Relative Permeability Coefficients Research Articles

Assisted Upscaling of Miscible CO2-Enhanced Oil Recovery Floods Using an Artificial Neural Network-Based Optimisation Algorithm

Due to the high computing cost of the fine-scale compositional simulations needed to effectively model miscible CO2 flooding, upscaling techniques are needed to approximate the behaviour of these fine-scale grids on more realistic coarse-scale models. The use of transport coefficients to better represent small-scale interactions, such as the time-dependent flux of the components within the hydrocarbon phases (molecular diffusion), and the pseudoisation of relative permeabilities to ensure the matching of large-scale effects, such as the volumetric fluxes of the phases, are two of these procedures. Most times, a mismatch between the phase fluxes of the integrated fine-scale and that of the coarse-scale is observed. By adjusting or calibrating some of the generated coarse-scale pseudo functions, such as the transport coefficients, absolute permeability, or relative permeability endpoints, the accuracy of the upscaling results can be improved. This procedure can be treated a reservoir history matching problem which is typically computationally expensive. In this study, we provide a framework for representing the dynamics of small-scale molecular diffusion and macro-scale heterogeneity-induced channelling related to miscible CO2 displacements on upscaled coarser grid reservoir models. The method used was based on the pseudoisation of relative permeability and transport coefficients and was applied to two benchmark reservoir models from the Society of Petroleum Engineers (SPE). Our results demonstrated that using effectively calibrated transport coefficients improved the upscaling results, so that the calculated pseudo-relative permeability functions can be ignored. We proposed a unique approach to upscaling miscible floods that utilised a genetic algorithm and a neural-network-based proxy model to minimise the associated computing cost. The data-driven approximation model considerably decreased the computing cost associated with the assisted tuning technique, and the optimisation algorithm was used to reduce the error between the predictions of the upscaled models. In conclusion, the methodology described in this study effectively captured the small- and large-scale behaviour related to the miscible displacements on upscaled coarse-scale reservoir models while reduced associated computational costs.

Effects of sodium carbonate on self-healing properties of cement–slag–limestone powder ternary cementitious material

Cement–slag–limestone ternary cementitious materials are cement-based materials with significant potential for applications, it exhibits extremely low carbon emissions and excellent workability. Now, to lower CO2 emissions of concrete industry the use of ternary blends is gradually popularized, and the investigation of their self-healing properties of it is of interest to the construction industry. So far, the effect of sodium carbonate on the self-healing of cement-slag-limestone ternary cementitious materials is not clear. In this study, we prepared ternary blends with different concentrations of sodium carbonate (0 %, 2.5 %, and 5 %) were prepared. And systematically investigated the self-healing ability of the samples through a combined macro-microscopic experimental method. Macroscopic aspects: The compressive strength of the samples was tested after 28 days of curing, and the changes in the crack width and relative permeability coefficients were recorded during the self-healing period. Microscopic aspects: The samples were examined for calcium and sodium ion leaching using an inductively coupled plasma optical emission spectrometer. The crack interiors were observed using a scanning electron microscope. And the healing compounds were tested using X-ray diffraction and attenuated total reflection Fourier transform infrared spectroscopy. The result shows, sodium carbonate reduced the 28-day compressive strength of the slurries and the number of leached calcium ions. The addition of 2.5 % sodium carbonate promoted the early permeability resistance repair of the ternary cement, and the addition of 5 % sodium carbonate reduced the self-healing ability of the ternary cement.

