Suspended Particles Transport and Deposition in Saturated Granular Porous Medium: Particle Size Effects

An experimental study on the transport and deposition of suspended particles (SP) in a saturated porous medium (calibrated sand) was undertaken. The influence of the size distribution of the SP under different flow rates is explored. To achieve this objective, three populations with different particles size distributions were selected. The median diameter $d_{50}$ of these populations was 3.5, 9.5, and $18.3~\upmu \hbox {m}$ . To study the effect of polydispersivity, a fourth population noted “Mixture” ( $d_{50} = 17.4\; \upmu \hbox {m}$ ) obtained by mixing in equal proportion (volume) the populations 3.5 and $18.3\;\upmu \hbox {m}$ was also used. The SP transfer was compared to the dissolved tracer (DT) one. Short pulse was the technique used to perform the SP and the DT injection in a column filled with the porous medium. The breakthrough curves were competently described with the analytical solution of a convection–dispersion equation with first-order deposition kinetics. The results showed that the transport of the SP was less rapid than the transport of the DT whatever the flow velocity and the size distribution of the injected SP. The mean diameter of the recovered particles increases with flow rate. The longitudinal dispersion increases, respectively, with the increasing of the flow rates and the SP size distribution. The SP were more dispersive in the porous medium than the DT. The results further showed that the deposition kinetics depends strongly on the size of the particle transported and their distribution.     

Effects of Particle Size Non-Uniformity on Transport and Retention in Saturated Porous Media

Short-pulse injection experiments are investigated to study the effects of particle size non-uniformity on the transport and retention in saturated porous media. Monodisperse particles (3, 10, and 16 \(\upmu \hbox {m}\) latex microspheres) and polydisperse particles (containing 3, 10, and 16 latex microspheres) were explored. The obtained results suggest considering not only the particle sizes but also their polydispersivity (particle size non-uniformity) in transport and retention. Although, the density of the suspended particles is close to that of water, results reveal a slow transport of particles compared to the dissolved tracer whatever their size and flow velocity. The recovered particles in the mixture experiments show that the retention of large particles (10 and 16 \(\upmu \hbox {m}\)) enhances the retention of small ones (3 \(\upmu \hbox {m}\)). However, the straining of 10 and 16 \(\upmu \hbox {m}\) particles in “mixture experiments” is smaller than their straining in “monodisperse experiments”. A linear relationship summarizing the simultaneous effect of particle sizes and flow velocity on deposition kinetics coefficient is proposed.     

Effects of Flow Velocity and Nonionic Surfactant on Colloid Straining in Saturated Porous Media Under Unfavorable Conditions

Knowledge of colloid straining mechanism in porous media is of importance for protecting groundwater from being contaminated by biocolloids (e.g., bacteria and protozoa) and by contaminants whose transport can be facilitated by mobile particles. This study examined effects of flow velocity on colloid straining in porous media under unfavorable chemical conditions. Saturated column experiments were conducted using glass beads as collector and a $3\,\mu \text{ m}$ carboxylate-modified polystyrene latex microsphere as model colloid. To unambiguously examine colloid straining mechanisms, attachment was minimized by extensively cleaning the collectors and adopting deionized water as solution. Results show that increasing flow velocity decreases colloid straining under unfavorable chemical conditions, in agreement with to theoretical finding in literature. This study additionally examined effects of nonionic surfactant (Triton X-100) on colloid straining in porous media under unfavorable chemical conditions. Results show that the addition of Triton X-100 decreases colloid straining and the decrease is enhanced by increasing the concentration of Triton X-100.     

Particle Detachment Under Velocity Alternation During Suspension Transport in Porous Media

Flow of suspensions in porous media with particle capture and detachment under alternate flow rates is discussed. The mathematical model contains the maximum retention concentration function of flow velocity that governs the particle release and is used instead of equation for particle detachment kinetics from the classical filtration model. An analytical model for suspension injection with alternate rates was derived, and a coreflood by suspension with alternate rates was carried out. The modelling and laboratory data are in a good agreement, which validates the modified particle detachment model with the maximum retention function.     

