User’s Guide for Estimating Carbon Dioxide and Methane Emissions from Natural Gas and Oil Systems Using the State Inventory Tool January 2023


User's Guide for Estimating
Carbon Dioxide and Methane
Emissions from Natural Gas
and Oil Systems Using the
State Inventory Tool

January 2023

Prepared by:
ICF

Prepared for:

State Energy and Environment Program,
U.S. Environmental Protection Agency

This section of the User's Guide provides instruction on using the Natural Gas and Oil
Systems module of the State Inventory Tool (SIT), and describes the methodology used for
estimating greenhouse gas emissions from natural gas and oil systems at the state level.

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Module 4 - Natural Gas and Oil Systems Module

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Table of Contents

1.1	Getting Started	2

1.2	Module Overview	4

1.2.1	Data Requirements	4

1.2.2	Tool Layout	5

1.3	Methodology	6

1.4	Uncertainty	17

1.5	References	17

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1.1 Getting Started

The Natural Gas and Oil Systems module was developed using Microsoft® Excel 2000. While
the module will operate with older versions of Excel, it functions best with Excel 2000 or
later. If you are using Excel 2007 or later, instructions for opening the module will vary as
outlined in the Excel basics below. Some of the Excel basics are outlined in the sections
below. Before you use the Natural Gas and Oil Systems module, make sure your computer
meets the system requirements. In order to install and run the Natural Gas and Oil Systems
module, you must have:

• IBM-PC compatible computer with the Windows 95 operating system or later;

• Microsoft® Excel 1997 or later, with calculation set to automatic and macros
enabled;

• Hard drive with at least 20MB free; and

• Monitor display setting of 800 x 600 or greater.

Microsoft Excel Settings

Excel 2003 and Earlier: For the SIT modules to function properly, Excel must be set to
automatic calculation. To check this setting, launch Microsoft Excel before opening the
Natural Gas and Oil Systems module. Go to the Tools menu and select "Options..." Click on
the "Calculations" tab and make sure that the radio button next to "Automatic" is selected,
and then click on "OK" to close the window. The security settings (discussed next) can also
be adjusted at this time.

Excel 2007 and Later: For the SIT modules to function properly, Excel must be set to
automatic calculation. Go to the Formulas ribbon and select "Calculation Options." Make
sure that the box next to the "Automatic" option is checked from the pop-up menu.

Microsoft Excel Security

Excel 2003 and Earlier: Because the SIT employs macros, you must have Excel security
set to medium (recommended) or low (not recommended). To change this setting, launch
Microsoft Excel before opening the Natural Gas and Oil Systems module. Once in Excel, go
to the Tools menu, click on the Macro sub-menu, and then select "Security" (see Figure 1).
The Security pop-up box will appear. Click on the "Security Level" tab and select medium.
When set to high, macros are automatically disabled; when set to medium, Excel will give
you the choice to enable macros; when set to low, macros are always enabled.

When Excel security is set to medium, users are asked upon opening the module whether to
enable macros. Macros must be enabled in order for the Natural Gas and Oil Systems
module to work. Once they are enabled, the module will open to the control worksheet. A
message box will appear welcoming the user to the module. Clicking on the "x" in the
upper-right-hand corner of the message box will close it.

Excel 2007 and Later: If Excel's security settings are set at the default level a Security
Warning appears above the formula box in Excel when the Natural Gas and Oil Systems
module is initially opened. The Security Warning lets the user know that some active
content from the spreadsheet has been disabled, meaning that Excel has prevented the
macros in the spreadsheet from functioning. Because SIT needs macros in order to function
properly, the user must click the "Options" button in the security message and then select,

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Module 4 - Natural Gas and Oil Systems Module January 2023

"Enable this content" in the pop-up box. Enabling the macro content for the SIT in this way
only enables macros temporarily in Excel but does not change the macro security settings.
Once macros are enabled, a message box will appear welcoming the user to module. Click
on the "x" in the upper right-hand corner to close the message box.

