Transport Behavior Of Particles Research Articles

Influence of the internal structure of straight microchannels on inertial transport behavior of particles

The rapid advancement of Micro-Electro-Mechanical Systems (MEMS) technology has established microfluidics as a pivotal field. This technology marks the onset of a new era in various applications, including drug testing, cell culture, and disease monitoring, underscoring its extensive practicality and potential for future exploration. This research delves into the intricate behavior of particle inertial migration within microchannels, particularly focusing on the impact of different channel structures and Reynolds numbers (Re). Our studies reveal that particles in microchannels with one-sided sharp-cornered microstructures migrate towards the sharp corner at a relative position of 0.4 under low flow rates, and towards the straight wall side at a relative position of 0.8 under high flow rates. The migration pattern of equilibrium positions varies with different arrangements of sharp-corner structures, achieving stability at the channel's center only when the sharp corners are symmetrically arranged on both sides. Our investigation into the shape of microstructures indicates that sharp-cornered structures generate a more stable secondary flow compared to rectangular and semi-circular structures, preventing particle aggregation at the outlet. To address the challenges associated with handling variable cross-section geometries and solid-wall boundaries in dissipative particle dynamics methods effectively, we have developed a dissipative particle dynamics model specifically for analyzing such microchannels. Building upon our previous research, this model introduces a conservative force coefficient for particles within the microstructured region and an interaction zone that only involves repulsive forces, aligning well with experimental outcomes. Through the study of microstructures' geometric shapes, this paper offers guidance for designing microchannels for particle enrichment. Furthermore, the dissipative particle dynamics model established for the particle flow and solid structure interaction within microstructured channels provides insights into the mesoscale dynamics of liquid-solid two-phase flow and particle motion. In conclusion, this paper aims to enhance particle motion sample preparation techniques, thereby broadening the scope of microfluidic applications in the biomedical field.

An experimental study of the effect of individual upper airway anatomical features on the deposition of dry powder inhaler formulations

This study aims to investigate the effects of different pharynx anatomical features on the delivery of inhaled aerosols. Six in-vitro upper airway models reconstructed using anatomical images acquired by Magnetic Resonance Imaging (MRI) were used for the experiments. A geometrically accurate airway model was produced, and five other different airway models, each missing one or more specific anatomical features: the uvula, epiglottis, and/or soft palate, were derived from the original model. Hence, the geometrical boundaries of the six models were the same except at regions where specific anatomical structures were removed, and this was done to allow meaningful comparisons between the different geometries to be made using specific measurements. Spray-dried mannitol powder (volume median particle size and span were 3.22 μm and 1.90 μm, respectively) was loaded into a capsule-based dry powder inhaler with different resistance, an Osmohaler™ (low resistance), or Handihaler® (high resistance), attached to the inlet of the airway model, which its outlet was connected to a Next-Generation Impactor (NGI). The studies were performed using flow rates of 30 and 60 LPM. High-performance liquid chromatography (HPLC) was used to quantify the mass deposition of particles in different stages of the NGI and airway replicas. Results from this study show that widening the space between the oral cavity and oropharynx, exemplified by one of the six replicas developed, significantly decreases upper airway deposition as well as increases the fine particle fraction. The case with the highest deposition (63.5%) occurred in the pharynx replica with the soft palate present (at 60 LPM with the Hanihaler), while the lowest deposition (26.0%) occurred in the replica without the soft palate and epiglottis (at 30 LPM with the Osmohaler). This study highlights that in addition to the resistance of the inhalers, their interactions with the human airway anatomical features are likely to play important roles in the subsequent lung dose. Results from this study are novel because while the effects of different inhaler resistance in a given airway replica is known, the effects contributed by specific pharynx anatomical features on particle transport behaviour have not been studied experimentally or reported on in the literature. This study shows that space adjacent to the soft palate affects particle deposition dramatically but the effect appears to be more significant when using the Handihaler and for the high flow rate cases.

Exploring the Impact of Surface Functionalization on the Reaction, Magnetophoretic, and Collective Transport Behavior of Nanoscale Zerovalent Iron.

