Porous Media Systems Research Articles

Flow performance of a self-assembly biopolymer/β-cyclodextrin/surfactant CO2 foam system in pollutant-free porous media as a flushing agent for in-situ soil remediation applications

The remediation of hydrocarbon contaminated soils is an active research field, in which different remediation technological approaches are currently under evaluation. In this research, a new technology based on a self-assembly biopolymer/β-Cyclodextrin/surfactant (bP/βCD/S) CO2 foam system was evaluated for in-situ soil remediation applications. The biopolymer and surfactant used in this study were xanthan gum and dodecyl trimethylammonium chloride (DTAC), respectively. The stability of the bP/βCD/S and the baseline biopolymer/surfactant, bP/S, CO2 foam systems at different brine salinity and hardness concentrations was evaluated in bulk. Subsequently, the flow behavior and the stability of both foam systems were evaluated through displacement experiments employing unconsolidated sand at different brine concentrations (2.1 and 8.4 wt%) at ambient temperature. The mobility control performance and the stability of both foam systems in contaminant-free sand were evaluated during the displacing experiments using the resistance and the residual resistance factors as performance indicators. The bulk stability tests demonstrate that the bP/βCD/S CO2 foam system displays higher stability relative to the bP/S foam system in both 2.1 wt% (e.g., salinity = 1.73 wt% and hardness = 0.37 wt%) and 8.4 wt% (e.g., salinity = 6.92 wt% and hardness = 1.48 wt%) brine systems. Likewise, the displacement experiments show that the bP/βCD/S CO2 system offers superior mobility control functionality and stability during flow in porous media relative to the baseline polymer/surfactant foam regardless of the brine ionic strength. Consequently, the bP/βCD/S CO2 foam system shows great potential as an effective integrated technology for in-situ soil remediation applications.

H\xf6lder regularity for porous medium systems

We establish Hölder continuity for locally bounded weak solutions to certain parabolic systems of porous medium type, i.e. ∂tu-div(m|u|m-1Du)=0,m>0.\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$\\begin{aligned} \\partial _t \\mathbf{u}-\\mathrm{div}(m|\\mathbf{u}|^{m-1}D\\mathbf{u})=0,\\quad m>0. \\end{aligned}$$\\end{document}As a consequence of our local Hölder estimates, a Liouville type result for bounded global solutions is also established. In addition, sufficient conditions are given to ensure local boundedness of local weak solutions.

Experimental study of premixed methane/air gas suppression by sliding porous media with different elasticity coefficients

Based on the self-designed sliding porous media system, the suppression effect of sliding porous devices with different elastic coefficients and different pore diameter on the propagation characteristics of premixed methane/air explosions with φ = 1 was investigated. The results show that the sliding porous media has a significant inhibition effect on the explosion flame and overpressure, which can reduce the propagation speed and duration of the flame and the maximum value of the downstream overpressure. The advantage of sliding porous media is to increase the contact time and distance between the device and the flame and shock wave produced by explosion, so as to increase the explosion energy consumption and achieve the purpose of explosion suppression.

Impact of Biosurfactants, Surfactin, and Rhamnolipid Produced from Bacillus subtilis and Pseudomonas aeruginosa, on the Enhanced Recovery of Crude Oil and Its Comparison with Commercial Surfactants

The continuous production of crude oil over the past several years has matured numerous oil reservoirs worldwide. The current study aims to increase the recovery of low-waxy-crude oil using biosurfactants produced by microorganisms. Ex situ biosurfactant-induced microbial-enhanced oil recovery (MEOR) is addressed in this work, and the substantial findings will be useful to predict its performance in reservoirs. Experiments were carried out to investigate the performance of MEOR in porous media using synthetic surfactants and biosurfactants. Mass spectrometry results show that the microorganisms Pseudomonas aeruginosa and Bacillus subtilis produced biosurfactants, such as rhamnolipid and surfactin with molecular weights of 1016 and 355 Da, respectively. The results indicate that higher-oil-recovery efficiency can be achieved using biosurfactants. The concentration of 200 ppm surfactin showed 15.43% of enhancement in oil recovery, whereas 200 ppm rhamnolipid exhibited 15.47% increase in the recovery of oil. However, at the same concentration, cetyltrimethylammonium bromide and sodium dodecyl sulfate enhanced the recovery of crude oil by 7 and 8.82%, respectively. The efficiency of biosurfactants in subsiding the interfacial tension between the crude oil and water system in porous media was observed to be the main cause for improved oil recovery. Enhanced oil recovery even at low concentrations and stability at high salinities, pH values, pressures, and temperatures make surfactin and rhamnolipid excellent candidates as biosurfactants and offer good prospects for their use in MEOR.

