Inderscience Publishers

Pore scale coupling of fluid displacement and unconsolidated sediment mechanics

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In unconsolidated sediments, capillary pressure in the pore space may be large enough to move grains apart during drainage. This motion alters the pore throat sizes which control subsequent displacement in the sediment. We present two grain scale models for this coupled process. In both cases, we assume fluid interfaces are controlled by capillary forces, and determine the detailed geometry of those interfaces. We compute the net force exerted on each grain by capillary pressure, including cohesion at grain contacts supporting pendular rings. We combine those forces to determine the movement of grains using: a) a kinematic model; b) a rigorous model where mechanical stress and elastic properties of grains are included via a discrete element method. This is the first coupling in 3D, albeit in samples of limited size. Preliminary results in disordered dense sphere packs suggest the development of high permeability gas channels rather than planar structures. [Received: May 05, 2011; Accepted: October 21, 2011]

Keywords: porous media, grain mechanics, capillarity, multiphase fluid flow, cohesion, drainage, pore scale coupling, fluid displacement, unconsolidated sediments, sediment mechanics, capillary pressure, grain scale modelling, kinematic modelling, mechanical stress, elasticity, discrete element method, high permeability, gas channels

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