This study provides a systematic analysis of the transport and magnetophoretic behavior of nanoscale zerovalent iron (nZVI) particles, both bare and surface functionalized by poly(ethylene glycol) (PEG) and carboxymethyl cellulose (CMC), after undergoing a chemical reaction. Here, a simple and well-investigated chemical reaction of methyl orange (MO) degradation by nZVI was used as a model reaction system, and the sand column transport and low-gradient magnetophoretic profiles of the nanoparticles were measured before and after the reaction. The results were compared over time and analyzed in the context of extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to understand the particle interactions involved. The colloidal stability of both bare and functionalized nZVI particles was enhanced after the reaction due to the consumption of metallic Fe content, resulting in a significant drop in their magnetic properties. As a result, they exhibited improved mobility across the sand column and a slower magnetophoretic collection rate compared to the unreacted particles. Here, the colloidal filtration theory (CFT) was employed to analyze the transport behavior of nZVI particles across the packed sand column. It has been observed that the surface properties of the reacted functionalized particles changed, possibly due to the entrapment of degraded products within the polymer adlayer. Moreover, quartz crystal microbalance with dissipation (QCM-D) measurements were performed to reveal the viscoelastic contribution of the adlayer formed by both bare and functionalized nZVI particles after the reaction on influencing their transport behavior across the sand column. Finally, we proposed the implementation of a high-gradient magnetic trap (HGMT) to reduce the transport distance of the colloidally stable CMC-nZVI, both before and after the reaction. This study sheds light on the behavioral changes of iron nanoparticles after the reaction and highlights environmental concerns regarding the presence of reacted nanoparticles.

Implementing the direct relaxation process in the stochastic particle method for flexible molecular collisions

Multi-scale phenomena are prevalent and significant across various disciplines. For multi-scale flow physics in the gas-kinetic theory based on Boltzmann equation or its simplified mathematical models (called Boltzmann model equations), the multi-scale mechanism can be modeled by the philosophy of unified modeling, where the free transport behaviors of gas particles and their collision behaviors are coupled by the temporal integral solutions (or characteristic line solutions) of Boltzmann model equations, which leads to a unified/multi-scale property in all scales. Also, the stochastic particle methods are based on these Boltzmann model equations. The corresponding numerical methods are, thus, limited by these model equations. This paper aims to overcome this restriction by replacing these modeled collision operators with a simple direct relaxation (DR) process. Since the collision term of Boltzmann model equation should fulfill the correct relaxation rates of non-equilibrium macro-variables, such as stress tensor and heat flux vector, along with other basic properties, such as conservation and H theorem, the DR process is designed to be directly based on these crucial relaxation rates. Therefore, with the DR strategy for calculating particle collisions, the numerical method can be established without constructing collision operator. Furthermore, the DR has the flexibility and simplicity to recover various models. In this work, Xu's and Yuan's new models are recovered in to illustrate the validation and performance of DR. Moreover, since at the inlet/outlet boundaries, subsonic, supersonic, and hypersonic flows can simultaneously exist, a generalized numerical boundary condition is also considered in the particle methods developed in this paper. Finally, the validation and accuracy of the present method are examined with a series of test cases.

Laboratory Studies on the Influence of Ionic Strength on Particle Transport Behavior in a Saturated Porous Medium

An experimental study has been undertaken to investigate the effect of flow velocity and ionic strength on the transport of suspended particles (SP) and their deposition in a saturated porous medium. The SP injections were carried out using a laboratory column filled with sand and a pulse injection method. Ionic strengths varying between 0 and 600 mM (NaCl) have prospected. Two velocities were tested: 0.15 and 0.30 cm/s. Selected polydisperse particles diameters ranging from 0.27 to 5 μm and a median diameter (dp50) equal to 2.25 μm were used. An analytical solution of the convection–dispersion equation with first-order deposition kinetics was used to describe the experimental breakthrough curves and to identify the transport parameters. The results show that the increase of ionic strength promotes the retention of the SP in the porous medium. In addition, retention is more important when the flow velocity is low. The deposition kinetics coefficient increases with increasing ionic strength and flow velocity.