A New Multiscale Computational Model for Low Salinity Waterflooding in Clay Bearing Sandstones

We develop a new multiscale model to compute effective properties such as relative permeability, contact angle and partition coefficients in low salinity enhanced oil recovery processes for two-phase flow in sandstones containing reactive surfaces of kaolinite clay. In this setting, we construct a three-scale approach which entails the local nanoscale description ruled by the electro-chemistry of a confined electrolyte solution containing Na+, $$Ca^{2+}$$ , $$H^+$$ , $$Cl^-$$ and $$OH^-$$ ions residing between bounded crude-oil droplets at residual saturation and clay substrate. Our analysis focuses on the case of surface complexation geochemical reactions between the ionic species of the invading water and the electrically charged kaolinite and oil–water interfaces. In this scenario, we construct a local electric double layer problem for the electric potential based on a non-symmetric Poisson–Boltzmann equation supplemented by nonlinear boundary conditions with the magnitude of the surface charge strongly dictated by the geochemical reactions. By invoking the local mechanical equilibrium of the electrolyte solution and solving numerically the nonlinear problem using the finite element method, we compute the local ionic profiles and reconstruct numerically the disjoining pressure and adsorption isotherms for each ionic species for a wide range of brine compositions and pH of the water phase. Furthermore, combining the disjoining pressure results with the Frumkin/Derjaguin wetting theory allows to compute the dependence of the contact angle on wettability, pH and salinity. Subsequently, the formal homogenization procedure is adopted to upscale the pore-scale flow and ion transport to the macroscale giving rise to a new Darcy scale coupled flow/transport model. The hyperbolic part of the nonlinear homogenized model is solved analytically in an 1D example of enhanced oil recovery.

BUILDING A LOW-LEVEL MODEL FOR TWO-PHASE FILTRATION

Background The article proposes a method for constructing low-level models for two-phase filtration based on a combination of a finite-difference solution and a detailed spatial approximation, which makes it possible to use approximating models for solving problems of optimal control of operational parameters of an oil reservoir. The combined motion of two phases is considered: wetting and non-wetting liquids. Aims and Objectives The two-phase filtration process is non-stationary for incompressibility of liquids and pore space. The phase saturations change and the relative permeability coefficients of the phases change as the fluids move. Therefore, at constant intensities of sources of liquids, the pressure field in the reservoir will vary with time. To construct an approximate solution based on lower-level models, the following approach is proposed. The considered area is divided into larger blocks, which allows to quickly carry out the calculation based on the finite-difference method. Spatial detailing is based on radial approximators associated with the calculated parameters of the integrated blocks. Results The distribution is obtained by calculation by the finite difference method on a 256x256 grid. It is revealed that, compared with the initial period of the process, there was a significant flooding of the reservoir. The results of the comparison are presented, from which it follows that the approximation of water saturation has detailed spatial detailing. The change in water saturation in the middle section of the region is shown. The presented method for constructing low-level models for two-phase filtration, based on a combination of a finite-difference solution and a detailed approximation, revealed the feasibility and continuity of using approximating models to solve the problems of rational experimental control of oil reservoir parameters.

Cooperativity and allostery in aquaporin 0 regulation by Ca2+

Aquaporin 0 (AQP0) is essential for eye lens homeostasis as is regulation of its water permeability by Ca2+, which occurs through interactions with calmodulin (CaM), but the underlying molecular mechanisms are not well understood. Here, we use molecular dynamics (MD) simulations on the microsecond timescale under an osmotic gradient to explicitly model water permeation through the AQP0 channel. To identify any structural features that are specific to water permeation through AQP0, we also performed simulations of aquaporin 1 (AQP1) and a pure mixed lipid bilayer under the same conditions. The relative single-channel water osmotic permeability coefficients (pf) calculated from all of our simulations are in reasonable agreement with experiment. Our simulations allowed us to characterize the dynamics of the key structural elements that modulate the diffusion of water single-files through the AQP0 and AQP1 pores. We find that CaM binding influences the collective dynamics of the whole AQP0 tetramer, promoting the closing of both the extracellular and intracellular gates by inducing cooperativity between neighboring subunits.

