 'a' and 'b' above.
b. Choose and apply a GOR threshold to identify a sub-population of "Oil Wells" that produce substantial
amounts of gas and should be classified as "Associated Gas." Note: Table 2 shows counts according to a
GOR threshold of 12.5 mcf/bbl, but other threshold values may be considered.
c. Estimate emissions from existing emission sources and methodology currently in the natural gas and
petroleum systems calculation spreadsheets.
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April 2015
Table B.l. Previous Inventory Well Counts Compared to 2015 Well Counts Options
Well Population
Methodology
2000
2005
2010
2011
2012
2012 Natural Gas Inventory
Associated Gas Wells
1990 to 2004 data: API Basic Petroleum Book - Producing Oil Wells
2005 to 2010 data: World Oil Magazine - Producing Oil Wells
246,700
230,604
245,309
Not reported
Not reported
Non-Associated Gas Wells
1990 to 2003 data: U.S. DOE/EIA - Producing Gas Wells
2004 to 2010 data: World Oil Magazine - Producing Gas Wells
341,678
395,272
484,795
Not reported
Not reported
Hydraulically
Fractured
From state oil and gas inventories of CBM and Barnett shale wells (TX only)
6,892
16,949
50,434
Not reported
Not reported
2014 Natural Gas Inventory ||
Non-Associated Gas Wells
'GAS' wells with > 0 gas production
'OIL' or 'O&G' wells with no liquids production and > 0 gas production
292,004
379,602
466,884
469,426
470,913
Hydraulically
Fractured
Subset of Non-Associated Gas Wells that were horizontally drilled or are in
coalbed, shale, or tight gas reservoirs (as classified using the EIA
Crosswalk)
112,547
166,966
220,400
226,038
227,862
Associated Gas Wells
'OIL' or 'O&G' wells with > 0 liquids and gas production
295,188
286,514
310,310
316,065
323,392
2014 Petroleum Inventory ||
Oil Wells
From EIA
534,000
498,000
520,000
536,000
536,000a
Stripper Wellsd
From IOGCC; subset of Oil Wells
411,629
401,072
394,016
394,016
394,016
2014 Inventory Total Active Wells (Non-Associated Gas Wells + Oil Wells)
826,004
877,602
986,884
1,005,426
1,006,913
2015 Proposed Option 1b ||
Gas Wells
'GAS' wells with > 0 gas production
'OIL' wells with no liquids production and > 0 gas production
'O&G' wells with GOR > 100 MCF/bbl
286,339
371,092
494,336
485,927
485,916
Hydraulically
Fractured0
Subset of Gas Wells that were horizontally drilled or are in coalbed, shale,
or tight gas reservoirs (as classified using the EIA Crosswalk)
128,546
188,012
266,010
264,304
267,213
Oil Wells
'OIL' wells with > 0 liquids production
'GAS' wells with no gas production and > 0 liquids production
'O&G' wells with GOR < 100 MCF/bbl
407,868
404,084
763,027
774,052
793,156
Hydraulically
Fractured0
Subset of Oil Wells that were horizontally drilled or are in coalbed, shale,
or tight gas reservoirs (as classified using the EIA Crosswalk)
73,291
79,985
148,979
161,388
175,600
Associated Gas Wells
Oil Wells with > 0 gas production
202,306
209,958
402,636
410,591
425,331
Stripper Wellsd
Subset of Oil Wells with < 10 bbl/day liquids production (3,650 bbl/year)
133,188
140,208
322,534
322,133
324,692
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April 2015
Table B.l. Previous Inventory Well Counts Compared to 2015 Well Counts Options
Well Population
Methodology
2000
2005
2010
2011
2012
2015 Inventory Total Active Wells - Option 1
694,207
775,176
1,257,363
1,259,979
1,279,072
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April 2015
Table B.l. Previous Inventory Well Counts Compared to 2015 Well Counts Options
Well Population
Methodology
2000
2005
2010
2011
2012
2015 Proposed Option 2 b ||
Gas Wells
Wells with GOR > 100 MCF/bbl
265,699
342,900
456,845
448,371
446,237
Hydraulically
Fractured0
Subset of Gas Wells that were horizontally drilled or are in coalbed, shale,
or tight gas reservoirs (as classified using the EIA Crosswalk)
118,580
173,314
245,348
242,840
243,947
Oil Wells
Wells with GOR < 100 MCF/bbl
428,508
432,276
800,518
811,608
832,835
Hydraulically
Fractured0
Subset of Oil Wells that were horizontally drilled or are in coalbed, shale,
or tight gas reservoirs (as classified using the EIA Crosswalk)
83,257
94,683
169,641
182,852
198,866
Associated Gas Wells
N/A - Remove from Natural Gas Inventory ||
Stripper Wellsd
Subset of Oil Wells with < 10 bbl/day liquids production (3,650 bbl/year)
312,626
316,710
669,887
671,715
677,514
2015 Inventory Total Active Wells - Option 2
694,207
775,176
1,257,363
1,259,979
1,279,072
2015 Proposed Option 3 b ||
Gas Wells
Wells with GOR > 100 MCF/bbl
265,699
342,900
456,845
448,371
446,237
Hydraulically
Fractured0
Subset of Gas Wells that were horizontally drilled or are in coalbed, shale,
or tight gas reservoirs (as classified using the EIA Crosswalk)
118,580
173,314
245,348
242,840
243,947
Oil Wells
Wells with GOR < 100 MCF/bbl
428,508
432,276
800,518
811,608
832,835
Hydraulically
Fractured0
Subset of Oil Wells that were horizontally drilled or are in coalbed, shale,
or tight gas reservoirs (as classified using the EIA Crosswalk)
83,257
94,683
169,641
182,852
198,866
Associated Gas Wells
Subset of Oil Wells with GOR > 12.5 MCF/bbl
53,856
62,351
82,617
82,384
85,456
Stripper Wellsd
Subset of Oil Wells with < 10 bbl/day liquids production (3,650 bbl/year)
312,626
316,710
669,887
671,715
677,514
12015 Inventory Total Active Wells - Option 3
694,207
775,176
1,257,363
1,259,979
1,279,072
a - EIA has not published 2012 final value. This number is ElA's 2011 estimate carried forward unchanged.
