A 30-day study led by Scottish and Canadian scientists showed that atmospheric pressure controls the timing and magnitude of fugitive gas emissions from leaky wellbores.
The finding is significant, as changes in atmospheric pressure are not routinely taken into account when assessing fugitive gas leakage from leaky oil and gas wells.
The scientists say their findings show that regulators around the world must take other environmental factors, especially atmospheric pressure changes, into consideration when assessing potential greenhouse gas leakage from onshore oil and gas wells.
Dr Aaron Cahill, from the Lyell Centre at Heriot-Watt University, said: “Fugitive emissions from hydrocarbon wells are a serious environmental issue. They release greenhouse gases into the atmosphere and can negatively affect the environment including groundwater resources.
“Our experiment showed that atmospheric or barometric pressure changes, decreases in which can lead to rain, had a profound effect on fugitive gas emissions.
“When air pressure decreased by 0.2 PSI over a period of hours or days, a very small amount considering bicycle tires require 50 PSI or so, the release of natural gas from the soil to the atmosphere increased 20 fold.
“Atmospheric pressure isn’t the only factor at work. Soil moisture, temperature, local geology and the type of energy well all play roles in the process, but our study showed changes in air pressure is a key driving force.
“Current monitoring strategies, which generally involve one-time, simple measurements of soil gas concentrations around a wellhead, don’t consider barometric pressure changes or other environmental parameters that control leakage.
"This means some cases of leakage won't be detected, for example, if air pressure has been high for a period of time. It also means any estimates for the volume of fugitive gas escaping from a well will simply be wrong; either under- or over-predicting how much gas is coming out of the ground.
“We need frequent, continuous monitoring if we are to accurately detect and quantify fugitive gas emissions at oil and gas sites.
“Unfortunately, wellbore integrity failure and gas leakage can develop in a portion of all energy wells including active, abandoned, conventional and unconventional wells.
“Improving monitoring methods to optimally detect leakage from energy wells is essential for identifying the wells that are leaking the most, and prioritizing repairs as required. Hopefully, this work sets us on the right path.”
During the experiment, the research team simulated wellbore leakage in the ground at a field site in Northeastern British Columbia, Canada, a highly developed area with over 25,000 energy wellbores. Thirty cubic metres of natural gas was continuously injected 12m below the ground surface over five days. The injected gas was tracked through the soil and into the atmosphere, while atmospheric pressure and other environmental parameters were also monitored to assess relationships.
The report can be read in full here: https://www.nature.com/articles/s41598-019-50426-3
This research was funded by Natural Resources Canada, Geoscience BC, the Natural Science and Engineering Research Council (NSERC) of Canada Research Tools and Instruments Grants Program, the Canadian Foundation for Innovation, and the British Columbia Oil and Gas Commission.
Read the article online at: https://www.oilfieldtechnology.com/special-reports/17102019/study-finds-atmospheric-pressure-controls-greenhouse-gas-emissions-from-leaky-oil-and-gas-wells/
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