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The paper presents the results of a systematic microfluidic study of the application of nanosuspensions for enhanced oil recovery. For the first time, approximately a dozen nanosuspensions prepared by the dilution of silica sols as displacement fluids were considered. The concentration of nanoparticles in the suspensions varied from 0.125 to 2 wt%, and their size ranged from 10 to 35 nm. Furthermore, the silica sols under consideration differed in their compositions of functional groups and pH. The effects of concentration, nanoparticle size, fluid flow rate, and the viscosity of the displaced oil were investigated using microfluidic technology. The microfluidic experiments demonstrated that the application of nanosuspensions for water flooding has significant potential. The efficiency of oil displacement by nanosuspensions was found to increase significantly (up to 30%) with the increasing concentration and decreasing average size of nanoparticles. The application of nanosuspensions for the enhancement of oil recovery is most appropriate for reservoirs with highly viscous oil.

Wetting hysteresis is the most important characteristic of microfluidic chips for modeling multiphase flows in rocks, including for oil production problems. Plasma modification of surface wetting characteristics is well studied, but there is a problem of stabilizing the resulting surface for use in a liquid hydrocarbon media. In this work, a simple and accessible technology for modifying the surface of PDMS and glass using a dielectric barrier discharge in a chamber based on the d’Arsonval apparatus has been developed. The surface wetting hysteresis for PDMS and glass was studied as a function of the plasma treatment time. It is shown that with the help of plasma treatment it is possible to change the wetting angles of the walls of microfluidic chips in a very wide range, thereby simulating the conditions of both hydrophobic and hydrophilic rocks. At the same time, PDMS has the widest possible range of changes in the wetting angle; the advancing contact angle decreases from 120° to 10°; receding contact angle—from 70° to 0° during plasma treatment. It has been shown that plasma treatment of a microfluidic chip, together with a 30 min primary extraction with oil and salt water, leads to a significant change in the wetting characteristics of its surface. This in total leads to an increase in the oil displacement efficiency from the chip by about 10%. In general, the results of the study showed that plasma surface treatment for the hydrophilization of microfluidic chips is a simple and affordable technology for controlling the wetting characteristics of microfluidic chips. PDMS in this case is a promising material.

Multiphase flows in porous media are widespread in nature and various technologies. One of the most common examples of this kind of task is the task of recovering oil from the rock. This article describes a mathematical model of the flow of a two-phase (immiscible) liquid based on a new approach of network hydrodynamics for a highly branched microchannel medium (simulating a porous space in the rock). The coupling of the flow and pressure fields in the network is performed using a well-proven SIMPLE algorithm in CFD problems; this approach allows us to use effective approaches to modeling 3D tasks. Phase transfer over the network is carried out by an explicit method with an adaptive time step. The article presents the results of verification of the model, with analytical calculations and in comparison with the results of experimental studies. As an experiment, the displacement of oil from a microchip (Dolomite: 3200284) simulating a porous medium was simulated. The good qualitative and quantitative compliance with the results calculated and the results of the experiment show the correct functioning of the model.

This article presents a new approach to determining the viscosity of Newtonian fluid. The approach is based on the analysis of the secondary Dean flow in a curved channel. The study of the flow patterns of water and aqueous solutions of glycerin in a microfluidic chip with a U-microchannel was carried out. The advantages of a microfluidic viscometer based on a secondary Dean flow are its simplicity, quickness, and high accuracy in determining the viscosity coefficient of a liquid. A viscosity image in a short movie represents fluid properties. It is revealed that the viscosity coefficient can be determined by the dependence of the recirculation angle of the secondary Dean flow. The article provides a correlation between the Dean number and the flow recirculation angle. The results of the field experiment, presented in the article, correlate with the data obtained using computational fluid dynamics and allow for selecting parameters to create microfluidic viscometers with a U-shaped microchannel.

The essential advantages of microfluidic studies are the excellent visualization of the processes of oil displacement from the porous medium model, simple cleaning, and the possibility of the repeated use of the microfluidic chip. The present article deals with the process of oil displacement by suspension flooding using a microfluidic chip, simulating a porous medium, and the suspensions of silicon dioxide nanoparticles (22 nm). The mass concentration of nanoparticles in suspensions ranged from 0.1 to 2 wt%. Five mass concentrations (0.125 wt%, 0.25 wt%, 0.5 wt%, 1 wt% and 2 wt%) were considered. The article presents the experimental photographs of the oil displacement process by water and SiO2 suspension. It is shown that, with the increasing concentration of nanoparticles, the oil recovery factor increases. A significant effect is observed at 0.5 wt% concentration of nanoparticles. It is shown that the increase in oil recovery during flooding by SiO2 suspension with the maximum concentration was 16%.