If the Security Warning does not appear when the module is first opened, it may be
necessary to change the security settings for macros. To change the setting, first exit out
of the Natural Gas and Oil Systems module and re-launch Microsoft Excel before opening
the Natural Gas and Oil Systems module. Next, click on the Microsoft Excel icon in the top
left of the screen. Scroll to the bottom of the menu and select the "Excel Options" button to
the right of the main menu. When the Excel Options box appears, select "Trust Center" in
left hand menu of the box. Next, click the gray "Trust Center Settings" button. When the
Trust Center options box appears, click "Macro Settings" in the left-hand menu and select
"Disable all macros with notification." Once the security level has been adjusted, open the
Stationary Combustion module and enable macros in the manner described in the preceding
paragraph.

Viewing and Printing Data and Results

The Natural Gas and Oil Systems module contains some features to allow users to adjust
the screen view and the appearance of the worksheets when they are printed. Once a
module has been opened, you can adjust the zoom by going to the Module Options Menu,
and either typing in a zoom percentage or selecting one from the drop-down menu. In
addition, data may not all appear on a single screen within each worksheet; if not, you may
need to scroll up or down to view additional information.

You may also adjust the print margins of the worksheets to ensure that desired portions of
the Natural Gas and Oil Systems module are printed. To do so, go to the File menu, and
then select "Print Preview." Click on "Page Break Preview" and drag the blue lines to the
desired positions (see Figure 2). To print this view, go to the File menu, and click "Print."
To return to the normal view, go to the File menu, click "Print Preview," and then click
"Normal View."

Figure 1. Changing Security Settings Figure 2. Adjusting Print Margins

Q Microsoft Excel - Bookl

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State Greenhouse Gas Inventory Tool User's Guide for the Natural Gas and Oil Module

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1.2 Module Overview

This User's Guide accompanies and explains the Natural Gas and Oil Systems module of the
SIT. The SIT was originally developed in conjunction with EPA's Emissions Inventory
Improvement Program (EIIP) in order to automate the steps states would need to take in
developing their own emission estimates in a manner that was consistent with prevailing
national and state guidelines. The result was a user-friendly and comprehensive set of
eleven modules that help users estimate greenhouse gas emissions at the state level.

Because most state inventories developed today rely heavily on the SIT, User's Guides have
been developed for each of the SIT modules. These User's Guides contain the most up-to-
date methodologies that are, for the most part, consistent with the Inventory of U.S.
Greenhouse Gas Emissions and Sinks (EPA 2022a). Users can refer to the chapters and
annexes of the U.S. Inventory to obtain additional information not found in the SIT or in the
companion User's Guide.

In 2021, EPA began publishing the results of the Inventory of U.S. Greenhouse Gas
Emissions and Sinks disaggregated by U.S. state (EPA 2022b) to make consistent state-
level GHG data available for all states for use by states, researchers, and the general public.
However, EPA recognizes that there will be differences between the state-level estimates
published by EPA and inventory estimates developed by states using the SIT or other tools.
Inventories compiled by states may differ for several reasons, and differences do not
necessarily mean that one set of estimates is more accurate, or "correct." In some cases,
the Inventory of U.S. Greenhous Gas Emissions and Sinks may be using different
methodologies, activity data, and emission factors, or may have access to the latest facility-
level information through the Greenhouse Gas Reporting Program (GHGRP). In other cases,
because of state laws and regulations, states may have adopted accounting decisions that
differ from those adopted by UNFCCC and IPCC to ensure comparability in national reporting
(e.g., use of different category definitions and emission scopes consistent with state laws
and regulations). Users of state GHG data should take care to review and understand
differences in accounting approaches to ensure that any comparisons of estimates are
equivalent or an apples-to-apples comparison of estimates.

The Natural Gas and Oil Systems module calculates methane (CH4) and carbon dioxide
(CO2) emissions from all phases of natural gas systems (including production, transmission,
venting and flaring, and distribution) and petroleum systems (including production, refining,
and transport). The module provides default data for all emission factors and provides
some activity data; however, EPA encourages the use of more comprehensive data sources
if they are available. Currently default data are not available in the SIT for the
transmission, and distribution of natural gas or the refining, and transportation of oil. If
using outside data sources, or for a more thorough understanding of the module, please
refer to the following discussion for data requirements and methodology.