Study on particle plugging in propagating fractures based on CFD-DEM

In the drilling and completion process of fractured formations, wellbore stability is a key factor affecting the safety of drilling and completing engineering. Previous studies have demonstrated that propping moderately and plugging fractures with soluble particles can improve formation fracture pressure. When it comes to particle transport in 3D rough propagation fractures, the interactions between particle-fracture-fluid need to be considered. Meanwhile, size-exclusion, particle bridging/strain effects all influence particle transport behavior and ultimately particle plugging effectiveness. However, adequate literature review shows that fracture plugging, and fracture propagation have not been considered together. In this study, a coupled CFD-DEM method was put forward to simulate the particle plugging process of propagating fracture, and the effects of positive pressure difference, fracture roughness, particle concentration, and particle shape on the plugging mechanism were examined. It is concluded through the study that: 1) Positive pressure difference too large will lead to excessive fracture aperture, making the particles unable to form effective plugging in the middle of the fracture; positive pressure difference too small will lead to fracture aperture too small, making particles unable to enter into and plug the fracture. 2) No matter how the concentration, particle size and friction coefficient change, they mainly affect the thickness of the plugging layer, while the front end of the particle is still dominated by single-particle bridging, and double-particles bridging and multiple-particles bridging are hardly ever seen. For the wellbore strengthening approaches, such as stress cages, fracture tip sealing, etc., specific analysis should be carried out according to the occurrence of extended fractures. For example, for fractures with low roughness, the particles rarely form effective tight plugging in the middle of the fracture, so it is more suitable for fracture tip sealing; For the fracture with high roughness, if the positive pressure difference is controlled properly to ensure reasonable fracture extension, the particle plugging effect will be good, and the stress cage method is recommended for borehole strengthening.

Transport of plastic particles in natural porous media under freeze-thaw treatment: Effects of porous media property.

Freeze-thaw (FT) cycles would alter physical and chemical properties of soil and thus influence the transport of plastic particles (one type of emerging contaminant with great concerns). This study was designed to investigate the effects of FT treatment on the mobility of plastic particles (nanoplastics as representative) in columns packed with natural soils (i.e. loamy sand and sandy soil, quartz sand employed as comparison). We found that FT treatment of different types of porous media would induce different transport behaviors of plastic particles. Specifically, FT treatment of quartz sand did not affect plastic particles mobility. While FT treatment of loamy sand and sandy soil increased plastic particles transport. The increased pore sizes and disintegration of small soil particles from soils (the detached soil would serve as mobile vehicle for the transport of plastic particle) led to the facilitated mobility of plastic particles in two types of soils after FT treatment. The presence of preferential flow paths induced by FT treatment also drove to the enhanced mobility of plastic particles in sandy soil with FT treatment. This study clearly showed that the mobility of model plastic particles in two types of natural soils was greatly enhanced by FT treatment.

Transport behaviors of biochar particles in saturated porous media under DC electric field

The mobility of biochar in saturated quartz sand under a direct current (DC) electric field was investigated by column transport test. The effects of biochar preparation temperature (350 and 550 °C), solution chemistry (pH of 4, 7, and 10, and ion strength of 1, 10, 100 mM) and voltage gradient (0, 0.5 and 1.0 V cm−1) on the mobility of biochar were explored. It was found that DC electric field could significantly promote the migration of biochar, and the recovery rate of particles could be improved by 0.5–6.1 folds under 0.5 V cm−1. Higher voltage potential, solution pH and ionic strength were more favorable for biochar migration. The transport of biochar could be well interpreted by deterministic nonequilibrium convection-dispersion equation model. The enhanced mobility caused by DC electric field was attributed to the following reasons: enhanced electromigration following electrostatic attraction from the anode; increasing surface negative charges and functional groups on biochar surface as a result of electrochemical oxidization; reducing size blocking of biochar particles by decreasing particle size. Moreover, the interaction between biochar particles and electrode could alter solution chemistry, in particular, increasing solution pH, which in turn facilitated the transport of biochar. This study provided a perspective to modulate the transport behavior of biochar particle in the soil for the remediation of polluted sites.

Effects of ionic strength and particle size on transport of microplastic and humic acid in porous media

As an emerging pollutant, the transport behavior of colloidal microplastic particles (CMPs) in saturated porous media may be affected by the simultaneous presence of other substances in the natural environment. In this study, colloidal polystyrene microplastic particles (PSMPs) were selected as the representative of CMPs to investigate the cotransport behaviors of CMPs in the presence of humic acid (HA) under varied environmental conditions (ionic strength: 1, 100 mM KCl; HA concentration: 0, 5, 10, 20 mg⋅L−1) in porous media. The presence of HA with different concentrations was found to increase the mobility of 1.0-μm and 0.2-μm CMPs in porous media in a non-linear and non-monotonic manner. Furthermore, the HA-facilitated transport of CMPs occurred under both electrostatically unfavorable and favorable attachment conditions (limited to the conditions examined in this study, corresponding to 1 and 100 mM KCl, respectively). The transport behavior of the smaller-sized CMPs (0.2-μm CMPs) was more sensitive to the change of ionic strength and the presence of HA than that of the larger-sized CMPs (1.0-μm CMPs). The cotransport process of CMPs and HA was affected by many factors. Modeling results showed that a small amount of competitive blocking occurred during the cotransport process. Moreover, both the presence of HA and change in ionic strength could affect the surface properties of CMPs. Thus, the cotransport behavior of CMPs with HA was different from the transport of individual CMPs in porous media. Experimental results revealed that HA induced complexity in the transport behavior of CMPs in the aqueous environment. Therefore, undeniably, a lot more systematic explorations are further demanded to better comprehend the CMPs cotransport mechanism in the presence of other substances.

