Attachment O

Leaks

Dave Picard

Clearstone Engineering, Ltd.
PEER REVIEW: OIL AND NATURAL GAS SECTOR LEAKS

1. Did this paper appropriately characterize the different studies and data sources that quantify 

VOC and methane emissions from leaks in the oil and natural gas sector? 

Response: The paper identified all the key studies and data sources that quantify VOC and 

methane emissions from leaks in the oil and natural gas sector. However, the following are a 

few areas where this information could have been better characterized:

• While the study touches on the matter, it should make a more clear distinction 

between: (1) quantifying emissions for the purpose of environmental reporting and 

(2) the quantification of emissions for the purpose of building a health, safety, 

environmental or business case for leak repairs. A leak at surface facilities may be 

defined as the loss of process fluid past a seal, mechanical connection or minor flaw 

at a rate that is in excess of normal tolerances allowed by the manufacturer or 

applicable health, safety and environmental standards. Those leaks in the first 

category should be fixed wherever this is economical to do (i.e., based on direct 

repair or replacement costs and the value of the process fluid being lost), while those 

in the latter category must be fixed regardless of the cost. Some companies prefer to 

simply detect and repair leaks and avoid the cost of quantifying them unless the leak 

is deemed uneconomical to repair and the significance of the leak from a health, 

safety and environmental perspective is in question. 

• Other than indicating they should not be applied to individual components, no 

indication is given regarding the accuracy of the leak-rate correlation and different 

emission factor methods and how the accuracy is impacted by the number of 

components considered. For example, the leak-rate correlations are extremely weak 

correlations and have uncertainty bands of ±2 to 3 orders of magnitude when applied 

to individual screening values. In general, screening values are a poor indicator of the 

leak rate.

• There is no discussion on how reliable the average facility-level or process unit-level 

component counts are, or discussion of the challenges of getting accurate component 

counts. It is much easier to train someone to operate a leak detection device than it is 

to train them to recognize what equipment is in active service and what service each 

component is in. So, developing component counts can be a noteworthy source of 

uncertainty. The potential issues of developing component counts from process 

drawings should also be acknowledged.

• A number of studies have been cited that contain information on the amount of CH4

and, in some cases, VOC emissions from leaks per facility. It would be useful to 

compare these data to the GRI/US EPA 1996 data used to derive the facility-level 

emission factors applied in the presented emission inventory estimates. There may be 

value in combining the data sets to get a larger, more statistically representative, data 

set upon which to base the emission factors. 

2. Please comment on the approaches for quantifying emissions and on the emission factors 

used in the data sources discussed. Please comment on the national estimates of emissions 

and emission factors for equipment leaks presented in this paper. Please comment on the 

activity data used to calculate these emissions, both on the total national and regional 

equipment counts. 

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Response: See the comments provide under Item 1 above.

3. Are the emission estimating procedures and leak detection methods presented here equally 

applicable to both oil and gas production, processing, and transmission and storage sectors?

Response: The presented leak detection methods are all aimed at detecting leaked gases and 

vapors in air at or downwind of the source. These emissions are primarily related to 

equipment components in Gas/Vapor, LPG and LNG service. The presented detection 

methods are equally applicable to oil and natural gas production, processing and transmission 

and storage sectors for the purpose of targeting these types of leaks.

Components in crude oil or NGL service tend to have low or no methane emissions and any 

leakage is generally readily detected by visual means. Components in this type of service 

mostly occur at oil production facilities and at production and processing facilities handling 

wet natural gas. Leak-prone components in crude oil or NGL service will normally feature 

drip pans to capture any leakage that occurs less any evaporation losses. The presented leak 

detection methods are much less applicable these types of leaks.

4. Are there ongoing or planned studies that will substantially improve the current 

understanding of VOC and methane emissions from leaks and available techniques for 

detecting those leaks? Please list the additional studies you are aware of. 

Response: I am not aware of any additional studies other than the work currently in 

progress through the Environmental Defense Fund.

5. Are there types of wells sites, gathering and boosting stations, processing plants, and 

transmission and storage stations that are more prone to leaks than others? Some factors that 

could affect the potential for leaks are the number and types of equipment, the maintenance 

of that equipment, and the age of the equipment, as well as factors that relate to the local 

geology. Please discuss these factors and others that you believe to be important. 

