Colloid Deposition In Porous Media Research Articles

A two-site filtration model for silica nanoaggregate mobility in porous media under high salinity conditions

A variable-viscosity colloid transport simulator is developed to model the mobility behavior of surface-engineered nanosilica aggregates (nSiO2) under high salinity conditions. A two-site (2S) filtration approach was incorporated to account for heterogeneous particle-collector surface interactions. 2S model was then implemented along with the conventional clean bed filtration (CFT) and maximum retention capacity (MRC) particle filtration models to simulate the results of a series of column tests conducted in brine (8% wt. NaCl and 2% wt. CaCl2)-saturated Ottawa sand columns at various pore velocities (7 to 71 m/day). Simulation results reveal the superiority of the MRC and 2S model classes over CFT model with respect to numerical performance criteria; a general decrease of normalized sum of squared residuals (ca. 20–90% reduction) and an enhanced degree of normality of model residuals were detected for 2S and MRC over CFT in all simulated experiments. Based on our findings, conformance with theories underpinning colloid deposition in porous media was the ultimate factor that set 2S and MRC model classes apart in terms of explaining the observed mobility trends. MRC and 2S models were evaluated based on the scaling of the fitted maximum retention capacity parameter with variation of experimental conditions. Two subclasses of 2S that consider a mix of favorable and unfavorable attachment sites with irreversible attachment to favorable sites (with and without physical straining effects) were found most consistent with filtration theory and shadow zone predictions, yielding theoretical conformity indices of 0.6 and higher, the highest among all implemented models. An explanation for such irreversible favorable deposition sites on the surface of silica nanoaggregates might be a partial depletion of stabilizing steric forces that had led to the formation of these aggregates.

Modeling colloid deposition on a protein layer adsorbed to iron-oxide-coated sand

Our recent study reported that conformation change of granule-associated Bovine Serum Albumin (BSA) may influence the role of the protein controlling colloid deposition in porous media (Flynn et al., 2012). The present study conceptualized the observed phenomena with an ellipsoid morphology model, describing BSA as an ellipsoid taking a side-on or end-on conformation on granular surface, and identified the following processes: (1) at low adsorbed concentrations, BSA exhibited a side-on conformation blocking colloid deposition; (2) at high adsorbed concentrations, BSA adapted to an end-on conformation promoted colloid deposition; and (3) colloid deposition on the BSA layer may progressively generate end-on molecules (sites) by conformation change of side-on BSA, resulting in sustained increasing deposition rates. Generally, the protein layer lowered colloid attenuation by the porous medium, suggesting the overall effect of BSA was inhibitory at the experimental time scale. A mathematical model was developed to interpret the ripening curves. Modeling analysis identified the site generation efficiency of colloid as a control on the ripening rate (declining rate in colloid concentrations), and this efficiency was higher for BSA adsorbed from a more dilute BSA solution.

Single Collector Attachment Efficiency of Colloid Capture by a Cylindrical Collector in Laminar Overland Flow

Little research has been conducted to investigate the fate and transport of colloids in shallow overland flow through dense vegetation under unfavorable chemical conditions. In this work, the single collector attachment efficiency (α) of colloid capture by a simulated plant stem (i.e., cylindrical collector) in laminar overland flow was measured directly in laboratory flow chamber experiments. Fluorescent microspheres of two sizes were used as experimental colloids. The colloid suspensions flowed toward a glass cylindrical rod installed in a small size flow channel at different laminar flow rates. Different solution ionic strengths (IS) were used in the experiments to simulate unfavorable attachment conditions. Our results showed that α increased with IS and decreased with flow velocity. Existing theoretical and empirical models of colloid attachment efficiency for porous media were used to simulate the experimental measurements in α and found to fall short in matching the experimental data. A new dimensionless (regression) equation was proposed that predicts the α of colloid capture by a cylindrical collector in laminar overland flow with reasonable accuracy. In addition, the equation was also effective in predicting the attachment efficiency of colloid deposition in porous media.