An experimental study of two-phase flow behaviour through pipes and hydraulically-fractured rock specimens

The use of foam-based fracturing fluids for hydraulic fracturing has been identified as a promising technique to extract unconventional natural gases. However, lack of knowledge of foam properties and the two-phase flow behaviour of foam under high pressure makes it challenging to use in field conditions. Therefore, this comprehensive study was conducted to investigate (1) the properties and flow behaviour of foams, under relatively high-pressure (7 MPa) conditions using a newly-developed high-pressure viewing window and (2) two-phase flow behaviour through fractured rock using the high-pressure triaxial test apparatus. Fracture permeability tests were conducted for a series of confining and injection pressures, to evaluate the relative permeability coefficients. The experimental results show that foam flow can have bubble, plug, slug or disperse flow patterns, based on the gas flow rate, at a constant pressure. Moreover, the results show that, at pressures above 1 MPa, the foam flow is almost homogeneous with a fine texture, which is favourable for proppant transport. The findings of this study reveal that, during foam injection into a fractured rock mass under two-phase conditions, the nitrogen phase dominates the flow rate while having higher relative permeability coefficients than the water phase, irrespective of the confining pressure.

English

Waterflooding has become by far the most widely applied method for enhanced oil recovery, accounting for more than half of oil production worldwide. Changes in the wettability of a porous medium and the chemical composition of the wetting fluid result to changes in oil recovery. In recent time, pore-network modeling has been used increasingly to study the effect of wettability on waterflood oil recovery and multiphase flow properties in different types of petroleum reservoirs. Starting from single pore models of fluid arrangements, computations of relative permeability, interfacial area, mass dissolution rate and many other physical properties have been made. Using realistic representations of the pore spaces of various rock systems, it is now possible to predict many petro-physical properties that govern fluid flow and transport in petroleum reservoir rock systems. Such properties include porosity, permeability, waterflood relative permeability, capillary pressure, phase saturations, and fluid transfer coefficients. This review looks briefly into some of the successes made so far on pore network modeling, with an emphasis on models of wettability trends and oil recovery by waterflooding. Key words: Wettability, pore scale modeling, petroleum reservoir, waterflooding, oil recovery.

Molecular transport through membranes: Accurate permeability coefficients from multidimensional potentials of mean force and local diffusion constants.

Estimating the permeability coefficient of small molecules through lipid bilayer membranes plays an important role in the development of effective drug candidates. In silico simulations can produce acceptable relative permeability coefficients for a series of small molecules; however, the absolute permeability coefficients from simulations are usually off by orders of magnitude. In addition to differences between the lipid bilayers used in vitro and in silico, the poor convergence of permeation free energy profiles and over-simplified diffusion models have contributed to these discrepancies. In this paper, we present a multidimensional inhomogeneous solubility-diffusion model to study the permeability of a small molecule drug (trimethoprim) passing through a POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) lipid bilayer. Our approach improves the permeation model in three ways: First, the free energy profile (potential of mean force, PMF) is two-dimensional in two key coordinates rather than simply one-dimensional along the direction normal to the bilayer. Second, the 2-D PMF calculation has improved convergence due to application of the recently developed transition-tempered metadynamics with randomly initialized replicas, while third, the local diffusivity coefficient was calculated along the direction of the minimum free energy path on the two-dimensional PMF. The permeability is then calculated as a line integral along the minimum free energy path of the PMF. With this approach, we report a considerably more accurate permeability coefficient (only 2-5 times larger than the experimental value). We also compare our approach with the common practice of computing permeability coefficients based only on the translation of the center of mass of the drug molecule. Our paper concludes with a discussion of approaches for minimizing the computational cost for the purpose of more rapidly screening a large number of drug candidate molecules.

Characterization and performance analysis of a chiral-metamaterial channel with Giant Optical Activity for terahertz communications

Technology in the THz frequency band has progressed rapidly in the last few years. The THz frequency band offers greater communication bandwidth than microwaves frequencies, and is becoming a standard for nanoscale communications. Traditional channel models for lower frequencies do not take into consideration specific properties as the very high molecular absorption or the very high reflection loss. In addition, in a propagation medium exhibiting a Giant Optical Activity, it is also important to derive the characteristics of the channel affected by chirality effects. This phenomenon occurs in particular material known as chiral-metamaterials in the (4–10) THz band.The main contribution of this paper consists in the analysis of specific parameters of a chiral-metamaterial, such as the relative electrical permittivity, magnetic permeability and chirality coefficients. These parameters are considered for the channel model derivation both in Line-of-Sight and No Line-of-Sight propagation.The chiral effect affects the channel through the presence of spectral windows, due to peaks of resonance of chiral parameter. Performance analysis of the chirality-affected channel is assessed in terms of (i) channel capacity, (ii) propagation delay, (iii) coherence bandwidth, and (iv) symbol rates, for different distances and propagation modes.

