Non-wetting Fluid Research Articles

Euler characteristic during drying of porous media

This study aims to elucidate the dynamics of fluid topology during drainage and evaporation of wetting and non-wetting fluids via evaluation of their Euler characteristic (EC) and Betti numbers from designed experiments. The results showed that the EC of the non-wetting fluid remained constant at a high wetting fluid saturation and then decreased nonlinearly. However, the EC of the wetting fluid exhibited more complex trends. In the 2-D micromodel, the number of loops decreased monotonously, reached zero, and remained constant for lower saturations, while the number of distinct components fluctuated because of the appearance and disappearance of disconnected clusters. In the 2-D model, the number of distinct components played a significant role; in the 3-D X-ray CT experiment, the number of loops of pendular rings dominated the EC. The findings suggest that the trends observed in the 2-D micromodel may not apply under 3-D conditions.

Simulating volume-controlled invasion of a non-wetting fluid in volumetric images using basic image processing tools

A new algorithm is presented for simulating volume-controlled invasion of a non-wetting phase into voxel images. This method is complementary to the traditional morphological image opening method which mimics pressure-based invasion. A key advantage of the volume-based approach is that fluid configuration at any saturation between 0 and 1 can obtained rather than the irregularly and widely spaced saturation steps obtained by pressure-based methods. Because of the incremental increases in saturation, it becomes possible to correctly predict defending phase trapping, which is not the case when pressure-based steps are applied. The algorithm is verified by comparing to morphological image opening and obtains near perfect agreement at equal saturations as expected from theory. It is also demonstrated that a volume-controlled capillary pressure curve can be obtained that displays the characteristic jumps in capillary pressure. Moreover, the envelop of peak pressures yields the pressure-based capillary pressure obtained by morphological opening, so in fact the results of the proposed algorithm are a superset of the morphological approach. Finally, results are compared to multiphase lattice Boltzmann and qualitatively similar results were achieved in substantially less time. The lattice Boltzmann method is more flexible in terms of variable contact angle and inclusion of viscous effects, but for quasi-static volume-based injection of a non-wetting fluid, the proposed method is viable alternative.

Investigation on the influence of capillary number on drainage in porous media using a lattice Boltzmann method

This work investigates the effect of the capillary number on the saturation of wetting and nonwetting phases during processes of drainage. A multicomponent Lattice Boltzmann model with a two-relaxation time scheme is used to simulate the flow in 2D and 3D digital models of porous rocks. The capillary number is varied by setting different values of the fluid inlet velocity, while viscosity and interfacial tension are fixed. The results show the invasion of nonwetting phase in the narrow pores of the media, forcing the wetting fluid to leave through the outlet. Different patterns are observed depending on the capillary number and the degree of porosity and heterogeneity of the models. Several pore-scale events are observed and play an important role in the trapping of wetting fluid. The nonwetting phase saturation is measured at breakthrough and quasi-steady states. In 2D models, the effect of the low velocity of the fluid at low Ca provides a better condition for fluid redistribution, causing a higher nonwetting fluid saturation. In 3D models, a lower value of Ca leads to more trapped wetting fluid mainly because of the media geometries. In all cases, the highest Ca range resulted in the highest nonwetting fluid saturation at a quasi-steady state. The saturation and relative permeability curves at the point of irreducible wetting phase saturation show that the degree of heterogeneity in 3D models has an important effect on sweeping effectiveness, which seems to be more significant than porosity or intrinsic permeability of the models.

Instability of co-flow in a Hele-Shaw cell with cross-flow varying thickness

We analyse the stability of the interface between two immiscible fluids both flowing in the horizontal direction in a thin cell with vertically varying gap width. The dispersion relation for the growth rate of each mode is derived. The stability is approximately determined by the sign of a simple expression, which incorporates the density difference between the fluids and the effect of surface tension in the along- and cross-cell directions. The latter arises from the varying channel width: if the non-wetting fluid is in the thinner part of the channel, the interface is unstable as it will preferentially migrate into the thicker part. The density difference may suppress or complement this effect. The system is always stable to sufficiently large wavenumbers owing to the along-flow component of surface tension.

