Time-lapse Electrical Resistivity Imaging of Methane Gas Migration in a Shallow Confined Aquifer

Abstract

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 time-lapse 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, centred 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.