Corneal health and contact lens wear: Ion chromatography as an electrolyte probe

Purpose: Tear osmolarity and the concentrations of ocular electrolytes in the eye are known to influence corneal health. Similarly, corneal cells are known to be sensitive to changes in electrolyte balance. Ion transport through contact lenses can influence electrolyte equilibration between preand post-lens tear film. Until now no suitable technique has been identified to quantify these effects. This study utilised ion chromatography to examine multiple ion transport through lenses and the measurement of ex-vivo tear samples. Methods:AmodifiedDionex ion chromatographenabled simultaneous measurement of Na+/K+/Ca2+ and Mg2+ concentrations in both single (5 l) tear samples and lens/membrane permeation studies. In addition to commercial contact lenses, conventional HEMA membranes (40% water) and acrylamide-based corneal model hydrogel membranes (ca 90% water) were mounted in purpose-designed permeability cells and the transport of mixed electrolytes (e.g. 0.25M NaCl, KCl and CaCl2) measured. Results: In baseline studies, the relative ratio of the main tear cations measured in healthy tear film samples was found to be Na+:K+:Ca2+:Mg2+ =140:11:1.2:1. This accord with the observation that the range of K+ concentrations in tears (ca 15–30mM) is high and Ca2+ and Mg2+ concentrations (ca 0.4–0.8 and 0.5–1.1mM) is low, relative to serum. The relative permeability coefficients of lenses and membranes were consistent (i.e. NaCl <KCl » CaCl2) ranging between 141.2×10−7: 148.2×10−7: 98.2×10−7 cm2/s (±5% for 90% acrylamide based hydrogel) and 2.8×10−7:3.2×10−7:0.7×10−7 cm2/s (±5% for 40% HEMA hydrogel). Conclusions: Ion chromatography enables tear electrolytes to be accurately monitored in 5 l samples. This, coupled with tear envelope sampling, provides a means of correlating clinical signs and symptoms with post-lens electrolyte concentrations and the ion permeability coefficients of individual lenses. Anisa Mahomed completed an MEng in Chemical Engineering and then obtained her PhD from the Biomaterials Research Group at Aston University. Her thesis discussed the aspects of the fabrication of novel hydrogels for dermal and ocular applications. She is currently a postdoctoral researcher and her interests include investigating factors that affect the uptake, release and transport of various species from hydrogels and developing analytical techniques to enable the understanding of clinical adverse events related to the use multipurpose solutions.

