UBC Theses and Dissertations
Characterization of gas migration and surface emissions through a controlled release experiment at the Hudson’s Hope field research station, BC, Canada. Soares, Julia Valentina
The expansion of unconventional oil and gas development has led to growing concern regarding the environmental impacts of gas migration (GM), which occurs at some wells. GM is the transport of natural gas outside of the well casing, which can lead to mobile fugitive gas (FG) that penetrates into neighbouring geological formations and can impact aquifers. FG that migrates to the surface contributes to greenhouse gas emissions that are difficult to quantify. This study is part of a research program that aims to increase knowledge of GM and FG through a controlled natural gas release experiment. The experiment was conducted near Hudson’s Hope in north-eastern British Columbia, Canada, a region of active unconventional natural gas development. The experimental site is underlain by heterogeneous quaternary deposits with a confining clay layer overlaying a sand aquifer. 100 m³ of a synthetic natural gas mixture was injected at the base of the aquifer at a constant rate for 66 days. This thesis focuses on monitoring of GM in the unsaturated zone and the quantification of surface effluxes. To this end, twelve long-term chambers were used to measure CO₂ and CH₄ effluxes, providing high resolution time-series data. Survey chamber measurements at 105 locations allowed for spatially distributed measurements at lower frequency. In addition, soil gas samples were collected from 22 soil gas sampling ports. The results illustrate that the injected gas migrated upgradient against the direction of groundwater flow and broke through at the surface six weeks after the injection started. Once the gas was detected, elevated CH4 fluxes were continuously detected at the surface in a constrained geographical region and only began to decrease one-week post-injection. Soil gas composition and isotopic data further support that the gas migrated through the soil towards the ground surface and that hydrocarbons were microbially oxidized. The free phase gas plume was only able to reach the surface due to the presence of a preferential pathway in the confining layer. Soil gas compositional data indicates that towards the end of the injection and post-injection, the free-phase gas plume began to explore alternative preferential pathways.
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