Scale dependency of fractional flow dimension in a fractured formation

Abstract

Abstract. In fractured media, the flow dimension was usually predefined before the determination of the hydraulic parameters in the past. However, it would be improper to make assumption about the flow geometry before site characterization because the hydraulic structures and flow paths are complex in the fractured media. An appropriate way to investigate the hydrodynamic behavior of a fracture system is to determine the hydrogeologic properties such as the flow dimension and aquifer parameters simultaneously. The objective of this study is to analyze a set of field data obtained from four observation wells during an 11-day hydraulic test at Chingshui geothermal field (CGF) in Taiwan for determining the hydrogeologic properties of the fractured formation. Based on the generalized radial flow (GRF) model and the optimization scheme, simulated annealing, an approach is therefore developed for the data analyses. The GRF model allows the flow dimension to be integer or fractional. We found that the fractional flow dimension increases near linearly with the distance between the pumping well and observation well, i.e., the flow dimension in the CGF exhibits scale-dependent phenomenon. This study provides insights into interpretation of fracture flow at CGF and gives a reference for characterizing the hydrogeologic properties of fractured media.