Predicting attachment efficiency of colloid deposition under unfavorable attachment conditions

This study presents an a priori model for predicting attachment efficiency of colloid deposition in porous media under unfavorable conditions. The model takes into account coupled effects of diffusion and hydrodynamic forces on colloid attachment efficiency that result from both primary and secondary minimum deposition. Effect of diffusion was quantified using the Maxwell approach, and influence of hydrodynamic drag was determined by comparing adhesive and hydrodynamic torques that act on the attached colloids. Main findings from this study include (1) the attachment efficiency does not change with increase of flow velocity until it reaches a critical value at which the attachment efficiency decreases as flow velocity further increases and (2) the attachment efficiency increases with increasing collector diameter when the condition that adhesive torque is greater than hydrodynamic torque is not guaranteed over the entire collector surface. Whereas the classic filtration theory only takes into account the effects of system hydrodynamics on single collector contact efficiency, we show additionally their effects on attachment efficiency. Furthermore, results of this study imply that in addition to the important role that collector size plays in the straining process, which has been the focus of many recent studies, it also influences the attachment process thus must be considered when describing colloid retention and transport in porous media under unfavorable attachment conditions.

Hemispheres-in-Cell Geometry to Predict Colloid Deposition in Porous Media

Hemispheres-in-Cell Geometry to Predict Colloid Deposition in Porous Media

Hemispheres-in-Cell Geometry to Predict Colloid Deposition in Porous Media

A "hemispheres-in-cell" geometry is provided for prediction of colloid retention during transport in porous media. This new geometry preserves the utilities provided in the Happel sphere-in-cell geometry; namely, the ability to predict deposition for a range of porosities, and representation of the influence of neighboring collectors on the fluid flow field. The new geometry, which includes grain to grain contact, is justified by the eventual goal of predicting colloid deposition in the presence of energy barriers, which has been shown in previous literature to involve deposition within grain to grain contacts for colloid:collector ratios greater than approximately 0.005. In order to serve as a platform for predicting deposition in the presence of energy barriers, the model must be shown capable of quantitatively predicting deposition in the absence of energy barriers, which is a requirement that was not met by previous grain to grain contact geometries. This paper describes development of the fluid flow field and particle trajectory simulations for the hemispheres-in-cell geometry in the absence of energy barriers, and demonstrates that the resulting simulations compare favorably to existing models and experiments. A correlation equation for predicting collector efficiencies in the hemispheres-in-cell model in the absence of energy barriers was developed via regression of numerical results to dimensionless parameters.

The Colloidal Approach. A Promising Route for Asphaltene Deposition Modelling

It is now widely recognized that asphaltene exist in crude oils both as dissolved and particulate matter and that asphatenic crude oils behave as colloidal systems. The objective of this research work is to check if, in porous media and under dynamic conditions, asphaltene also behave as colloids. In this case, their deposition kinetic should obey the classical laws for colloid deposition in porous media. To achieve this, asphaltene deposition kinetics has been investigated as a function of the main controlling parameters such as flow rate, asphaltene aggregation state, resin content and crude origin. The study has been performed, first under well controlled condition using model fluids and porous media, and then under more representative conditions using actual crude oils and outcrop sandstones. The results confirmed that, indeed, the kinetics of asphaltene deposition in porous media obeys the general scaling low of colloid deposition. They allowed us to propose general scaling laws for the deposition kinetics in the form , η is the capture efficiency and γ the shear rate. The exponents s are universal exponents that are characteristic of the deposition regimes while the power law pre-factors A encompass all the specific features of the system considered (asphaltene and porous media). These kinetic laws show that the thickness of the deposit increases rapidly with decreasing shear rate. Accordingly and under favourable conditions, a thick deposit is expected to form during heavy oil extraction from high permeability formations and under low flow rate conditions. Such deposition could then have significant impact on the efficiency of heavy oil recovery. Therefore, its impact on permeability and on flow properties of reservoir fluids needs to be assessed as a part of process optimisation and evaluation. The Colloidal approach provides a new and promising route for asphaltene deposition and associated permeability damage modelling.

Significance of straining in colloid deposition: Evidence and implications

Considerable research suggests that colloid deposition in porous media is frequently not consistent with filtration theory predictions under unfavorable attachment conditions. Filtration theory was developed from an analysis of colloid attachment to the solid‐water interface of a single spherical grain collector and therefore does not include the potential influence of pore structure, grain‐grain junctions, and surface roughness on straining deposition. This work highlights recent experimental evidence that indicates that straining can play an important role in colloid deposition under unfavorable attachment conditions and may explain many of the reported limitations of filtration theory. This conclusion is based upon pore size distribution information, size exclusion, time‐ and concentration‐dependent deposition behavior, colloid size distribution information, hyperexponential deposition profiles, the dependence of deposition on colloid and porous medium size, batch release rates, micromodel observations, and deposition at textural interfaces. The implications of straining in unsaturated and heterogeneous systems are also discussed, as well as the potential influence of system solution chemistry and hydrodynamics. The inability of attachment theory predictions to describe experimental colloid transport data under unfavorable conditions is demonstrated. Specific tests to identify the occurrence and/or absence of straining and attachment are proposed.

