Stable and unstable capillary fingering in porous media with a gradient in grain size

Abstract

Multiphase flows in complex porous networks occur in many natural processes and engineering applications. We present an analytical, experimental and numerical investigation of slow drainage in porous media that exhibit a gradient in grain size. We show that the effect of such structural gradient is similar to that of an external force field on the obtained drainage patterns, when it either stabilises or destabilises the invasion front. For instance, gravity can enhance or reverse the drainage pattern in graded porous media. In particular, we show that the width of stable drainage fronts scales both with the spatial gradient of the necessary pressure for pore invasion and with the local distribution of this (disordered) threshold. The scaling exponent results from percolation theory and is − 0.57 for 2D systems. Overall, introducing a dimensionless Fluctuation number, we propose a unifying theory for the up-scaling of dual immiscible fluid flows covering most classical scenarii.

A simplified pore-scale model for slow drainage including film-flow effects

“…For the study of flow through films formed by corners and capillary bridges, an important geometric feature of quasi-2D models is the intersection of the structures representing the porous media grains, e.g. cylinders [44,[50][51][52] or spheres [28,[53][54][55], with the planes containing them. Following the piston-like displacement of the interface, fluid collected in these regions can play a fundamental role in wetting-phase continuity by linking capillary bridges formed between pairs of grains, as indicated in Figure 1.…”

Contact Characteristics and Characterization Methods of CO2 and Crude Oil in Visual Porous Medium

“…Hu et al [23] used the improved Shan-Chen lattice Boltzmann model to conduct numerical simulation of soil water distribution and showed that the pore diameter had a great influence on the water-gas two-phase distribution in soil. Tom Vincent-Dospital et al [24] analyzed the water-gas two-phase displacement in porous media with particle size gradient, and the research results showed that the fluid seepage morphology is related to the pressure gradient and pore diameter distribution required for fluid to enter the porous medium. The aforementioned studies fully show that the porosity, particle size distribution, and pore size distribution in porous media have significant effects on fluid flow path, distribution location of two-phase fluid, and displacement efficiency in the process of water-gas two-phase displacement.…”