Search Results (27)

The investigation of fluid flow channeling and viscous fingering during immiscible two-phase displacement in subsurface porous media is crucial for optimizing CO₂ geological sequestration and improving hydrocarbon recovery. In this study, we develop a pore-scale numerical framework for unsteady state immiscible displacement based on a body-centered cubic percolation network, which explicitly captures the coupled effects of pore-scale heterogeneity, capillary number, and unfavorable viscosity ratio on flow channeling and viscous fingering. The simulations reveal that viscous fingering and flow channeling preferentially occur along overlapping high conductivity pathways that conform to the minimum energy dissipation principle. Along these preferential routes, the local balance between viscous and capillary forces governs the stability of the two-phase interface and gives rise to distinct patterns and intensities of viscous fingering in the invading phase. Building on these insights, we establish a theoretical framework that quantifies how the critical pore radius and capillary number control the onset and growth of interfacial instabilities during immiscible displacement. The model demonstrates that lowering the injection rate, and hence, the effective capillary number, suppresses viscous fingering, leading to more stable displacement fronts. These findings provide practical guidance for the design of injection schemes, helping to enhance oil and gas recovery and improve the storage efficiency and security of CO₂ geological sequestration projects. Full article

During the process of CO₂ displacing shear-thinning oil, the occurrence of fingering is a key factor contributing to a reduction in both displacement and sequestration efficiency. Existing studies typically use the average viscosity to calculate the viscosity ratio M for shear-thinning oil, overlooking the non-uniform viscosity distribution resulting from uneven shear stress. Consequently, a phase diagram based on M fails to accurately capture the underlying mechanism influencing fingering. We investigate the influence of shear-thinning on fingering patterns by analyzing viscosity heterogeneity during immiscible CO₂ flooding in porous media. The results showed the following: (1) An increase in zero-shear viscosity (μ₀) resulted in a greater viscosity difference between the two phases, which intensified interface instability, and the power-law index (n) diminished the shear-thinning effect, promoted fingering formation, and significantly reduced displacement efficiency, with a maximum reduction of 28.6% observed in this study. (2) Shear-thinning oil was more prone to capillary fingering compared to Newtonian oil under the same capillary number Ca and viscosity ratio M. (3) Intense pressure fluctuations at the displacement front combined with non-uniform viscosity distribution exacerbate interfacial instability and make shear-thinning oil more prone to capillary fingering. This study provides guidance for optimizing displacement strategies for shear-thinning fluids and advancing the practical implementation of CO₂ flooding technology. Full article

Viscous fingering is an interfacial instability that occurs when multiple fluids displace each other. This research focuses on the interface instability during immiscible displacement of shear-thinning fluids by CO₂. By controlling velocity and applying heat to the upper and lower walls, the influence of velocity and temperature on viscous fingering during CO₂ displacement is investigated. Moreover, by modifying the geometric conditions of the classical Hele-Shaw cells (HSCs), a novel analytical framework for viscous fingering is proposed. The primary methodology involves implementing a minute depth gradient distribution within the HSC, coupled with the Volume of Fluid (VOF) multiphase model, which systematically reveals the dynamic suppression mechanism of shear-thinning effects on viscous finger bifurcation. The results indicate that temperature elevation leads to increased sweep efficiency, reduced residual non-Newtonian fluid in the displaced zone, and enhanced displacement efficiency. Furthermore, increased velocity leads to reduced sweep efficiency. However, at lower velocities, displacement efficiency remains relatively low due to limited sweep coverage. The direction and magnitude of the depth gradient significantly govern the morphology and extension length of viscous fingering. Both positive and negative depth gradients promote fingering development on their respective sides, as the gradient establishes anisotropic permeability that prioritizes flow pathways in specific orientations, thereby intensifying finger propagation. Full article

