Investigating the Hydro-geochemical Impact of Fugitive Methane on Groundwater: The Borden Aquifer Controlled Release Study

Abstract:

Shale gas development by hydraulic fracturing is believed by many to have the potential to transform the world’s energy economy. The propensity of this technique to cause significant environmental impact is strongly contested and lacks evidence. Fugitive methane (CH₄), potentially mobilized during well drilling, the complex extraction process and/or leaking well seals over time is arguably the greatest concern. Advanced understanding of CH₄ mobility and fate in the subsurface is needed in order to assess risks, design suitable monitoring systems and gain public trust. Currently knowledge on subsurface CH₄ mobilization and migration at scales relevant to shale gas development is lacking. Consequently a shallow aquifer controlled CH₄ release experiment is being conducted at the Borden aquifer research facility (an unconfined, unconsolidated silicate sand aquifer) in Ontario, Canada. During the experiment, 100 m³ of gas phase CH4 was injected into the saturated zone over approximately 60 days through 2 inclined sparging wells (4.5 and 9 m depth) at rates relevant to natural gas well casing vent flows. The gas mobility and fate is being comprehensively monitored temporally and spatially in both the saturated and unsaturated zones considering; aqueous chemistry (including stable isotopes), soil gas characterization, surface efflux, geophysics (GPR and ERT), real time sensors (total dissolved gas pressure, soil moisture content, CH₄ and CO₂), mineralogical and microbiological characterization before, during and after injection. An overview of this unique study will be given including experimental design, monitoring system configuration and preliminary results. This multidisciplinary study will provide important insights regarding the mechanisms and rates for shallow CH₄ migration, attenuation and water quality impacts that will inform baseline groundwater monitoring programs and retrospective forensic studies.