Response: Fugitive emissions management requires ongoing attention. Leaking 

components, even after successful repair, will eventually reoccur without proper 

inspection and maintenance. It is also recognized that different types of components and 

service applications have different leak potentials, and therefore, will require different 

levels of attention.

This is apparent in Table 1 below even though it includes compressor seals as a leak 

category which is not the focus of the oil gas sector leaks white paper. If the leak 

potential (i.e., average emission rate per component) for a connector is set to 1 (see the 

final right-hand column in Table 1), then the leak potential for block valves is 9 times 

greater, the value for control valves is 37, open-ended lines is 205, a reciprocating 

compressor seal is 2400 and so on. Based on these statistics, their percentage contribution 

to total fugitive emissions and their leak frequencies, leak detection efforts should be 

focused mostly on the top 5 categories shown in Table 1, namely: blowdown systems, 

centrifugal compressor seals, reciprocating compressor seals, pressure relief valves and 

open-ended lines. Collectively, these five categories account for only 1.2 percent of the 

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total component population but contribute more than 88 percent of the total emissions 

from fugitive equipment leaks.

The amount of leakage at a facility will be related to the number of high-leak-potential 

components employed at the facility, the quality of the facility’s inspection and 

maintenance program, the toxicity or odor potential of the process fluids, and (to some 

extent) the age of the facility.

Facilities that suffer from neglect, regardless of whether they are new or old will, will 

have greater leak frequencies than those that do not. Facilities that are experiencing 

dramatic declines in throughput, are believed to be approaching the end of their useful 

life or have gone through numerous ownership changes are most likely to suffer from 

neglect. Components that are in sour or odorized service will tend to have lower leak 

frequencies and large leaks than components in sweet gas service.

Components in fuel gas service tend to have greater leak frequencies than components in 

process gas service.

The amount of emissions from a leaking component is generally independent of the size 

of the component.

Leakage into vent systems, compressor seals, pressure relief valves and open-ended lines 

tend to be the most common sources of big leaks. Still, components such as connectors 

Table 1: Sample leak statistics for gas transmission facilities.

Source Number 

of 

Sources1

Leak

Frequency2

Average 

Emissions

(kg/h/source)2

Percent of 

Component 

Population

Contribution 

to Total 

Emissions 

(%)

Relative 

Leak 

Potential

Station or Unit 

Blowdown System

219 59.8 3.41E+00 0.131 53.116 7616

Compressor Seal –

Centrifugal

103 64.1 1.27E+00 0.062 9.310 2838

Compressor Seal –

Reciprocating

167 40.1 1.07E+00 0.100 12.764 2400

Pressure Relief Valve 612 31.2 1.62E-01 0.366 7.062 362

Open-ended Line 928 58.1 9.18E-02 0.555 6.070 205

Orifice Meter 185 22.7 4.86E-02 0.111 0.641 109

Control Valve 782 9 1.65E-02 0.468 0.919 37

Pressure Regulator 816 7 7.95E-03 0.488 0.462 18

Block Valve 17029 2.8 4.13E-03 10.190 5.011 9

Connector 145829 0.9 4.47E-04 87.264 4.644 1

Other Flow Meter 443 1.8 9.94E-06 0.265 0.000 0.02

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and valves can, on occasion, also be major leak sources. Examples of situations where 

this or other unexpected significant leak contributions may occur include the following:

• Connections left untightened after a scheduled turnaround or maintenance which

go unnoticed due to high background noise levels or because the component is in 

a difficult to access or infrequently visited location (e.g., at high elevation 

location or on a pipe rack).

• Holes that have developed in equipment or piping due to corrosion, abrasion or 

damage.

• Components that have been improperly installed or that were neglected to be 

installed (e.g., a pressure gauge removed during maintenance work is not put back 

into its port and the valve on the port is in an open or partially open position).

• Major failures of valve stem packing systems (e.g., blowout of the packing 

material).

6. Did this paper capture the full range of technologies available to identify leaks at oil and 

natural gas facilities? 

Response: The paper did not discuss area and building monitoring systems, use of 

odourants, and mass balance techniques. A discussion of building and area monitoring 

systems is warranted as there is sometimes a perception that these are effective in detecting 

leaks; they are only effective in detecting leaks that are either sufficiently large to appreciably 

affect the air quality of the monitored building or area, or are located very close to the gas 

sensors used by the sensors.

7. Please comment on the pros and cons of the different leak detection technologies. Please 

discuss efficacy, cost and feasibility for various applications. 

