Discrete Fracture Modelling of the Aspo LPT-2,Large Scale Pumping and Tracer Test

not registered

This report describes FracMan discrete fracture flow transport modelling of the LPT-2, large-scale pumping and tracer test, at the SKB Aspo Hard Rock Laboratory. This work was carried out under the international cooperation program of the AsPo Task Force on Groundwater Flow and Transport of Solutes. The scale of simulation was approximately a one-kilometer cube. The discrete fracture model contains two major fracture types - fracture zones, which were located deterministically according to SKB's conceptual model of the Aspo site, and fractures outside the fracture zones which were generated stochastically. The geometric and hydraulic properties of each group were developed from the SKB modeling database, except for non-zone fracture length which we developed from our own mapping of surface outcrops. Two separate models were prepared for the March and September, 1993, task force meetings respectively. The March model represented the fracture zones as 10-m thick Planar regions containing populations of 30-m radius discrete fractures. The September model represented the fracture zones as single planes, which were discretized on a 20- to 30-m scale for a geostatistical assignment of properties. The September model also included conditioning of the properties to the borehole data. Both models generally reproduce the drawdown and transient pressure interference responses of the experiment. The tracer breakthroughs were simulated using only the September model. Calibration runs of the transport model varied the mean transport aperture, aperture variance, and aperture correlation length. The results of this modelling exercise show that a discrete fracture model can be applied at kilometer scales if the flow is dominated by a small portion of fracture population. The results also show that the SKB conceptual model is consistent with the field measurements.