ABSTRACT:

The injection of fluid results in a change in formation pressure and stress state, which may induce fracture initiation. This study investigates fracture initiation induced by fluid-rock interactions at the particle/pore level. Computational fluid dynamics (CFD) coupled with the discrete element method (DEM) is used to model fluid flow through a granular medium. We adopt the resolved CFD-DEM approach which models the solid phase using the fictitious domain method and captures the particle-particle/fluid interactions even at high particle concentrations. Two benchmark problems with analytical solutions are used to verify the resolved CFD-DEM approach. A third problem explores flow through a defect. The fracture initiation manifests through a cluster of bond breakage caused by the drag force exceeding the local skeletal force. The fluid flow localization caused by positive feedback at weak points related to local heterogeneity promotes fracture propagation. We perform sensitivity analyses for several parameters including injection velocity, fluid viscosity and principal stresses. This work, for the first time, uses the resolved CFD-DEM approach to study how particle-scale processes contribute to the injection-related fracture initiation.

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