1.2.1 Data Requirements

To calculate CH4andC02 emissions from natural gas and oil systems, the following data are
required:

• The number of wells and offshore platforms;

• Amount of natural gas vented and flared;

• The number of miles of gathering pipeline;

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•	The number of gas processing plants and compressor stations;

•	The number of miles of transmission pipeline;

•	The number of miles of distribution pipeline, if possible, by type (e.g., cast iron,
steel, plastic)

•	The total number of services (e.g., gas meters);

•	Data on oil production, refining, and transportation; and

•	Emission factors for each of the above activities.

A complete list of the activities for which activity data and emission factors are necessary to
complete the Natural Gas and Oil Systems module is provided in Table 1.

Table 1. Data Requirements for the Natural Gas and Oil Systems Module

Module Worksheet

Activity Data and Emission Factors Required

Natural Gas - Production

Number of wells

Number of shallow-water off-shore platforms

Number of deep-water off-shore platforms

Emission factors for all of the above (MT ChU/well or platform)

Natural Gas -
Transmission

Miles of gathering pipeline

Number of gas processing plants

Number of gas transmission compressor stations1

Number of gas storage compressor stations1

Miles of transmission pipeline

Number of LNG storage compressor stations

Emission factors for all of the above (MT ChU/unit)

Natural Gas - Distribution

Miles of cast iron distribution pipeline2
Miles of unprotected steel distribution pipeline2
Miles of protected steel distribution pipeline2
Miles of plastic distribution pipeline2
Number of services
Number of unprotected steel services
Number of protected steel services
Emission factors for all of the above (MT ChU/unit)

Emission factor for alternate method* (MT ChU/per mile of distribution
pipeline)

Natural Gas - Venting and
Flarinq

Billion BTUs of natural gas vented and flared

Emission factor (MT CC^/Billion Btu natural qas vented and flared)

Petroleum Systems

Barrels of oil produced

Barrels of oil refined

Barrels of oil transported

Emission factor (kg CH4/IOOO barrels)

1	An alternate method is available in which only total transmission pipeline miles are required, and the
number of gas transmission and storage compressor stations is calculated based on this entry.

2	An alternate method is available in which only total distribution pipeline miles are required, rather
than by pipeline type.

1.2.2 Tool Layout

Because there are multiple sections to complete within the Natural Gas and Oil Systems
module, it is important to understand the module's overall design. The layout of the Natural
Gas and Oil Systems module and the purpose of its worksheets are presented in Figure 3.

State Greenhouse Gas Inventory Tool User's Guide for the Natural Gas and Oil Module

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Figure 3. Flow of Information in the Natural Gas and Oil Systems Module*

Control Worksheet

Individual Sector Worksheets

1. Choose a State

2. Natural Gas Production

Enter production activity data

2.- 6. Enter emission factors and activity data for:

3. Natural Gas Transmission

Natural Gas Production

Enter transmission activity data

Natural Gas Transmission J

4. Natural Gas Distribution

Natural Gas Distribution ""

Enter distribution activity data

Natural Gas Venting and Flaring

5. Natural Gas Venting and Flaring

Petroleum Systems

Enter venting and flaring activity data and percent flared

6. Petroleum Systems

Enter petroleum systems activity data

7. View Summary Data

+ Summary Data

I Presented in both table and graphical formats in MMTC02E

8. Export Data

Uncertainty

Review information on uncertainty associated with the default data

* These worksheets are the primary worksheets used in the Natural Gas and Oil Systems module; subsequent
worksheets are used to populate the default data and are provided for informational purposes only.

1.3 Methodology

This section provides instructions for using the Natural Gas and Oil Systems module of the
SIT to estimate fugitive emissions from natural gas and oil systems. Emissions are
calculated for several subcategories, including the production, flaring, transmission, and
distribution of natural gas and the production, refining, and transportation of oil. Within the
Natural Gas and Oil Systems module, it is important to account for emissions from natural
gas and petroleum
systems separately
because the
emission factors
and methods are
fuel specific.