Plasma protein influx in contact lens wear

Purpose: Tear osmolarity and the concentrations of ocular electrolytes in the eye are known to influence corneal health. Similarly, corneal cells are known to be sensitive to changes in electrolyte balance. Ion transport through contact lenses can influence electrolyte equilibration between preand post-lens tear film. Until now no suitable technique has been identified to quantify these effects. This study utilised ion chromatography to examine multiple ion transport through lenses and the measurement of ex-vivo tear samples. Methods:AmodifiedDionex ion chromatographenabled simultaneous measurement of Na+/K+/Ca2+ and Mg2+ concentrations in both single (5 l) tear samples and lens/membrane permeation studies. In addition to commercial contact lenses, conventional HEMA membranes (40% water) and acrylamide-based corneal model hydrogel membranes (ca 90% water) were mounted in purpose-designed permeability cells and the transport of mixed electrolytes (e.g. 0.25M NaCl, KCl and CaCl2) measured. Results: In baseline studies, the relative ratio of the main tear cations measured in healthy tear film samples was found to be Na+:K+:Ca2+:Mg2+ =140:11:1.2:1. This accord with the observation that the range of K+ concentrations in tears (ca 15–30mM) is high and Ca2+ and Mg2+ concentrations (ca 0.4–0.8 and 0.5–1.1mM) is low, relative to serum. The relative permeability coefficients of lenses and membranes were consistent (i.e. NaCl <KCl » CaCl2) ranging between 141.2×10−7: 148.2×10−7: 98.2×10−7 cm2/s (±5% for 90% acrylamide based hydrogel) and 2.8×10−7:3.2×10−7:0.7×10−7 cm2/s (±5% for 40% HEMA hydrogel). Conclusions: Ion chromatography enables tear electrolytes to be accurately monitored in 5 l samples. This, coupled with tear envelope sampling, provides a means of correlating clinical signs and symptoms with post-lens electrolyte concentrations and the ion permeability coefficients of individual lenses. Anisa Mahomed completed an MEng in Chemical Engineering and then obtained her PhD from the Biomaterials Research Group at Aston University. Her thesis discussed the aspects of the fabrication of novel hydrogels for dermal and ocular applications. She is currently a postdoctoral researcher and her interests include investigating factors that affect the uptake, release and transport of various species from hydrogels and developing analytical techniques to enable the understanding of clinical adverse events related to the use multipurpose solutions.

Investigation of Generalized Relative Permeability Coefficients for Electrically Assisted Oil Recovery in Oil Formations

Evaluation of relative permeability coefficients is one of the key steps in reliable simulation of two-phase flow in porous media. An extensive body of work exists on evaluation of these coefficients for two-phase flow under pressure gradient. Oil transport under an applied electrical gradient in porous media is also governed by the principles of two-phase flow, but is less understood. In this paper, relative permeability coefficients under applied electric field are evaluated for a specific case of two- phase fluid flow in water-wet porous media, where the second fluid phase is oil. It is postulated that the viscous drag on the oil phase, exerted by the electro-osmotic flow of the water phase, is responsible for the transport of oil in the absence of a pressure gradient. Reliable prediction of the flow patterns necessitates accurate representation and determination of the relative permeability coefficients under the electrical gradient. The contribution of each phase to the flow is represented mathematically, and the relative permeability coefficients are evaluated through electro-osmotic flow measurements conducted on oil bearing rock cores.

Large scale applicability of the steam-over-solvent injection in fractured reservoirs (SOS-FR) method: Optimal operating conditions through numerical simulation

Heavy oil reserves are considered to be the upcoming hydrocarbon resource. Yet, more efficient methods are needed as there are substantial economic and environmental drawbacks to the sole injection of steam and solvents. A combined application of these methods yielded promising results in the laboratory experiments. But optimal application conditions and cost lowering options need to be determined. Steam-over-solvent injection in fractured reservoirs (SOS-FR) is a recently proposed method, which consists of an alternate injection of steam and hydrocarbon solvents to improve oil recovery over steam injection and to accelerate the solvent retrieval rate. This method was suggested to take advantages of sole thermal and solvent recovery methods in a staged technique and also to reduce the drawbacks of such methods using a hybrid one. For simplicity, the initial tests were done for hot-water conditions instead of steam and liquid solvents (Al-Bahlani and Babadagli, 2008, Al-Bahlani and Babadagli, 2009a, Al-Bahlani and Babadagli, 2009b, Al-Bahlani and Babadagli, 2011b). In our modification to this method, we introduced CO2 as an alternative to hydrocarbon solvents for only one pressure and temperature condition (Naderi and Babadagli, 2012a, Naderi and Babadagli, 2012b). The initial results of this study showed a moderate recovery of 50% OOIP on average for unfavorable matrix conditions (oil wet). In the present study, the SOS-FR applications with CO2 were tested at various conditions numerically and with different timings to improve recovery. First, the effect of different parameters was studied to obtain the best match between the simulation and experimental results. This exercise not only provided data for field scale simulations (relative permeability and diffusion coefficients) but also clarified the impact of different rock and fluid properties on the mechanics of the proposed EOR technique. Finally, an optimization scheme was suggested for field scale applications. In this exercise, a field scale numerical model of experiments was performed based on an experimentally validated core scale model and the optimal conditions (solvent type, application pressure and temperature and duration of cycles) were determined to maximize the recovery.

