| Autor: |
Forde, Olenka N., Cahill, Aaron G., Mayer, Bernhard, Beckie, Roger D., Mayer, K. Ulrich |
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| Zdroj: |
Geophysical Research Letters; 8/16/2022, Vol. 49 Issue 15, p1-10, 10p |
| Abstrakt: |
Fugitive gas migration (GM) from compromised oil and gas wells remains a global concern. To understand environmental impacts from GM there is a need to characterize the transport and fate of fugitive gas in the vadose zone. We simulated subsurface wellbore leakage by injecting natural gas into thick unsaturated glacio‐lacustrine deposits in a region of petroleum development in Western Canada. Methane and carbon dioxide effluxes were monitored and soil‐gas samples were collected for molecular and stable carbon isotope analyses. A conceptual model was developed to demonstrate the physical and biogeochemical processes that control the spatial‐temporal variability of GM. Methane oxidation partially attenuated natural gas; however, gas transport and fate were strongly influenced by variations in grain‐size distribution and barometric pressure, resulting in episodic effluxes and lateral gas transport. To accurately detect, quantify and assess GM at oil and gas sites, adequate site characterization and continuous, spatially dense monitoring are necessary. Plain Language Summary: Natural gas leaking from imperfectly sealed oil and gas wells can lead to explosive conditions in soil gas and methane emissions to the atmosphere. To understand the impacts and improve monitoring practices of fugitive gas migration, there is a need to characterize processes that control gas transport and fate in the unsaturated zone. We simulated subsurface wellbore leakage by injecting natural gas into thick unsaturated deposits in a region of petroleum development in Western Canada. The response was monitored by measuring methane and carbon dioxide concentrations and emissions on the ground surface and in soil gas in the unsaturated zone. Our results show that numerous compounding processes influence methane concentrations in the unsaturated zone and emissions to the atmosphere. While microbially mediated reactions consume methane in the unsaturated zone, variations in soil grain sizes and changes in barometric pressure strongly influence gas transport, which can lead to high episodic emissions in unpredictable locations. To accurately detect, quantify and assess fugitive gas migration at oil and gas well sites, adequate site characterization and continuous, spatially dense monitoring are necessary. Key Points: Fugitive gas migrated to the ground surface despite a deep vadose zone with low‐permeability silts and claysA preferential pathway and intervals of decreased barometric pressure resulted in a hotspot with high episodic methane effluxesLow‐permeability sediments and intervals of increased barometric pressure favored lateral gas migration and progressive methane oxidation [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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