Because the
methodology
differs for each
subcategory, they
are discussed
separately, and

Box 1: State Energy Data Sources

Note that no default activity data are available for the transmission or distribution of
natural gas. If state-specific data sources are not available, users can obtain much of
the required data from the Energy Information Administration (EIA)
ChttD://eia.doe.aov1. The Mineral Management Services (MMS) also provides a
comprehensive source of data for off-shore oil and gas production activities
f http://www.mms.gov'). In addition, the Office of Pipeline Safety (OPS) has detailed
and exhaustive data on all kinds of pipeline (transmission, gathering, distribution,
services) that is accessible to the public on its website

Chttp://ops.dot.gov/stats.htm1. The SIT has more detailed recommendations for data
sources for each activity on the gas and oil data sources worksheets.

specific examples are provided.

The Natural Gas and Oil Systems module automatically calculates emissions after you enter
activity data for each worksheet (and select or enter the emission factors on the control
worksheet). The tool provides default data for venting and flaring of natural gas and the
number of natural gas wells, but data must be obtained for the remaining subcategories
(see Box 1 for suggestions on where to find data).

The Natural Gas and Oil Systems module follows the general methodology outlined in the
EIIP guidance, however because of the automation of the calculations within the tool, the
order of steps discussed in this User's Guide do not follow the order of steps discussed
within the EIIP guidance document. This User's Guide provides an overview of the
estimation methodology used in the Natural Gas and Oil Systems module by walking
through the following steps: (1) select a state; (2) enter emission factors and activity data
for natural gas production; (3) enter emission factors and activity data for natural gas
transmission; (4) enter emission factors and activity data for natural gas distribution; (5)
enter emission factors and activity data for natural gas venting and flaring; (6) enter

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emission factors and activity data for petroleum systems; (7) review summary information;
and (8) export data.

For all subcategories, the basic process is to multiply the activity data by the emission factor
to obtain the emission estimate, which is then converted to million metric tons carbon
dioxide equivalent (MMTCO2E) by multiplying by the GWP of ChU (25) and dividing by 106.
The general equation used to calculate emissions from natural gas systems is shown in
Equation 1. The equation used for venting and flaring of natural gas is similar but includes
the flaring percent and does not include the GWP because emissions are already in units of
CO2, as shown in Equation 2. The equation used for petroleum systems is shown in
Equation 3.

Equation 1. General Emission Equation for Natural Gas Systems

Emissions (MMTCO2E) =

Activity Data x Emission Factor (MT CH4/unit activity data) x 25

(GWP)

Equation 2. Emission Equation for Venting and Flaring of Natural Gas

Emissions (MMTCO2E) =

Activity Data (BBtu) x Emission Factor (MT C02/BBtu) x % flared

-r 106 (MT/MMT)

Equation 3. General Emission Equation for Petroleum Systems

Emissions (MMTCO2E) =

Activity Data ('000 barrels) x Emission Factor (kg ChU/'OOO barrels) -r
1,000 (kg/MT) X 25 (GWP) -r 106 (MT/MMT)

Step (1) Select a State

To begin, select the state for which you would like to perform the analysis. This step will
automatically select the appropriate state default data for the remainder of the calculations
throughout the tool.

Step (2) Enter Emission Factors and Activity Data for Natural Gas Production
Control Worksheet

On the control worksheet, either select the default data provided or enter user-specified gas
and activity-specific emission factors that will be used throughout the tool. To proceed with
the default emission factors, select the "Check/Uncheck AN" button or check the default box
directly to the right of individual yellow input cells. Note that these numbers can be
overwritten if you discover that the data for your state differ from the default data provided
by the tool. To enter user-specified inputs, enter data directly into the yellow input cells. If
the user-specific inputs do not match the default data in the control worksheet (i.e., the
default value is overwritten), the text will appear red. See Figure 4 for locations of the
"Check/Uncheck AN" buttons, individual default check boxes, and yellow input cells.
Information on emission factors is discussed below.

