Understanding Shallow and Deep Flow to Assess the Risk of Hydrocarbon Development on Groundwater Quality

Abstract : In the Haldimand sector of Gaspé, Québec, Canada, a study was carried out to assess the potential risk on a shallow fractured rock aquifer system due to development of a tight sandstone petroleum reservoir. Petroleum exploration wells are being drilled in the forested core of a hilly 50 km2 peninsula by the sea (up to 200 m amsl) and where local residents rely on groundwater wells for their water supply. The study used existing hydrogeological, geological and petroleum exploration data and more recently acquired field characterization data. Groundwater and surface water sampling within a 2 km radius of a proposed new drill pad. All samples were subject to chemical analyses. Fracturing controls groundwater flow especially in the upper 15 m of the rock aquifer. Recharge occurs on topographic highs where the glacial till cover is thin. Quite wide variations in groundwater geochemistry were encountered. Groundwater residence times can thus be quite long. Methane is of mixed origin but is preferentially associated with the relatively more evolved water types. The SALTFLOW model was used to simulate density-dependent groundwater flow and salt transport within the peninsula as well as the adjacent highlands along a 2D vertical section.