Existence and weak–strong uniqueness of solutions to the Cahn–Hilliard–Navier–Stokes–Darcy system in superposed free flow and porous media

We study a diffuse interface model for two-phase flows of similar densities in superposed free flow and porous media. The model consists of the Navier–Stokes–Cahn–Hilliard system in free flow and the Darcy–Cahn–Hilliard system in porous media coupled through a set of domain interface boundary conditions. These domain interface boundary conditions include the nonlinear Lions interface condition and the linear Beavers–Joseph–Saffman–Jones interface condition. We establish global existence of weak solutions in three dimension. We also show that the strong solution if exists agrees with the weak solutions.

Convective carbon dioxide dissolution in a closed porous medium at high-pressure real-gas conditions

We combine modeling and measurements to investigate the dynamics of convective carbon dioxide (CO2) dissolution in a pressure-volume-temperature cell, extending a recent study by Wen et al. (J. Fluid Mech., vol. 854, 2018, pp. 56–87) at low-pressure under ideal-gas conditions to high-pressure and real-gas conditions. Pressure-dependent compressibility and solubility are included to model the evolution of CO2 concentration in the gas phase and at the interface, respectively. Simple ordinary-differential-equation models are developed to capture the mean behavior of the convecting system at large Rayleigh number and are then verified by using both numerical simulations and laboratory experiments. The prefactor for the linear scaling of convective CO2 dissolution is evaluated – for the first time – by using pressure-decay experiments in bead packs at reservoir conditions. The results show that our models could quantitatively predict the process of the convective CO2 dissolution in pressure-decay experiments. Moreover, the results also reveal that for increasing gas pressure in closed systems, the negative feedback of the pressure drop – resulting from the dissolution of CO2 in the liquid – is weakened due to the decrease of the solubility constant at real-gas conditions. Our analysis provides a new direction for determination and validation of the convective dissolution flux of CO2 in porous media systems.

Flagella and Their Properties Affect the Transport and Deposition Behaviors of Escherichia coli in Quartz Sand.

The effects of flagella and their properties on bacterial transport and deposition behaviors were examined by using four types of Escherichia coli (E. coli) with or without flagella, as well as with normal or sticky flagella. Packed column, quartz crystal microbalance with dissipation, visible parallel-plate flow chamber system, and visible flow chamber packed with porous media system were employed to investigate the deposition mechanisms of bacteria with different properties of flagella. We found that the presence of flagella favored E. coli deposition onto quartz sand/silica surfaces. Moreover, by changing the porous media porosity and directly observing the bacterial deposition process, local sites with high roughness, narrow flow channels, and grain-to-grain contacts were found to be the major sites for bacterial deposition. Particularly, flagella could help bacteria swim near and then deposit at these sites. In addition, we found that due to the stronger adhesive forces, sticky flagella could further enhance bacterial deposition onto quartz sand/silica surfaces. Elution experiments indicated that flagella could help bacteria attach onto sand surfaces more irreversibly. Clearly, flagella and their properties would have obvious impacts on the transport/deposition behaviors of bacteria in porous media.

A physically-based entropy production rate method to simulate sharp-front transport problems in porous medium systems

Sharp-front problems arising from equations that tend toward a hyperbolic limit occur routinely in modeling transport phenomena in porous medium systems. Numerical methods to approximate hyperbolic conservation equations are mature for finite volume methods. However, irregularly shaped domains make finite element methods (FEMs) an attractive approach for many subsurface problems. For conforming FEM approaches, sharp fronts continue to pose a computational challenge. We build on recent work to develop and evaluate an entropy viscosity approach. Recent theoretical advancements have resulted in the formulation of entropy inequality equations for many porous medium problems, which we use to compute a physically-based entropy production rate for both linear and nonlinear species transport problems. The entropy production rate is in turn used to add dissipation to the approximation of the hyperbolic operator using an entropy-viscosity formulation. We demonstrate how existing, problem-specific theoretical results can be leveraged in a generic and efficient numerical method to create problem-specific dissipation functions.

Study of Rheological Property and Flow Behavior for Nanoparticles Enhanced VES System in Porous Media

In this paper, a composite sample (VES and SiO2 nanoparticle) was used to overcome the deficiencies of polymer. The rheological character of the VES/nanoparticles hybrid and flow behavior in porous media were examined. It was found that SiO2 nanoparticles exhibited viscosifying action and improved the oil tolerance. In addition, the VES solution without nanoparticles showed a lower capacity to recover oil, which might be attributed to the fact that wormlike micelles would be destroyed in crude oil. On the contrary, an enhanced oil recovery of 9.68% was achieved in the composited experiment for the VES sample with nanoparticles which is relatively stable with oil.

