Dimensional Threshold for Fracture Linkage and Hooking

Summary Fracture connectivity in rocks depends on spatial properties of the pattern including length, abundance and orientation. When fractures form a single-strike set, they hardly cross-cut each other and the connectivity is limited. Linkage probability increases with increasing fracture abundance and length as small fractures connect to each other to form longer ones. A process for parallel fracture linkage is the hooking, where two converging fracture tips mutually deviate and then converge to connect due to the interaction of their crack-tip stresses. Quantifying the processes and conditions for fracture linkage in single-strike fracture sets is crucial to better predicting fluid flow in Naturally Fractured Reservoirs. For 1734 fractures in Permian shales (Lodeve Basin, SE France), we measured geometrical parameters, characterizing the underlapping, overlapping and linkage stages, deciphering the threshold values, shape ratios and limiting conditions. The hook affect fractures of similar length (L2≈L1). Its set up depends on the spacing (S) and fracture length (Lh) with S ≈ 0.15 Lh. Once initiated with the fracture deviation length (L) L≈ 0.4 Lh , fractures reach the link only when spacing is reduced to S ≈ 0.02 Lh and the convergence (C) is <0.1 L. These conditions apply to multi-scale fractures.