The life span and dynamics of immiscible viscous fingering in rectilinear displacements

We investigate the dynamics, interactions, and decay of immiscible viscous fingers in two and three dimensions over time in a high-aspect ratio (up to 100:1) system. The behavior is related to the viscosity ratio and a macroscopic capillary number. The same four fingering regimes are observed as in miscible displacements (spreading of the interface between wetting and non-wetting fluid but no fingers, the growth of many fingers that can be described by perturbation analysis, non-linear interactions between fingers and decay to a single finger) for low viscosity ratio and high capillary to viscous ratios. At higher viscosity ratios and lower capillary to viscous ratios, periodic tip-splitting and decay results in a fluctuation between one and two fingers at late time. This has not been seen in miscible displacements. We provide a stability plot that can be used to identify when this will occur. Similar behaviors were seen in both two and three dimensions, suggesting that learnings from two-dimensional (2D) linear displacements can be applied to similar three-dimensional (3D) flows. In particular, the square root of the number of fingers seen in the 3D simulations and their decay with time was almost identical to 2D.

Investigation of pore size distribution by mercury intrusion porosimetry (MIP) technique applied on different OSB panels

Mercury intrusion porosimetry (MIP) is a technique used to characterize the pore size distribution and resin penetration in lignocellulosic materials, such as oriented strand board specimens (OSB), a multilayer panel utilized in structural applications. The method is based on the isostatic injection, under very high pressure, of a non-wetting fluid (mercury) into the porous material to determine parameters such as pore size distribution and percentage of porosity of the specimens. In this study, five different OSB were analyzed; they contained different wood species, resin type, and resin content. The panels manufactured with castor oil polyurethane resin showed porosity values in the range of 54.7 and 27.8%. This was a promising result compared with those obtained for panels made with phenolic resins, which are currently commercialized in Brazil.

A fully implicit coupled pore-network/free-flow model for the pore-scale simulation of drying processes

We present a fully coupled pore-network/free-flow model providing pore-scale insight into drying processes. We solve the Navier–Stokes equations with component transport in the free-flow region, coupled to a dynamic two-phase, two-component pore-network model (PNM) in the porous domain. The dynamic multi-physics model allows to temporally resolve drying processes in-between capillary equilibrium states. All simulations are non-isothermal and use pressure- and temperature-depended fluid properties. Carefully chosen coupling conditions and a monolithic solver ensure local conservation of mass, momentum, and energy fluxes, in particular at the interface between both model domains. We solve for wetting and non-wetting fluid pressure fields and consider advective gas transport in the network. Numerical examples demonstrate that the coupled model is able to cover a wide range of physical processes relevant for drying and show the mutual interaction of the two subregions. The model is implemented in the modular open-source framework DuMu such that extensions are straight-forward.

Fast Spontaneous Transport of a Non-wetting Fluid in a Disordered Nanoporous Medium

Fast Spontaneous Transport of a Non-wetting Fluid in a Disordered Nanoporous Medium

Discovery of Dynamic Two-Phase Flow in Porous Media Using Two-Dimensional Multiphase Lattice Boltzmann Simulation

