Intersections between the fractures of a network defines its connectivity and constitute a key component both for the hydrogeological and mechanical behavior of fractured rock masses. Existing analyses of 2D field trace maps provide a framework for analyzing 2D fracture intersection distributions. In this paper, we perform a complete analysis of 3D fracture intersections distribution of various DFN models and investigate how it can be related to the 2D distribution of intersecting virtual outcrops. The DFN models are either fully random (with no correlation between fractures) or defined from a genetic process (named UFM model). By comparing with natural 2D field trace maps, we show that, unlike the fully random DFN model which produces only X intersections, the UFM model is quantitatively consistent with the intersection distribution observed on field trace maps. The analysis framework developed here can be used as a relevant metric to select DFN models in terms of connectivity and give insights on the 3D topology of fracture networks.
Fracture connectivity plays a major role on the hydrogeological and mechanical behavior of fractured rock mass (Davy et al., 2018; De Dreuzy et al., 2001). Most studies focus on describing connectivity from a density description using percolation parameter (Berkowitz, 1995; Bour and Davy, 1998). It is also possible to quantify network connectivity from a topological approach as fracture intersections statistics can be easily established in 2D from outcrop observations (Sanderson and Nixon, 2015). In this kind of approach, the fracture network is described as a graph of nodes (representing fracture intersections and terminations), linked by fracture segments (Fig. 1.a). Nodes can thus correspond to isolated fracture tips, or T and X intersections. Those statistics can serve as a proxy to characterize fracture networks (Fig. 1.b), and even estimate their connectivity and hydrological behavior (Saevik and Nixon, 2017).