Abstract
We rigorously model immiscible displacements in unconsolidated sediments subject to confining stress. Fluid-fluid interfaces are assumed controlled by capillary forces, and the progressive quasi-static (PQS) algorithm based on the level set method determines the pore level geometry of those interfaces. From the pore-level fluid configuration we compute the net force exerted on each sediment grain by capillary pressure, including cohesion at grain contacts supporting pendular rings. We combine those forces with mechanical stress and elastic properties of grains to determine the resultant movement of grains using a discrete element method code (Itasca's PFC3D). To our knowledge this is the first rigorous coupling of capillarity and grain solid mechanics in 3D. When grains can move in response to net force exerted by the nonwetting phase, small variations in the distribution of pore throat sizes lead to self-reinforcing, focused channels of nonwetting phase during drainage. When forces exerted by capillary pressure are the same magnitude as the force required to displace grains, this channeling prevents the emergence of a recognizable fracture.
