CFD-DEM modeling of fracture initiation with polymer injection in granular media

We numerically study the mechanisms and conditions for fracture initiation in weakly cohesive granular media induced by non-Newtonian polymer solutions. A coupled computational fluid dynamics–discrete element method (CFD-DEM) approach is utilized to model fluid flow in a porous medium. The flow behavior of polymer solutions and the drag force acting on particles are calculated using a power-law model. The adequacy of the numerical model is confirmed by comparing the results with a laboratory experiment. The numerical results are consistent with the experimental data presenting similar trends in dimensionless parameters that incorporate fluid flow rate, rheology, peak pressure, and confining stress. The results show that fluid flow rate, rheology, and solid material characteristics strongly influence fracture initiation behavior. Injection of a more viscous guar-based solution results in wider fractures induced by grain displacement, whereas a less viscous XG-based solution creates more linear fractures dominated by infiltration. The ratio of peak pressures between two fluids is higher in the rigid material than in the softer material. Finally, the dimensionless parameters 1/Π₁ and τ₂, which account for fluid and solid material properties accordingly, are effective indicators in determining fracture initiation induced by shear-thinning fluids. Our numerical results show that fracture initiation occurs above 1/Π₁ = 0.06 and τ₂ = 2 ⋅ 10⁻⁷.