METHANE’S ROLE IN PROMOTING SUSTAINABLE DEVELOPMENT IN THE OIL 

AND NATURAL GAS INDUSTRY 

This paper was originally published for the 24th World Gas Conference that took place in 

Buenos Aires, Argentina on 5-9 October 2009 and is contained in the conference 

proceedings. 

Carey Bylin1

, Don Robinson2, Sandra Seastream3, Brian Gillis4, Javier Bocanegra5, Bonnie Ellwood6, Larry 

S. Richards7

, Fernando Cornejo8, Alexandr Ishkov9, Gretta Akopova10, Nadezhda Boyarchuk11

1. U.S. Environmental Protection Agency 

2. ICF International 

3. ICF International 

4. ICF International 

5. Petróleos Mexicanos (PEMEX) 

6. EnCana Oil & Gas (USA), Inc. 

7. Hy-Bon Engineering 

8. Pluspetrol 

9. Gazprom 

10. VNIIGAZ 

11. VNIIGAZ 

Keywords: 1. methane; 2. climate change; 3. energy efficiency; 4. cost-effective; 5. sustainability 

1 
Introduction

Methane’s unique role as a greenhouse gas and as the primary component of natural gas means that 

reducing methane emissions can yield significant economic, environmental and operational benefits. 

Methane emission mitigation activities undertaken by oil and natural gas companies prevent the loss of 

a valuable non-renewable resource by directing this clean energy source to beneficial use either via 

sales or internal use. At the same time, companies are reducing their emissions of greenhouse gases, 

improving operational safety and enhancing the efficiency of their operations. Further economic and 

operational benefits can result when methane mitigation activities reduce maintenance and fuel 

requirements or result in the capture of other valuable hydrocarbon resources. Numerous proven costeffective technologies and practices exist that oil and natural gas companies have implemented to 

reduce methane emissions while also generating positive cash flows from utilizing the methane. 

This paper summarizes a number of established methods to identify, measure, and reduce methane 

emissions from a variety of equipment and processes in oil and gas production and natural gas 

processing and transmission facilities. The following detailed discussions provide background on 

expected levels of vented and fugitive methane emissions from natural gas processing plants, 

compressor stations, storage tanks, centrifugal compressors, and well completion activities, based on 

published data and industry experience. This information is supported with case studies covering 

mitigation activities that have been undertaken by Petróleos Mexicanos (PEMEX) in Mexico, Pluspetrol 

in Argentina, EnCana Oil & Gas (USA), Inc. in the United States, and Gazprom in Russia. For each 

case study, operational, economic and environmental considerations are discussed to show how these 

companies are delivering greater revenue as well as environmental, efficiency and safety benefits 

while also conserving natural gas resources worldwide. 

Background 

By 2010, it is estimated that annual methane emissions from the global oil and natural gas industry will 

total 1.354 billion tonnes carbon dioxide equivalent1

. This equates to 94.2 billion m3or U.S.$10.0 billion 

to U.S.$23.3 billion (at gas values of U.S.$106/thousand m3

 to U.S.$247/ thousand m3) worth of 

natural gas lost to the atmosphere. By 2020, it is anticipated that these figures will increase by 35%, 

reaching 1.827 billion tonnes carbon dioxide equivalent, which equates to 127.9 billion m3 of natural 

gas lost to the atmosphere. Methane represented 14 percent of total anthropogenic (man-made) 

emissions of greenhouse gases in 2004.2

 Emissions from the oil and natural gas industry are the 

largest anthropogenic source and second largest overall source of global methane emissions, 

accounting for 18 percent of worldwide methane emissions. With an atmospheric lifetime of 12 years, 

methane plays a critical role in achieving short-term climate impacts. A 2008 report by the 

Intergovernmental Panel on Climate Change (IPCC) shows that, over a relatively short time frame (20 

years), the warming effect of year 2000 methane and carbon dioxide emissions will be the same, even 

though the volume of methane emissions is significantly smaller.3

 

In the oil and natural gas sector, the majority of methane emissions result from oil and natural gas 

production, and gas processing, transmission, and distribution operations. These emissions can take 

the form of unintentional leaks, intentional or designed venting from operational processes, and 

emissions due to maintenance or operational disruptions. Emissions from normal operations include: 

natural gas engines and turbine exhaust that includes uncombusted methane; bleed and discharge 

emissions from natural gas-driven pneumatic devices; vents from reciprocating and centrifugal 

compressors; emissions from storage tanks; and well workover, blowdown and completion activities. 

Fugitive leaks from system components can occur as gas moves through hundreds of valves, 

processing mechanisms, compressors, pipe connectors, pressure, level and temperature control 

valves, and other equipment. Whenever the gas moves through valves and piping connectors under 

high pressure, leaks can develop that allow methane to escape to the atmosphere. Maintenance 

emissions originate from pipelines, compressors, and other equipment when they are taken offline and 

natural gas is vented in order to safely perform maintenance activities. Pressure surge relief systems 

and accidents can lead to system upset emissions. 

 

To advance global reductions in methane emissions levels from the oil and natural gas sector, as well 

as other sources, the Methane to Markets Partnership was launched in 2004. Methane to Markets is 

an international public-private partnership that promotes cost-effective recovery of methane for use as 

a clean energy source. Participants currently include 28 national governments, including the U.S., 

Argentina, Mexico and Russia, and the European Commission, as well as over 900 other public and 

private sector organizations. With a focus on four major anthropogenic sources of methane emissions 

(oil and gas systems, agriculture (animal waste management), coal mines, and landfills), the 

2 
Partnership acts as a mechanism to bring together interested parties from national governments, 

private sector entities, development banks, non-governmental organizations, financial and technical 

experts, and other stakeholders to facilitate methane project development and implementation around 

the world. 

In the oil and natural gas sector, the U.S. Environmental Protection Agency (EPA) contributes to these 

goals by drawing on a 16-year partnership with the oil and natural gas industry to promote technology 

transfer and capacity building in relation to numerous cost-effective methane mitigation options. Since 

1993, oil and natural gas companies have partnered with the U.S. EPA’s Natural Gas STAR Program 

to promote development, implementation and reporting of profitable, voluntary methane emission 

mitigation activities. This collaboration has resulted in the identification by industry of over eighty costeffective methane mitigation technologies and practices. 

Overview: Technical Mitigation Options & Case Studies 

Through the Natural Gas STAR Program, in conjunction with the Methane to Markets Partnership, oil 

and natural gas companies are increasingly sharing information about successful implementation of 

methane mitigation projects. As the following case studies will show, companies can draw on existing 

commercially available, cost-effective technologies and practices to reduce methane emissions. By 

mitigating natural gas losses and contributing to gas sales and use, these activities can be a positive 

near-term focus for oil and gas companies interested in reducing their emissions of greenhouse gases 

and enhancing efficient management of this energy resource. The following sections discuss methane 

mitigation opportunities, including conducting methane emission detection and quantification surveys, 

implementing reduced emission completions, installing tank vapor recovery, and upgrading 

compressor seals. Paybacks range from 0.2 years to 3 years and these activities have broad 

applicability globally and across the industry. 

Mitigation Opportunity - Methane Emission Detection and Quantification 

Background 

Operators at virtually every type of natural gas industry site have benefited by focusing on methane 

emission detection and quantification programs, given that repair of leaking components often 

amounts to tightening valves and connectors with immediate payback. In addition to finding leaking 

components, such targeted identification and quantification exercises also include quantification of 

process vent emissions from equipment such as tanks and compressors, providing oil and gas 

companies with the information needed to identify and prioritize focus areas for mitigation projects 

Fugitive emissions from equipment leaks are unintentional losses and may arise due to normal wear 

and tear, improper or incomplete assembly of components, inadequate material specification, 

manufacturing defects, damage during installation or use, corrosion, fouling and environmental effects. 

Components also tend to have greater average emissions when subjected to frequent thermal cycling, 

vibrations or cryogenic service. Typically a small percentage of equipment components have any 

measurable leakage, and of those normally a small percentage contributes to the majority of the 

emissions. Thus, the control of fugitive emissions is a matter of minimizing the potential for big leaks 

and providing early detection and repair. 

Implementing a directed inspection and maintenance (DI&M) program is a proven, cost-effective way 

to detect, measure, prioritize, and address equipment leaks or other vented sources to reduce 

methane emissions. A DI&M program begins with a baseline survey to identify and quantify leaks. 

Repairs are then made to the leaking components that are cost-effective to fix, based on criteria such 

as repair cost, expected life of the repair, and payback period. Subsequent surveys are designed 

based on data from previous surveys, allowing operators to concentrate on the components that are 

most likely to leak and are profitable to repair. 

Emission Detection and Measurement 

A key barrier to addressing methane emissions has been the inability of companies to quickly and 

accurately detect, and subsequently quantify, methane emissions. Methane is a colorless, odorless 

gas and therefore emissions often go unnoticed. Though there are a variety of leak detection methods 

available, including soap bubble screening, electronic screening (“sniffers”), Toxic Vapor Analyzers 

and Organic Vapor Analyzers, ultrasound and acoustic leak detection, recent technology 

developments are improving operators’ ability to comprehensively identify methane emission sources. 