b -The 2015 proposed options do not include state-specific manipulations performed to develop final well populations for natural gas systems. For the 2014 Inventory, the state-specific
manipulations included: early time series years for KY (operators were not required to report production prior to 1997), and later time series years for KY, TN, and MD (there is a lag in
publically available data for these states). The counts presented in this memorandum are using OECA's May 2014 data release of Drillinglnfo. However, the final 2015 Inventory counts
will use a future OECA release (scheduled for December 2014). As a result, state-specific manipulations necessary for the 2015 proposed options may not be necessary with the future
OECA release. Differences between OECA's May 2014 data release and the future OECA release will include: 2011 data for KY (currently only through 2010); 2012 and 2013 data for MD
(currently only through 2011); and 2013 for 24 additional states (currently only partially complete for 2013, which is why 2013 counts are not included in this memorandum). As a result
of using the future OECA data release and implementing the state-specific manipulations, the counts for 2011 through 2013 will increase.
c - Though not a topic discussed in this memorandum, the counts of hydraulically fractured gas and oil wells using current Inventory methodology are shown for the proposed 2015
Inventory options.
d - Though not a topic discussed in this memorandum, the counts of stripper wells (a subset of oil wells) for the proposed 2015 Inventory options are calculated based on Drillinglnfo
production data (whereas current methodology obtains stripper well counts from IOGCC).
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April 2015
Comparison of Approaches Under Consideration
Option 1 retains the current Inventory methodology for identifying "Non-associated Gas Wells" and "Associated Gas
Wells." This approach will produce well count activity data most consistent with previous Inventories. Option 1 is the
only option that gives weight to the production type classification field in the OECA-processed version of the Drillinglnfo
database (this field is based on an OECA-developed crosswalk that assigns the hundreds of reported state production
types into simplified categories of 'GAS', 'OIL', and 'O&G'); using this production type classification field does not lend
itself to straightforward reproduction of well counts by non-EPA entities. Option 1 carries forward the current
methodology of addressing a sub-population of oil wells that are "Associated Gas Wells," which is relatively simple: any
wells with production type of 'OIL' or 'O&G' that produce any amounts of both oil and gas in a given year are considered
"Associated Gas Wells." Option 3 discussed below also develops a population of "Associated Gas Wells" but by a more
nuanced approach that takes into account the relative amounts of oil and gas from co-producing wells (e.g., a well that
produces only 10 mcf gas and 20,000 bbl oil per year may not be considered "Associated Gas").
Both Options 2 and 3 simplify the current Inventory methodology in the interest of easier reproducibility; wells are
apportioned into categories based on solely on GOR, with no consideration to the OECA-assigned production type
classification. Option 2 additionally simplifies the current Inventory methodology in that associated gas wells are not a
separate sub-population within natural gas systems; however, the disadvantage that comes with this simplification is
that emissions from oil wells that produce some gas (but less than the GOR threshold chosen to define gas wells, e.g.,
100 mcf/bbl) will be quantified solely by the petroleum systems "Oil Well" emission sources and factors. Option 2 may
therefore underestimate emissions from oil wells that produce substantial gas.
Option 3 is a more in-depth approach compared to Option 2 because it treats oil wells with significant gas production
differently than "Non-associated Gas Wells" or "Oil Wells" (as they could be expected to have emissions somewhere
between the two populations). Two main challenges come into consideration with Option 3:
1. Potentially revised emission sources and methodology will need to be developed for the "Associated Gas Wells"
population. The current Inventory methodology is a starting point, but it only assigns one emission source to
"Associated Gas Wells" - fugitives from meters/piping. Appendix A details the activity data basis and general
methodology for production sector emission sources in the natural gas and petroleum systems inventories, for
further consideration on this topic. EPA is considering whether this one emission source accurately represents
the incremental emissions from an "Associated Gas Well" compared to an "Oil Well."
2. The GOR selected to define the "Associated Gas Wells" population will need to be thoughtfully chosen and well-
documented. Table 2 presents counts based on 12.5 mcf/bbl, which is a value cited in an attachment to an EPA
white paper regarding hydraulically fractured oil well completions. The basis for the 12.5 value is unclear. A
value should be selected to acknowledge that it is intended to represent oil wells with significant gas production
(i.e., would have more GHG emissions than the typical oil well)but not represent oil-producing wells that have
so much gas production that they should actually be classified as gas wells.
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