Quantification and mapping of methane emissions using eddy covariance in a controlled subsurface synthetic natural gas release experiment

Unprecedented expansion of unconventional energy resource development has caused concerns about fugitive gas emissions, the patterns of which are not well understood. This study was conducted in north-eastern British Columbia, which is a region of active petroleum resource development, and there is evidence of gas migration at gas wells. A controlled gas injection experiment was conducted at the Hudson’s Hope Field Research Station (HHFRS) near Hudson’s Hope, where 1.5 m³ of synthetic natural gas was injected daily for a period of 66 days, 26 m below the ground (below the water table). The eddy covariance (EC) technique was used to monitor emissions into the atmosphere resulting from the controlled release, with the aim to quantify and potentially locate the emissions using flux footprint analysis. The EC tower was set up 26.4 m north-east of the injection point. Methane fluxes as high as 0.22 µmol m⁻² s⁻¹ were observed during the injection period when wind was from the injection area. Additionally, continuous CO₂ and H₂O fluxes were measured using an enclosed-path infrared gas analyzer, LI-7200 (LI-COR Inc.). A set of climate instruments including soil and radiation sensors were also installed to monitor weather conditions and energy balance closure. Down-scaling the EC fluxes to quantify emissions indicated that the volume released into the atmosphere ranged from 21.9 m³ to 24.6 m³. However, it was conjectured that this could be an underestimate because flux footprint models are applied to releases occurring at the ground and not at a height above the surface, and in this case, there was evidence that most of the emissions were from a ~1-m high well-head. The results suggest the need for an alternate flux footprint model, which considers the height of the source. Furthermore, an inversion approach was tested in an attempt to locate the leak and the results were compared with the original information about the location of the leak, as observed using chamber measurements and a groundwater sampling well. A point source controlled-release experiment was also conducted by releasing 93% v/v methane into the atmosphere to evaluate the flux footprint models being used in this study.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat