Establishment of baseline natural gas concentrations and assessment of gas migration pathways using multi-level groundwater monitoring systems in the Liard Basin, Canada

The Liard Basin, located in the northwest corner of the Western Canada Sedimentary Basin, spans the borders of British Columbia, the Yukon and the Northwest Territories. The Liard Basin has been developed for conventional oil and gas since the 1950's. Recent discoveries have indicated that the basin contains Canada's second largest natural gas reserve, which has led to interest in its future development through unconventional technologies. The potential development of this basin has spurred concerns regarding impacts of stray gas to freshwater resources such as surface water and shallow freshwater aquifers. Natural gas migration may be one of the most significant threats to both groundwater and greenhouse gas emissions through subsurface pathways originating from deeper reserves. Canada's northern communities and government agencies are particularly concerned of the downstream impacts of petroleum development on fresh water supplies. This study aims to establish a transferable framework for continuous long-term monitoring of groundwater quality and quantity at a regional scale for the purpose of evaluating impacts of shale gas development. Understanding future impacts will hinge on the establishment of baseline natural gas concentrations and assessment of potential gas migration pathways. This study examines hydraulic and geochemical data obtained from a Westbay™ multi-level system (MLS) consisting of 25-30 ports between 0 and 150 m below ground surface. Continuous lithology logs and temporary hydraulic profiling information was combined with borehole and surface geophysical measurements to design the MLS; hydrogeologic units were refined using hydraulic characteristics and background hydrochemistry of the fresh groundwater zone. Preliminary monitoring and characterization of hydraulic conditions and water quality was used to assess vertical flow potential across confining shale units within the Dunvegan Sandstone, which is considered to be an important regional bedrock aquifer. The future development of a MLS network will be used to establish baseline conditions as they relate to fugitive gas presence, character and migration pathways in the shallow groundwater system before unconventional oil and gas development occurs.