DISCRETE FRACTURE NETWORK INTERPRETATION OF FIELD TRACER MIGRATION IN SPARSELY FRACTURED ROCK

Field tracer migration in sparsely fractured rock is analyzed with a discrete fracture network model that has been calibrated on fracture and flow data from the Stripa-3D experiment in Sweden. Comparison between transport simulations in the flow-calibrated discrete model and tracer tests of the field experiment confirms the fracture network parameters obtained from the flow analysis except for the variance of the fracture conductivities which had to be increased. The discrete model reproduces the uneven spatial distribution of flow and tracers, the complex dispersive behavior, and channeling effects that have been observed in the field experiment. As a result of flow channeling, transport occurs along preferential paths whose transport properties may substantially deviate from the medium average properties. For example, porosity and wetted fracture surface area available to sorption may be reduced by almost 2 orders of magnitude compared to the medium average values.