Risk Assessment for Groundwater Contamination from Hydraulic Fractured Shale to Aquifers

Abstract Using hydraulic fracturing in shale gas and oil reservoirs to develop natural oil and gas has caused concern regarding the risk of groundwater contamination. Failed well casing, bulk media and fractures are three potential pathways that allow the transport of contaminants from the fractured shale to aquifers. Models built and simulated by CMG are used to investigate the potential risk of water contamination from hydraulic fractured shale to aquifers. This study focuses on the role of vertical fractures permeability/failing casing, aquifer permeability, reservoir permeability, distance between reservoir and aquifer, distance between fracture and water well in aquifer in controlling the contamination risk at environmentally sensitive locations. The results show that risk strongly depends on well casing quality, initial water saturation, and fracture parameters. Furthermore, the measured risk value is more sensitive to leakage depth and leakage rate through well casing/permeable fracture when compared to the hydrogeological properties. The study shows that transport could require up to tens of thousands of years to move contaminants to the surface when well casing is integrity and without fractures/fault in the overburden layers, but also that fracking the shale could reduce that transport time to tens or hundreds of years. Conductive faults or fracture zones could reduce the travel time further. Well casing failure would reduce the travel time to months. The study identifies the important of well integrity for minimal risk to water contamination in fracturing, also the finding requires that monitoring systems be employed to track the movement of contaminants when fractures and faults appear in the overburden layers.