SURFICIAL EMISSIONS OF METHANE IN RESPONSE TO A CONTROLLED INJECTION EXPERIMENT IN THE BORDEN AQUIFER, ONTARIO, CANADA

Increased energy resource development has led to concerns on the potential environmental risks associated with fugitive methane (CH₄) migration related to natural gas extraction. In particular, there are concerns related to groundwater contamination and greenhouse gas emissions (GHG). To better understand the issue, a controlled experiment was conducted in the Borden aquifer, Ontario, Canada. CH₄ gas was continually injected at various rates for 73 days into a sand aquifer at 4.5 m and 9 m depths. Long-term geochemical, microbial, and geophysical analyses in the saturated zone were complemented with vadose zone and surficial monitoring. Surface effluxes for CH₄ and carbon dioxide (CO₂) were measured using flux chambers connected to a laser-based gas analyzer. Sensors were installed in the vadose zone to measure oxygen (O₂), volumetric water content, electrical conductivity, and temperature. Vadose zone soil gas samples were collected for analyses of gas composition and stable carbon isotopes in CH₄ and CO₂. Primary results demonstrate that the injection system influenced the spatial distribution of CH₄, while external factors such as barometric pressure influenced the temporal evolution of gas emissions. Within 24 hours of commencing the experiment, a surficial CH₄ plume formed in the vicinity of the injection location. Increasing injection rates resulted in greater lateral migration with higher CH₄ concentrations. Preferential gas migration was also observed with the temporal measurements, providing evidence for aquifer heterogeneity. Throughout the experiment episodic CH₄ effluxes resulted in large gas emissions independent of the injection rate. This research will contribute to a greater understanding on the fate of fugitive CH₄ in order to determine the most suitable monitoring strategies to evaluate the potential environmental risks associated with shale gas development.