Mechanistic modeling of vascular tumor growth: an extension of Biot’s theory to hierarchical bi-compartment porous medium systems

Existing continuum multiphase tumor growth models typically do not include microvasculature, or if present, this is modeled as a non-deformable network of vessels. Vasculature behavior and blood flow are usually non-coupled with the underlying tumor phenomenology from the mechanical viewpoint; hence, phenomena like vessel compression/occlusion modifying microcirculation and oxygen supply cannot be taken into account. Here, the tumor tissue is modeled as a reactive bi-compartment porous medium: the extracellular matrix constitutes the solid scaffold; blood flows in the vascular porosity, whereas the extravascular porous compartment is saturated by two cell phases and interstitial fluid (mixture of water and nutrient species). The pressure difference between blood and the extravascular overall pressure is sustained by vessel walls and drives shrinkage or dilatation of the vascular porosity. Model closure is achieved thanks to a consistent non-conventional definition of the Biot’s effective stress tensor. Angiogenesis is modeled by introducing a vascularization state variable and accounting for tumor angiogenic factors and endothelial cells. Closure relationships and mass exchange terms related to vessel formation are detailed in a numerical example reproducing the principal features of angiogenesis. This example is preceded by a first pedagogical numerical study on one-dimensional bio-consolidation. Results demonstrate that the bi-compartment poromechanical model is fully coupled (the external loads impact fluid flow in both porous compartments) and that it can serve as a basis for further applications like modeling of drug delivery and tissue ulceration.

COMPUTATIONAL METHODOLOGY TO ANALYZE THE EFFECT OF MASS TRANSFER RATE ON ATTENUATION OF LEAKED CARBON DIOXIDE IN SHALLOW AQUIFERS

Exsolution and re-dissolution of CO2 gas within heterogeneous porous media are investigated using experimental data and mathematical modeling. In a set of bench-scale experiments, water saturated with CO2 under a given pressure is injected into a 2-D water-saturated porous media system, causing CO2 gas to exsolve and migrate upwards. A layer of fine sand mimicking a heterogeneity within a shallow aquifer is present in the tank to study accumulation and trapping of exsolved CO2. Then, clean water is injected into the system and the accumulated CO2 dissolves back into the flowing water. Simulated exsolution and dissolution mass transfer processes are studied using both nearequilibrium and kinetic approaches and compared to experimental data under conditions that do and do not include lateral background water flow. The mathematical model is based on the mixed hybrid finite element method that allows for accurate simulation of both advection- and diffusion- dominated processes.

Influence of pressure on the formation process of CH4 hydrate in porous media below the freezing point

AbstractNatural gas hydrates are mainly stored in the pores of the sedimentary layer in permafrost regions, and the formation characters in porous media were particularly important for the exploitation and utilization of natural gas hydrates. So, it is essential to understand the formation process of methane hydrate in porous media below freezing point. In this study, the formation process of methane hydrate was studied in a closed system in porous media below freezing point. The results indicated that the initial pressure played an important role in the formation characteristics of methane hydrate in porous media below freezing point. The higher the initial pressure was, the larger the formation rate of methane hydrate. And the maximum formation rate attained 6.46 × 10−4 mol/h when the initial pressure was 9.0 MPa under the same temperature and particle size conditions. Furthermore, the final conversion rate was larger at higher initial pressure and the final conversion rate attained 56.5% at an initial pressure of 9.0 MPa. Furthermore, the pressure disturbance could improve the formation process of methane hydrate and the final conversion rate was larger to some extent. The relevant results will provide a theoretical reference for natural gas hydrates exploitation.

Foam Quality of Foams Formed on Capillaries and Porous Media Systems

Foams are of great importance as a result of their expansive presence in everyday life—they are used in the food, cosmetic, and process industries, and in detergency, oil recovery, and firefighting. There is a little understanding of foam formation using soft porous media in terms of the quality of foam and foam formation. Interaction of foams with porous media has recently been investigated in a study by Arjmandi-Tash et al., where three different regimes of foam drainage in contact with porous media were observed. In this study, the amount of foam generated using porous media with surfactant solutions is investigated. The aim is to understand the quality of foam produced using porous media. The effect of capillary sizes and arrangement of porous in porous media has on the quality of foam is investigated. This is then followed by the use of soft porous media for foam formation to understand how the foam is generated on the surface of the porous media and the effect that different conditions (such as concentration) have on the quality of the foam. The quality of foam is a blanket term for bubble size, liquid volume fraction, and stability of the foam. The liquid volume fraction is calculated using a homemade dynamic foam analyser, which is used to obtain the distribution of liquid volume fraction along with the foam height. Soft porous media does not influence substantially the rate of decay of foam produced, however, it decreases the average diameter of the bubbles, whilst increasing the range of bubble sizes due to the wide range of pore sizes present in the soft porous media. The foam analyser showed the expected behaviour that, as the foam decays and becomes drier, the liquid volume fraction of the foam falls, and therefore the conductivity of foam also decreases, indicating the usefulness of the home-made device for future investigations.