FEM Analyses for T‐H‐M‐M Coupling Processes in Dual‐Porosity Rock Mass under Stress Corrosion and Pressure Solution

The models of stress corrosion and pressure solution established by Yasuhara et al. were introduced into the 2D FEM code of thermo‐hydro‐mechanical‐migratory coupling analysis for dual‐porosity medium developed by the authors. Aiming at a hypothetical model for geological disposal of nuclear waste in an unsaturated rock mass from which there is a nuclide leak, two computation conditions were designed. Then the corresponding two‐dimensional numerical simulation for the coupled thermo‐hydro‐mechanical‐migratory processes were carried out, and the states of temperatures, rates and magnitudes of aperture closure, pore and fracture pressures, flow velocities, nuclide concentrations and stresses in the rock mass were investigated. The results show: the aperture closure rates caused by stress corrosion are almost six orders higher than those caused by pressure solution, and the two kinds of closure rates climb up and then decline, furthermore tend towards stability; when the effects of stress corrosion and pressure solution are considered, the negative fracture pressures in near field rise very highly; the fracture aperture and porosity are decreases in the case 1, so the relative permeability coefficients reduce, therefore the nuclide concentrations in pore and fracture in this case are higher than those in case 2.

Absorption and Metabolism of Chlorogenic Acids in Cultured Gastric Epithelial Monolayers

Gastric absorption of feruloylquinic acid and di-O-caffeoylquinic acid analogs has never been investigated despite their potential contribution to the proposed beneficial health effects leading to reduced risk of type 2 diabetes. Using a cultured gastric epithelial model, with an acidic apical pH, the relative permeability coefficients (P(app)) and metabolic fate of a series of chlorogenic acids (CGAs) were investigated. Mechanistic studies were performed in the apical to basal direction and demonstrated differential rates of absorption for different CGA subgroups. For the first time, we show intact absorption of feruloylquinic acids and caffeoylquinic acid lactones across the gastric epithelium (P(app) ∼ 0.2 cm/s). Transport seemed to be mainly by passive diffusion, because good linearity was observed over the incubation period and test concentrations, and we speculate that a potential carrier-mediated component may be involved in uptake of certain 4-acyl CGA isomers. In contrast, absorption of intact di-O-caffeoylquinic acids was rapid (P(app) ∼ 2-10 cm/s) but nonlinear with respect to time and concentration dependence, which was potentially limited by interaction with an efflux transporter and/or pH gradient dependence. For the first time, methylation is shown in gastric mucosa. Furthermore, isoferulic acid, dimethoxycinnamic acid, and ferulic acid were identified as novel gastric metabolites of CGA biotransformation. We propose that the stomach is the first location for the release of hydroxycinnamic acids, which could explain their early detection after coffee consumption.

Impermeability of Wet-Sieving Fine Aggregate Concrete Made from Ordinary Concrete

The research is part of wet-sieving concrete technique for building thermal insulated reinforced concrete composite wall. The fine aggregate concrete is made from ordinary concrete passing sieve with square mash of 15 mm for casting surface concrete layer of the wall, the recomposed concrete is made of residual concrete stayed on sieve and ordinary concrete for casting reinforced concrete structural wall. The impermeability of fine aggregate concrete and recomposed concrete are measured by water permeation method and chloride-ion permeation method, the relative permeability and chloride-ion diffusion coefficients of concrete are determined. Based on the test, the effects of the changes of aggregate series, sand ratio and cement paste on the impermeability of concrete are analyzed.