The dynamic two-phase flow in porous media was theoretically developed based on mass, momentum conservation, and fundamental constitutive relationships for simulating immiscible fluid-fluid retention behavior and seepage in the natural geomaterial. The simulation of transient two-phase flow seepage is, therefore, dependent on both the hydraulic boundaries applied and the immiscible fluid-fluid retention behavior experimentally measured. Many previous studies manifested the velocity-dependent capillary pressure–saturation relationship (Pc-S) and relative permeability (Kr-S). However, those works were experimentally conducted on a continuum scale. To discover the dynamic effects from the microscale, the Computational Fluid Dynamic (CFD) is usually adopted as a novel method. Compared to the conventional CFD methods solving Naiver–Stokes (NS) equations incorporated with the fluid phase separation schemes, the two-phase Lattice Boltzmann Method (LBM) can generate the immiscible fluid-fluid interface using the fluid-fluid/solid interactions at a microscale. Therefore, the Shan–Chen multiphase multicomponent LBM was conducted in this study to simulate the transient two-phase flow in porous media. The simulation outputs demonstrate a preferential flow path in porous media after the non-wetting phase fluid is injected until, finally, the void space is fully occupied by the non-wetting phase fluid. In addition, the inter-relationships for each pair of continuum state variables for a Representative Elementary Volume (REV) of porous media were analyzed for further exploring the dynamic nonequilibrium effects. On one hand, the simulating outcomes reconfirmed previous findings that the dynamic effects are dependent on both the transient seepage velocity and interfacial area dynamics. Nevertheless, in comparison to many previous experimental studies showing the various distances between the parallelly dynamic and static Pc-S relationships by applying various constant flux boundary conditions, this study is the first contribution showing the Pc-S striking into the nonequilibrium condition to yield dynamic nonequilibrium effects and finally returning to the equilibrium static Pc-S by applying various pressure boundary conditions. On the other hand, the flow regimes and relative permeability were discussed with this simulating results in regards to the appropriateness of neglecting inertial effects (both accelerating and convective) in multiphase hydrodynamics for a highly pervious porous media. Based on those research findings, the two-phase LBM can be demonstrated to be a powerful tool for investigating dynamic nonequilibrium effects for transient multiphase flow in porous media from the microscale to the REV scale. Finally, future investigations were proposed with discussions on the limitations of this numerical modeling method.

Prediction of three-phase relative permeabilities of Berea sandstone using lattice Boltzmann method

Three-phase flows through a pore network of Berea sandstone are studied numerically under critical interfacial tension conditions. Results show that the relative permeability of each fluid increases as its own saturation increases. The specific interfacial length between wetting and nonwetting fluids monotonously decreases with increasing the saturation of intermediate-wetting fluid, while the other two specific interfacial lengths exhibit a nonmonotonous variation. As the wetting (nonwetting) fluid becomes less wetting (nonwetting), the relative permeability of wetting fluid monotonously increases, while the other two relative permeabilities show a nonmonotonous trend. Due to the presence of a spreading layer, the specific interfacial length between wetting and nonwetting fluids always stabilizes at a low level. As the viscosity ratio of wetting (nonwetting) to intermediate-wetting fluids increases, the relative permeability of wetting (nonwetting) fluid increases. With the viscosity ratio deviating from unity, the phase interfaces become increasingly unstable, leading to an increased specific interfacial length.

Pore‐Scale Modeling of Spontaneous Imbibition in Porous Media Using the Lattice Boltzmann Method

AbstractA new color‐gradient lattice Boltzmann model is developed to simulate spontaneous imbibition in a porous media micromodel, which needs only two‐dimensional computational cost but considers essential three‐dimensional effects. A modified periodic boundary condition is introduced to deal with inlet and outlet boundaries with great ease and effectiveness. This model is first validated against analytical solutions and micromodel experiment. It is then used to study the spontaneous imbibition process in a homogeneous micromodel for varying viscosity ratios and contact angles. Depending on the viscosity ratio (λ) of wetting to nonwetting fluids, three different imbibition patterns are observed, namely unstable displacement (UD), stable displacement (SD), and crossover from UD to SD, which occur at , , and , respectively. When the crossover occurs, the wetting fluid saturation at breakthrough increases between two plateaus corresponding to UD and SD, respectively. Consistent with theoretical predictions from a single capillary, the wetting fluid saturation versus time follows the relation of for , and for . Due to the increased capillary valve resistance, increasing wetting phase contact angle is found to promote the flow instability, resulting in the development of preferential flow paths and thus some nonwetting fluid trapped in the flow direction. In addition, it is theoretically and numerically demonstrated that the effect of contact angle cannot be properly described by the theoretical equations derived from a single capillary because of the presence of capillary valve effect, which can be suppressed by decreasing contact angle or micromodel depth.

