Thermal or optical gas imaging (OGI) is essential in the detection of methane leaks and for various types of oil and gas sector maintenance, including preventive, corrective, and curative maintenance, as well as periodic inspections and continuous monitoring of pipelines.
New technologies such as drones, remote sensors, and artificial intelligence, in conjunction with thermal imaging, have enabled a wide range of technical applications for gas detection.
OGI cameras use a spectrally filtered camera to visualise otherwise undistinguishable gas leaks by measuring the infrared radiation passing through a volume of gas, and they can be operated from satellites, aeroplanes, drones, vehicles, and as handheld devices.
Noble gases such as helium, oxygen, and nitrogen cannot be directly imaged, but hundreds of other industrial gases that absorb infrared energy can be visualised with OGI, such as benzene, butane, and methane.
This method of remote sensing has numerous advantages, allowing operators to scan and survey broad areas that may be hard to reach otherwise, a particular benefit to pipeline maintenance.
Fugitive methane emissions are an often-invisible consequence of fossil fuel production, but can be reduced and mitigated through reliable monitoring and stronger policy action.
Though not as prevalent in the atmosphere as carbon dioxide, methane is 86 times more potent and is responsible for almost a third of emissions-induced increases in temperature since the start of the industrial era.
It has been estimated that the global oil and gas industry emits 13 million tonnes of methane from operations each year, and that if just 3.2 per cent of methane brought up from wells leaked rather than being burnt, natural gas would become even less eco-friendly than coal.
The primary safety benefit of OGI cameras is their visual range – unlike other tools, these provide the ability to visualise unsafe conditions from a safe distance.
Uncooled infrared imaging devices are available at much lower prices when compared to cooled models (which use quantum detectors that require cryogenic temperatures), and this affordability has led companies to redefine the relationship between equipment and personnel.
The lower prices of handheld OGI devices allow other workers, such as maintenance repair technicians, to use the technology, allowing for a more widely distribution and use within the workplace.
Uncooled cameras are generally less sensitive and have higher detection limits, restricting the number of gases they can detect.
However, these devices still have great utility in certain circumstances, such as in downstream applications where methane is not a primary concern but ethylene is.
An uncooled camera, according to Yousheng Zeng and Jon Morris of Providence Photonics, can achieve comparable sensitivity for ethylene as a cooled camera, but at a substantially lower cost.
Refinery employees equipped with OGI can ascertain whether an area contains toxic gas build-up, limiting exposure to gas that would normally set off a wearable gas monitor.
Similarly, workers gauging large tanks can judge the emission characteristics of the tank before placing themselves in any potential gas cloud.
OGI gives workers actionable and precise information about the toxicity in their immediate surroundings without endangering them to detect such hazards.
One of the complications posed by OGI is the volume of footage and associated data produced by thermal cameras, creating a need for more sophisticated software and expanded processing capacity.
A possible solution, evidenced by a project conducted by the Southwest Research Institute (SwRI) and the US Department of Energy’s National Energy Technology Laboratory, is to develop automated inspections of oil and gas facilities.
This involves using smart leak detection technology which can remotely detect methane leaks in real time with the aid of a drone.
SwRI manager of research development Maria Araujo said the institute had already developed the technology for stationary applications but autonomous performance from drones would make life easier for operators, and importantly, reduce the volume of data needing to be streamed.
Araujo said: “One of the efficacy points of drone inspection is normally just the ability to monitor large areas, but now you have a moving platform that can potentially quantify the methane leak.
“Once you have a moving platform like that, you can potentially get additional information aside from a strict 2D image point that may allow you to quantify the size of that leak with an OGI.”
Quantitative OGI is another possible method of addressing the volume of OGI data, where cooled hydrocarbon OGI is combined with an algorithmic solution that quantifies gas leaks invisible to the naked eye.
OGI cameras have historically been limited to qualitative analysis, indicating a leak is occurring but not quantifying how much is leaking.
Other detection methods such as a toxic vapour analyser (TVA), colloquially known as a ‘sniffer’, or a Bacharach Hi Flow Sampler (BHFS), can quantify a variety of gas leaks in mass leak rate and volumetric leak rate, as well as concentration path length.
A TVA offers concentration analysis but no measurement of flow, while a BHFS is capable of measuring both flow and concentration.
However, both TVA and BHFS devices can return differing interpretations of the same leak, depending on where and when the leak is sampled and how the device is positioned.
This limitation is a result of these devices’ functionality – they provide a leak snapshot in time while a quantitative OGI system provides a rolling average leak rate over time.
Multiple studies have stated the results of quantitative OGI had great potential in the context of detecting gas leaks in a variety of environmental situations.
The authors of one such study in 2016, conducted by Concawe Environmental Science for European Refining, noted quantitative OGI was a promising technology for detecting fugitive emission sources and quantifying the mass release rate for each individual leak.