Laboratory Investigation of Variable-Density Flow and Solute Transport in Unsaturated–Saturated Porous Media

In many groundwater systems, fluid density and viscosity may vary in space and time as a function of changes in concentration and temperature of the fluid. When dense groundwater plumes interact with less dense ambient groundwater, these density variations can significantly affect flow and transport processes. Under certain conditions, gravitational instabilities in the form of lobe-shaped fingers can occur. This process is significant because it can lead to more rapid and spatially extensive solute transport. This paper presents new experiments carried out in a sand filled glass flow container under both fully saturated and variably-saturated conditions and focuses upon the processes that occur at the capillary fringe and below the water table, as affected by a dense contaminant plumes migration through the unsaturated zone. Source fluids stained with Rhodamine-WT were introduced at the upper boundary of the tank at a range of low and high densities. In addition to the fluid density gradients and porous medium permeability that determine the onset conditions for instabilities in fully saturated experiments, volumetric water content appears critical in the variably-saturated laboratory runs. Plume behaviour at the water table appears dependent upon the density of the fluid that accumulates there. For neutral and low density fluids, plumes accumulate at the water table and then spread laterally above it and the water table forms a barrier to further vertical flow as pore water velocities reduce with increasing water content. For medium and high density fluids, vertical movement continues as instabilities form at the capillary fringe and fingers begin to grow at the water table boundary and move downwards into the saturated zone. In these cases, lateral spreading of the plume is small. Despite these more qualitative observations, the exact nature of the relevant stability criteria for the onset and growth of instabilities in variably-saturated porous media presently remain unclear. All experimental results suggest, however, that the unsaturated zone and position of the water table must be considered in contaminant studies in order to predict the migration pathways, rates and ultimate fate of dense contaminant plumes. It is possible that the results of experiments presented in this paper could form a useful basis for the testing of variable-density (and variably-saturated) groundwater flow and solute transport numerical codes because they offer controlled physical laboratory analogs for comparison. They also provide a strong basis for the development of more rigorous mathematical formulations that are likely to be either developed or tested using numerical flow and solute transport simulators.     

Network Model of Flow,Transport and Biofilm Effects in Porous Media

In this paper, we develop a network model to determine porosity and permeability changes in a porous medium as a result of changes in the amount of biomass. The biomass is in the form of biofilms. Biofilms form when certain types of bacteria reproduce, bond to surfaces, and produce extracellular polymer (EPS) filaments that link together the bacteria. The pore spaces are modeled as a system of interconnected pipes in two and three dimensions. The radii of the pipes are given by a lognormal probability distribution. Volumetric flow rates through each of the pipes, and through the medium, are determined by solving a linear system of equations, with a symmetric and positive definite matrix. Transport through the medium is modeled by upwind, explicit finite difference approximations in the individual pipes. Methods for handling the boundary conditions between pipes and for visualizing the results of numerical simulations are developed. Increases in biomass, as a result of transport and reaction, decrease the pipe radii, which decreases the permeability of the medium. Relationships between biomass accumulation and permeability and porosity reduction are presented.     

Particle Deposition in Porous Media: Analysis of Hydrodynamic and Weak Inertial Effects

We have studied the transport and capture of non-Brownian particles in porous media, when the particles are mainly submitted to hydrodynamic and weak inertial effects. Visualization experiments have been performed using several models of porous media which consist of transparent etched networks of interconnected channels. Typical particle deposits have been observed at the corners of the grains of the porous medium. Their shape and their orientation were dependent on flow rate and on the anisotropy of the flow field. A trajectory analysis model has been applied to a porous medium made of a doubly periodic array of rectangular grains very close to the experimental model. This numerical model has been used to localize particle deposits and to determine particle capture efficiency on the grains over a range of low Stokes numbers, grain aspect ratios and flow-field anisotropy ratios. The results have been interpreted in terms of shape of particle deposits and compared successfully to experimental observations.     