One relatively new technology to detect hydrocarbon emissions is an infrared (IR) camera, which gives 

the camera operator a live, real-time visual image of methane emissions (see Exhibit 1). Hydrocarbon 

3 
emissions absorb infrared light at a certain wavelength. The IR camera uses this characteristic to 

detect and visually show the source of methane or other hydrocarbon emissions. The IR camera scans 

the components in real time at 30 to 50 Hz4

 scan frequency and spectral range of 3 to 5 microns. This 

scanned area is then converted into a live image in real time such that the gas plumes are visible due 

to their absorption of the IR light. Imaging can be performed from a distance from the target and the 

process doesn’t impact plant operations. Operators regularly state that infrared cameras pay back in 

the first several uses due to the value of the gas saved from the leaks that are found and repaired. 

 

Exhibit 1 Infrared Camera Display of Gas Plume Invisible to the Eye 

Another infrared emission screening device is the Remote Methane Leak Detector (RMLD)5

. The 

handheld RMLD allows remote detection of methane gas emissions, indicating presence of methane 

with audible signals and a Parts-per-Million-Meter (ppm-m) numeric display. Methane emissions 

absorb infrared light at a certain wavelength and the RMLD uses this characteristic to detect and 

indicate the presence of methane. The RMLD transmits an infrared laser beam and has a separate, 

visible spotting laser to guide the operator in pointing the IR beam. If methane is not present, the 

infrared laser is reflected back at the instrument by a background object. The extent to which the 

reflected beam is absorbed by methane indicates the extent to which methane gas is present in the 

beam’s path, reported in ppm-m. 

Once emissions are identified, the next step is to measure volumes of emissions to quantify emissions 

levels and fully analyze costs, benefits and outcomes of mitigation options. High volume samplers and 

calibrated bagging can be used to accurately quantify emissions rates from components in a DI&M 

program. High volume samplers work by pulling the emissions, plus a large volume sample of the air 

around the leaking component, into the instrument through a vacuum sampling hose. Dual 

hydrocarbon detectors then measure the concentration of hydrocarbon gas in the captured sample, as 

well as the ambient hydrocarbon gas concentration. Sample measurements are corrected for the 

ambient hydrocarbon concentration, and a mass leak rate is calculated by multiplying the flow rate of 

the air and gas pumped through the instrument by the difference between the ambient gas 

concentration and the gas concentration in the air stream. Methane emissions are obtained by 

calibrating the hydrocarbon detectors to a range of concentrations of methane-in-air. High volume 

samplers measure leak rates up to 0.2 m3

 per minute, equivalent to 326 m3 per day 

 

Leak rates greater than 0.2 m3 per minute can be measured using bagging techniques or flow meters. 

Calibrated bagging uses bags of known volume (e.g., 1 m3

, 2 m3), made from antistatic plastic with a 

neck shaped for easy sealing around the emission source. Measurements are made by sealing the 

bag around the emissions stream (usually a vent pipe) and measuring the time it takes for the bag to 

inflate to full capacity. This rate is used to calculate annual flow rates. Leak rate measurement using 

bagging techniques is accurate within ± 10 to 15 percent. 

Rotameters and other flow meters are used to measure extremely large leaks that would overwhelm 

the high flow sampler or calibrated bags. Rotameters channel gas flow vertically upward from a leak 

source through a tapered calibrated tube. The flow lifts a "float bob" within the tube, indicating the leak 

rate. Because rotameters are bulky, these instruments work best for open-ended lines and similar 

4 
components, where the entire flow can be channeled upward through the meter. Rotameters and other 

flow metering devices can supplement measurements made using bagging or high volume samplers. 

In addition to identification and measurement, a key element to accurately calculating methane 

emissions rates is knowledge of the composition of the gas stream. This allows the operator to 

calculate the volumes of methane and other valuable hydrocarbons they are losing, which will facilitate 

economic analysis of mitigation options. 

Methane Emission Detection and Quantification – PEMEX Case Study 

Background 

Petroleos Mexicanos (PEMEX) began exploring methane emissions capture as a business opportunity 

in 2004, with its participation in the Methane to Markets Partnership as a Co-Chair of the Oil & Gas 

Sector Subcommittee. PEMEX, Mexico’s nationally owned petroleum company, is a major natural gas 

and petroleum supplier and is responsible for about one-third of Mexico’s revenue. Fugitive methane 

emissions reduction became a priority project due to its merits of economic results, safety and 

environmental benefits. PEMEX pursues methane emission reductions with the goals of reducing their 

greenhouse gas emissions, increasing safety and operational efficiency, and generating revenues from 

methane emissions recovery. 

Emission reduction activities began in 2006 with a multi-faceted approach, including DI&M, to address 

compressors, energy efficiency, fugitive emissions, and other sources in three of its gas processing 

complexes. PEMEX’s eleven gas processing and compression facilities represent thousands of valves, 

connectors, open-ended lines, compressor seals, and other components, each of which is a potential 

path of methane emissions to the atmosphere and source of product loss. At the outset of their DI&M 

efforts, the company sought to learn the extent of fugitive and vented methane emissions losses, 

identify component types within facilities that are prone to leaks, assess leaking components for 

repairs, and determine cost-effectiveness of mitigation options. Through this effort, they built internal 

expertise for leak detection and measurement and developed cost effective best practices for a 

sustained leak detection and repair program. 

Through its partnership with Methane to Markets, PEMEX developed a facility-level DI&M program that 

it has replicated at a total of six locations to date. PEMEX began with a baseline field study to identify 

and quantify fugitive methane emissions from all components, providing the initial data set for further 

business decisions. PEMEX then identified leaks and vents 

that were cost-effective to repair, conducted follow-up 

surveys, and reviewed leak data to identify trends to direct 

future DI&M work. 

PEMEX Facilities with DI&M Projects 

1. Pemex Gas and Basic 

Petrochemicals Nuevo Pemex 

(processing) 

2. Poza Rica (processing) 

3. Burgos (processing) 

4. Cactus (processing) 

5. Ciudad Pemex (processing) 

6. Pemex Exploration and Production 

Cunduacan (compressor station) 

Survey instruments included electronic screening devices, 

infrared cameras, and the Remote Methane Leak Detector 

(RMLD). Quantification instruments for methane included 

the Hi Flow Sampler® and calibrated vent bags. Leak repair 

work was conducted by PEMEX personnel and included 

tightening, regreasing, repacking of valve stems, valve 

replacement, and centrifugal compressor seal retrofit. 

Results

Results for the baseline surveys are summarized in Exhibit 2. The baseline surveys identified a total of 

12,255 thousand m3

/year of fugitive methane emissions from these six facilities. Methane emissions at 

individual facilities varied greatly, from 30 to 6,770 thousand m3

/year. 

Exhibit 2 Summary of Fugitive Methane Emissions by PEMEX Facility 

Facility Number of 

Leaks

Methane emissions, 

thousand m3/year

Poza Rica 194 6,770 

Nuevo PEMEX 132 2,571 

Ciudad PEMEX 17 2,022 

Cactus 14 137 

Burgos 16 30 

Cunduacan 52 724 

Total 425 12,255 

5 
The facility level results illustrate the value of baseline surveys as an initial step in a DI&M project in 

that the results allowed management to focus subsequent work on facilities with the most significant 

opportunities. In the case of the PEMEX baseline surveys, it was discovered that more recent 

construction had fewer component leaks, which is a useful result for decision-making when replicating 

survey work at other locations. In the cases of Poza Rica, Nuevo PEMEX, Ciudad PEMEX, and 

Cunduacan, a significant portion of the methane emissions are derived from the de-gassing vents of 

centrifugal compressors using wet seals. During normal operation of centrifugal compressors with oilbased or “wet” seals, a large amount of gas may become entrained in the seal oil, which must then be 

de-gassed in order to maintain viscosity and lubricity. Given that the de-gassed methane is often 

vented to the atmosphere, seal oil de-gassing can be a large source of methane emissions. These 

emissions are classified as a process-related vented emissions rather than fugitive leaks, but were 

included in the field study since they are a potentially large source and therefore critical for establishing 

integrated baseline analyses of methane emissions from these processing facilities. Emissions from 

centrifugal compressor seal oil de-gassing is treated in more detail in a later section. 

Methane emissions by component type are further explored in Exhibit 3 which categorizes leaking 

components discovered during the baseline survey by type. For each component type, Exhibit 3 lists 

the number of leaks discovered during the baseline surveys and the methane emissions rate in 

thousand m3

/year. Typical repair cost for each component type and value of emissions is also 

provided. 

Exhibit 3 Summary of Fugitive Methane Emissions by Component Type

 Component 

Number 

of leaks 

Methane 

emissions, 

thousand 

m3/year 

Typical 

repair cost 

per leak , 

U.S. $ 

Gas value at U.S. 

