Geostatistical inversion of cross-hole pumping tests for identifying preferential flow channels within a shear zone

Cross-hole pumping tests within a subvertical shear zone in granite were in terpreted using a geostatistical inverse approach. The objective was to ide ntify flow channels that influence tracer experiments. The spatial correlat ion structure of transmissivity (T) was unknown. Therefore, a wide variety of geostatistical hypotheses were made for estimating a total of 40 T field s, that honor equally well the pumping tests, the static head measurements, and the point T data. All estimated T fields reveal channels with similar topology and with a preferred horizontal orientation, possibly due to verti cal displacements within the subvertical shear zone. This shows that invers e geostatistical modeling of abundant hydraulic measurements can be useful to reveal a coarse heterogeneity structure, even when data are insufficient to identify the geostatistical structure. However, numerical simulations o f a field tracer test were highly sensitive to the geostatistical hypothese s. In summary, T fields leading to successful hydraulic data fitting do not necessarily lead to successful transport predictions, even when they appea r to reproduce the coarse heterogeneity structure.