Mechanisms of Particle Transport Acceleration in Porous Media

Experimental data show that the groundwater transport of radionuclides in porous media is frequently facilitated when accompanied with colloid particles. This is usually explained by the size exclusion mechanism which implies that the particles move through the largest pores where the flow velocity is higher. We call attention to three other mechanisms which influence the colloid particle motion, while determining both the probable transport facilitation and retardation. First of all, it is shown that the transport facilitation may be significantly reduced and even transformed into a retardation due to the growth of the effective suspension viscosity (a friction-limited facilitation). Secondly, we will show that the transport of particles through the largest pores can be retarded due to a reduced connectivity of the large-pore cluster (a percolation-breakup retardation). Thirdly, we highlight the Fermi mechanism of acceleration known in statistical physics which is based on the elastic collisions between particles. All three effects are analyzed in terms of the velocity enhancement factor, by using statistical models of porous media in the form of a capillary bundle and a 3D capillary network. Optimal and critical regimes of velocity enhancement are quantified. Estimations show that for realistic parameters, the maximal facilitation of colloid transport is close to the experimentally observed data.     

Opportunities for Particles and Particle Suspensions to Experience Enhanced Transport in Porous Media: A Review

Transport in Porous Media - The possibility of broaching, or the release of fluids at the seafloor due to a damaged or faulty well, is a hazard that must be assessed in the well permitting process....     

Stochastic Simulations of NAPL Mass Transport in Variably Saturated Heterogeneous Porous Media

A multiphase flow and transport numerical model is developed to study the effects of porous media heterogeneities on residual NAPL mass partitioning and transport of dissolved and/or volatilized NAPL mass in variably saturated media. The results indicate the significance of porous media heterogeneity in influencing the mass transfer processes and NAPL transport in the subsurface. Among the parameters investigated in this study, the heterogeneity of the permeability field has the most significant influence on the NAPL mass partitioning and transport. In general, the heterogeneity of the porous media properties enhances the NAPL mass plume spreading in both the water phase and the gas phase while the influence on the water phase is much more significant. Overall, the porous media property heterogeneities tend to increase the accumulation of NAPL mass in the water phase. The nonequilibrium mass transfer processes result in the expected trend of decreasing the NAPL mass dissipation rate and causing long-term groundwater contamination.     

Predicting Vertical Flow Barriers Using Tracer Diffusion in Partially Saturated,Layered Porous Media

Sudden changes in isotopic tracer concentration in pore waters have been interpreted as indicating barriers to vertical advective flow through porous rocks in the subsurface, e.g. step changes in \(^{87}\hbox {Sr}/^{86}\) Sr ratio are often used in the oil and gas industry as a signature of reservoir compartmentalisation. This study shows that this is not necessarily the case. It can take millions of years for such step changes to equilibrate by diffusion if there is no flow resulting from pressure or density gradients even in high permeability, high porosity rocks, particularly if the water saturation is low. Changes in tracer concentration gradients can be good indicators of changes in porosity (or water saturation) between layers. In contrast changes in sorption without a change in porosity are almost impossible to identify. The time taken for concentration gradients to equilibrate is affected by the layer properties but can be quickly estimated from the harmonic average of the effective diffusion coefficient for each layer and a simple analytical expression for a homogeneous system. This was achieved by performing a sensitivity analysis on different layer properties (porosity contrast, saturation contrast, sorption contrast, thickness ratio) using existing analytical solutions for diffusion in layered systems.     

Nonequilibrium Effects and Multiphase Flow in Porous Media

In this paper we develop a more general formulation for transient multiphase flow in porous media based on physics observed in core-scale and micromodel experiments. We account for non-equilibrium effects by considering redistribution time and treat saturation by evolving locally moving time-averages of the saturation. Several families of models arise from approximations to the general formulation with various degrees of accuracy. The classical Buckley-Leverett and Barenblatt expressions are special cases of these families. We explore the behaviors of a number of special cases arising from the proposed general formulation using established and novel numerical schemes that provide nonlinear physics-based preconditioning. The agreement observed between numerical and experimental results demonstrates the consistency of the proposed abstraction.     