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Figure 4. Control Worksheet for the Natural Gas and Oil Systems Module

E3 State Inventory Tool - Natural Gas and Oil Systems

File Edit Module Options

Stote Inventory Tool - Emissions from Natural Gas and Oil Systems

1. Choose a state. | California | ~ |

This is very important- it selects the correct default variables for your si

| Consult EIIP Guidance |
Reset ALL!

2. - 5. Enter emission factors and activity data for natui
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Module 4 - Natural Gas and Oil Systems Module

January 2023

For the natural gas production sector, enter emission factors on the control sheet in the
yellow cells. The default emission factors for natural gas wells vary by year and region,
while the default emission factors for offshore deep-water and shallow-water platforms do
not vary by region or year. The emission factors for natural gas well production are based
on the emission factors used in U.S. EPA (2022a) and are ultimately based on GRI data
source estimates.

Natural Gas Production Worksheet

Most gas production is from gas or oil wells. Gathering lines are used to bring raw gas to a
collection point or points within a production field. Because ChU is the major component of
natural gas, leaks or venting from the gathering systems result in Chk emissions.

Natural gas is usually processed in gas plants to remove and process the natural gas liquids
and to prepare the natural gas for pipeline transportation. During processing, natural gas is
dried, and a variety of processes may be used to remove most of the heavier hydrocarbons,
or condensate, from the gas. Processed gas is then injected into the natural gas
transmission system, and the heavier hydrocarbons are marketed separately. Major ChU
emission sources in the gas processing are compressor fugitives, compressor exhaust,
vents, pneumatic devices, and blowdown.

On the natural gas production worksheet, shown in Figure 5, the orange cells indicate where
the required activity data are entered manually. Default data for natural gas well
production from EIA (2022c) is available for most states. Emissions are calculated by
multiplying activity data by the appropriate emission factor to obtain the total ChU emissions
in metric tons. Then, the total emissions are converted into MMTCO2E, by multiplying by
the GWP for ChU (25) and dividing by 106 (Equation 1).

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Figure 5. Example of Activity Data and Emission Factors Applied in the Natural Gas

Production Worksheet

E State Inventory Tool - Natural Gas and Oil Systems

Step (3) Enter Emission Factors and Activity Data for Natural Gas Transmission

Transmission pipelines are large diameter, high-pressure lines that transport gas from
production fields, processing plants, storage facilities, and other sources of supply over long
distances to local distribution companies or to large volume customers. A variety of
facilities support the overall system, including metering stations, maintenance facilities, and
compressor stations located along pipeline routes. Compressor stations, which maintain the
pressure in the pipeline, generally include upstream scrubbers, where the incoming gas is
cleaned of particles and liquids before entering the compressors. Reciprocating engines and
turbines are used to drive the compressors. Major ChU emission sources are chronic leaks,
compressor fugitives, compressor exhaust, vents, and pneumatic devices.

Control Worksheet

On the control sheet, enter emission factors (in metric tons of ChU per unit) for gathering
pipeline, gas processing plants, gas transmission compressor stations, gas storage
compressor stations, transmission pipeline, and LNG storage compressor stations.

State Greenhouse Gas Inventory Tool User's Guide for the Natural Gas and Oil Module

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Natural Gas Transmission Worksheet

For the transmission worksheet, an alternate method is available if data on the number of
gas transmission and storage stations is not accessible. To use the alternate method, check
the box at the top of each year's calculations, and make sure to enter 'miles of transmission
pipeline' in the activity data. The tool will then estimate the quantity of these stations
based on transmission pipeline mileage. An example of the transmission worksheet is
shown in Figure 6 (input cells shown in blue).

Figure 6. Example of Activity Data and Emission Factors Applied in the Natural Gas
Transmission Worksheet

E State Inventory Tool - Natural Gas and Oil Systems

i S] File Edit Module Options

I Type a question for help

3. Emission from Natural &as Activities in California

Return to
Control Sheet

Check All Boxes

Clear All Data

Number Of Gas Transmission Compressor
Stations/Mile of Transmission Pipeline

0.0060 Number Of Gas Storage Compressor

Stations/Mile of Transmission Pipeline

Natural Gas - Transmission 1990

Activity Data

Emission

metric tons CH, per gear perl
activity unit

Check box if no data for
compressor stations

Miles of gathering pipeline
Number of gas processing plants
Number of LNG storage compressor st

Miles of transmission pipeline „>

I K I 0.61 = I —

- I.I

Number of gas transmission compressor stations
Number of gas storage compressor stations

—

Required Activity Data

Emission Factors

Total

Natural Gas - Transmission 1991

stations f o r th is year.