$106/thousand m3 

($3/Mcf) 

Gas value at U.S. 

$247/thousand m3

($7/Mcf) 

compressor 

seal 38

 

10,178.3 

 

240,0006 1,078,335 2,516,116 

valve stem 

packing 35

 

572.2 

 

300 60,624 141,455 

gate valve stem 

packing 157

 

440.4 

 

442 46,658 108,869 

open ended 

line 22

 

305.4 

 

68 32,351 75,485 

control valve 

stem packing 44

 

186.9 

 

356 19,804 46,210 

flange 55

 

159.7 

 

146 16,917 39,472 

plug valve stem 

packing 10

 

104.0 

 

68 11,013 25,697 

grease fitting 8

 

70.1 

 

442 7,428 17,331 

valve seat 3

 

66.7 

 

300 7,069 16,495 

threaded 

connection 14

 

33.2 

 

20 3,512 8,196 

plug valve seat 3

 

32.8 

 

68 3,470 8,096 

other 4

 

27.1 

 

68 2,870 6,696 

compressor 

starter vent 3

 

23.1 

 

200 2,445 5,704 

regulator 2

 

18.1 

 

175 1,920 4,479 

control valve 

seat 6

 

16.6 

 

200 1,763 4,114 

tube fitting 10

 

15.6 

 

20 1,656 3,864 

gate valve seat 6

 

2.7 

 

75 281 655 

6 
needle valve 

stem packing 2

 

1.3 

 

442 137 319 

pressure relief 

(safety) valve 2

 

1.2 

 

68 131 306 

globe valve 

stem packing 1

 

0.2 

 

442 16 37 

Total 425

 

12,255.4 1,298,399 3,029,598 

The PEMEX baseline survey results illustrate a common principle of DI&M: a small number of leak 

sources are responsible for the majority of methane emissions and can be targeted for repair and 

follow-up monitoring. Across the six facilities sampled, approximately 425 components out of a total of 

7,500 components were found to have measurable emissions. By volume, the largest contributor was 

centrifugal compressor wet seals, which account for only 9 percent of the number of emitting 

components but 83 percent of total emissions (10,178 thousand m3

/year). The second largest 

emissions source is general valve stem packing, followed by gate valve stem packing. The top three 

sources account for 54 percent of the number of emitting components but 91 percent of the emissions 

volume. 

PEMEX reviewed the baseline survey data and directed major repair, replacement, and retrofit efforts 

at the top three sources by volume. PEMEX began retrofitting wet seal centrifugal compressors with 

dry seals. It began with three compressor units at Ciudad PEMEX in 2007 and will replicate the 

process in at least 15 more compressors in 2010. They also instituted a valve repair and replacement 

program to target stem packing leaks, open-ended line leaks, and valve seat leaks. 

Valves can develop leaks either externally around the packing or internally in the valve seat. For 

external valve leaks, tightening packing, repacking or regreasing immediately upon leak discovery is a 

very cost-effective mitigation option, typically providing an immediate payback given the low cost of 

packing materials and the negligible field staff time required. Internal leaks can be mitigated often by 

just tightening valve closure, by removing and rehabilitating the valve or replacing it outright. 

Additionally, a sustained maintenance schedule of valve servicing and flushing can reduce the 

frequency of fugitive emissions since an accumulation of debris can obstruct the valve seat as it is 

actuated over time, creating a pathway for gas to the atmosphere. PEMEX determined the most costeffective solution for each valve leak type by considering the cost of various valve mitigation options, 

the potential value of the methane savings, and operating schedules at each facility such as scheduled 

shutdowns for plant-wide maintenance. 

In addition to the valve program, PEMEX also addressed other emissions where cost-effective. For 

example, tube fitting leaks can often be eliminated through tightening tubing connectors and provide 

immediate payback based on the value of the avoided methane emissions. 

Implementation Benefits 

Cost-effectiveness is discussed here by defining mitigation costs and methane savings, and then 

presenting typical project economics7

. DI&M costs include survey costs and repair costs. Typical 

baseline survey costs range from U.S. $15,000 to 20,000 per large gas plant facility. Periodic follow-up 

survey costs are lower (U.S. $9,000 to 15,000) since emphasis can be placed on specific facility areas 

or component types identified in the baseline. Repair and maintenance costs will vary by equipment 

type and corresponding mitigation option chosen. 

Companies can control costs by designing DI&M strategies for each facility. For example, PEMEX’s 

initial DI&M work at its Cactus, New PEMEX, and Ciudad PEMEX facilities was optimized based on 

time and resource constraints. The three facilities were included in a single one-week survey, and 

facility areas were prioritized for survey work. As a result, baseline survey costs were shared amongst 

three locations, providing PEMEX with an initial sense of how fugitives vary by facility, but at the 

expense of being less comprehensive. This flexibility was important for future PEMEX decision-making 

on replicating the work at other locations. A company can also choose to utilize external service 

providers or purchase equipment and develop an internal team. For the baseline surveys, PEMEX and 

Methane to Markets used third parties as a way to provide facility staff access to new technologies and 

additional expertise. 

Determining the value of gas saved is required to estimate project economics and prioritize repair and 

other mitigation activities. The 12,255 thousand m3

/year of methane emissions discovered in the 

PEMEX baseline surveys represents a recovery opportunity of over U.S. $1.3 million at U.S. 

7 
$3/thousand cubic feet (Mcf) ($106/thousand m3

) or a value of U.S. $3 million per year at U.S. $7/Mcf 

($247/thousand m3

). 

PEMEX’s repair effort addressed both emissions from leaking components and centrifugal compressor 

vents. To better study the economics of leak repair alone, Exhibit 4 evaluates non-capital intensive 

repair activities typical of routine preventive or corrective maintenance, using methane emissions rates 

from the PEMEX field studies paired with typical costs for this project type. A methane emissions 

reduction of 2,077 thousand m3

/year, or all component leaks found by PEMEX, was assumed for 

emissions reductions to illustrate project economics. Simple payback period was calculated using two 

gas values, U.S. $3/Mcf ($106/thousand m3

) and U.S. $7/Mcf ($247/thousand m3). 

Exhibit 4 DI&M Project Summary, Leak Identification, Quantification, and Repair 

CAPITAL COSTS U.S. $90,000 baseline surveys for 6 facilities 

(U.S. $15,000 per facility) 

PERIODIC LABOR & 

MAINTENANCE COSTS 

U.S. $115,246 repair costs 

U.S. $54,000 follow-up surveys for 6 facilities 

Gas Price per thousand m3 U.S. $106 U.S. $247 

Annual Value of Gas Saved, 

U.S. $ 220,064 513,482 

Payback Period in Years 1.2 0.5 

Exhibit 4 shows that the value of the recovered gas value alone pays for the leak survey and repair 

work in 1.2 years or less, depending on how the gas is valued. DI&M surveys identify needed repairs, 

many of which can be considered routine maintenance activities, from which companies can save a 

significant volume of methane. In the case of the leak volumes found by PEMEX, repairs provide 

additional annual revenue from gas sales ranging from U.S. $220,064 to U.S. $513,482. 

Exhibit 5 depicts project economics for both the leak repairs as well as for wet seal centrifugal 

compressor retrofit to dry seals. Exhibit 5 includes the same fugitive emissions reduction of 2,077 

thousand m3

/year from Exhibit 4 and also includes the actual measured emissions reduction of 1,918 

thousand m3

/year realized by retrofit of three wet seal centrifugal compressors, for a total emissions 

reduction of 4,849 thousand m3

 methane/year. Simple payback period was calculated using assumed 

repair and other mitigation costs, as well as two gas values. 

Exhibit 5 DI&M Project Summary, Leak Identification, Quantification, Repair, and 

Centrifugal Compressor Retrofit 

CAPITAL COSTS U.S. $90,000 baseline surveys for 6 facilities 

U.S. $720,000 for dry seal retrofit of 3 centrifugal 

compressors 

PERIODIC LABOR & 

MAINTENANCE COSTS 

U.S. $115,246 repair costs 

U.S. $54,000 followup surveys for 6 facilities 

COST SAVINGS U.S. $189,000 reduced operating costs from 3 

centrifugal compressors 

 

Gas Price per thousand m3 U.S. $106 U.S. $247 

Annual Value of Gas Saved, 

U.S. $ 423,313 987,731 

Payback Period in Years 1.6 0.8 

Exhibit 5 shows how a DI&M program can be harnessed for additional methane emissions mitigation 

project work such as replacement of wet seals on centrifugal compressors. The combined 

DI&M/centrifugal compressor project requires a higher initial capital investment, but can result in 

increased annual revenues of U.S.$423,313 to U.S.$987,731 and gives a payback period of 0.8 to 1.6 

8 
years depending on gas value. Centrifugal compressor emissions and mitigation are discussed in 

detail in another section of this paper. 