High-performance displacement by microgel-in-oil suspension in heterogeneous porous media: Microscale visualization and quantification

Hypothesis: Preferential flow in porous media is commonly encountered and decreases the multiphase displacement efficiency. Here, we synthesized microgel-in-oil in suspension and demonstrated that microgel-in-oil as a novel additive could present self-adaptive transport behavior and introduce a novel multiphase displacement mode for improving displacement efficiency in heterogeneous porous media.Experiments: We investigated the microgel-in-oil formation process and characterized their morphology with fluorescence microscopy and Cryo-SEM. The suspension displacement performance in heterogeneous porous media was evaluated using a microfluidic chip containing a preferential flow pathway (PFP) and a parallel matrix region. The displacement results of microgel-in-oil were compared to plain microgel particles and analyzed from pore-scale particle transport behavior to macroscopic multiphase flow patterns.Findings: The results show that suspension with moderate microgel-in-oil yields the optimal displacement efficiency. Fewer microgel-in-oil cannot alter the flow direction, while too many microgel-in-oil would block the PFP region. The topological analysis identified that suspensions with moderate microgel-in-oil content could achieve the strongest sweeping and carrying abilities that contribute to the highest displacement efficiency. The synergistic transport of microgel-in-oil and plain microgel particles would result in local pressure fluctuations to divert displacing fluid from PFP into the matrix region, which explains the above flow behavior.

Coal particle transport behavior in a rotating drill pipe used for negative pressure pneumatic conveying

Conveying gas velocity, rotation speed, and particle diameter are all common parameters in a negative pressure pneumatic conveying system that affect the system's energy consumption and design. Herein, the effect of the above three parameters on the transport behavior of coal particles was investigated by coupling Computational Fluid Dynamics and the Discrete Element Method (CFD–DEM) approach. The numerical results indicate that increasing gas velocity increased the number of coal particles entering the drill pipe. An increase in particle velocity increased conveying efficiency. With increasing particle diameter, the number of coal particles entering the drill pipe decreased. The particle velocity decreased, resulting in a decrease in conveying efficiency. In contrast, as the rotation speed increased, the particle distribution within the drill pipe became more dispersed, and the swirling flow trajectory became more apparent. The number of coal particles and conveying efficiency were decreased, although the effect on particle velocity was negligible.

A unified equation of settling velocity for particles settling in cylinder, annulus and fracture

In petroleum drilling and completion, the transports of solid particles through drill pipe, dill-hole annulus and fractures are important dynamic processes. Unlike particle transport in infinite space, the transports of cuttings, proppant and formation sand are hindered by finite boundary. Therefore, accurately describing particle transport behavior in different vessels is conducive to improving drilling safety and efficiency, especially with the rapid development of coiled tubing drilling and hydraulic fracturing technology. In this study, the particle settling experiment was carried out to study the particle settling behavior in the pipe, annulus and parallel plates filled with power-law fluids, involving the particle Reynolds number of 0.01–123.87, the dimensionless diameter of 0.20–0.80, the flow index of 0.48–0.69. Firstly, the wall effect of annulus is revealed through analyzing the settling process of the particles. Then the geometric continuity among the pipe, annulus and parallel plates was determined by introducing the ratio of inner diameter to outer diameter of the annulus, further the unified dimensionless diameter was defined to confirm the relationship between the three in terms of wall effect. In addition, a dimensionless term independent of settling velocity is introduced to establish a unified explicit settling velocity equation applicable to tubes, annulus and fractures with mean relative error of 9.36%. Finally, a calculation example is provided to clarify how to use the explicit model of settling velocity. This paper is the first study of annulus wall effects based on geometric continuity and will provide theoretical guidance for improving cuttings transport, proppant placement and sand management.

