Site DFN modeling: assessment of 3D statistical distributions at different scales, and of statistically identical fracture domains. SKB sites examples

Abstract : We perform site scale DFN modeling using a geometrical and quantitative approach. The DFN model is a statistical model which defines the density of fractures having given geometrical properties (size and orientation) and which includes an intrinsic variability term. The density variability term is defined from a scaling analysis. Density terms are calculated in 3D using stereological rules and assumptions about the underlying DFN scaling model. This allows combining data acquired at different scales and from different support shapes.Local datasets and related models are first characterized and then clustered into statistically identical models. This classification process determines the minimum number of Statistical Fracture Models (SFMs, density distribution functions) which describes a database and relative site. It aims at providing, up to site scale, the best possible division into SFMs such that (i) within a SFM fracturing properties are statistically compatible with a single parent DFN model and (ii) DFN models associated to distinct SFMs are different (statistical parameters can be distinguished).The method is applied to the SKB Forsmark and Äspö sites in Sweden. The selected databases encompass up to hundreds of thousands records of fractures from various supports (cored boreholes, tunnel and surface outcrops). We discuss the classification process and the resulting fracture network description.