Miles of gathering pipeline
Number of gas processing plants
Number of LNG storage compressor st

in pipeline | | „ I _ . . _ . . _ .

m \ Control / Natural Gas - Production \ Natural Gas - Transmission / Natural Gas - Distribution / Natural Gas - Venting Flaring / Petrol* U

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Step (4) Enter Emission Factors and Activity Data for Natural Gas Distribution

Distribution pipelines are extensive networks of generally small diameter, low-pressure
pipelines. Gas enters distribution networks from transmission systems at city gate stations,
where the pressure is reduced for distribution within cities or towns. Major ChU emission
sources are chronic leaks, meters, regulators, and mishaps.

Control Worksheet

If you are using the preferred method of calculating emissions from natural gas distribution,
enter emission factors (in metric tons of Chk per mile of pipeline) for cast iron distribution
pipeline, unprotected steel distribution pipeline, protected steel distribution pipeline, and
plastic distribution pipeline. If you are using the alternate method, you need only enter an
emission factor of metric tons of ChU per mile of distribution pipeline (all types of pipeline).
Then for both methods, enter the emission factors for all natural gas services (i.e., end-
users), for unprotected steel services, and for protected steel services.

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Natural Gas Distribution Worksheet

For distribution, states are encouraged to use the method provided for calculating emissions
from specific types of distribution pipeline. However, an alternate method is offered based
on a single emission factor for total distribution pipeline. If data are unavailable for the
mileage of specific pipeline types, then check the box at the top of each year's calculations
and enter the total pipeline mileage where indicated. The green input cells in Figure 7 show
where activity data are required.

Figure 7. Example of Activity Data and Emission Factors Applied in the Natural Gas
Distribution Worksheet

E State Inventory Tool - Natural Gas and Oil Systems |[ a11[ X |

Step (5) Enter Emission Factors and Activity Data for Natural Gas Venting and
Flaring

Control Worksheet

Enter the emission factor for natural gas venting and flaring on the control worksheet. This
emission factor must account for both vented and flared natural gas. The default emission
factor is taken from U.S. EPA (2022a).

Natural Gas Venting and Flaring Worksheet

The venting and flaring worksheet is unique because it calculates CO2 emissions from
flaring, and it requires both activity data for the amount of natural gas vented and flared,
and the percent of gas flared. Default activity data are available in the SIT for most states

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from the EIA Natural Gas Navigator.1 An example of the use of the activity data, emission
factor, and percent flared can be seen in Figure 8 (input cells are shown in pink). While the
required activity data for this worksheet is the total amount that is vented and flared, the
emissions calculations are for the amount of gas that's flared. The SIT assumes that 80
percent of this gas is flared and that the remaining 20 percent (i.e., the amount that's
vented) must be accounted for in the petroleum systems production category. Because
there is no default data for petroleum systems in the SIT, the user must make sure that the
amount of gas flared is not double counted when calculating emissions from the petroleum
systems category.

Venting and flaring refer to the disposal of gas that cannot be contained or otherwise
handled. Venting and flaring activities are associated with combined oil and gas production
and take place in production areas where gas pipeline infrastructure is incomplete, and the
natural gas is not injected into reservoirs.

Figure 8. Example of Activity Data and Emission Factor Applied in the Natural Gas
Venting and Flaring Worksheet

E State Inventory Tool - Natural Gas and OK Systems

Step (6) Enter Emission Factors and Activity Data for Petroleum Systems
Control Worksheet

The petroleum system emission factors used in the SIT are implied emission factors derived
from U.S. EPA (2022a). Using the available published oil system emission estimates, the
implied emission factors were developed by dividing the emission estimates from each of
the major activity groups (production, refining, and transportation) by the appropriate
activity data at the national level. These implied emission factors are calculated for each
year in the SIT. States are encouraged to use state-specific emission factors if data are
available, as actual emissions depend on site-specific characteristics including facility
design, operation, and maintenance.