A generalized analytical model for estimating the rate of imbibition/drainage of wetting/nonwetting fluids in capillaries

Displacing one fluid by another immiscible with it is a phenomenon of greatest importance and exists in various applications from large scale oil productions to small scale microfluidics. Modeling this phenomenon is crucial, particularly, with respect to estimating penetration rates. Although considerable amounts of research works have been conducted to understand the physics involved in this phenomenon, they remain adherent to particular applications. This includes, for example, imbibition scenarios in which a wetting fluid imbibes inside a capillary tube even without the need to initiate the penetration. On the other hand, drainage scenarios, in which a nonwetting fluid displaces a wetting one, requires such initiation by providing external boosting. There are several external factors that influence the rate at which the meniscus advances inside a capillary tube. The most common such forces include pressure force, capillary force, and gravity force. Several of the modeling approaches have considered the case in which the displaced fluids are gases (e.g., air), particularly in applications related to infiltration studies in porous media. This allowed researchers to ignore the frictional resistance of the displaced fluid and only considers the other denser fluid. However, there exists other applications in which this is not correct and it may not be appropriate to ignore the displaced fluid. In this work, a new generalized model is introduced that accounts for all the physics involved in this process and also does not ignore the displaced fluid. For validation, it is shown that the derived model reduces to all the special cases for which analytical solutions exist, (including that of a single-phase flows). Furthermore, comparisons with computational fluid dynamics simulation (CFD) of drainage/imbibition scenarios show very good match with the results of the derived model, which builds confidence in the modeling approach.

Suspensions of lyophobic nanoporous particles as smart materials for energy absorption

HypothesisSuspensions of nanoporous particles in non-wetting fluids (lyophobic nanoporous suspensions, LPNPS) are explored as energy absorbing materials for shock absorbers, bumpers, and energy storage. Upon application of pressure, the non-wetting fluid invades the pores transforming the impact energy into the interfacial energy that can be stored and released on demand. ExperimentsHere, we present a comprehensive experimental study of the dynamics of LPNPS compression within a wide range of shock impact energy for three types of mesoporous materials (Libersorb 23, Polysorb-1, and Silochrome-1.5) with water and Wood alloy as non-wetting fluids. FindingsThree different regimes of the LPNPS compression-expansion cycle in response to the shock impact are distinguished as the impact energy increases: without fluid penetration into the pores, with partial penetration, and with complete pore filling. In two latter regimes, the suspension compressibility in the process of rapid compression increases by 2–4 decimal decades. This giant effect is associated with the onset of penetration of the non-wetting fluid into the nanopores upon achievement of a certain threshold pressure. The dynamic threshold pressure exceeds the threshold pressure of quasistatic intrusion and does not depends on the impact pressure, temperature, and suspension composition. A dynamic model of suspension compression is suggested that allows to separate the effects of the fluid intrusion into the pores and the elastic deformation of the system.

Oil Drainage in a Capillary Tube: Experimental and Numerical Study

In this paper, we investigate experimentally and numerically the dynamics of the drainage of a transparent capillary tube (radius 0.4 mm). A non-wetting fluid (gas) displaces a wetting fluid (oil). The gas phase is continuously injected at an extremity of the capillary tube (inlet section) at a constant injection-rate $$Q_{inj}$$ , ranging from 0.1 to 10 ml/h, corresponding to capillary numbers Ca varying between $$5 \cdot 10^{ - 4}$$ and $$5 \cdot 10^{ - 2}$$ . Oil phase, initially filling the tube, leaves the system at the second opened extremity (outlet section).We consider in this work the compressibility of non-wetting fluid (gas), viscous forces in the liquid column, capillary forces and gravity. The effect of several parameters, such as $$Q_{inj}$$ j and gravity, on the progress of the gas–liquid interface has been investigated.

