Atmospheric pressure impacts greenhousegas emissions from leaky oil and gas wells18 October 2019

Fluctuations in atmospheric pressure can heavilyinfluence how much natural gas leaks from wells belowthe ground surface at oil and gas sites, according to newUniversity of British Columbia research. However,current monitoring strategies do not take thisphenomenon into account, and therefore may be under-or over-estimating the true magnitude of gas emissions.Credit: Aaron Cahill

Fluctuations in atmospheric pressure can heavilyinfluence how much natural gas leaks from wellsbelow the ground surface at oil and gas sites,according to new University of British Columbiaresearch. However, current monitoring strategiesdo not take this phenomenon into account, andtherefore may be under- or over-estimating the truemagnitude of gas emissions.

The unintentional leakage of natural gas from oiland gas wells into the surroundingsubsurface—known as fugitive gas migration—is amajor environmental concern that can lead togroundwater contamination and the emission ofgreenhouse gases into the atmosphere.

"Currently, subsurface gas migration is monitoredusing infrequent or short-term location-restrictivemeasurements," said Olenka Forde, a geologicalsciences Ph.D. student at UBC and lead author ofthe study published in Scientific Reports. "Ourstudy shows that the magnitude of gas emissions tothe atmosphere can depend on atmosphericpressure before and during the time of monitoring,so short-term, one-time measurements may not berepresentative of average emissions."

Variations in atmospheric pressure tend tocompress or expand soil gas, with the mostsignificant impact at sites with deep water tables,explains Forde. During a high-pressure system, soilgas is compressed and pushes leaked natural gasdeeper underground, where it will likely not bedetected at the surface. When atmosphericpressure declines, natural gas trapped below thesurface during the previous high-pressureconditions can escape to the atmosphere,contributing to greenhouse gas emissions.

Fluctuations in atmospheric pressure can heavilyinfluence how much natural gas leaks from wells belowthe ground surface at oil and gas sites, according to new

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University of British Columbia research. However, currentmonitoring strategies do not take this phenomenon intoaccount, and therefore may be under- or over-estimatingthe true magnitude of gas emissions. Credit: Aaron Cahill

To evaluate this effect, the team ran a fieldexperiment in an area of significant historic andongoing oil and gas development near Hudson'sHope, in northern B.C. Over a period of five days,30 cubic metres of natural gas (98.3 per centmethane) was continuously injected 12 metresbelow the ground surface. Atmospheric pressureand methane emissions were then continuouslymeasured for 24 days during and after gasinjection. The researchers controlled for depth andrate of well leakage, which are key factors thatinfluence fugitive gas migration.

"We found that the magnitude and duration ofatmospheric pressure changes directly influencedthe amount of natural gas coming out the groundand being emitted into the atmosphere," saidForde. "Under high pressure conditions, methaneemissions decreased, sometimes even below thedetection limit. But when atmospheric pressuredecreased, methane emissions increasedrapidly—at times more than 20-fold in less than 24hours."

As a result, continuous monitoring over a longerperiod of time is key. "This will help to moreaccurately detect and evaluate gas migrations andemissions and thus, the risks posed by leaking oiland gas wells," said Forde.

There are over four million onshore hydrocarbonwells around the world, a portion of which areknown to suffer loss of structural integrity, whichcan lead to this type of subsurface leakage andresulting greenhouse gas emissions.

"The results of our study allow us to move towardsrefining and improving regulations and monitoringmethods," said co-author Aaron Cahill, co-directorof the Energy and Environment Research Initiativeat UBC. "This will help determine which leaky wellsshould be prioritized for remedial action to limit themost substantial greenhouse gas emissions."

More information: Olenka N. Forde et al,Barometric-pumping controls fugitive gas emissionsfrom a vadose zone natural gas release, ScientificReports (2019). DOI: 10.1038/s41598-019-50426-3

Provided by University of British Columbia

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APA citation: Atmospheric pressure impacts greenhouse gas emissions from leaky oil and gas wells(2019, October 18) retrieved 29 January 2022 from https://phys.org/news/2019-10-atmospheric-pressure-impacts-greenhouse-gas.html

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