Thus, Exhibit 4 represents the cost-effectiveness of DI&M even when there is only minimal capital 

investment available for mitigation. By identifying and repairing leaking components, a significant 

volume of natural gas previously lost to the atmosphere is now maintained in the system, with resulting 

gas savings adding to revenue through sales or contributing to internal fuel supplies, in either case 

contributing to domestic gas supplies. Exhibit 5 represents the cost-effectiveness of DI&M paired with 

compressor seal emissions reduction, in which a larger capital investment provides for even greater 

savings and benefits. 

Next steps

Through its baseline fugitive methane emissions surveys, PEMEX confirmed that DI&M at its facilities 

is not only cost-effective but also profitable. The dual accomplishments of reducing emissions and 

increasing throughput contribute to operational safety, efficiency and environmental performance while 

increasing revenues. As demonstrated above, these activities can pay back in less than one year, 

which in addition to being beneficial economically, can also increase engagement at the management 

and field level and contribute to the likelihood of successful replication at other locations. Based on the 

economic and sustainability merits of the work, PEMEX is continuing to explore replication of DI&M 

programs at other facilities. In 2007, PEMEX Gas purchased infrared cameras for all of its gas 

processing plants. In mid-2009, PEMEX Gas is undertaking a training session for a special DI&M team 

that will help focus on fugitive emissions throughout the PEMEX Gas system. Additionally, PEMEX, in 

cooperation with Methane to Markets, has also initiated a comprehensive marginal abatement curve 

analyses for methane and is using data gathered during measurement studies to inform these 

analyses. These analyses will be used to quantify the total volume of cost-effective methane reduction 

potential in PEMEX operations and the company intends to use these analyses in setting climate 

policy goals and allocating capital resources. 

Mitigation Opportunity – Reduced Emission Completions 

Background 

Increased natural gas demand over the last few decades has increased drilling of new wells in more 

expensive and more technologically challenging unconventional gas reservoirs, including those in low 

porosity and permeability (tight) formations. High demand for gas and high prices also justify extra 

efforts to reinvigorate production from existing wells in tight reservoirs where the down-hole pressure 

and gas production rates have declined, a process known as well workovers or well-reworking. In both 

cases (completions of new wells in tight formations and workovers of existing wells), hydraulic 

fracturing the reservoir rock with very high pressure water bearing proppant (generally sand) that 

“props open” the reservoir is the preferred method of gas recovery. 

These new and workover wells may require multiple intervals of hydraulic fracturing, depending on the 

pay thickness in the reservoir. Based on the amount of load recovery of fluids between fractures, 

these multiple interval completions can take anywhere from one day to several weeks. After hydraulic 

fracturing, the well produces at a high rate to clear the well bore and formation of the load fluids prior to 

gas flow. The typical historical practice for this initial well completion step has been to flow the well to 

a pit or tanks where sand and slugs of water are captured and hydrocarbon liquids and gas are vented 

to the atmosphere or flared. This process is utilized until the gas meets specific pipeline specifications 

and can go to a permanent sales line. After all of the intervals are fractured, a workover rig or coiled 

tubing unit will clean out the well prior to the final production phase. The initial well completion is not 

finished until one to two days after the well has been cleaned out and connected to a permanent sales 

line. 

Reduced emissions completions (RECs, also called “Green Completion”) capture much of the gas that 

would have been otherwise vented or flared during the completion process. RECs use portable twophase completion flowback equipment that is specifically designed and sized for the initial high rate of 

water, sand and gas flow. Sand traps are used to remove the finer solids present in the production 

stream and a plug catcher removes any large solids, such as drill cuttings, that could damage the 

separation equipment. In addition to the separation equipment, RECs may require a compressor to 

withdraw gas from the sales line to pump down the well casing for artificial gas lift of the fluids, plus a 

wet screw compressor to aid in boosting low pressure gas back into the sales line until normal 

reservoir flow and pressure are established. 

9 
Initial coordination between permitting and construction prior to the completion phase is essential to 

insure a permanent sales line is within a reasonable distance of the wellhead. Wells that are 

refractured and worked over normally already have a sales line, and consequently, RECs can also be 

utilized. Depending on the gas gathering system, it may be necessary to dehydrate the produced gas 

before it enters the sales pipeline. Moisture levels are reduced to pipeline quality gas specifications 

with the permanent or a portable dehydrator and flow is measured with a permanent custody transfer 

meter. 

The portable two-phase completion flowback equipment used during RECs is only used for cleaning 

up the well; therefore, it is essential that all the equipment can be readily transported from different 

sites to be used in a number of well completions. A truck-mounted skid is ideal for transporting the 

equipment between sites and is large enough to carry all the necessary equipment. In a large basin 

that has a high level of drilling activity, it may be economic for a gas producer to build its own REC 

skid. For some producers, contracting a third party to perform completions may be a better fit with their 

annual drilling program. 

Natural gas flared or vented during well completion and testing can be as much as 700 thousand m3

per well (US$75,000 to US$175,0008

 in lost revenue), depending on well production rates, the number 

of zones completed, and the amount of time it takes to complete each zone. This gas is unprocessed 

and also contains volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) along with 

methane. Flaring gas reduces methane, VOC and HAP emissions by as much as 90%, but creates 

NOX and other combustion by-products in the process. A burning flare is safer than venting by 

reducing the chance of flamable gases in the air. Flaring is not always a practical option when the well 

is located near residential areas or where there is a high risk of forest fires. Most importantly, flaring 

results in the waste of natural gas, lost revenue, and air pollutant emissions. 

RECs bring economic benefits as well as environmental benefits. Some operators have reported that 

RECs reduce completion time, allowing them to bring some wells online more quickly. Because flow is 

measured with a permanent custody transfer meter, gas savings, and corresponding increases in 

revenue, can be accurately assessed. The incremental costs associated with the rental of third party 

equipment for performing RECs can be offset by the additional revenue from the sale of gas and 

condensate. According to data collected by the U.S. EPA, RECs have become a major source of oil 

and gas sector methane emission reductions in the U.S. since 2000. EPA Natural Gas STAR partner 

companies reported that emission reductions between 2000 and 2005 from RECs have increased from 

566 thousand m3

 to cumulatively over 198,240 thousand m3. This represents additional natural gas 

being delivered to consumers as well as increased revenue from sales of recovered natural gas of 

over US$49 million in 2005 (at US$247/ thousand m3

). 

Not all gas fields will benefit from flowback units. Wells without a production sales line within a 

reasonable distance will not be able to utilize flowback units. Wildcat, exploratory, and step-out wells 

are examples of these types of wells. When a well initially flows back 100% liquid and very little sand 

then the benefits of a flowback unit are also significantly reduced. In this case the completion fluid 

would flow to a tank, and after initial high water rates, the gas production is connected to the 

permanent separation equipment. Consequently there is no need to flare due to the distinct phases 

producing from the well. Some separation equipment requires a minimum gas pressure to actuate the 

pneumatic level controller inside the vessel. A small amount of flaring or venting would be needed if 

the gas production was not at the minimum separation pressure. 

Reduced Emission Completions – EnCana Case Study 

EnCana Corporation is the largest natural gas producer in North America, with 1.4 trillion cubic feet of 

natural gas production in 2008. EnCana Oil & Gas (USA) Inc. is a 2007 U.S. EPA Natural Gas STAR 

Award winner and is dedicated to ongoing environmental excellence through innovative energy 

efficiency initiatives. EnCana is committed to environmental stewardship through minimizing the 

impacts from activities through creative and innovative application of technology. 

The Jonah Field is one of EnCana’s key resource plays and is located 30 miles south of Pinedale, 

Wyoming. Jonah Field is geographically small at approximately 23,000 acres, but produces 1.5 

percent of the daily natural gas needs in the United States. EnCana has contributed to the 

development of this field since 2002 and plans to continue drilling for several years. 

Background 

10 
EnCana’s completion technique involves hydraulically fracturing multiple intervals within a well. 

Between fracturings, a composite flow through bridge plug is used to separate the lower interval from 

the interval being fractured. After each fracturing, the well is flowed back to clean up any residual 

fluids in the formation. Once the entire well bore is fractured, a workover rig or coiled tubing unit is 

brought in to drill out the composite plugs. Prior to 2003, the flowback gas was sent directly to a flare 

until the entire well bore was completed and then the well was connected to sales. During this time, 

the liquids were placed into a pit on location. 

In 2003, when plans for the Jonah Infill Drilling Project Environmental Impact Statement (JIDP EIS) 

were being developed, public and regulators raised concerns about the completion flares emissions. 

To address these concerns, EnCana developed a method of RECs. The use of flareless flowback 

demonstrates that EnCana is committed to environmentally responsible methods of development 

throughout the life of the field. 

Results 

In mid-2003, EnCana began using flareless flowback units in the Jonah Field. These units separate the 

gas from the liquids and send the gas downstream through central separation equipment with other 

producing wells and thus avoid flaring. A flowback unit includes a plug catcher device to remove large 

particles created in drill out operations from the separation equipment. The recovered oil is piped to 

storage tanks for future sale and the water enters the Jonah Field water recycling program. A 24-hour, 

two-person crew hooks up the flow lines from the wellhead to the separation device and then to the 

gas sales lines and condensate tanks. To reduce the amount of sand production and sand crushing 

inside the reservoir, initial completion flowback is not immediately unloaded to atmospheric pressures. 