Study on the effect of pore-scale heterogeneity and flow rate during repetitive two-phase fluid flow in microfluidic porous media

Various energy recovery, storage, conversion and environmental operations may involve repetitive fluid injection and thus, cyclic drainage–imbibition processes. We conducted an experimental study for which polydimethylsiloxane (PDMS)-based micromodels were fabricated with three different levels of pore-space heterogeneity (coefficient of variation, where COV = 0, 0.25 and 0.5) to represent consolidated and/or partially consolidated sandstones. A total of 10 injection-withdrawal cycles were applied to each micromodel at two different flow rates (0.01 and 0.1 ml min −1 ). The experimental results were analysed in terms of flow morphology, sweep efficiency, residual saturation, the connection of fluids and the pressure gradient. The pattern of the invasion and displacement of the non-wetting fluid converged more readily in the homogeneous model (COV = 0) as the repetitive drainage–imbibition process continued. The overall sweep efficiency converged between 0.4 and 0.6 at all tested flow rates, regardless of different flow rates and COV in this study. In contrast, the effective sweep efficiency was observed to increase with higher COV at the lower flow rate, while that trend became reversed at the higher flow rate. Similarly, the residual saturation of the non-wetting fluid was largest at COV = 0 for the lower flow rate, but it was the opposite for the higher flow-rate case. However, the Minkowski functionals for the boundary length and connectedness of the non-wetting fluid remained quite constant during repetitive fluid flow. Implications of the study results for porous media-compressed air energy storage (PM-CAES) are discussed as a complementary analysis at the end of this paper. Supplementary material: Figures showing the distribution of water (Fig. S1) and oil (Fig. S2) at the end of each drainage and imbibition step in different microfluidic pore-network models are available at https://doi.org/10.6084/m9.figshare.c.5276814 Thematic collection: This article is part of the Energy Geoscience Series available at: https://www.lyellcollection.org/cc/energy-geoscience-series

Spontaneous imbibition in tight porous media with different wettability: Pore-scale simulation

Spontaneous imbibition is significantly influenced by rock wettability, and it has been extensively studied in core-based experiments and numerical simulations owing to its important role in the development of oil/gas reservoir. Due to the fine pore structure and complex wettability of tight sandstone, an in-depth exploration of the effects of wettability on the pore-scale flow physics during spontaneous imbibition is of great value to complement traditional experimental studies and enhance the understanding of microscopic flow mechanisms during the development of tight oil reservoirs. Based on a X-ray computed tomography scanning experiment and a lattice Boltzmann multiphase model, in this work, we systematically investigate the effects of different hydrophilic strengths on the evolution of the imbibition fronts within the micropores and the degree of nonwetting fluid recovery during spontaneous imbibition of tight sandstone. The results show that the wettability significantly affects the morphological characteristics of the imbibition fronts. Under strong hydrophilic conditions, the wetting fluid preferentially invades the pore corner in the form of angular flow. As the contact angle increases, the hysteresis effect at the main terminal interface decreases, and the two-phase interface becomes regular and compact. Wettability also significantly affects the imbibition rate and the nonwetting fluid recovery degree. The smaller the contact angle, the faster the imbibition rate and the higher the recovery degree of nonwetting fluids during the cocurrent spontaneous imbibition.

Interpreting dynamics of snap-off in a constricted capillary from the energy dissipation principle

Snap-off usually occurs during two-phase fluid displacement in a constricted capillary, where the nonwetting phase fluid is cut into blobs or ganglia due to surface tension. Snap-off has been intensely recognized as a predominant pore-scale mechanism that may be responsible for the breakup and trapping of the nonwetting phase in complex geophysical structures. Herein, we investigated the dynamics of snap-off in a constricted pore and throat structure with a square cross-section using the volume of fluid method. Despite the geometric constraint dictated by Roof, a new judging diagram for the occurrence of snap-off was proposed as a function of Ca number and viscosity ratio. Our prediction from the numerical simulation is consistent with the analytical solution derived from the balance of capillary and hydrodynamic pressure. Furthermore, the associated transient energy balance was thoroughly studied, considering the alteration of the surface energy, kinetic energy, total input energy, and viscous dissipation during the period of snap-off. The results indicated that snap-off is always characterized by a sharp decline in the surface energy, which resulted in a surge in the kinetic energy and viscous dissipation. In addition, we observed a sharp surge in the viscous dissipation rate curve associated with such energy change, which is attributed to the redistribution of the velocity field. The sudden surge unanimously decreased while increasing the Ca number or viscosity ratio. Meanwhile, the position at which snap-off took place was shifted downstream of the throat, explaining the condition of the snap-off had become much more difficult.

