Triggering interfacial instabilities during forced imbibition by adjusting the aspect ratio in depth-variable microfluidic porous media.

We present a comprehensive description of the aspect ratio impact on interfacial instability in porous media where a wetting liquid displaces a nonwetting fluid. Building on microfluidic experiments, we evidence imbibition scenarios yielding interfacial instabilities and macroscopic morphologies under different depth confinements, which were controlled by aspect ratio and capillary number. We report a phenomenon whereby a smaller aspect ratio of depth-variable microfluidic porous media and lower capillary number trigger interfacial instability during forced imbibition; otherwise, a larger aspect ratio of uniform-depth microfluidic porous media and higher capillary number will suppress the interfacial instability, which seemingly ignored or contradicts conventional expectations with compact and faceted growth during imbibition. Pore-scale theoretical analytical models, numerical simulations, as well as microfluidic experiments were combined for characteristics of microscopic interfacial dynamics and macroscopic displacement results as a function of aspect ratio, depth variation, and capillary number. Our results present a complete dynamic view of the imbibition process over a full range of regimes from interfacial stabilization to destabilization. We predict the mode of imbibition in porous media based on pore-scale interfacial behavior, which fits well with microfluidic experiments. The study provides insights into the role of aspect ratio in controlling interfacial instabilities in microfluidic porous media. The finding provides design or prediction principles for engineered porous media, such as microfluidic devices, membranes, fabric, exchange columns, and even soil and rocks concerning their desired immiscible imbibition behavior.

Multiphase displacement manipulated by micro/nanoparticle suspensions in porous media via microfluidic experiments: From interface science to multiphase flow patterns.

Multiphase displacement in porous media can be adjusted by micro/nanoparticle suspensions, which is widespread in many scientific and industrial contexts. Direct visualization of suspension flow dynamics and corresponding multiphase patterns is crucial to understanding displacement mechanisms and eventually optimizing these processes in geological, biological, chemical, and other engineering systems. However, suspension flow inside the opaque realistic porous media makes direct observation challenging. The advances in microfluidic experiments have provided us with alternative methods to observe suspension influence on the interface and multiphase flow behaviors at high temporal and spatial resolutions. Macroscale processes are controlled by microscale interfacial behaviors, which are affected by multiple physical factors, such as particle adsorption, capillarity, and hydrodynamics. These properties exerted on the suspension flow in porous media may lead to interesting interfacial phenomena and new displacement consequences. As an underpinning science, understanding and controlling the suspension transport process from interface to flow patterns in porous media is critical for a lower operating cost to improve resource production while reducing harmful emissions and other environmental impacts. This review summarizes the basic properties of different micro/nanoparticle suspensions and the state-of-the-art microfluidic techniques for displacement research activities in porous media. Various suspension transport behaviors and displacement mechanisms explored by microfluidic experiments are comprehensively reviewed. This review is expected to boost both experimental and theoretical understanding of suspension transport and interfacial interaction processes in porous media. It also brings forward the challenges and opportunities for future research in controlling complex fluid flow in porous media for diverse applications.

High-performance displacement by microgel-in-oil suspension in heterogeneous porous media: Microscale visualization and quantification.

HYPOTHESIS: Preferential flow in porous media is commonly encountered and decreases the multiphase displacement efficiency. Here, we synthesized microgel-in-oil in suspension and demonstrated that microgel-in-oil as a novel additive could present self-adaptive transport behavior and introduce a novel multiphase displacement mode for improving displacement efficiency in heterogeneous porous media. EXPERIMENTS: We investigated the microgel-in-oil formation process and characterized their morphology with fluorescence microscopy and Cryo-SEM. The suspension displacement performance in heterogeneous porous media was evaluated using a microfluidic chip containing a preferential flow pathway (PFP) and a parallel matrix region. The displacement results of microgel-in-oil were compared to plain microgel particles and analyzed from pore-scale particle transport behavior to macroscopic multiphase flow patterns. FINDINGS: The results show that suspension with moderate microgel-in-oil yields the optimal displacement efficiency. Fewer microgel-in-oil cannot alter the flow direction, while too many microgel-in-oil would block the PFP region. The topological analysis identified that suspensions with moderate microgel-in-oil content could achieve the strongest sweeping and carrying abilities that contribute to the highest displacement efficiency. The synergistic transport of microgel-in-oil and plain microgel particles would result in local pressure fluctuations to divert displacing fluid from PFP into the matrix region, which explains the above flow behavior.