Instead, the well is brought on slowly through a series of chokes which are designated by the flowback 

crew. A 24-hour flowback crew is needed to accommodate the choke schedule and the 24-hour 

hydraulic fracturing. In the Jonah Field, the flowback equipment and the crew are supplied by a thirdparty contractor. 

The flowback process is not entirely flareless. When the well initially starts flowing back, there is more 

liquid than gas and the gas pressure may not be high enough to go to the sales line. During this short 

time, the flowback crew will send the gas to a flare. Exhibit 6 shows the percent of gas that was sent 

to flare during the years listed. The amount of gas flared depends upon the sales pipeline pressure. 

In 2007, the Jonah Field gathering endpoint was at 600 psi. After adding a compressor station, the 

pressure gradually dropped and is now operating at 250 psi. Therefore, the 0.1% flared in 2009 (YTD) 

should be an indicative value for the rest of the year. 

Exhibit 6 Flared Volume 

Year Total Gas through Unit % Flared 

thousand m3/year 

2001 0 0.00% 

2002 0 0.00% 

2003 12,999 3.70% 

2004 176,632 1.01% 

2005 509,335 0.61% 

2006* 267,936 1.46% 

2007 240,493 0.87% 

2008 420,042 0.45% 

2009YTD 80,655 0.10% 

*Increased Energized Fracturing Fluids 

A common completion technique in tight gas reservoirs is to energize the hydraulic fracturing with 

nitrogen or carbon dioxide to increase the percent of pumped liquids from the formation back to 

surface. Nitrogen or carbon dioxide mixes with reservoir gas to create a flowback gas that is not 

acceptable for sales due to downstream sales criteria gas quality. Use of nitrogen or carbon dioxide 

increases the amount of gas sent to flare. Jonah is a high pressured reservoir and, therefore, typically 

has adequate energy to remove fracturing fluids without nitrogen and carbon dioxide. Some gas 

reservoirs require energized fluids to optimize fracturing and, therefore, will not see as high an 

efficiency for utilizing flowback units. In 2006 the Jonah Field energized multiple intervals to assist with 

liquid recovery and, consequently, increased the percent flared as shown in Exhibit 6. 

11 
Flowback units allow the fluids from the fracturing process to be recycled. Instead of using fresh water 

from local aquifers for fracturing, Jonah uses a combination of 60% produced water from nearby 

production wells and 40% recycled drilling/completions fluids. 

Through the years, the Jonah Field team has developed a technique so that more than one well can 

produce through a single flowback unit. Up to three wells have been placed through the same 

flowback unit without any operational issues. The biggest concern with increasing the number of wells 

is the lack of individual well data for analysis. Also, instead of a two–person, 24-hour crew EnCana 

has moved to a one-person, 24-hour crew for multiple units. The maximum number of units 

supervised by a one-person crew to date has been three. By these developments, the overall 

flowback equipment and crew cost per well are significantly reduced. This technique significantly 

reduces equipment rental times by better utilization. 

Implementation Benefits 

The amount of gas sold rather than flared is substantial, and the overall REC project paid out within 

the first year. The net present value (NPV) of the project in 2003 was US$190,070,000. The cost and 

sales revenue is shown in Table 2. 

Exhibit 7 Economics9

 

Year Gas to Sales Gas Price Cost of Flow Back 

Gas Sale 

Revenue 

 

thousand 

m3/year US$/MCF Unit and Crew US$ US$ 

2003 12,517 $4.62 ($3,036,200) $2,040,973 

2004 174,848 $5.87 ($8,857,800) $36,260,555 

2005 506,248 $7.80 ($9,112,400) $139,454,713 

2006* 264,027 $6.34 ($16,800,000) $59,151,099 

2007 238,398 $4.43 ($37,728,000) $37,268,080 

2008 418,173 $7.01 ($40,425,000) $103,438,462 

2009YTD 80,570 $3.19 ($9,075,000) $9,063,281 

*Increased Energized Fracturing Fluids 

Conclusions and Other RECs 

Flowback units have significantly reduced air emissions in the Jonah Field. Due to the naturally high 

pressure of the reservoir this field has seen a high rate of success and does not require energizing 

fluids to move fracturing fluids from the well bore. 

Another method of RECs used in the Jonah Field is remote hydraulic fracturing. Remote fracturing 

involves setting up a hydraulic fracturing crew and equipment on one location and running pipelines 

across the surface up to 762 meters away to fracture a well remotely. This technique reduces 

movement of heavy fracturing equipment from one to two times per day to about once every one to 

two days. The emissions reduction has not been quantified, but there is a benefit in significantly 

reducing fracturing crews moving and rigging-up time. 

Mitigation Opportunity – Vapor Recovery from Tanks 

Background 

Production field tanks hold crude oil and condensate to stabilize flow or for trucking or pipeline 

transportation. During transfer from the gas-oil separators to field storage tanks, light hydrocarbons 

dissolved in the liquids—including methane—vaporize (flash) and vent to the atmosphere. Tanks can 

vent 0.2 to 1.2 m3

 per year of methane per barrel of oil or condensate. Sites without vapor recovery 

therefore may lose significant volumes of product in this manner. 

One way to capture this gas and yield significant economic savings is to install vapor recovery units 

(VRUs) on storage tanks. Over the past five years, this technology is consistently in the top five “best 

management practices” reported by U.S. oil and gas companies for reducing methane emissions. 

While most methane capture projects deal with the compression of relatively dry (1,000 Btu) gas from 

suction pressures over 50 psig, one of the more challenging technologies for methane capture is the 

vapor recovery of associated gas from field storage tanks. This gas is typically very wet, and at 

pressures less than 1 psig. 

12 
Operators have opted to install VRUs at production sites in Latin American and globally due to the 

combined benefits of reduced methane emissions; utilization of methane as an onsite fuel source or 

sales gas; and recovery and sale of valuable heavier hydrocarbons such as propane and butane. An 

additional benefit is that VRUs serve as a collection point for other sources of low-pressure methane 

emissions throughout the facility. Re-directing these low-pressure methane emission sources to the 

VRU allows for the capture and use or sale of natural gas previously vented to the atmosphere. 

VRUs can recover about 95 percent of tank vapors, which contain methane as well as other valuable 

heavier hydrocarbons. The volume of gas vapor coming off a storage tank depends on many factors. 

Vapor losses are primarily a function of oil or condensate throughput, gravity, temperature, and gas-oil 

separator pressure. There are three types of losses: 1) flash losses occur when crude oil or 

condensate is transferred from a gas-oil separator at higher pressure to a storage tank at atmospheric 

pressure; 2) working losses occur when crude or condensate levels change and when liquid in tank is 

agitated; and 3) standing losses occur with daily and seasonal temperature and barometric pressure 

changes. 

The makeup of these vapors varies, but the largest component is often methane (between 40 and 60 

percent). Other components include more complex hydrocarbon compounds such as ethane, propane, 

butane, and natural gasoline (pentane-plus heavier hydrocarbons including hazardous air pollutants 

such as benzene, toluene, ethyl-benzene and xylenes, collectively referred to as BTEX). Production 

gas often includes other non-hydrocarbon gases such as nitrogen, helium, hydrogen sulfide and 

carbon dioxide. Since recovered vapors contain hydrocarbons heavier than methane, on a volumetric 

basis, they can be more valuable than methane alone. 

 

VRUs can provide significant environmental and economic benefits for oil and gas producers. The 

gases flashed from crude oil and condensate and captured by VRUs can be sold at a profit or used as 

a fuel in facility operations. Additionally, other sources of low-pressure methane vented throughout the 

facility can be directed to the VRU for capture. These recovered vapors can be: 

 Piped to natural gas gathering pipelines for sale at a premium price as high Btu natural gas. 

 Used as a fuel for onsite operations. 

 Piped to a stripper unit to separate natural gas liquids (NGLs) and methane when the volume and 

price for NGLs are attractive. 

Vapor Recovery Unit Design Considerations 

Unlike typical pipeline compression, the design of vapor recovery units requires several added 

elements which allow the units to operate effectively in extremely low pressure and highly variable flow 

of wet gas applications. The compressor is the heart of the system, and compressor selection is key 

for these wet gas applications. Preferred options include rotary screw, scroll, venturi jet, and rotary 

vane compressors. Rotary vane compressors are typically the lowest cost alternative. These units 

handle wet gas very well (although not liquid slugs) and large volumes, but are limited on discharge 

pressure to 70 psig. Scroll compressors work well and have a large pressure range (from zero to 325 

psig), but are limited on volume (generally 150 mcfd (4.2 thousand m3

/day) for two dual modules). Oil 

flooded rotary screw compressors are a great option and the most versatile, especially when coupled 

with a variable frequency drive – and can handle the widest range of pressures and volumes. 