Miscible gas flooding improves oil displacement through mass exchange between oil and gas phases. It is one of the most efficient enhanced oil recovery methods for intermediate density oil reservoirs. In this work, analytical solutions for saturation, concentration and pressure are derived for oil displacement by a partially miscible gas injection at a constant rate. The mathematical model considers two-phase, three-component fluid flow in a one-dimensional homogeneous reservoir initially saturated by a single oil phase. Phase saturations and component concentrations are described by a $2\times 2$ hyperbolic system of partial differential equations, which is solved by the method of characteristics. Once this Goursat–Riemann problem is solved, the pressure drop between two points in the porous media is obtained by the integration of Darcy’s law. The solution of this problem may present three different fluid regions depending on the rock–fluid parameters: a single-phase gas region near the injection point, followed by a two-phase region where mass transfer takes place and a single-phase oil region. We considered the single-phase gas and the two-phase gas/oil regions as incompressible, while the single-phase oil region may be incompressible or slightly compressible. The solutions derived in this work are applied for a specific set of rock and fluid properties. For this data set, the two-phase region displays rarefaction waves, shock waves and constant states. The pressure behavior depends on the physical model (incompressible, compressible and finite or infinite porous media). In all cases, the injection pressure is the result of the sum of two terms: one represents the effect of the mobility contrast between phases and the other represents the single-phase oil solution. The solutions obtained in this work are compared to an equivalent immiscible solution, which shows that the miscible displacement is more efficient. Full article

Understanding the mechanisms of snap-off during gas–liquid immiscible displacement is of great significance in the petroleum industry to enhance oil and gas recovery. In this work, based on the original pseudo-potential lattice Boltzmann method, we improved the fluid–fluid force and fluid–solid force scheme. Additionally, we integrated the Redlich–Kwong equation of state into the lattice Boltzmann model and employed the exact difference method to incorporate external forces within the lattice Boltzmann framework. Based on this model, a pore–throat–pore system was built, enabling gas–liquid to flow through it to investigate the snap-off phenomenon. The results showed the following: (1) The snap-off phenomenon is related to three key factors: the displacement pressure, the pore–throat length ratio, and the pore–throat width ratio. (2) The snap-off phenomenon occurs only when the displacement pressure is within a certain range. When the displacement pressure is larger than the upper limit, the snap-off will be inhibited, and when the pressure is less than the lower limit, the gas–liquid interface cannot overcome the pore–throat and results in a “pinning” effect. (3) The snap-off phenomenon is controlled using the pore–throat structures: e.g., length ratio and the width ratio between pore and throat. It is found that the snap-off phenomenon could easily occur in a “long-narrow” pore–throat system, and yet hardly in a “short-wide” pore–throat system. Full article

Surfactants play a crucial role in tertiary oil recovery by reducing the interfacial tension between immiscible phases, altering surface wettability, and improving foam film stability. Oil reservoirs have high temperatures and high pressures, making it difficult and hazardous to conduct lab experiments. In this context, molecular dynamics (MD) simulation is a valuable tool for complementing experiments. It can effectively study the microscopic behaviors (such as diffusion, adsorption, and aggregation) of the surfactant molecules in the pore fluids and predict the thermodynamics and kinetics of these systems with a high degree of accuracy. MD simulation also overcomes the limitations of traditional experiments, which often lack the necessary temporal–spatial resolution. Comparing simulated results with experimental data can provide a comprehensive explanation from a microscopic standpoint. This article reviews the state-of-the-art MD simulations of surfactant adsorption and resulting interfacial properties at gas/oil–water interfaces. Initially, the article discusses interfacial properties and methods for evaluating surfactant-formed monolayers, considering variations in interfacial concentration, molecular structure of the surfactants, and synergistic effect of surfactant mixtures. Then, it covers methods for characterizing microstructure at various interfaces and the evolution process of the monolayers’ packing state as a function of interfacial concentration and the surfactants’ molecular structure. Next, it examines the interactions between surfactants and the aqueous phase, focusing on headgroup solvation and counterion condensation. Finally, it analyzes the influence of hydrophobic phase molecular composition on interactions between surfactants and the hydrophobic phase. This review deepened our understanding of the micro-level mechanisms of oil displacement by surfactants and is beneficial for screening and designing surfactants for oil field applications. Full article