Transport mechanism of deformable micro-gel particle through micropores with mechanical properties characterized by AFM.

Deformable micro-gel particles (DMP) have been used to enhanced oil recovery (EOR) in reservoirs with unfavourable conditions. Direct pore-scale understanding of the DMP transport mechanism is important for further improvements of its EOR performance. To consider the interaction between soft particle and fluid in complex pore-throat geometries, we perform an Immersed Boundary-Lattice Boltzmann (IB-LB) simulation of DMP passing through a throat. A spring-network model is used to capture the deformation of DMP. In order to obtain appropriate simulation parameters that represent the real mechanical properties of DMP, we propose a procedure via fitting the DMP elastic modulus data measured by the nano-indentation experiments using Atomic Force Microscope (AFM). The pore-scale modelling obtains the critical pressure of the DMP for different particle-throat diameter ratios and elastic modulus. It is found that two-clog particle transport mode is observed in a contracted throat, the relationship between the critical pressure and the elastic modulus/particle-throat diameter ratio follows a power law. The particle-throat diameter ratio shows a greater impact on the critical pressure difference than the elastic modulus of particles.

Synthetic Multifunctional Graphene Composites with Reshaping and Self-Healing Features via a Facile Biomineralization-Inspired Process.

Since graphene is a type of 2D carbon material with excellent mechanical, electrical, thermal, and optical properties, the efficient preparation of graphene macroscopic assemblies is significant in the potentially large-scale application of graphene sheets. Conventional preparation methods of graphene macroscopic assemblies need strict conditions, and, once formed, the assemblies cannot be edited, reshaped, or recycled. Herein, inspired by the biomineralization process, a feasible approach of shapeable, multimanipulatable, and recyclable gel-like composite consisting of graphene oxide/poly(acrylic acid)/amorphous calcium carbonate (GO-PAA-ACC) is designed. This GO-PAA-ACC material can be facilely synthesized at room temperature with a cross-linking network structure formed during the preparation process. Remarkably, it is stretchable, malleable, self-healable, and easy to process in the wet state, but tough and rigid in the dried state. In addition, these two states can be readily switched by adjusting the water content, which shows recyclability and can be used for 3D printing to form varied architectures. Furthermore, GO-PAA-ACC can be functionalized or processed to meet a variety of specific application requirements (e.g., energy-storage, actuators). The preparation method of GO-PAA-ACC composite in this work also provides a novel strategy for the versatile macroscopic assembly of other materials, which is low-cost, efficient, and convenient for broad application.

Lattice Boltzmann model for three-phase viscoelastic fluid flow.

A lattice Boltzmann (LB) framework is developed for simulation of three-phase viscoelastic fluid flows in complex geometries. This model is based on a Rothman-Keller type model for immiscible multiphase flows which ensures mass conservation of each component in porous media even for a high density ratio. To account for the viscoelastic effects, the Maxwell constitutive relation is correctly introduced into the momentum equation, which leads to a modified lattice Boltzmann evolution equation for Maxwell fluids by removing the normal but excess viscous term. Our simulation tests indicate that this excess viscous term may induce significant errors. After three benchmark cases, the displacement processes of oil by dispersed polymer are studied as a typical example of three-phase viscoelastic fluid flow. The results show that increasing either the polymer intrinsic viscosity or the elastic modulus will enhance the oil recovery.