Fractures are key elements governing permeability and flow paths in crystalline rocks and sedimentary layers with low matrix porosity. The ability to predict those properties, crucial for some industrial applications such as risk assessment of sub-surface nuclear waste disposal, strongly relies on our ability to properly describe the fracture network characteristics. A usual method is to define 3D Discrete Fracture Network (DFN) models to represent the geological environment. This consists in combining various data on fracture geometrical properties (density, size and orientation distributions) and on hydraulic data (borehole flow logs), to produce 3D statistical distributions and upscaling functions of both fracture geometrical and transmissivity distributions. The hydraulic data are mainly used to determine the fracture transmissivity distribution and to calibrate it to direct observations. However, this approach is not univocal and various DFN models can match the observations.
We suggest investigating further the potential information contained in borehole flow logs by considering two main flow indicators - the equivalent hydraulic conductivity and the flow channeling indicator – and by focusing especially on their scaling and variability properties. These two properties were first used to analyze the 3D flow structure of Hydro DFN models in permeameter-like conditions and are now adapted to more realistic site conditions and borehole flow logging, as 1D-like borehole flow indicators.
