Single- and two-phase flow in microfluidic porous media analogs based on Voronoi tessellation

Abstract

The objective of this study was to create a microfluidic model of complex porous media for studying single and multiphase flows. Most experimental porous media models consist of periodic geometries that lend themselves to comparison with well-developed theoretical predictions. However, many real porous media such as geological formations and biological tissues contain a degree of randomness and complexity at certain length scales that is not adequately represented in periodic geometries. To design an experimental tool to study these complex geometries, we created microfluidic models of random homogeneous and heterogeneous networks based on Voronoi tessellations. These networks consisted of approximately 600 grains separated by a highly connected network of channels with an overall porosity of 0.11-0.20. We found that introducing heterogeneities in the form of large cavities within the network changed the permeability in a way that cannot be predicted by the classical porosity-permeability relationship known as the Kozeny equation. The values of permeability found in experiments were in excellent agreement with those calculated from three-dimensional lattice Boltzmann simulations. In two-phase flow experiments of oil displacement with water we found that the wettability of channel walls determined the pattern of water invasion, while the network topology determined the residual oil saturation. The presence of cavities increased the microscopic sweeping efficiency in water-oil displacement. These results suggest that complex network topologies lead to fluid flow behavior that is difficult to predict based solely on porosity. The novelty of this approach is a unique geometry generation algorithm coupled with microfabrication techniques to produce pore scale models of stochastic homogeneous and heterogeneous porous media. The ability to perform and visualize multiphase flow experiments within these geometries will be useful in measuring the mechanism(s) of displacement within micro- and nanoscale pores.

Lattice Boltzmann simulation of immiscible fluid displacement in porous media: Homogeneous versus heterogeneous pore network

“…The viscosity ratio is defined as the ratio of the advancing non-wetting fluid viscosity to the defending wetting fluid viscosity (η w ), i.e., M = η n /η w . In addition, recent laboratory studies [41][42][43][44] have shown the strong influence of subcore scale heterogeneities on steady-state migration patterns, spatial distributions, and fluid saturations. To gain a better understanding of pore-scale two-phase displacement mechanisms, a series of numerical simulations are conducted to study the effect of Ca and M on displacement stability and fluid saturation in a homogeneous and a heterogeneous pore networks, and the obtained results are compared to indicate the effect of media heterogeneity.…”

Waterflooding of Surfactant and Polymer Solutions in a Porous Media Micromodel

“…Our IMPES model will be adjusted by using closure expressions [78] for saturation curves that incorporate surface tension as it influences capillary pressure. We also aim to control the pore structure of our system through photolithography techniques [16,26] and perform microparticle image velocimetry measurements [29] to map streamline profiles that can be compared to expected flow distributions as calculated by finite element analysis [79]. The approach we have used here can be used to evaluate other enhanced oil recovery systems, including other types of polymers or surfactants [80], nanoparticles [81,82], and foams [83,84].…”

“…Although advances in microfabrication technology allow for the manufacturing of complex pore structures [19], most micromodels used to study multiphase fluid flow through pore media have been done in rectangular pore bodies and throats [16,[20][21][22][23][24][25]. Computer-aided design of microchannels [26,27] can be used to mimic heterogeneous porous media structure. However, this method produces 2D pore structures that are not representative of 3D pore space.…”

Direct Numerical Simulation of Pore-Scale Fluid Flow and Transport

“…1, do not reflect the 3D connectivity of real porous media; however, they can be used as computationally affordable alternatives to 3D geometry models to study the qualitative effect of pore geometry [17]. In addition, 2D textures can be directly molded into Polydimethylsiloxane (PDMS) and bounded to glass to build high-precision microfluidic / nanofluidic porous media analogs [18]. 3D porous media geometry models are constructed similar to the 2D models.…”