1 Available online at: https://www.eia.gov/dnav/ng/NG PROD WELLS SI A.htm

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Petroleum Systems Worksheet

Required data for the petroleum systems worksheet include the amount of oil produced
(including venting), refined, and transported in the state. Figure 9 shows an example of the
data used for this sector, the yellow cells are input cells. Default data are not provided in
the SIT, so users must input data for emissions to be estimated. If state-specific data
sources are not available, users can obtain oil production data from EIA's Petroleum Supply
Annual.2 Refining data can be calculated using data from the Petroleum Supply Annual and
the calculator provided in the SIT on the oil data sources worksheet. Currently, no uniform
data source has been identified for oil transportation activities, so in the absence of other
information it is recommended that users assume that the amount of oil transported is
equivalent to the amount of oil refined in the state.

Figure 9. Example of Activity Data and Emission Factors Applied in the Petroleum
Systems Worksheet

E State Inventory Tool - Natural Gas and Oil Systems

a File Edit Module Options

Type a question For help
K L

J E

6. Emissions from Petroleum Systems in California

Return to
Control Sheet

So to Summar
Sheet

Petroleum Systems

1990

17 Default Activity Data?

Emission Factor Metric Tons CH«

kg CH< per year per
1000 bbl

Oil Production
Oil Refining
Oil Transportatior
Total

Petroleum Systems

Oil Production
Oil Refining
Oil Transportatior
Total

192,281

4.04

1.10

Emission Factors

1.10

MMTCOiE

'000 barr

Activity Data

* 1 1-34l

Petroleum Systems

Oil Production
Oil Refining
Oil Transportatior
Total

Default Activity Data?

Emission Factor

kg CH< per year per
1000 bbl

Metric Tons CH«

~' / Natural Gas - Transmission I Natural Gas - Distribution I Natural Gas - Venting Flaring \ Petroleum Systems I Summary / Uncertaint' I <,

CH4 emissions from oil systems are estimated using the "Tier 1" approach developed by the
IPCC (IPCC 1997). The approach is simpler than the method used for natural gas systems,
but it is also less accurate. The SIT calculates emissions by multiplying the required state-
level data on oil production, refining, and transportation by the appropriate emission factors
and summing across activity types to calculate total emissions, as shown in Equation 3. The
general sources of ChU emissions from oil systems that should be accounted for can be
categorized into emissions from: (1) normal operations, (2) routine maintenance, and (3)
system upsets and accidents.

1 Available online at: http://www.eia.aov/petroleum/supplv/annual/volumel/.

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Normal operations include emissions from the day-to-day operations of a facility. Oil
production and transportation facilities can emit ChU due to a wide variety of operating
practices and factors, including emissions from pneumatic devices, leaks from system
components, emissions from process vents, emissions from starting and stopping
reciprocating engines or turbines, and emissions during drilling activities.

Routine maintenance includes regular and periodic activities performed in the operation of
the facility. These activities may be conducted frequently, such as launching and receiving
scrapers (pigs) in a pipeline, or infrequently, such as evacuation of pipes ("blowdown") for
periodic testing or repair. In each case, the required procedures release gas from the
affected equipment. Releases also occur during maintenance of wells ("well workovers")
and during replacement or maintenance of fittings.

System upsets are unplanned events in the system. The most common upset is a sudden
pressure surge resulting from the failure of a pressure regulator. The potential for
unplanned pressure surges is considered during facility design, and facilities are provided
with pressure relief systems to protect the equipment from damage due to the increased
pressure. Relief systems vary in design. In some cases, gases released through relief
valves may be collected and transported to a flare for combustion or re-compressed and
reinjected into the system. In these cases, ChU emissions associated with pressure relief
events will be small. In older facilities, relief systems may vent gases directly into the
atmosphere or send gases to flare systems where complete combustion may not be
achieved. The frequency of system upsets varies with the facility design and the operating
practices. In particular, facilities operating well below capacity are less likely to experience
system upsets and related emissions. Emissions associated with accidents are also included
in the category of upsets.

