Fluid-driven fractures in granular materials

The initiation and propagation process of a fluid-driven fracture in granular materials is inherently a hydro-mechanical coupling problem. The bonded-particle method (BPM) was utilised to simulate the hydraulic fracturing process in granular materials, and different failure mechanisms were evaluated by analysing the formation of microcracks. Hydraulic conductivity is determined by pore size and connectivity in the direction of flow. A strain-dependent formulation was presented to highlight the inherent link between hydraulic conductivity and pore size. The results show that the BPM is capable of realistically predicting fluid-driven fractures in granular material. Using the BPM, the numbers of fluid-driven fractures induced by different failure modes can be determined. It is concluded that for consolidated formations, the initiation and propagation of fluid-driven fractures are dominated by tensile failure, which has been recognised in the field of geology and geomechanics. However, for unconsolidated formations, shear failure seems to be more important during the hydraulic fracturing process. As described in this article, the number of shear failure cracks is twice that of tension failure cracks, which has not been widely recognised. Overall, the simulation results of the fluid-driven fracture are in accordance with the experimental data observed by other researchers.