Study on pore network model of porous media hydrate permeability

Considering the influence of hydrate on fluid flow in porous media, the relationship between hydrate saturation and absolute permeability of porous media is studied by using pore network model. The absolute permeability of hydrate free porous media is calculated and the convergence is studied. The absolute permeability of hydrate bearing porous media is calculated, the phase equilibrium migration is studied, and the pore network model of hydrate porous media system is calculated. The results show that: (1)when the throat number in the pore network model is greater than 3000, the calculation result is relatively stable; (2)under the condition that the throat diameter follows the log-normal distribution, the permeability decreases faster with the increase of the standard deviation; (3)the calculation results of the network model are consistent with the experimental data, which proves its feasibility to a certain extent.

Pore-scale simulation of salt fingers in porous media using a coupled iterative source-correction immersed boundary-lattice Boltzmann solver

In the conventional representative elementary volume-scale models, details of fluid movement, thermal transfer and mass transport in the porous media are relatively hard to capture, while the understanding of them is crucial in many diverse engineering and environmental applications such as running nuclear power facilities or pollutant diffusion in soil environment. In this paper, a pore-scale lattice Boltzmann method (LBM) modeling of double diffusion systems in saturated porous media is developed to investigate the role played by pore structure in the behavior of salt finger phenomena together with their fluid flow mechanism. An iterative source-correction immersed boundary method is developed to describe the solid skeleton with different boundary conditions for velocity field, heat transfer, and mass transport, respectively. The natural convection in a vertical annulus and the conjugate heat transfer problem in a two-layer horizontal annulus are employed to verify the accuracy and the applicability of the immersed boundary method for Dirichlet-type, Neumann-type and conjugate heat transfer boundary conditions, respectively. Comparisons between the present results and existing investigation show a very good agreement and demonstrate that the double diffusive process in porous media can be predicted with a good accuracy by the proposed model. Subsequently, the instability evolution process of salt finger-type of double diffusive convection in porous media is investigated, with a focus on the structure and behavior of salt fingers and the kinetic energy evolution. The obtained simulation results show that in saturated porous media, relatively large vertical mass fluxes can be generated even if the density distribution is of dynamical stability.

High Order Homogenization of the Stokes System in a Periodic Porous Medium

We derive high order homogenized models for the incompressible Stokes system in a cubic domain filled with periodic obstacles. These models have the potential to unify the three classical limit problems (namely the ``unchanged' Stokes system, the Brinkman model, and the Darcy's law) corresponding to various asymptotic regimes of the ratio $\eta\equiv a_{\epsilon}/\epsilon$ between the radius $a_{\epsilon}$ of the holes and the size $\epsilon$ of the periodic cell. What is more, a novel, rather surprising feature of our higher order effective equations is the occurrence of odd order differential operators when the obstacles are not symmetric. Our derivation relies on the method of two-scale power series expansions and on the existence of a ``criminal' ansatz, which allows to reconstruct the oscillating velocity and pressure $(\u_{\epsilon},p_{\epsilon})$ as a linear combination of the derivatives of their formal average $(\u_{\epsilon}^{*},p_{\epsilon}^{*})$ weighted by suitable corrector tensors. The formal average $(\u_\epsilon^{*},p_{\epsilon}^{*})$ is itself the solution to a formal, infinite order homogenized equation, whose truncation at any finite order is in general ill-posed. Inspired by the variational truncation method of \cite{smyshlyaev2000rigorous,cherednichenko2016full}, we derive, for any $K\in\N$, a well-posed model of order $2K+2$ which yields approximations of the original solutions with an error of order $O(\epsilon^{K+3})$ in the $L^{2}$ norm. Furthermore, the error improves up to the order $O(\epsilon^{2K+4})$ if a slight modification of this model remains well-posed. Finally, we find asymptotics of all homogenized tensors in the low volume fraction limit $\eta\rightarrow 0$ and in dimension $d\>3$. This allows us to obtain that our effective equations converge coefficient-wise to either of the Brinkman or Darcy regimes which arise when $\eta$ is respectively equivalent, or greater than the critical scaling $\eta_{\mathrm{crit}}\sim\epsilon^{2/(d-2)}$

