Evaluating Shallow Aquifer Vulnerability to Potential Shale Gas Exploration and Development in Eastern Canada

In Quebec (eastern Canada), public concerns led to a de facto moratorium in 2010 for the St. Lawrence Lowlands, where the underlying Utica Shale is known to contain significant gas resources. As only a few exploration gas wells have been drilled, this area may still be considered “virgin” with respect to exploitation. In 2012, a multidisciplinary project was initiated to evaluate shallow aquifer vulnerability to eventual shale gas exploration and exploitation in the St-Edouard area (500 km2), near Quebec City. It involved multiple components, including tectonostratigraphy, geophysics, geomechanics, hydrogeology, rock organic geochemistry and an extensive groundwater geochemical study. This project thus attempted to evaluate the potential presence of preferential natural pathways that could allow the migration of fluids from shale gas horizons to shallow aquifers using multiple field evidence. Specific aspects related to groundwater geochemistry were also studied: natural variations of methane concentration and isotopes over time and with sampling techniques. Strategic data were acquired from the study of 30 residential wells, 4 deep shale gas wells and 15 new shallow observation wells drilled into shale.
Results showed that dissolved methane is ubiquitous and that its presence is mostly related to specific aquifer conditions such as long water residence times and absence of oxygen. While there is evidence that small amounts of deep formation brines migrate into shallow aquifers near a normal fault, there is no indication that deep thermogenic gas from the Utica Shale is currently reaching the surface through this fault zone or elsewhere in this region.