Time-lapse Electrical Resistivity Imaging of Methane Gas Migration in a Shallow Confined Aquifer
Timothy A. Cary
In order to quantify, and develop tools to monitor, fugitive methane emissions from well-bore environments, a field experiment was carried out in which an 85% methane composite gas was injected into a near surface confined aquifer at a rate of 1.5 m3 per day, for 66 days. The site is located in north-eastern British Columbia where the Quaternary glacial deposits are typical of the environment for the majority of energy wells in Western Canada. Temperature corrected timelapse electrical resistivity tomography (ERT) was utilized to monitor the migration and fate of the gas plume during the injection period. Three permanently installed ERT lines were deployed, centered on or close to the injection location. The data were inverted using SimPEG producing time-lapse difference images. Results show resistivity increases of up to 15% near the injection zone. The gas plume is interpreted as migrating upward and spreading laterally beneath a low permeability layer.