Evolution of fracturing through multiple growth intervals in volumetric contraction networks

Detailed analyses of 21 fracture measurements from a columnar basalt outcrop and 265 fractures within a large-domain mudtray were used to study the influence of fracture growth intervals on vertical fracture propagation and mechanical fracture interaction. Several metrics specific to fracture propagation in volumetric contraction networks (VCNs) are proposed to describe the influence of network-scale stress perturbations on triple junction migration to show that VCN patterns will remain in a state on non-equilibrium. The angle of displacement along fracture walls varied during each fracture growth interval in response to changing triple junction positions and effectively preserved the propagation history of the network. Variations in the orientation of VCN fractures in the vertical and horizontal planes are influenced by the strike of the fracture during the previous growth interval and stress perturbations through the well-connected network. Localized stress perturbations were characterized by introducing network perturbation factors at triple junctions and along fractures to account for the complex connectivity structure of VCNs. Fractures were shown to either rotate or straighten as new growth intervals develop which led to further adjustments of nearby triple junction positions in later forming growth intervals. The degree of triple junction clustering is controlled by the average length of adjacent connected fractures. Longer fractures are more stable and exhibit more consistent orientations through multiple fracture growth intervals than shorter fractures. These findings highlight the universality of network-scale perturbations, self-organization of triple junctions, and mechanical interaction during vertical fracture propagation in volumetric contraction fracture networks in different materials.