Use of a gamma ray attenuation technique to study colloid deposition in porous media

An experimental study of colloidal deposition in porous media is presented. The local deposition is determined through a local measurement of porosity variation using a γ-ray attenuation technique. The basic principle of this technique is described and the accuracy measurement is discussed. An experimental setup was designed using an artificial porous medium flushed with several pore volumes of a latex suspension. The damage to the porous medium was determined from permeability reduction and porosity measurements. A good agreement was obtained for a monolayer deposit. The discrepancy between global and local measurements of multilayer deposition is discussed.

Blocking and ripening of colloids in porous media and their implications for bacterial transport

A model accounting for the dynamics of colloid deposition in porous media was developed and applied to systems containing similarly charged particles and collectors. Colloid breakthrough and intracolumn retention data confirmed that blocking reduced overall colloidal adhesion to soil. The surface coverage at which blocking occurred varied for the type of colloid, as shown by changes in the clean-bed collision efficiency, α 0, and the excluded area parameter, β. Excluded area parameters were relatively high due to unfavorable interactions between particles and collectors, and ranged from 11.5 for one bacterium ( Pseudomonas putida KT2442) to 13.7 and 24.1 for carboxylated latex microspheres with differing degrees of charged groups on their surfaces. Differences in β values for the three colloids were correlated with electrophoretic mobility, with the most negatively charged colloid (carboxylated latex; CL microspheres) having the highest β. No correlation between hydrophobicity and α 0 or β was found. Besides using colloidal particles capable of blocking, the addition of chemical additives to the soil has been suggested as a means for reducing attachment of colloids to porous media. Dextran addition caused an order-of-magnitude reduction in the overall α (for carboxylated-modified latex; CMLs). This reduction was not attributed to blocking, but to the sorption of dextran to the soil which lowered α 0. The filtration-based numerical model used to fit the α 0 and β parameters was used to demonstrate that blocking could result in significantly enhanced bacterial transport in field situations.

Dynamics of Colloid Deposition in Porous Media: Blocking Based on Random Sequential Adsorption

An improved theoretical model is presented for quantifying the dynamics of colloid deposition in granular porous media. The model characterizes the transient aspects ofirreversible particle deposition onto spherical collector surfaces where repulsive electrostatic forces between colloidal particles limit deposition to monolayer coverage. The transient deposition rate normally associated with particle deposition is depicted in the model by a dynamic blocking function derived from random sequential adsorption (RSA) mechanics. The RSA blocking function has a nonlinear power law dependence on surface coverage, in contrast to the linear Langmuirian blocking function used in previous dynamic deposition models for porous media. A technique involving the calculation of the jamming limit from experimental particle breakthrough curves is utilized for determining the excluded area parameter, an integral component of the dynamic blocking function. Parameter estimation and curve fitting techniques are not required by the model as all parameter values are calculated a priori using available theoretical principles. Parameter values are incorporated into the theoretical model to produce theoretical particle breakthrough curves based on both RSA and Langmuirian dynamic blocking functions. A comparison of theoretical results with experimental particle breakthrough curves demonstrates the utility of RSA mechanics as a means of describing particle blocking dynamics associated with colloid deposition in granular porous media.

Dynamics of colloid deposition in porous media: Modeling the role of retained particles

A model for the dynamics of colloid deposition in porous media is developed by combining macroscopic and microscopic theories of particle deposition. The model considers the non-uniform coverage of collector surfaces by retained particles during the deposition process. A flux-correcting function is introduced that enables the determination of the overall colloid deposition rate as a function of surface coverage. A non-linear dependence of particle deposition rate on surface coverage is obtained, in agreement with experimental data of particle deposition. It is shown that the model is successful in describing the blocking (excluded-area) effect in particle deposition dynamics.