Geostatistical Inversion of Cross‐Hole Pumping Tests for Identifying Preferential Flow Channels Within a Shear Zone

Abstract

Abstract Cross‐hole pumping tests within a subvertical shear zone in granite were interpreted using a geostatistical inverse approach. The objective was to identify flow channels that influence tracer experiments. The spatial correlation structure of transmissivity (T) was unknown. Therefore, a wide variety of geostatistical hypotheses were made for estimating a total of 40 T fields, 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 vertical displacements within the subvertical shear zone. This shows that inverse 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 of a field tracer test were highly sensitive to the geostatistical hypotheses. In summary, T fields leading to successful hydraulic data fitting do not necessarily lead to successful transport predictions, even when they appear to reproduce the coarse heterogeneity structure.