Coupled DEM-CFD Modeling of Fluid Injection into Granular Media

摘要

Failure induced by fluid pressurization in a cylindrical wellbore in purely frictional media is investigated numerically using the discrete element method code PFC~(3D) with the coupled computational fluid dynamics add-on option. The numerical model corresponds to the case of injection in fully saturated media with the invading fluid being the same as the pore fluid in the matrix. Depending on the injection velocity, behaviors of the particle assembly show transitions from flow in a fixed bed type of responses, to localized failure, and to the near wellbore fluidization scenario. Critical velocities associated with the transitions can be identified from the variation of the normalized wellbore expansion rate as a function of the injection velocity. The failure mechanisms observed in the numerical simulations show characteristics of the slip line field in the classical plasticity theory. The shear band features also resemble the shear fracture observed in the injection experiments in sands reported in the literature.