Transient and steady-state relative permeabilities from two-phase flow experiments in planar pore networks

The water k rw and oil k ro relative permeability curves of a glass-etched planar pore network are estimated with history matching from transient displacement experiments performed at varying values of the capillary number, Ca, for two fluid systems: one of intermediate and one of strong wettability. The transient k rw , k ro are compared to corresponding ones measured with the steady-state method on the same porous medium [Avraam DG, Payatakes AC. Flow regimes and relative permeabilities during steady-state two-phase flow in porous media. J Fluid Mech 1995;293:207–36; Avraam DG, Payatakes AC. Generalized relative permeability coefficients during steady-state two-phase flow in porous media and correlation with the flow mechanisms. Transport Porous Med 1995;20:135–68; Avraam DG, Payatakes AC. Flow mechanisms, relative permeabilities, and coupling effects in steady-state two-phase flow through porous media. The case of strong wettability. Ind Eng Chem Res 1999;38:778–86.], and potential differences from them are interpreted in the light of the differences between the transient growth pattern, and the steady-state two-phase flow regime. For intermediate wettability, the transient k ro and k rw exceed the corresponding steady-state functions at low Ca values and have the tendency to become smaller than the steady-state ones at high Ca values. For strong wettability, the transient k ro and k rw are increasing functions of Ca, the transient k ro is higher than the steady-state one, whereas the transient k rw decreases substantially and becomes lower than the steady-state one at low Ca values. The dynamic capillary pressure estimated from transient experiments is a decreasing function of Ca in agreement with previous theoretical and experimental studies.

Numerical simulation for separation of multi-phase immiscible fluids in porous media

Based on a lattice Boltzmann method and general principles of porous flow, a numerical technique is presented for analysing the separation of multi-phase immiscible fluids in porous media. The total body force acting on fluid particles is modified by adding relative permeability in Nithiarasu's expression with an additional surface tension term. As a test of this model, we simulate the phase separation for the case of two immiscible fluids. The numerical results show that the two coupling relative permeability coefficients K12 and K21 have the same magnitude, so the linear flux-forcing relationships satisfy Onsager reciprocity. Phase separation phenomenon is shown with the time evolution of density distribution and bears a strong similarity to the results obtained from other numerical models and the flows in sands. At the same time, the dynamical rules in this model are local, therefore it can be run on massively parallel computers with well computational efficiency.

Permeation of Small Molecules through a Lipid Bilayer: A Computer Simulation Study

To reach their biological target, drugs have to cross cell membranes, and understanding passive membrane permeation is therefore crucial for rational drug design. Molecular dynamics simulations offer a powerful way of studying permeation at the single molecule level, yielding detailed dynamic and thermodynamic data. Biological membranes have a very inhomogeneous character and a highly anisotropic behavior. Starting from a computer model proven to reproduce the physical properties of such a complex system, the permeation of small organic molecules across a lipid bilayer model has been studied. Free energy profiles and diffusion coefficients along the bilayer normal have been calculated for small organic molecules by means of all-atom molecular dynamics (MD) simulations constraining the compounds at chosen depths inside the membrane. These data also allow for the calculation of permeability coefficients, the results for which have been compared with experimental data. The calculated permeability coefficients are generally 1 order of magnitude larger than the equivalent experimental data, but the molecules' relative permeability coefficients are reproduced.

Immiscible displacement in a channel: simulations of fingering in two dimensions

In this paper, we use a lattice Boltzmann (LB) multiphase/multicomponent model to study the flow of two immiscible fluids with different viscosities. The approach is first validated for a two-dimensional layered flow. The velocity profiles and the relative permeability coefficients are compared with the analytic results. We then apply this method to studying fingering in a two-dimensional channel where one fluid is displaced by another. The effects of viscosity ratio, capillary number, and wettability are investigated. The simulation results show that with the increase of the viscosity ratio or capillary number, both the finger width and the slip distance of the contact lines decrease, while the finger length increases. With the decrease of the wettability of the displacing fluid, the finger length and its change rate with time increase while the slip distance of the contact lines and its change rate with time decrease, and the minimum capillary number to form a stable finger decreases. Hence the finger growth is enhanced when the displacing fluid is nonwetting to the wall and otherwise suppressed. An indented part near the beginning of the fingers is clearly observed when a wetting fluid is displacing a nonwetting one. The finger width, however remains nearly unchanged when the wettability of the fluids changes.