EPA-600 /R-96-CSOb 

June 1996 

METHANE EMISSIONS FROM 

TiiE NATURAL GAS INDUSTRY 

VOLUME 2: TECHNICAL REPORT 

FINAL REPORT 

Prepared by: 

Matthew R. Harrison 

Lisa M. Campbell 

Theresa M. Shires 

R. Michael Cowgill 

Radian International LLC 

8501 N. Mopac Blvd. 

P.O. Box 201088 

Austin, TX 78720-1088 

DCN: 650-049-20-01 

For 

GRI Project Manager: Robert A. Lott 

GAS RESEARCH INSTITUTE 

Contract No. 5091-251-2171 

8600 West Bryn Mawr A venue 

Chicago, IL 60631 

and 

EPA Project Manager: David A. Kirchgessner 

U.S. ENVIRONMENTAL PROTECTION AGENCY 

Contract No. 68-01-0031 

National Risk Management Research Laboratory 

Research Triangie Park, NC 27711 
3.0 METHODS 

This section characterizes the natural gas industry and describes in general terms 

the methods used to define and extrapolate err.issions for all source types or categories that 

comprise the industry. 

3.1 Emission Source Characterization 

The first step for estimating methane emissions from the U.S. natural gas industry 

is to identify and characterize each emission source within the industry, so that all significant 

sources are included. To fully characterize the industry. sources were defined by equipment 

type, mode of operation, and type of emissions. 

"While this section draws a general picture of the industry, it is not intended to be a 

definitive picture of any company or of the industry regarding specific operational practices and 

procedures. Rather, it is intended to define the general industry equipment practices and 

procedures used in 1992, the base year of the p:-ogram, that could lead to measurable emissions 

of methane. Details that were useful for detennining methane emissions are contained in specific 

reports (see Table 2-1). 

3.1.1 General Industry Description 

The natural gas industry uses wells to produce natural gas existing in underground 

formations, then processes, compresses, and trar1sports the gas to the customer. Transportation 

and distribution of natural gas involve interstate and intrastate pipeline transportation, storage, 

and fmally distribution of the gas by local distribution pipeline networks. 

9 
The generally accepted segments of the natural gas industry are: 

!) Production 

2) Processing 

3) Transmission/storage 

4) Distribution 

Each of these segments is shown in the flow chart for the industry in Figure 3-1. Some of the 

major equipment in each segment is s:town in Table 3-1. Each segment is described in more 

detail in the following subsections. 

This project set specific boundaries for each segment of the industry that specify 

what equipment is included in the study. The guideline used for setting the boundaries was to 

include only the equipment in each segment that is required for marketing natural gas. For 

example, oil production equipment is excluded if it is used to produce oil and not natural gas. 

Similarly, gas processing equipment associated with the fractionation of propane, butane, and 

natural gas liquids are excluded from consideration. In distribution, all equipment up to and 

including the customer's meter are included. End-user emissions are not included in this 

estimate. 

Each industry segment is described in more detail in the following subsections: 

Production Segment Description 

The production segment is comprised of gas and oil wells and the surface 

equipment required to produce gas. The well includes the holes drilled through subsurface rock 

to reach the producing formation and the subsurface equipment such as casing and tubing pipe. 

Gas and oil surface equipment can include separators, heaters, heater-treaters, tanks, dehydrators, 

compressors, pumps, and pipelines. 

10 
PRODUCTION 

Surface Facilities 

Liquids 

PROCESSING 

Liquids 

TRANSMISSION/ 

STORAGE 

I 

I 

I 

I 

I 

Direct 1 

Compressor 

Stations 

Sales 1 

DISTRIBUTION 

Main and 

Service Pipelines 

I 

I 

I 

.-~c~~~~~~--~~~~f~~~~~ Pipelines I 

I 

I 

I 

I 

I 

I 

L-J c l-----r-~~l~i ~_i~--~~a-~ IH~+---4M 

Storage 

Underground 

Storage 

Reservoir 

Customer Meters 

IIJ Compressor 

@ Meter 

Q Pressure 

1>'<1 Regulator 

Figure 3-1. Gas Industry Flow Chart 
Segment 

Production 

Processing 

Transmission 

Storage 

Distribution 

TABLE 3-1. INDUSTRY CHARACTERIZATION 

·Facilities 

1 

Well Sites, 

Central Gathering Facilities 

' 

1 Gas Plants 

i Transmission Pipeline Networks, 

I Compressor Stations, 

, Meter and Pressure Regulating Stations 

I 

, Underground Injection/Withdrawal 

' 

' 

i Facilities, and Liquefied Natural Gas 

' (LNG) Facilities 

' 

i Main and Service Pipeline Networks, 

' 

: Meter and Pressure Regulating Stations ' 

12 

I Equipment at the Facility 

I 

· Wellheads, Separators, 

Pneumatic Devices, Chemical 

Injection Pumps, Dehydrators, 

Compressors, Heaters, Meters, 

Pipelines 

Vessels, Dehydrators, 

\ Compressors, Acid Gas 

I Removal (AGR) Units, Heaters, 

1 Pneumatic Devices 

~Vessels, Compressors, Pipelines, 

\ Meters/Pressure Regulators, 

i Pneumatic Devices 

i 

) Wellheads, Vessels, 

j Compressors, Dehydrators, 

. Heaters, Pneumatic Devices 

; Pipelines, Meters and Pressure 

I Regulators, Pneumatic Devices, 

: Customer Meters 
The definition for gas industry production equipment excludes equipment 

associated with oil production. Also, unmarketed natural gas, such as that produced by oil wells 

that vent gas or that reinject gas for gas lift circulation only, are not considered part of the natural 

gas industry. Figure 3-2 shows the general equipment found in the oil and gas production 

segment, as well as the boundaries between gas and oil production equipment used by this study. 