Step (7) Review Summary Information

The steps above provide estimates of total emissions for each natural gas and oil activity.
These are summed over all activities, for each year, and the information is collected on the
summary worksheet. The summary worksheet displays results in MMTCO2E, as well as by
individual gas. Additionally, the summary worksheet provides an overview of sources
excluded from the current emission estimates. Users should check this list to see if they
wish to go back and enter data for any of the omitted activities. Figure 10 shows the
summary worksheet that sums the emissions from all sectors in the Natural Gas and Oil
Systems module. In addition, the results are displayed in graphical format at the bottom of
the summary worksheet.

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Figure 10. Example of the Summary Worksheet in the Natural Gas and Oil Systems
Module

Step (8) Export Data

The final step is to export the summary data. Exporting data allows the estimates from
each module to be combined later by the Synthesis Module to produce a comprehensive
greenhouse gas inventory for the state.

To access the "Export Data" button, return
to the control worksheet and scroll down to
the bottom (8). Click on the "Export Data"
button and a message box will open that
reminds the user to make sure all steps of
the module have been completed. If you
make any changes to the Natural Gas and
Oil Systems module later, you will then
need to re-export the results.

Clicking "OK" prompts you to save the file. The file is already named, so you only need to
choose a convenient place to save the file. After the file is saved, a message box will
appear indicating that the data was successfully exported.

While completing the modules, you are encouraged to save each completed module; doing
so will enable you to easily make changes without re-running it entirely.

Following data export, the module may be reset and run for an additional state.
Alternatively, you may run the remaining modules of the SIT to obtain a comprehensive
profile of emissions for your state.

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Note: the resulting export file should not be
modified. The export file contains a summary
worksheet that allows users to view the results, as well as
a separate data worksheet with an unformatted version of
the results. The second worksheet, the data worksheet,
contains the information that is exported to the Synthesis
Tool. Users may not modify that worksheet.
Adding/removing rows, moving data, or making other
modifications jeopardizes the ability of the Synthesis
Module to accurately analyze the data.

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1.4 Uncertainty

In the upper right-hand corner of the summary worksheet is a button: "Review discussion of
uncertainty associated with these results." By clicking on this button, you are taken to a
worksheet that discusses the uncertainty surrounding the activity data and emission factors,
and how the uncertainty estimates for this source category affect the uncertainty of the
emission estimates for your state.

1.5 References

EIA, 2022a. EIA's Monthly Energy Review. "September 2022 Monthly Energy Review."
Available at: https://eia.aov/totalenerav/data/monthlv/Ddf/mer.Ddf

EIA 2022b. EIA's Natural Gas Navigator. "Number of Producing Gas Wells." Available at:
https://www.eia.aov/dnav/na/NG PROD WELLS SI A.htm

EIA 2022c. EIA's Natural Gas Navigator. "Number of Gas Producing Oil Wells." Available at:
https://www.eia.aov/dnav/na/NG PROD OILWELLS SI A.htm

GRI. 1996. Methane Emissions from the Natural Gas Industry, Gas Research Institute and
U.S. Environmental Protection Agency. EPA-600/R-96-080a.

IPCC. 1997. IPCC Guidelines for National Greenhouse Gas Inventories, 3 volumes: Vol. 1,
Reporting Instructions; Vol. 2, Workbook; Vol. 3, Draft Reference Manual.
Intergovernmental Panel on Climate Change, Organization for Economic Co-Operation
and Development. Paris, France.

U.S. EPA. 2022a. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2020.
Office of Atmospheric Programs, U.S. Environmental Protection Agency. EPA 430-R-22-
003. Available at: https://www.epa.gov/ohgemissions/inventorv-us-oreenhouse-oas-
emissions-and-sinks

U.S. EPA. 2022b. Inventory of U.S. Greenhouse Gas Emissions and Sinks By State: 1990 -
2020. Office of Atmospheric Programs, U.S. Environmental Protection Agency. Available
at:

https://www.epa.aov/svstem/files/documents/202208/StateGHGI Methodology Report
August 2022.pdf

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