Response:

• OGI – this technology provides the ability to visualize leaks in real time and record 

the information. Such information has proven to be much more compelling evidence 

for management to approve the time and resources needed to control leaks than the 

output of other technologies. The technology is not as sensitive as other technologies 

in detecting leaks, but it is much more efficient in finding the big leaks that contribute 

most of the leakage emissions. The key disadvantage of the technology is the high 

capital cost of the instrument.

• Method 21 – These methods are more sensitive than the OGI and have much lower 

capital costs, but are more time-consuming to apply, are susceptible to fouling, and 

require regular calibration and servicing.

• Soap Solution – this is a simple technique that has good sensitivity, the lowest capital 

cost and is not affected by interferences from other nearby sources. It cannot be 

applied to cold or hot surfaces and can be time-consuming to apply. 

• Remove Monitoring – This method requires favorable wind conditions, needs to be 

able to accurately measure small perturbations in pollutant concentrations above 

background levels, is susceptible to interferences from other nearby sources, does not 

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distinguish between leakage and our other emission sources, can be costly, requires a 

much greater level of training and knowledge to apply and does not pinpoint the 

location of individual leaks. Rather, it provides a practicable means of measuring 

total emissions from a facility or process area.

• Acoustical – this method does not distinguish between natural gas leaks and leaks of 

other types of gases such as steam, air or nitrogen. Moreover, the method should not 

be used after a rain or in an area where soap tests have just been performed as the 

wetted surfaces may adversely affect the detection capability of the method. The 

technology is moderately priced. 

8. Please comment on the prevalence of the use of the different leak detection technologies at 

oil and gas facilities. Which technologies are the most commonly used? Does the type of 

facility (e.g., well site versus gathering and boosting station) affect which leak detection 

technology is used?

Response: In the absence of a formal leak detection program, leaks are largely detected 

based on OVA techniques by operations and maintenance staff as they conduct their normal 

activities, and by building and area monitoring systems. However, where formal leak surveys 

are required there is an overwhelming tendency for upstream oil and natural gas companies to 

either invest in OGI cameras or retain service providers that use OGI cameras.

9. Please provide information on current frequencies of revisit of existing voluntary leak 

detection programs in industry and how the costs and emission reductions achieved vary with 

different frequencies of revisit.

Response: No information available.

10. Please comment on the potential for using ambient/mobile monitoring technologies in 

conjunction with OGI technology. This would be a two-phase approach where the 

ambient/mobile monitoring technology is used to detect the presence of a leak and the OGI 

technology is used to identify the leaking component. Please discuss efficacy, cost and 

feasibility.

Response: While the proposed strategy is a pragmatic approach to efficiently finding 

noteworthy sources of leakage, it has not been widely adopted. This is largely due to the lack 

of readily available and practicable ambient/mobile monitoring technologies and/or service 

providers.

11. Please comment on the cost of detecting a leak when compared to the cost to repair a leak. 

Multiple studies described in this paper suggest that detecting leaks is far more costly than 

repairing leaks and, due to generally low costs of repair and the subsequent product recovery, 

it is almost always economical to repair leaks once they are found. Please comment on this 

overall conclusion.

Response: The statement that leaks are far more costly to find than to repair is a 

generality. Many leaks are easy to fix and simply require the tightening of a connector or 

packing gland, but these are not necessarily the leaks that contribute most to total leakage at a 

site. 

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12. If the conclusion is correct that it is almost always economical to repair leaks once they are 

found, then how important is the quantification of emissions from leaks when implementing a 

program to detect and repair leaks? 

Response: The quantification of emissions is not necessary to drive a repair decision if 

the leaking component is easy and inexpensive to fix or if the amount of emissions is clearly 

sufficient to pose a health, safety, or environmental concern (e.g., if it causes personal, area 

or building monitoring systems to alarm). Quantification is more important where companies 

adopt leak reductions as a key performance indicator.

13. Please comment on the state of innovation in leak detection technologies. Are there new 

technologies under development that are not discussed in this paper? Are there significant 

advancements being made in the technologies that are not described in this paper? 

Response: There is a reasonable amount of innovation underway to develop more 

powerful and cost-effective leak detection and quantification systems. Most of this effort is 

focused on developing lower cost gas sensors, intelligent multi-sensor fixed monitoring 

systems that incorporate information on the site structures and meteorological data to detect 

and quantify leaks, and manned and unmanned vehicle-based plume transect systems for 

quantification of emissions.

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