TECHNICAL ARTICLE
Estimating CO 2
Emissions and Gas Leaks
Around Scope 1 emissions, Dr. Jane Hodgkinson, a reader in Applied Photonics at Cranfield University, who has extensive experience working in the energy sector, says there are two major routes to downstream greenhouse gas emissions: combustion products and gas leaks.
When it comes to estimating the CO 2 produced by burning oil and gas( Scope 3), Dr. Hodgkinson thinks it likely that Shell, Equinor, and Ithaca would base their calculations on metering. She explained that this methodology assumes that“ a known proportion of everything they produce will be burnt and will result in a certain proportion of CO 2 emission”.
She added,“… There must be production plans so they should know what volumes they will aim to produce. Some of their product will not be combusted( e. g., oil to plastic, bitumen used in asphalt), but they will probably have a business plan for how much of each type of product they will generate. The calculation would be fairly straightforward.”
As for estimating gas leaks such as methane( Scope 1 and Scope 3), Dr. Hodgkinson says that“ there may be some assumptions” that Shell, Equinor and Ithaca would need to make about gas emissions. She thinks that they would“ probably assume that a certain proportion of throughput is leaked,” based on existing environmental reporting from gas transmission, distribution, transport, and storage infrastructure.
Regarding Scope 3 emissions, Neil Harris, a Professor of Atmospheric Informatics at Cranfield University, believes that the CO 2 end product“ is unavoidable” and that they can only claim any offset of that if there were credible CO 2 removal technologies.“ However,” there are not any at the moment and in any case the operations would be controlled by others, so there is nothing they( oil and gas companies) can do,” he added.
Dr. Jasmin Cooper, a Research Associate at Imperial College London, who has carried out extensive research on fugitive methane emissions, agreed. In terms of greenhouse gas emissions, while“ it is relatively easy” for energy companies to estimate how much greenhouse gas will be emitted from petrol, diesel, and natural gas supply chains, guessing the emissions for other petroleum-based products“ is less straight forward,” Dr. Cooper said.
“ Chemicals made from oil and gas( ethane, ethylene, etc.) have much more complex supply chains and depending on what the eventual end use is, CO 2 may or may not be emitted. For example, ethylene is used to make plastics, other chemicals, and to ripen fruit, so there will be much higher uncertainty in how much CO 2 will be emitted from these supply chains. Obviously, CO 2 in these instances will not always be from burning, but also from degradation of the products,” Dr. Cooper explained.
This begs the question how far down the downstream value chain would an environmental impact statement need to cover. Dr. Cooper says that while oil and gas companies have a good grasp of their gas and liquid fuels supply chains, she thinks estimating emissions from the chemical production chains would pose a much greater challenge.“ They( oil and gas companies) may know the whole value chain( to end of
life disposal) but tracking molecules of fossil fuel-based chemicals produced by oil and gas companies is tricky as companies who buy ethane or ethylene from them will buy the same chemical from other companies. This is mixed together to make a new product. This in turn may be used to make another product, for example- polypropylene used to make packaging, which is then used for a product bought in a shop.”
When it comes to estimating methane emissions, Dr. Jane Hodgkinson believes that sensor technology“ can play a role in establishing reporting of existing infrastructure” while it can also“ be instrumental in upgrading old infrastructure to enable better detection of leaks.”
However, she added,“ Gas leaks are very difficult to detect and locate, and simply detecting them isn’ t enough – companies also need to act on this information and prevent the leak.”
It is a view shared by Professor Harris, but he says that legacy monitoring sensor technology“ is not a scalable solution” as the cost of such techniques is“ high and there are many oil and gas sites with the potential to leak.
The problem is that there are on-site sensors which are good for detecting methane, but not necessarily measuring it,” he said.
Inequality Between Sensors
The uncomfortable reality is that not all sensors are equal. The detection limits of legacy tools, such as fixed-point sensors and satellite technology, are too high, while conventional monitoring systems, such as optical gas imag-
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