The hydrodynamic and thermal interaction of water with the high-temperature melt of a heavy metal was studied via the Volume-of-Fluid (VOF) method formulated for three immiscible phases (liquid melt, water, and water vapor), with account for phase changes. The VOF method relies on a first-principle description of phase interactions, including drag, heat transfer, and water evaporation, in contrast to multifluid models relying on empirical correlations. The verification of the VOF model implemented in OpenFOAM software was performed by solving one- and two-dimensional reference problems. Water jet penetration into a melt pool was first calculated in two-dimensional problem formulation, and the results were compared with analytical models and empirical correlations available, with emphasis on the effects of jet velocity and diameter. Three-dimensional simulations were performed in geometry, corresponding to known experiments performed in a narrow planar vessel with a semi-circular bottom. The VOF results obtained for water jet impact on molten heavy metal (lead–bismuth eutectic alloy at the temperature 820 K) are here presented for a water temperature of 298 K, jet diameter 6 mm, and jet velocity 6.2 m/s. Development of a cavity filled with a three-phase melt–water–vapor mixture is revealed, including its propagation down to the vessel bottom, with lateral displacement of melt, and subsequent detachment from the bottom due to gravitational settling of melt. The best agreement of predicted cavity depth, velocity, and aspect ratio with experiments (within 10%) was achieved at the stage of downward cavity propagation; at the later stages, the differences increased to about 30%. Adequacy of the numerical mesh containing about 5.6 million cells was demonstrated by comparing the penetration dynamics obtained on a sequence of meshes with the cell size ranging from 180 to 350 µm. Full article

Foam flooding is an efficient and promising technology of enhanced oil recovery that significantly improves sweep efficiency of immiscible displacement processes by providing favorable mobility control on displacing fluids. Although the advantages in flexibility and efficiency are apparent, accurate prediction and effective control of foam flooding in field applications are still difficult to achieve due to the complexity in multiphase interactions. Also, conventional field-scale or mesoscale foam models are inadequate to simulate recent experimental findings in feasibility of foam injection in tight reservoirs. Microscale modeling of foam behavior has been applied to further connect those pore-scale interactions and mesoscale multiphase properties such as foam texture and the relative permeability of foam banks. Modification on a microscale foam model based on a pore-filling event network method is proposed to simulate its propagation in grain-based pore networks with varying degrees of heterogeneity. The impacts of foam injection strategy and oil-weakening phenomena are successfully incorporated. Corresponding microfluidic experiments are performed to validate the simulation results in dynamic displacement pattern as well as interfacial configuration. The proposed modeling method of foam propagation in grain-based networks successfully captures the effects of lamellae configurations corresponding to various foaming processes. The results of the simulation suggest that the wettability of rock has an impact on the relevance between reservoir heterogeneity and the formation of immobile foam banks, which supports the core idea of the recently proposed foam injection strategy in tight oil reservoirs with severe heterogeneity, that of focusing more on the IFT adjustment ability of foam, instead of arbitrarily pursuing high-quality strong foam restricted by permeability constraints. Full article

The variation of the classical viscous fingering instability is studied numerically in this work. An investigation of the viscous fingering phenomenon of immiscible displacement in the Hele–Shaw cell (HSC), where the displaced fluid is a shear-thinning fluid, was carried out numerically using the volume of fluid (VOF) method by adding a minor depth gradient or altering the geometry of the top plate in the HSC. The findings demonstrate how the presence of depth gradients can change the stability of the interface and offer a chance to regulate and adapt the fingering instability in response to the viscous fingering properties of air driving non-Newtonian fluids under various depth gradients. The relative breadth will shrink under the influence of the depth gradient, and the negative consequences of the gradient will be increasingly noticeable. Specifically, under different power-law indices, we found that with the enhancement of shear-thinning characteristics (lower power-law exponent n) in both positive and negative depth gradients, the fingers that protrude from the viscous fingers become shorter and thicker, resulting in higher displacement efficiency. Additionally, several modifications were performed to the upper plate’s design, and the findings revealed that the shape had no effect on the viscous fingering and only had an impact on the longitudinal amplitude. Based on the aforementioned traits, we may alter the HSC’s form or depth gradient to provide high-quality and effective work. Full article

