Constraining a Discrete Fracture Network static model for the Tunnel City Group sandstones in Cottage Grove-WI using Outcrops and Boreholes
Parameterizing fracture geometry in bedrock is crucial to explaining groundwater flow and transport. In this study, outcrops and boreholes were integrated using an existing sequence stratigraphic framework to conceptualize the Discrete Fracture Networks (DFN) of the upper 19 m of a contaminated sandstone in Wisconsin. Natural-gamma signatures and sedimentary facies associations observed in outcrops corresponded to three hydrogeological units (HGUs) delineated from boreholes. Three joints sets (NE, NW, NNW) and one subhorizontal fracture set were identified. Measurements of fracture attitude, size and spacing provided inputs for a three-dimensional DFN simulation using FracMan. Fracture connectivity was found to be controlled by sparse throughgoing subvertical fractures in the bottom HGU, and by densely spaced stratabound joints in the overlying HGUs. Using numerically calculated equivalent fracture permeability tensors, the bottom HGU was found to be less sensitive to joint removal than the overlying HGUs. Results will support subsequent flow and transport modelling strategies.