However, these units generally cost more initially and have higher operating costs than rotary vanes. 

Screw compressors utilizing ductile iron rotors and rotary vanes using ductile iron bodies work well in 

these applications due to the corrosive nature of some gas streams containing significant quantities of 

H2S, CO2, or high levels of water vapor. Venturi jet systems are designed in same manner, utilizing a 

venturi jet powered by high pressure produced water (Vapor Jet®) or high pressure process gas 

(EVRU®) in lieu of a compressor. Each system works well in its niche, but has limitations on 

discharge pressure (40psig to 60 psig) and requires approximately a four to one power fluid to suction 

gas ratio. 

Packaging designs should incorporate transmitters to monitor tank pressures, an on-skid bypass 

system to re-circulate gas to minimize shutdowns, and a computer driven automated system of liquid 

and pressure controls to minimize field maintenance and insure the system never pulls air into the 

tanks and into the recovered gas. Electric motor drive units are recommended as the fuel gas provided 

at many tank batteries contains contaminants or liquids that make running small horsepower natural 

gas engines problematic. A good gas analysis from the tanks is critical in order to evaluate the dew 

point of the gas, and the dew point should be considered in system design. Facility design 

considerations should include a gas blanketing system that is designed to backfill the tanks with fuel 

gas or nitrogen as the tanks are emptied of oil. A closed system is imperative, so a review to insure all 

thief hatches and safety relief valves on the tanks are sealed and operational and the tank fixed roof is 

13 
in good repair are also important. Finally, it is recommended that a sloping line (4 inch minimum 

diameter) is run from the tanks to the VRU, with no low spots or U traps in the line that could fill with 

condensate and block the low pressure gas flow. 

In sizing the VRU, emissions from tanks should be quantified by measurement to ensure adequate 

capacities based on fluctuations of volume over time. When measuring tank vapors, two key factors to 

achieving accurate measurements include: measuring flow of vapors over time to capture a complete 

tank cycle from full to empty back to full, and ensuring that all emissions escaping from the tank are 

directed to a single flow measurement point such that true volume can be captured. One method for 

measuring tank emissions is the Daniels’ turbine meter, which can be affixed to a tank outlet and used 

to measure flows exceeding 17 actual cubic meters (am3). An orifice well tester and recording 

manometer (pressure gauge) can be used to measure maximum emissions rates since it is the 

maximum rate that is used to size a VRU. Orifice meters, however, might not be suitable for measuring 

total volumes over time due to the low pressures at tanks. 

Estimating tank vapors might be useful for very preliminary consideration of VRU installation. There 

are two approaches to estimating the level of vapor emissions from crude oil tanks. Both use the gasoil ratio (GOR) at a given pressure and temperature and are expressed in standard cubic feet per 

barrel of oil (scf per bbl). 

The first approach analyzes API gravity and separator pressure to determine GOR (Exhibit 8). 

Exhibit 810 Estimated Volumes of Tank Vapors 

Pressure of Vessel Dumping to Tank (Psig)

Vapor Vented from Tanks,

cubic foot / barrel

Gas/Oil Ratio

110

100

90

80

70

60

50

40

30

10

20

10 20 30 40 50 60 70 80

Under 30° API

30° API to

40

39° API

° API and Over

o API = API gravity

API Gravities

These curves were constructed using empirical flash data from laboratory studies and field 

measurements. As illustrated, this graph can be used to approximate total potential vapor emissions 

from a barrel of oil. Once the emissions rate per barrel is estimated, the total quantity of emissions 

from the tank can be determined by multiplying the per barrel estimate by the total amount of oil cycled 

through the tank. The shortcoming of this approach is that it does not generate information about the 

composition of the vapors emitted. In particular, it cannot distinguish between VOC and HAP, which 

can be significant for air quality monitoring, as well as determining the value of the emitted vapors. 

The second approach is to use the software package E&P Tank. Developed by API and the Gas 

Research Institute (now the Gas Technology Institute), this software estimates emissions from all three 

sources—flashing, working, and standing—using thermodynamic flash calculations for flash losses 

and a fixed roof tank simulation model for working and standing losses. An operator must have several 

pieces of information before using E&P Tank, including: 

1. Separator pressure and temperature. 

2. Separator oil composition. 

3. Reference pressure. 

4. Reid vapor pressure of sales oil. 

5. Sales oil production rate. 

6. API gravity of sales oil. 

14 
E&P Tank also allows operators to input more detailed information about operating conditions, which 

helps refine emissions estimates. With additional data about tank size, shape, internal temperatures, 

and ambient temperatures, the software can produce more precise estimates. This flexibility in model 

design allows users to employ the model to match available information. Since separator oil 

composition is a key input in the model, E&P Tank includes a detailed sampling and analysis protocol 

for separator oil. 

Vapor Recovery from Tanks – Pluspetrol Case Study 

Background 

Founded in Argentina in 1976, Grupo Pluspetrol began its operations with an enhanced recovery 

project in the province of Neuquen. Pluspetrol began evaluating the opportunity to capture the vent 

methane at the Palmar Largo facility in 2007. After a detailed engineering review, the company 

determined it was economical to capture the vent gas from their two tanks (2,000 m3

 and 330 m3). 

Producing 320 m3

 per day of 43 degree API gravity crude oil through the facility, the project sought to 

capture approximately 15,000 m3

/day (500 mcfd) of low pressure vent gas. 

Vent gas from oil storage tanks is typically 2,200 to 2,400 Btu – which makes it a very valuable, but 

also very wet gas stream. As an example, the vent gas from this location had a specific gravity of 

1.35, versus the process gas stream of 1.03. Pluspetrol’s goals were to maximize condensate 

production from this gas stream, and compress the remaining gas into their gas plant to be used in the 

circuit of “gas lift” for enhanced oil recovery. Based on the field conditions, Pluspetrol selected a fully 

automated vapor recovery unit utilizing a rotary vane compressor and electric drive motor to help 

minimize downtime. Hy-bon Engineering in Midland Texas was selected for the design and 

manufacture of the vapor recovery unit, installed earlier this year. 

In this installation, 15,000 m3

/day (500 mcfd) is captured from the oil storage tanks and pulled through 

a fin fan cooler in order to drop out condensate, then piped to a vessel to capture the condensate, and 

compressed by the VRU to 65 psig to the on-site plant (Exhibit 9). The automated vapor recovery unit 

has a programmable logic controller (PLC), which automatically monitors and pumps liquids from the 

vessels, maintains all key components within their safe operating ranges, and shifts the unit between 

on, off and bypass depending on fluctuating tank pressures. An electric motor drive unit was selected 

to minimize downtime and take advantage of the available power on location. The overall installation 

was designed with no “U traps” in the piping, and sloping lines where possible from the tanks to help 

insure proper gas flow. A rotary vane compressor was used in this application due to the extremely 

wet nature of the gas, coupled with a relatively low discharge pressure of 65 psig. These compressors 

are also easy to rebuild in the field, which is an advantage in remote locations. 

Exhibit 9 Pluspetrol Salta Argentina 125 150- HP VRU 

15 
Pluspetrol anticipated capturing 10 m3

 (or 63 bbls)/day of condensate and a significant quantity of 

residual gas. The compressed gas, which totals approximately 7,500 m3

/day, goes to a gas plant to be 

prepared for use in the gas lift system. In this way, gas used for gas lift is maintained in a closed loop 

system. Recovered condensate goes to the liquid storage tank (oil + water). Total fluid condensate is 

measured in the separator and indirect measures allow for approximation of the amount of other 

liquids in the tank. Pluspetrol is capturing 10 to 13 m3

 /day of condensate, and 3 to 4 m3 /day of other 

liquids (approximated volume). There is more water produced in the process than was originally 

estimated. 

Overall payback on the project was originally projected at 30 months. After installation and 

commissioning in early 2009, Pluspetrol found that actual daily condensate and gas production 

exceeded expected levels. Final payback numbers are still in process due to one of the production 

tanks being taken out of service for repair earlier this year, but anticipated payback is estimated to be 

20 to 30 months based on the following factors. The cost of installing the VRU was U.S.$350,000, 

including material, equipment (air cooler, separator, pumps and VRU compressor) and labor. Ongoing costs include U.S.$1000/month (operation and maintenance) and oil transport costs of 

U.S.$3.34/bbl (or U.S.$21.01/ m3

). Revenues were calculated according to an oil sale price of 

U.S.$35/bbl (or U.S.$220.14/ m3

). Evaluating the project over 5 years, and assuming a decline in 

production, payback is calculated to be 20 to 30 months, assuming condensate production levels of 13 

to 10 m3

/day, respectively. This assumes a flat oil price for the next 5 years, so an improvement in this 

price will result in a payback of less than 20 months. 

Considering local pricing for natural gas (generally less than U.S.$71/ thousand m3

 or U.S.$2/mcf), the 

potential for condensate recovery from these high Btu gas streams really helps the project economics 

– a factor often overlooked by companies in evaluating VRU projects. 