The present investigation analyzes the transient multilayer electro-osmotic flow through an annular microchannel with hydrophobic walls. The fluids are considered immiscible and viscoelastic, following the Maxwell rheological model. In the problem examined, the linearized Poisson–Boltzmann and Cauchy momentum equations are used to determine the electric potential distribution and the flow field, respectively. Here, different interfacial phenomena are studied through the imposed boundary conditions, such as the hydrodynamic slip and specified zeta potentials at solid–liquid interfaces, the velocity continuity, the electroviscous stresses balance, the potential difference, and the continuity of electrical displacements at the interfaces between fluids. The semi-analytic solution uses the Laplace transform theory. In the results, the velocity profiles and velocity tracking show the oscillatory behavior of flow, which strongly depends on the dimensionless relaxation time. Furthermore, the hydrodynamic slip on the channel walls contributes to the release of energy stored in the fluids due to elastic effects at the start-up of the flow. Similarly, other dimensionless parameters are also investigated. This research aims to predict the parallel flow behavior in microfluidic devices under electro-osmotic effects. Full article

Understanding the displacement of the resident wetting fluid in porous media is crucial to the remediation strategy. When pollutants or nutrients are dissolved in the surface wetting fluid and enter the unsaturated zone, the resident wetting fluid in the porous system may remain or be easily flushed out and finally arrive in the groundwater. The fate and transport of the resident wetting fluid determine the policy priorities on soil or groundwater. In this study, the displacement of the resident wetting fluid by the invading wetting fluid in porous media was simulated using direct numerical simulation (DNS). Based on the simulations of the displacements in porous media, the effect of the non-wetting fluid on the displacement was evaluated by observation and quantification, which were difficult to achieve in laboratory experiments. The result can also explain the unknown phenomenon in previous column experiments, namely that the old water is continuously released from the unsaturated porous media even after a long period of flushing with the new water. The effects of the interfacial tension, contact angle, and injection rate, which affected the immiscible fluid–fluid flow pattern, were also evaluated. Since pollutants dissolved in the wetting fluid could change the physical properties of the wetting fluid, the interfacial tensions of the resident wetting fluid and the invading wetting fluid were set separately in the simulation. Moreover, our simulation demonstrated that the consecutive drainage–imbibition cycles could improve the displacement of the resident wetting fluid in porous media. The successful simulation in this study implied that this method can be applied to predict other immiscible fluid–fluid flow in natural or industrial processes. Full article

The oscillation of the liquid interface in axisymmetric Hele-Shaw cells (conical and flat) is experimentally studied. The cuvettes, which are thin conical layers of constant thickness and flat radial Hele-Shaw cells, are filled with two immiscible liquids of similar densities and a large contrast in viscosity. The axis of symmetry of the cell is oriented vertically; the interface without oscillations is axially symmetric. An oscillating pressure drop is set at the cell boundaries, due to which the interface performs radial oscillations in the form of an oscillating “tongue” of a low-viscosity liquid, periodically penetrating into a more viscous liquid. An increase in the oscillation amplitude leads to the development of a system of azimuthally periodic structures (fingers) at the interface. The fingers grow when the viscous liquid is forced out of the layer and reach their maximum in the phase of maximum displacement of the interface. In the reverse course, the structures decrease in size and, at a certain phase of oscillations, take the form of small pits directed toward the low-viscosity fluid. In a conical cell, a bifurcation of period doubling with an increase in amplitude is found; in a flat cell, it is absent. A slow azimuthal drift of finger structures is found. It is shown that the drift is associated with the inhomogeneity of the amplitude of fluid oscillations in different radial directions. The fingers move from the region of a larger to the region of a lower amplitude of the interface oscillations. Full article