Experimental Investigation on the Filtering Flow Law of Pre-gelled Particle in Porous Media

Pre-gelled particle (PPG) is a new profile control agent showing high heat resistance and salt tolerance. Single- and double-tube PPG flow experiments were carried out to study the flow law in porous media, the mechanism of profile control, surface deposition and re-migration, plugging deposition and restart, and the permeability variation due to the retention of PPG using sand-packed model. The results showed that PPG, when encountered with throats in the porous media flow, were deformed due to a higher pressure to go through the throats and pressure would reduce once PPG passed through. In this case, the purpose of dynamic profile control was achieved without damage to the formation. The results further showed that PPG owned a smaller coefficient of surface deposition and a higher coefficient of re-migration, so PPG would migrate to the deep formation rather than deposit near the well bore which was favorable to the deep dynamic profile control. The diameter of the re-migration particles increased with the increase in the viscosity and the flow rate of the PPG-carrying fluid and showed a exponential relationship with the product of viscosity and real flow rate of the carrier flow. The pressure gradient needed by the plugged PPG to re-migrate exponentially increased with the ratio of diameters of PPG and throats. The residual permeability coefficient showed a relationship with the amount of particles deposited on the surface in the function of Carman?CKozeny, and it exponentially decreased with an increasing amount of throats blocked by PPG.     

Comments on ‘Analytical Solution for the Effect of Viscous Dissipation on Mixed Convection in Saturated Porous Media’, Transport in Porous Media 41, 197–209, 2000

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Influence of Internal Structure and Medium Length on Transport and Deposition of Suspended Particles: A Laboratory Study

A laboratory study was undertaken on the transport and the deposition of suspended particles (silt of modal diametre 6 μm) in three columns of different length, filled with glass beads or gravel. Tracer tests were carried out at various flow velocities by short pulses of a mixture of suspended particles/dissolved tracer. The breakthrough curves were competently described with the analytical solution of a convection dispersion equation with a first-order deposition rate and the hydro-dispersive parameters were deduced. For the same experimental conditions, the results showed a difference in the behaviour of the suspended particles transport and deposition rates within the two porous media tested. The internal structure of both media governs the particle-grain collision frequency as well as the particles trapping. The scale effect was highlighted and affects the dispersivity, the size exclusion effect, the recovery rates and the deposition rates. Longitudinal dispersion increases with mean pore velocity and is described with a nonlinear relationship. The dispersivity increases with the column length. The size exclusion effect is more important in the short column. The recovery rate increases with flow velocity and decreases while increasing column length. The deposition rates increases until a critical flow velocity then decreases. This critical velocity is also sensitive to the scale effect, and increases with the column length.     

Non-isothermal Permeability Impairment by Fines Migration and Deposition in Porous Media including Dispersive Transport

Particle migration and deposition, and resulting permeability impairment occurring in porous media are described by a practical phenomenological model considering temperature variation and particle transport by advection and dispersion. Variation of the filter coefficient and permeability of porous matrix by temperature and particle deposition, and other essential factors are considered by means of the special correlations of the relevant variables and dimensionless numbers. Comparison of the numerical results, obtained using a finite-difference numerical scheme with and without considering the dispersion mechanism and temperature variation, reveals the significance of such effects on fines migration and deposition, and consequent permeability impairment in porous media. Improved model presented in this article can be instrumental for scientifically guided experimentation, analysis, and optimal design of processes involving in transport of colloidal and fine particles through geological subsurface formations.     

Surfactant Concentration and End Effects on Foam Flow in Porous Media

Foaming injected gas is a useful and promising technique for achieving mobility control in porous media. Typically, such foams are aqueous. In the presence of foam, gas and liquid flow behavior is determined by bubble size or foam texture. The thin-liquid films that separate foam into bubbles must be relatively stable for a foam to be finely textured and thereby be effective as a displacing or blocking agent. Film stability is a strong function of surfactant concentration and type. This work studies foam flow behavior at a variety of surfactant concentrations using experiments and a numerical model. Thus, the foam behavior examined spans from strong to weak.Specifically, a suite of foam displacements over a range of surfactant concentrations in a roughly 7m², one-dimensional sandpack are monitored using X-ray computed tomography (CT). Sequential pressure taps are employed to measure flow resistance. Nitrogen is the gas and an alpha olefin sulfonate (AOS 1416) in brine is the foamer. Surfactant concentrations studied vary from 0.005 to 1wt%. Because foam mobility depends strongly upon its texture, a bubble population balance model is both useful and necessary to describe the experimental results thoroughly and self consistently. Excellent agreement is found between experiment and theory.