Mitigation Opportunity – Installing Dry Seals on Centrifugal Compressors 

Background 

Centrifugal compressors are becoming more widely used in processing and transmission of natural 

gas11. Seals on the rotating shafts prevent the high-pressure natural gas from escaping the 

compressor casing. Traditionally, these seals use high-pressure oil as a barrier against escaping gas. 

While oil seals form a good barrier to prevent the release of gas at the seal face, in some cases these 

oil seals can still result in large emissions of methane. 

Centrifugal compressors increase natural gas pressure when a series of rotating impellers accelerate 

the gas. The impellers are driven by a rapidly spinning shaft, and this shaft extends from the 

compressor case to bearings at each end. Where the drive shaft exits the compressor case presents 

an opening for gas leakage to occur. Compressor seals fill the space around the shaft and prevent gas 

from contaminating the bearing lubrication and leading to the atmosphere. Traditionally, centrifugal 

compressor seals use rings that are lubricated by circulating seal oil between them. Two stationary 

rings form a barrier for high-pressure gas inside the compressor, and in between the stationary rings is 

a third ring rotating on the shaft. High-pressure seal oil is pumped between the rings to form a thin 

layer of lubrication and to act as another barrier between the natural gas and the atmosphere. 

When properly installed, this “wet seal” assembly is effective at minimizing gas leakage past the shaft, 

but in some cases large volumes of gas can be absorbed by the seal oil. While very little gas escapes 

through the oil barrier, the gas comes into contact with the seal oil under the high pressure at the 

“inboard” (compressor side) seal oil/gas interface. This may result in a significant amount of gas being 

absorbed by the seal oil, thus contaminating it. Seal oil is de-gasified to maintain its viscosity and 

lubricity (using heaters, flash tanks, and degassing techniques) and recirculated. Because the purged 

methane is commonly vented to the atmosphere, the seal oil degasifying process results in methane 

emissions. 

It has been found that there is variability in the volume of methane emissions from centrifugal 

compressor wet seal de-gassing in any given compressor. One source estimates that methane 

emissions from wet seals can range from 1.1 to 5.7 m3

/minute12. Other recent emissions rate 

measurements highlight this variability. Methane to Markets experience, combined with another 

assessment of four natural gas facilities13, has identified measurements from 48 wet seal centrifugal 

compressors, with methane emissions totaling 14,860 thousand m3

 methane/year. The data, which 

show that seal oil degassing rates for individual compressors could range from 0 to 2,756 thousand 

m3

/year, can be divided into two groups: a low-emitting group (33 compressors) and a high-emitting 

16 
group (15 compressors). The low emitters have an average emission rate of 26 thousand m3

methane/year for a single compressor. The high emitters have an average emission rate of 934 

thousand m3

 methane/year for a single compressor. Most measurements were conducted using antistatic calibrated vent bags, where a bag of a known volume was placed over the de-gassing vent stack 

to completely capture the emission, inflation time was measured, and the gas stream was adjusted for 

methane content. 

These findings point to the potentially large volumes of methane emissions from this source at facilities 

world-wide and the need to do measurement to identify specific units to target for repair/retrofit when 

instituting a methane emissions reduction project. In addition to potential methane emissions, there are 

other disadvantages to wet seals. Compressors operating with wet seals also require extra equipment 

and operating expenses to circulate, regenerate, and replenish seal oil. Seal oil can also leak into the 

natural gas stream, contaminating the product and fouling the pipeline. 

Mitigation Option: Install Dry Seals 

An alternative to the traditional wet (oil) seal system is the mechanical dry seal system. This seal 

system does not use any circulating seal oil. Dry seals operate mechanically under the opposing force 

created by hydrodynamic grooves and static pressure. Dry seals, which use high-pressure gas to 

seal the compressor, emit a much smaller quantity of natural gas (0.014 to 0.085 m3

/minute per 

seal14). A compressor dry seal upgrade therefore reduces methane emissions as much as 2,637 

thousand m3

 /8,000-hour year15, or U.S.$279,522 to U.S.$651,339 (at U.S.$106/thousand m3 to 

U.S.$247/thousand m3 ). Maximum expected methane venting to the atmosphere under normal 

operation from each compressor dry seal would be 11 m3

/hour. 

Exhibits 10 through 12 show typical project economics for dry seal conversions assuming a range of 

potential emissions levels and gas prices. Each exhibit shows typical capital costs to retrofit one 

compressor, operating costs, and operating cost savings16. 

Exhibit 10 Economics of Low-Emitting Centrifugal Compressor (150 thousand m3 methane/year) 

PROJECT SUMMARY: Replacement of Low-Emitting Wet Seals 

CAPITAL 

COSTS 

U.S. $240,000 for dry seal retrofit of one centrifugal compressors 

PERIODIC 

LABOR & 

MAINTENANCE 

COSTS 

U.S. $10,000 for operation and maintenance of dry seal 

COST 

SAVINGS 

U.S. $73,000 avoided operation and maintenance of wet seal 

 

Gas Price per 

thousand m3

U.S. $106 U.S. $247 

Annual Value 

of Gas Saved 

U.S. 

$15,892 U.S. $37,080 

Payback 

Period in Years 3.0 2.4 

Exhibit 11 Economics of Moderate-Emitting Centrifugal Compressor (934 thousand m3 methane/year) 

PROJECT SUMMARY: Replacement of Moderate-Emitting Wet Seals 

CAPITAL 

COSTS 

U.S. $240,000 for dry seal retrofit of one centrifugal compressors 

PERIODIC 

LABOR & 

MAINTENANCE 

COSTS 

U.S. $10,000 for operation and maintenance of dry seal 

COST 

SAVINGS 

U.S. $73,000 avoided operation and maintenance of wet seal 

 

17 
Gas Price per 

thousand m3

U.S. $106 U.S. $247 

Annual Value 

of Gas Saved 

U.S. 

$98,952 U.S. $230,887 

Payback 

Period in Years 1.5 0.82 

Exhibit 12 Economics of High-Emitting Centrifugal Compressor (2756 thousand m3 methane/year) 

PROJECT SUMMARY: Replacement of High-Emitting Wet Seals 

CAPITAL 

COSTS 

U.S. $240,000 for dry seal retrofit of one centrifugal compressors 

PERIODIC 

LABOR & 

MAINTENANCE 

COSTS 

U.S. $10,000 for operation and maintenance of dry seal 

COST 

SAVINGS 

U.S. $73,000 avoided operation and maintenance of wet seal 

 

Gas Price per 

thousand m3

U.S. $106 U.S. $247 

Annual Value 

of Gas Saved 

U.S. 

$291,982 U.S. $681,291 

Payback 

Period in Years 0.48 0.27 

These exhibits show that targeting specific centrifugal compressors for retrofit can lead to economic 

projects with paybacks with 3 years or less. This economic benefit is based on methane savings, as 

well as operational and efficiency improvements. Dry seal installations are mechanically simpler than 

wet seals and require fewer auxiliary components for handling seal oil, so power consumption is 

reduced, reliability is improved and maintenance costs are lower. Additionally, substituting dry seals 

for wet seals eliminates seal oil leakage into the pipeline, thus avoiding contamination of the gas. 

Because of these benefits, companies worldwide are benefiting in a variety of ways from implementing 

dry seals on their centrifugal compressors. 

Installing Dry Seals on Centrifugal Compressors – Gazprom Case Study 

Background 

Gazprom is the largest natural gas company in the world, possessing the largest natural gas reserves 

and operating the largest gas transmission system globally. The Unified Gas Supply System of Russia 

spans 156.9 thousand km and has over 4,000 centrifugal compressors in operation. Gazprom and its 

subsidiaries also service 514.2 thousand km (80 percent) of the national gas distribution pipelines, and 

in 2006 supplied 316.3 billion cubic meters (bcm) of gas to 79,750 population centers in Russia. 

Gazprom has been actively involved in the Methane to Markets partnership and other methane 

mitigation activities participating in international methane conferences in Novosibirsk (2000) and 

Tomsk (2005) as well as hosting the Methane to Markets seminar in Moscow in 2008. 

Implementation of Dry Gas Seals in Gazprom’s System 

In reviewing available data and information on compressor seals, Gazprom determined dry gas seals 

are more economic than wet oil seals on centrifugal compressors and identified a range of additional 

benefits. These added benefits included the elimination of oil contamination of combustible gas, 

increased compressor capacity, and minimal maintenance. Gazprom also determined that the cost of a 

new centrifugal compressor with dry seals does not exceed the cost of a unit with wet seals and 

overall, wet seals are economically inefficient as compared to dry seals. Furthermore, industry 

standards, such as those from the International Organization of Standards (ISO) and the American 

Petroleum Institute (API), advise against using wet oil seals in new compressors for safety reasons. 

