Abstract

A discrete fracture network model has been applied to increase the probability of sinking a successful groundwater production borehole at a well-field in Carboniferous rocks in southwest Ireland. The model employs the FracMan software to explicitly represent fractures. Model construction is based on a synthesis of data from a variety of geological and hydrogeological sources. The model is verified and calibrated against borehole measurements and multiborehole pumping tests. The process of model construction indicates that the intensity of flowing fractures is controlled primarily by fracture zones running through the well-field, and that there is also a relationship between flowing fractures and zones of weathered dolomite. Simulations allow the optimal orientation of any production borehole to be determined, and suggest that the most favourable orientation increases the mean number of flowing fractures intersected by up to 30%. The likely yield for different borehole locations can be assessed by conducting flow simulations. Within fracture zones, the probability of a successful production well is high. Flow simulations are also used to quantify the degree of hydraulic interference between boreholes. The results of the modelling can be used to assess the most significant uncertainties and develop a programme of future site characterization that addresses them.