Fluid injection into an unconsolidated medium is modeled numerically using the DEM code D®. The injection process is modeled with the simplification that fluid leakoff is negligible. The fluid can penetrate in between grains and fluid front advances only if the gap size between two neighboring grains exceed a threshold value. Such a simplification can be considered as similar to taking into account of the effect of surface tension. Dependence of the fluid-grain displacement patterns on the threshold gap size is analyzed for the cases of constant rate injection. A bifurcation analysis for cavity expansion of a thick-walled cylinder is performed to predict the borehole pressure versus volume relationship. The critical pressure corresponding to the onset of bifurcation is compared with the peak injection pressure obtained from the numerical simulations.

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