Abstract

Fracture mechanics modelling of fracture pattern development was used to analyse pattern geometry and population statistics for natural opening-mode fractures. Orthogonal fracture network geometries were generated under biaxial extension loading conditions from a slightly anisotropic initial strain state. Fracture statistics were analysed by grouping all fracture orientations into one population for these unique orthogonal pattern geometries. Fracture aperture distributions resembled negative exponential curve shapes, consistent with published observations for stratabound fractures in sedimentary rock. Fracture length distributions had a strongly power-law shape, and showed that longer fractures grew first and reached their fullest extent before shorter fractures began propagating. The power-law shape of the length distribution was first established by the growth of the longest fractures in the population, followed by the later growth of shorter fractures that extended the power-law shape to smaller sizes. The shortest fracture length at which the power-law distribution was truncated varied with the magnitude of the applied strain. Other variations in fracture pattern results were tied to mechanical layer thickness and subcritical crack growth propagation properties of the fractured media.