A new third-party study by Matthew Johnson and others at Carleton University’s Energy and Emissions Research Laboratory was published in January 2023. The study evaluated aerial survey data from Bridger Photonics’ Gas Mapping LiDAR (GML) first-generation sensors in combination with subsequent on-site investigations of the detected sources using ground crews equipped with optical gas imaging (OGI) cameras. The follow-up investigations aimed to validate Bridger’s aerial measurements and refine emission source attribution for a Canadian oil and gas production basin.
The authors state that “Success in reducing oil and gas sector methane emissions is contingent on understanding the sources driving emissions, associated options for mitigation, and the effectiveness of regulations in achieving intended outcomes.” This study evaluates the sources of emissions and mitigation options in an active oil and gas production region of British Columbia, Canada, which is subject to leak detection and repair (LDAR) surveys three times per year under current Canadian regulations for certain equipment types.
Here are the main takeaways from the study:
Takeaway 1: Aerial detection of emissions found the dominant sources of emissions were compressors (combustion slip), tanks, and flares.
Compressors, storage tanks, and unlit flares were determined to be the dominant sources of methane emissions in the studied region (see Figure 1b in the research paper). This study builds on past research with similar findings by evaluating these three sources in greater detail for each equipment type.
Compressors:
Natural gas is often used as the fuel source to power compressors on oil and gas production sites because it is readily available. More than half of the measured methane from the aerial surveys was attributed to compressors.
Methane slip, also known as combustion slip, or uncombusted methane in the compressor exhaust, was the dominant emission source* for compressors.
- The detection frequency in the study by aerial GML for each compressor package type are as follows (“controlled” compressors refer to those that use one or more built-in control(s) to regulate and minimize emissions output):
- 68% for uncontrolled gas fired
- 78% for controlled gas fired
- 37% for uncontrolled electric drive
- 0% for controlled electric drive
The population emission factors derived in the study based on the GML measured sources followed the same pattern, with the counterintuitive finding of higher emissions and a higher detection frequency from controlled natural gas driven compressors compared to uncontrolled. This suggests “that aerial detected emissions are dominated by methane slip in the engine combustion exhaust.” The 0% detection frequency of controlled electric drive compressors (i.e. no detections) indicates that the increased utilization of these would help facilitate the reduction of emissions.
Other notable compressor-related findings describe that:
- For controlled gas driven compressors, crankcase venting was an additional source of emissions.
- For uncontrolled gas- and electric-drive units, rod packing vents were also a dominant emission source.
- Combustion slip emissions varied widely from manufacturer specifications, and there were also differences between lean-burn and rich-burn engines, however aerially measured emissions from these different engine types were very similar when normalized to a per brake horsepower basis.
Storage Tanks:
Storage tank emissions constituted 18% of measured methane from the GML aerial surveys.
- Tank emissions were from both controlled and uncontrolled tanks (i.e., tanks both with and those without controls to regulate and minimize emissions output).
- On-site inspections revealed emissions sources from controlled versus uncontrolled tanks were variable.
- In some cases, for controlled tanks, the source was upstream of the control device (e.g., pressure relief valves, or thief hatch seals).
- For uncontrolled tanks, emissions were all a result of direct venting.
Unlit Flares:
Unlit flares were only approximately 4% of total aerially detected sources, yet they were the third largest contributor to aerial measured methane emissions at 7%, since unlit flares are often large emitters. This finding is similar to past research that identified flares as a major emission source that often goes undetected by OGI ground crew surveys and fixed methane sensors.
- Several detected unlit flare emissions were due to flares being operated as vents.
- In other cases, flares were unlit, but facility plans indicated that they should be lit.
Why It Matters:
A stronger understanding of specifically where the majority of emissions are coming from, down to the sub-equipment level, can make emissions mitigation and reduction efforts more targeted and efficient for operators. This, especially when coupled with root cause analysis, is critical for developing robust emission mitigation programs that do not simply identify and address emissions but prevent leaks from occurring in the first place, allowing operators to keep gas in the pipes.
Takeaway 2: Standard OGI surveys using ground crews three times per year still miss substantial emissions sources.
In this study, measurements were taken in British Columbia, a region representative of typical Canadian oil and gas operations. This study therefore underscores the limitations of traditional LDAR programs in Canada. Due to the overlap between the United States’ and Canadian environmental regulatory structure for emissions leak detection, many of the learnings and approaches described in this publication may also apply to the U.S. As the study puts it, “In this sense, sources examined in this study are examples of what persists under a prescribed LDAR program and the further challenges that remain in eliminating methane emissions as part of reaching net-zero emission objectives.”
There are several factors that limit OGI effectiveness including the fact that combustion slip “cannot readily be seen by OGI cameras”* and given that tanks and unlit flares are often missed during OGI scans. Tanks and flares often go undetected by OGI cameras because of the lack of visual access to the elevated tops of the equipment, the limited effective range of the OGI cameras, thermal contrast issues, and/or OGI surveyor experience and affiliation. Aerial scans capture the missed emissions from these major sources, apart from very small leaks below GML’s chosen detection sensitivity that don’t appreciably impact the operators’ aggregate emissions in typical basins.
Why It Matters:
Because substantial emission sources are missed despite British Columbia’s requirement of LDAR screenings three times per year, additional emissions monitoring, reporting, and verification (MRV) is necessary in addition to the standard LDAR surveys to reach reduction targets and net-zero goals. Beyond LDAR surveys and additional emissions MRV initiatives, preventing emissions through upgrades or retrofits (i.e. installing electrified compressors) that decrease emissions generation in the first place are also necessary to reach near-term reduction targets and eventual net-zero goals. In future regulatory rulemaking, we at Bridger Photonics advocate for the incentivization of advanced technology capable of detecting and locating the significant emissions that are beyond the monitoring scope and detection capabilities of traditional LDAR programs based on existing regulatory frameworks.
Read the full study linked here.
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