Surfactant-Polymer Interactions in a Combined Enhanced Oil Recovery Flooding

The traditional Enhanced Oil Recovery (EOR) processes allow improving the performance of mature oilfields after waterflooding projects. Chemical EOR processes modify different physical properties of the fluids and/or the rock in order to mobilize the oil that remains trapped. Furthermore, combined processes have been proposed to improve the performance, using the properties and synergy of the chemical agents. This paper presents a novel simulator developed for a combined surfactant/polymer flooding in EOR processes. It studies the flow of a two-phase, five-component system (aqueous and organic phases with water, petroleum, surfactant, polymer and salt) in porous media. Polymer and surfactant together affect each other’s interfacial and rheological properties as well as the adsorption rates. This is known in the industry as Surfactant-Polymer Interaction (SPI). The simulations showed that optimum results occur when both chemical agents are injected overlapped, with the polymer in the first place. This procedure decreases the surfactant’s adsorption rates, rendering higher recovery factors. The presence of the salt as fifth component slightly modifies the adsorption rates of both polymer and surfactant, but its influence on the phase behavior allows increasing the surfactant’s sweep efficiency.

Quantification of the fluid saturation of three phases of NAPL/Water/Gas in 2D porous media systems using a light transmission technique

Determining transient fluid saturations in a multi-phase system is important for understanding the system’s flow characteristics and performing effective subsurface remediation. This paper investigates the models to quantify the fluid saturations of three phases of NAPL/Water/Gas in 2D porous media systems using a noninvasive light transmission technique. Four light intensity-saturation models (LISMs) to quantify fluid saturations from light intensities with only two parameters are proposed. Four LISMs can be divided into two classes: one based on assumption A of individual drainage and the other based on assumption B of combined drainage. LISMs are verified by two experiments conducted in NAPL invading into Water/Air and Water/Biogenic-Gas conditions, respectively. Results show that the model which based on assumption A and drainage of water first is the best type and show the strongest linear correlation between calculated results and measured data (R2 of 0.974 for air condition and R2 of 0.996 for biogenic gas condition). This study developed the innovative LISMs and applied them to three phases of NAPL/Water/Gas systems, which provides a methodology to acquire effective three fluid saturations in a continuous, quantitative, and real time way.

The study of bubble size distribution in reservoir during foam flooding and optimization design of gas alternating foaming liquid injection

Foam flooding is one of the enhanced oil recovery (EOR) technologies that have great development potentials. The theoretical models of foam flooding at present include empirical models and mechanism models. The empirical models usually simplify the blocking effect of foam system in porous medium as a reduction coefficient of fluid mobility (mainly for gas phase). The mechanism models introduce the processes of foam propagation and decay, and its numerical simulation theory views these two processes as chemical reactions that involve reactants and products. However, these two kinds of foam models do not represent the micro-mechanical effects between the gas bubble and pore-throat in porous medium. In this work, a geometric model of pore-throat was established based on the core data of rate-controlled porosimetry. Then, the snap-off time of generating gas bubble in core sample was calculated with the data of foam flooding experiment. Finally, combined with numerical simulation, the distribution of bubble size in reservoir during foam flooding was calculated. Comparing different plans of gas alternating foaming liquid injection, it was found that when consuming the same amount of gas and foaming liquid, the increasing-ratio of gas alternating foaming liquid injection has a larger sweep range of foam and a more extended zone of effective-sized bubble than the constant-ratio injection does, which indicates that the increasing-ratio of gas alternating foaming liquid injection has a higher efficiency.

Characterization on Temporal Evolution of Porosity, Permeability, and Reactive Specific Surface Based on Fractal Model During Mineral Dissolution

AbstractAccurately understanding the temporal changes in hydrological properties induced by mineral dissolution is of great importance for characterization on reactive transport system in porous media. A theoretical model for characterizing the temporal evolution of rock porosity, permeability, and reactive specific surface during mineral dissolution under two different scenarios is developed with introduction of fractal dimensions of porous media. In the first scenario, dissolution rate is assumed as a linear function of temporal pore size, and changes in fractal dimensions are closely related to the time. The second scenario allows for the constant fractal dimension and an inverse relation between dissolution rate and time. The proposed model is fully verified with some published literatures, and most of results show the excellent/good fit with experimental/simulated data. The validation of the proposed model is also briefly discussed, mainly affected by reactive transport regimes.