We investigate the effect of horizontal quasi-periodic oscillation on the stability of two superimposed immiscible fluid layers confined in a horizontal Hele-Shaw cell. To approximate real oscillations, a quasi-periodic oscillation with two incommensurate frequencies is considered. Thus, the linear stability analysis leads to a quasi-periodic oscillator, with damping, which describes the evolution of the amplitude of the interface. Two types of quasi-periodic instabilities occur: the low-wavenumber Kelvin-Helmholtz instability and the large-wavenumber resonances. We mainly show that, for equal amplitudes of the superimposed accelerations, and for a low irrational frequency ratio, there is competition between several resonance modes allowing a very large selection of the wavenumber from lower to higher values. This is a way to control the sizes of the waves. Furthermore, increasing the frequency ratio has a stabilizing effect for both types of instability whose thresholds are found to correspond to quasi-periodic solutions using the frequency spectrum. For a ratio of the two superimposed displacement amplitudes equal to unity and less than unity, the number of resonances and competition between their modes also become significant for the intermediate values of the ratio of frequencies. The effects of other physical and geometrical parameters, such as the damping coefficient, density ratio, and heights of the two fluid layers, are also examined. Full article

The viscous fingering phenomenon often occurs when a low-viscosity fluid displaces a high-viscosity fluid in a homogeneous porous media, which is an undesirable displacement process in many engineering applications. The influence of wetting gradient on this process has been studied over a wide range of capillary numbers (7.5 × 10⁻⁶ to 1.8 × 10⁻⁴), viscosity ratios (0.0025 to 0.04), and porosities (0.48 to 0.68), employing the lattice Boltzmann method. Our results demonstrate that the flow front stability can be improved by the gradual increase in wettability of the porous media. When the capillary number is less than 3.5 × 10⁻⁵, the viscous fingering can be successfully suppressed and the transition from unstable to stable displacement can be achieved by the wetting gradient. Moreover, under the conditions of high viscosity ratio (M > 0.01) and large porosity (Φ > 0.58), wetting gradient improves the stability of the flow front more significantly. Full article

Water displacing oil is one of the main emptying methods for mobile pipelines. It has the advantages of being a simple process and highly safe. At present, the determination of a water displacing oil scheme of mobile pipelines is based on the oil–oil alternating transport theory of product oil pipelines. However, the insolubility of the oil phase and the water phase results in a great difference between the flow characteristics of water displacing oil and the oil–oil alternating transport of a product oil pipeline. In addition, due to the effect of buoyancy, the oil phase gathers at the high point of the pipeline and forms a liquid accumulation, which is difficult to carry away by water flow, resulting in the low emptying efficiency of the mobile pipeline. The essence of water displacing oil in a mobile pipeline is an oil–water two-phase unsteady displacement flow, involving liquid–liquid displacement flow, oil–water two-phase flow and water carrying oil. Aiming at such problems, domestic and foreign scholars have carried out a large number of theoretical and experimental studies, established the oil–water mixing model of water displacing oil and the relationship between macroscopic quantity (flow pattern, pressure drop and water content) and microscopic quantity (local flow field and droplet dispersion pattern, etc.) under each flow type, and explored the influence of pipeline diameter, oil phase velocity, pipeline inclination angle and other parameters on the capacity of carrying liquid accumulation. On this basis, this paper analyzes the shortcomings of the current research on the oil–water flow characteristics of water displacing oil in a mobile pipeline from three aspects: the formation mechanism of the oil–water mixture, displacing flow characteristics of immiscible fluids and flow characteristics of water carrying oil. Five future research directions are proposed, including the interface morphology and flow field characteristics of oil–water two-phase layered flow, local mixing characteristics of an oil–water two-phase dual continuous flow interface, droplet distribution and flow characteristics of oil–water two-phase dispersed flow, unsteady flow characteristics of the oil–water mixture of water displacing oil and oil accumulation and flow characteristics in topographic relief pipes. Full article