The boundary between oil and gas equipment shov.n in Figure 3-2 affects the gas 

industry emissions estimate since it excludes some high emission rate production equipment 

associated with oil production. An accounting oftotal production segment emissions, or just oil 

industry emissions, 'Wi11 have to include the oil industry equipment excluded from this study 

(such as some pnewnatics, some chemical injection pumps, and oil tanks). 

Gas Processing Segment Description 

Natural gas processing plants recover high value liquid products from the gas 

stream and maintain the quality (i.e., content and heating value) of the gas stream. The liquid 

products include natural gasoline, butane, propane, and in some cases, ethane. The products are 

removed by compression and cooling or by absorption. 

A gas plant may have fractionation towers and stabilization towers to further 

purify the individual components of the product stream. The back end of the gas plant, such as 

the fractionation train, is excluded from the gas industry defmition since its function is to purify 

and market liquid products. Also, the back end of the gas plant has negligible methane emissions 

since the liquids handled have little methane content. 

The front end of the gas plant often contains dehydration facilities, wet gas 

compression, and the absorption or compression and refrigeration process. All natural gas 

processing plants are considered part of the natural gas industry, and methane emissions from 

these facilities are included in this study. 

!3 
-

0 

-

"' 

-

"' :: 

OH Wd> ,--A r::::=t 

Wellhead ! L__.l l__J 

~ Compressor 

Oil Well 

w~Jlhe•d r--------, (producing 

gas} 

Coal Bed 

Methane Well 

Gas Well 

Wellbe•d 

Petrokum Industry 

,.... ---- -rCOI!lj)ft$SOf 

------

Sa!rWattt 

T~k 

~ 

~ 

~ Vapor Recovery 

Comp"'ssor 

Pe1rokum Industry 

Figure 3-2. Gas Industry Boundaries 

14 
Transmission and Storage Segment Description 

The transmission segment moves the natural gas from the gas plant or directly 

from field production to local distribution companies (LDCs). Gas is often transported across 

many states, such as from the Gulf Coast to the Eastern seaboard of the United States. The 

transmission segment consists of large diameter pipeline, compressor stations, and metering 

facilities. All of these facilities and all of the equipment they contain are considered part of the 

natural gas industry. 

Transmission compressor stations usually consist of piping manifolds, 

reciprocating engines or gas turbines, reciprocating or centrifugal compressors, and generators, 

as shown in Figure 3-3. Dehydrators may be included but are not typically present because of 

upstream gas drying. Some transmission compressor stations may also include metering 

facilities. 

Transmission companies also have metering and regulating stations (M&PR) 

where they exchange gas with other transmission companies, or where they deliver gas to LDCs 

or industrial customers. These stations may contain heaters, small dehydrators, and odorant 

addition equipment. 

Most storage facilities exist to store natural gas produced during off-peak times 

(usually summer) so that gas can be produced and delivered during peak demand. Storage 

facilities are often located close to consumption centers so that cross-country transmission 

pipelines do not have to be sized for peak demand. Storage facilities can be below or above· 

ground. Above-ground facilities are liquefied natural gas (LNG) facilities that liquefY the gas by 

supercooling and then storing the liquid phase methane in above ground, heavily insulated 

storage tanks. Below-grotmd facilities compress and store the gas (in vapor phase) in one of 

several fonnations: I) spent gas production fields, 2) aquifers,·or 3) salt caverns. Below-ground 

storage is the predominant means of gas storage. 

!5 
Gas 

from 

Pipeline 

TRANSMISSION ABOVE GROUND STORAGE 

COMPRESSOR STATION 

g Cooling 

Compressors ~ LNG Process Tank 

c 

Heaters I 

c 

Gas Transmission Pipeline 

c from 

Pipeline 

BELOW GROUND STORAGE 

c 

Compressor 

c 

~.~.~ Station 

Wells 

Dehydrator ~ ~ ~ Storage Field 

Figure 3-3. Transmission and Storage Stations 
Most storage stations consist of a compressor station that is very similar to a 

transmission compression station (see Figure 3-3). UndergroWld storage facilities also have 

storage field wells, and usually have dehydrators to remove water absorbed by the gas while 

Wlderground. All storage equipment is included in boundaries of the natural gas industry defined 

by this project. 

Distribution Segment Definition 

The distribution segment receives high pressure gas from transmission pipelines, 

reduces the pressure, and delivers the gas to residential, commercial, and industrial consumers. 

Tills segment includes pipelines (mains and services), M&PR stations and customer meters. All 

of these facilities are considered to be an integral part of the gas industry. Figure 3-4 shows a 

schematic of the distribution segment and the equipment that it includes. 

3.1.2 Operating Mode 

After identifying the major equipment (source types) in each industry segment, 

emissions from each source were identified by examining the operating modes of the equipment 

that may lead to emissions, and by associating one of three possible types of emissions from the 

source: fugitive emissions, vented emissions, or combustion emissions. 

The cause of emissions is directly related to the operating mode of the equipment. 

Since more than one cause of emissions can be associated with a particular piece of equipment, it 

is important to identify the various operating modes in order to identify all emissions. In general, 

the operating modes are: 

• Start-up; 

• Normal operations; 

• Maintenance; 

• Upsets; and 

• Mishaps. 

17