Determination of the throat size distribution of a porous medium as an inverse optimization problem combining pore network modeling and genetic and hill climbing algorithms.

The pore size distribution of a porous medium is often estimated from the retention curve or the invading fluid flow rate curve using simple relationships more or less explicitly based on the consideration that the porous medium is made of a bundle of cylindrical parallel tubes. This type of determination is tested using pore network simulations. Starting from two- or three-dimensional networks, the characteristics of which are known a priori, the estimation of the throat size distribution (TSD) is performed using the standard methods in the case of drainage. Results show a significant discrepancy with the input data. The disagreement is more pronounced when the fluid flow rate curve is employed together with the parallel tubes assumption. The physical origins of these shortcomings are identified. A method, based on pore network simulations combined with a genetic algorithm and the hill climbing algorithm, is then designed, which makes simultaneous use of the nonwetting fluid flow rate curve and the retention curve of the medium. Very significant improvement is achieved in the estimation of the TSD using this procedure.

Effects of pore-size disorder and wettability on forced imbibition in porous media

Imbibition is the process by which the wetting fluid displaces the non-wetting fluid driven by capillary force. It occurs in many natural and industrial processes, such as enhanced oil recovery and geological carbon sequestration. The imbibition process is highly affected by wettability, viscosity ratio and injection flow rate, and the competition between these factors becomes more complicated when pore-size disorder is involved. In this study, we systematically investigate forced imbibition in four two-dimensional (2D) porous media with different disorders over a broad range of wettability conditions and flow rates. We analyze the relationship between the interfacial length and the invading fluid saturation, and the relationship between displacement front and invading fluid saturation. Results show that disorder and wettability have different impacts on the imbibition process under different capillary numbers. At low capillary number, displacement process is not sensitive to disorder due to the contradicting effects and the imbibition process is governed by the wettability. At intermediate capillary number, only the largest disorder has obvious influence on the displacement process due to the highest entry pressure. The transition from capillary fingering to viscous fingering occurs leading to a higher displacement efficiency. At high capillary number, disorder has a great influence on the front morphology and displacement efficiency while the wettability has relatively weak impact. The pattern transition is also observed at strong imbibition because of the competing effects between the capillary force and the viscous force.

Experimental assessment of the hydro-mechanical behaviour of a shale caprock during CO2 injection

The presented experimental study focuses on the hydro-mechanical characterisation of a shale caprock (Opalinus Clay) in contact with carbon dioxide. The objective of this paper, consists in the evaluation of the material's sealing capacity in terms of entry-pressure, mechanical behaviour and sensitivity of the transport properties to chemo-mechanical effects induced by gaseous and liquid CO2 injection. Two types of Opalinus Clay core samples are tested; shaly and carbonate-rich. The sealing capacity has been evaluated on the shaly OPA according to the stepwise and the residual methods and compared to the results from mercury intrusion porosimetry. The obtained results and the differences associated to the different involved physical processes are discussed and compared with literature data. Injection tests carried out in saturated and unsaturated conditions have revealed that sub-critical CO2 propagation in a water saturated material is not associated with generation of fractures. On the other hand, the generation of capillary forces is affecting the mechanical behaviour beside the sealing capacity. The impact of chemical effects on the permeability of both types of OPA is analysed with long-term CO2 injection tests, where no significant variations of permeability are measured during the exposure time investigated. The challenges related to this type of analysis with laboratory scale experiments are illustrated and new insights on the behaviour of Opalinus Clay when subjected to injection of a non-wetting fluid are highlighted.