ABSTRACT:

The process of fluid injection into dense granular media is analyzed using the DEM code PFC2D

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coupled with a pore network scheme. A simple approach to calibrate the microscale parameters to match the permeability of a particle assembly, predicted from the Kozeny-Carman correlation, is first established. The effect of the injection rate on the grain displacement and fluid flow mechanisms is examined. The numerical results illustrate that, as the injection rate increases, the granular medium behaviors change from that of a rigid porous medium to localized failure that leads to development of fluid channels. Existence of the fluid channels is also reflected in the fluid flow patterns. The numerical results are consistent with previous experimental observations of the injection experiments performed in a Hele-Shaw cell.

1. INTRODUCTION

Numerical analysis using the DEM code PFC2D

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[1] coupled with a pore network model is conducted in this study to model the fluid injection process in dense granular media. A better understanding of how a dense granular medium responds when fluid is injected into the medium is of great interest to engineering applications such as compensation grouting, environmental remediation and reservoir stimulation in soft formations. Injection experiments performed using aqueous glycerin solutions as the invading fluid and dry Ottawa F110 as the granular material in a Hele-Shaw cell have revealed many interesting features [2, 3]. Four distinct fluid-grain displacement regimes are identified from these injection tests, namely, a simple radial flow regime, an infiltration-dominated regime, a grain displacementdominated regime, and a viscous fingering-dominated regime. As the injection velocity and the invading fluid viscosity increase, the behaviors of fluid flow change from infiltration-governed to infiltrationlimited. Meanwhile, the granular medium response displays a transition from that of a rigid porous medium to fluid-like behaviors characterized by ramified fluidgrain interface morphology.

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