Review on evaluations of anisotropic hydraulic properties in the fractured rock mass

Abstract Evaluating the hydraulic properties of fractured rock masses in the subsurface is crucial for geoengineering applications and mitigating geohazards. Understanding these properties around faults is particularly important due to their impact on fluid behavior. Various methods have been developed to evaluate formation permeability, including in situ tests on boreholes, laboratory tests on rock samples, and evaluations based on borehole logging data. This paper reviews previous studies on the permeability of fractured rock and classifies these studies into three approaches: in situ permeability tests conducted using boreholes, laboratory permeability tests performed on samples, and hydraulic property evaluations based on well logging data. It also presents research focused on analytical evaluations of fault permeability, with particular emphasis on fracture geometry. Additionally, permeability values obtained by different methods at identical well sites are compared, and the challenges involved are discussed. Results show that permeability estimates differ significantly among methods, reflecting both methodological characteristics and the influence of mesoscale fractures on the effective evaluation scale. These findings highlight the strong scale dependence of hydraulic properties in fault zones and underscore the need to select evaluation methods appropriate to the target scale and purpose. Furthermore, where technically feasible, combining multiple approaches provides a more robust framework for characterizing permeability in fractured rock masses, particularly in fault zones containing fractures of various sizes.