GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 299-11
Presentation Time: 4:05 PM


FORDE, Olenka1, MAYER, K. Ulrich1, CAHILL, Aaron1, PARKER, Beth2 and CHERRY, John A.2, (1)Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC V6T1Z4, Canada, (2)G360 Centre for Applied Groundwater Research, School of Engineering, University of Guelph, 50 Stone Road East, Guelph, ON N1G2W1, 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.