18 
Based on these factors, Gazprom recognized the clear benefits of dry gas seals and plans to 

implement broad scale upgrades of its over 4,000 centrifugal compressors to replace wet seals with 

dry gas seals. There are several companies producing and implementing dry gas seal systems. John 

Crane Inc., UK, a British and Russian company, a developer and producer of high-tech sealing 

systems, complex sealing solutions and service equipment, has been successfully working in Russia 

since 2003. In particular, Gazprom is using John Crane dry gas-dynamic seals and control panels at its 

facilities. Throughout 2006-2008, Gazprom completed dry seal upgrades of 60 compressor units and is 

planning to continue these upgrades system wide. 

Outcomes 

Gazprom now has substantial experience in the development, adoption and operation of dry seal 

systems for compressor units with capacity ranging from 6.3 up to 25 MW. Practical use by Gazprom 

shows that replacement of dry hydrodynamic seals has a range of significant advantages over using 

wet oil seals. For wet seal compressors, for isolation of injector shafts, seals are applied with oil as an 

isolating material (floating-ring seals, front oil seals). The most common disadvantages of wet seals 

include operational complexity; large support system causing safety concerns; increased chance of 

rejection and increased costs of maintenance and repair work; high energy consumption; fire hazard 

and danger to the environment; and oil contamination of gas flow (the longer the seal in use, the higher 

the contamination will be). 

Gazprom determined that the best solution to address these issues is to begin replacement of wet 

seals with dry gas seals broadly across the entire Gazprom system. They have already completed this 

effort successfully at eleven facilities, resulting in the following key benefits: 

 Elimination of combustible gas contamination by oil. Oil contamination of the gas had resulted in 

gas pipeline discharge capacity reducing by 1-2 %. This issue is alleviated with the installation of 

dry seals. 

 Decrease in compressor’s capacity losses by reducing friction in seals. Friction in wet seals 

causes substantial reductions in capacity of the compressor (10 times and more). When 

compressor throughput capacity is lowered by 1%, compressor efficiency drops by several 

percent. Therefore, the positive impacts of dry seals are increased efficiency in compressors with 

turbine drives 

 Increase in operational life. Dry seals are designed to last the lifetime of a compressor. Dry seal 

systems do not require oil circulation components and treatment facilities, such as a seal oil pump 

and cooling fan, and degassing facilities such as heaters and flash tanks. Because dry seals have 

fewer ancillary components, they require minimal maintenance (once every 1-3 years) mostly 

consisting of visual examination and replacement, if needed, of filter elements and seal rings. This 

translates into lower maintenance costs, higher overall reliability and less compressor downtime. 

 Energy efficiency. Because dry seals have no accessory oil circulation pumps and systems, they 

avoid “parasitic” equipment power losses. Wet systems require 50 to 100 kiloWatt/hour, while dry 

seal systems need about 5 kiloWatt of power per hour. 

Gazprom has identified and observed through practical experience the clear economic and operational 

advantages allowing the company to justify retrofitting centrifugal compressors with dry gas seals 

broadly across their system. In addition to the benefits described above, dry seals also have important 

environmental and economic benefits, especially through reductions in methane emissions to the 

atmosphere. Estimates of the methane emission rate from a dry seal are 1.5 to 3.5 m3

/hour (according 

to most recent publications). According to Gazprom’s inspection, the emission rate from a wet oil seal 

ranges from 1.1 – 27.5 m3

/hour. However, further study, analysis, and measurements are needed to 

accurately quantify the specific methane emission reductions achieved by replacing wet with dry gas 

seals in their system. As indicated from the emissions rates above, while methane emissions are 

reduced by installing dry gas seals, Gazprom has also found that they do not completely eliminate 

emissions. Gazprom continues to build on their implementation success with their ongoing efforts to 

continue replacing centrifugal compressor wet seals with dry seals throughout their operations. 

Overall Results from Technical Case Studies 

Methane emissions reduction projects are increasingly becoming a focus of the oil and natural gas 

community due to their multiple benefits and attractive project economics. Companies operating in many 

different market environments have successfully identified methane emissions as a climate change and 

economic issue, reviewed proven project types, implemented mitigation activities and now continue to reap 

benefits after implementation. The five projects highlighted here have resulted in a significant volume of 

methane emission reductions, with payback periods ranging from 0.2 years to 3 years. It has been 

demonstrated that in some cases, benefits exceed the value of the natural gas saved, with recovered 

19 
20 

 

condensate, cost savings, efficiency improvements and maintenance savings being additional positive 

outcomes. 

The five case studies here also illustrate the different operator approaches and project magnitudes. 

PEMEX’s focus on DI&M resulted in potential methane emissions reduction of 4,849 thousand m3

/year, or 

U.S.$423,000 to U.S.$987,000 (at gas values of U.S.$106/thousand m3

 to U.S.$247/ thousand m3). PEMEX 

used this project as a pilot effort at a subset of facilities and is using results to potentially replicate the work 

across its supply chain. Mitigation efforts also varied from targeted maintenance activities to relatively 

capital-intensive wet seal to dry seal conversion in their centrifugal compressors. EnCana’s use of reduced 

emission completions reduced methane emissions by 418,173 thousand m3

 in 2008, or U.S. $44 million to 

U.S.$103 million worth of gas (at gas values of U.S.$106/thousand m3

 to U.S.$247/ thousand m3) and is an 

operating practice that can be perpetuated on future well completions. The Pluspetrol case study of tank 

vapor recovery illustrates their capture and use of 7,500 m3

 natural gas per day, as well as 10 to 13 m3 of 

valuable condensate. Pluspetrol has reduced methane emissions by utilizing the natural gas in a closedloop gas lift system, while selling 3,650 to 4,745 m3

 /year of condensate worth over U.S.$803,000 to 

U.S.$1.045 million (at condensate value of U.S.$35/bbl or U.S.$220.14/ m3

), helping to drive positive 

economics. This installation of a control technology provides long-term benefits of capturing multiple 

hydrocarbon resources for sale and internal use. Centrifugal compressor wet seal replacement implemented 

by Gazprom and other companies demonstrates that such activities have potential methane emissions 

reductions up to 2,758 thousand m3

/year per compressor, or U.S.$292,000 to U.S.$681,000 (at gas values 

of U.S.$106/thousand m3

 to U.S.$247/ thousand m3) and shows how methane emissions reduction can be a 

quantifiable co-benefit in addition to increased efficiency, lower operating costs and other operational 

benefits.

Conclusion 

The case studies presented here and the complete range of projects being implemented by industry 

demonstrate that reducing methane emissions can yield significant, quantifiable benefits that can be 

replicated throughout oil and natural gas operations. Identification and quantification of existing 

methane emissions constitutes a key first step for project evaluation and implementation. Once 

emissions sources and levels are identified, quantified, and monetized, proven methane recovery 

technologies can provide compelling economic and environmental benefits, in addition to operational 

and maintenance improvements, cost savings, and enhanced safety. In some cases, these benefits 

also include recovery of other valuable hydrocarbon resources, which can further improve project 

economics. With mitigation options that range from installation of new technology, to retrofit of existing 

technology, to changes in operating practices, companies can choose activities that fit within available 

resources and can accelerate implementation by aligning resources and capital to implement a range 

of methane emissions reduction projects. 

References 

1

 Global Anthropogenic Non-CO2 Greenhouse Gas Emissions: 1990-2020, U.S. Environmental Protection 

Agency, June 2006 

2

 IPCC Climate Change 2007: Synthesis Report. <http://www.ipcc.ch/pdf/assessmentreport/ar4/syr/ar4_syr.pdf> 

3

 IPCC, 2008. Forth Assessment Report: Chapter 2: Changes in Atmospheric Constituents and in Radiative 

Forcing. <http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch02.pdf> 4

 Specifications stated for FLIR Gas FindIR IR camera. 

<flirthermography.com/media/GasFindIR%20Brochure.pdf> 

5

 Remote Methane Leak Detection Manual. Heath Consultants. 

heathus.com/_hc/index.cfm/products/gas/rmld/

6

 This is an average cost for retrofitting wet seal to dry seal systems. Actual costs may vary. 7

 These are average costs and may not necessarily reflect actual implementation costs incurred by Pemex. 8

 Assuming a natural gas cost of U.S.$106/thousand m3 to U.S.$247/ thousand m3

9

 Gas prices based on Northwest Pipeline regional costs. 

10 EPA. Natural Gas STAR Lessons Learned Installing Vapor Recovery Units on Crude Oil Storage Tanks.

Griswold & Amber, 1978. <http://www.epa.gov/gasstar/documents/ll_final_vap.pdf> 11 EPA. Natural Gas STAR Lessons Learned Replacing Wet Seals with Dry Seals in Centrifugal 

Compressors. < http://epa.gov/gasstar/documents/ll_wetseals.pdf> 12 ibid same citation as 11 

13 EPA/GTI/Clearstone. Identification and Evaluation of Opportunities to Reduce Methane Losses at Four 

Gas Processing Plants. June 20, 2002. <http://epa.gov/gasstar/documents/four_plants.pdf>. 14 ibid same citation as 11 
21 

 

15 ibid same citation as 11 

16 ibid same citation as 11