Recent advances in the understanding of alveolar flow.

Understanding the dynamics of airflow in alveoli and its effect on the behavior of particle transport and deposition is important for understanding lung functions and the cause of many lung diseases. The studies on these areas have drawn substantial attention over the last few decades. This Review discusses the recent progress in the investigation of behavior of airflow in alveoli. The information obtained from studies on the structure of the lung airway tree and alveolar topology is provided first. The current research progress on the modeling of alveoli is then reviewed. The alveolar cell parameters at different generation of branches, issues to model real alveolar flow, and the current numerical and experimental approaches are discussed. The findings on flow behavior, in particular, flow patterns and the mechanism of chaotic flow generation in the alveoli are reviewed next. The different flow patterns under different geometrical and flow conditions are discussed. Finally, developments on microfluidic devices such as lung-on-a-chip devices are reviewed. The issues of current devices are discussed.

Studying the effect of shear induced lift on the transport behavior of solid particles in an inclined channel using 2D segregation-dispersion model

In this study, a 2D segregation-dispersion model has been used to study the effect of shear induced lift on elutriation within a Reflux Classifier under continuous process conditions. The Reflux Classifier is a beneficiating technology comprising a fluidized bed with a set of parallel inclined channels above it. A 2D segregation-dispersion model of the device was utilized to study the mechanism of shear induced lift introduced as a contribution to the dispersion in the x-direction within the inclined channel. A multi-solid feed, 42 types of particle species having different densities and sizes, was simulated. It was observed that due to the shear induced lift, a phenomenon of particle resuspension occurred causing relatively higher solid volume fractions in the middle zone of the inclined channel. This happened because the coarse low-density particles experienced a higher shear induced lift and their concentration increased toward the middle zone. These coarse low-density particles and fine low-density particles moved out from the system via the overflow. Whereas, the fine dense particles experienced a low shear induced lift, hence, settled, slide backward, and discharged in the underflow. The lower Ep values ranging from 0.03 to 0.05 were obtained showing an improved separation performance.

Numerical Study on Particle Transport and Placement Behaviors of Ultralow Density Particles in Fracture-Vuggy Reservoirs

Summary A solid/liquid two-phase flow numerical model based on the computational fluid dynamics-discrete element method (CFD-DEM) model was established to study the transport and settlement law of ultralow-density (ULD) particles during the waterdrive channel adjustment of the Tahe carbonate fractured-vuggy reservoir. The mass, momentum, and turbulence equations of the fluid phase were established in Euler coordinates, whereas the particle motion equations were established based on Newton’s second law. The interaction between the ULD particles was described using a soft sphere model, and the water and particle phases were bidirectionally coupled. Meanwhile, virtual experiments were conducted to calibrate the contact parameters of the particles, and parallel plate experiments were performed to validate the model. Using numerical simulations of particle transport behavior in fractures, the process and characteristics of particle transport and placement in fractures are demonstrated, which can be described by the settlement profile angle and equilibrium gap height. According to parameterized simulations, the change law of the settlement profile angle and equilibrium gap height with different parameters such as particle size, pump displacement, and fracture width are demonstrated, which is helpful for the prediction of migration and accumulation of ULD particles in fracture-vuggy reservoirs.

Spatial configuration of charge and hydrophobicity tune particle transport through mucus

Mucus is a selectively permeable hydrogel that protects wet epithelia from pathogen invasion and poses a barrier to drug delivery. Determining the parameters of a particle that promote or prevent passage through mucus is critical, as it will enable predictions about the mucosal passage of pathogens and inform the design of therapeutics. The effect of particle net charge and size on mucosal transport has been characterized using simple model particles; however, predictions of mucosal passage remain challenging. Here, we utilize rationally designed peptides to examine the integrated contributions of charge, hydrophobicity, and spatial configuration on mucosal transport. We find that net charge does not entirely predict transport. Specifically, for cationic peptides, the inclusion of hydrophobic residues and the position of charged and hydrophobic residues within the peptide impact mucosal transport. We have developed a simple model of mucosal transport that predicts how previously unexplored amino acid sequences achieve slow versus fast passage through mucus. This model may be used as a basis to predict transport behavior of natural peptide-based particles, such as antimicrobial peptides or viruses, and assist in the engineering of synthetic sequences with desired transport properties.

Retention and transport behavior of microplastic particles in water-saturated porous media

Microplastic (MP) pollution has become a global concern given its wide occurrence and potential ecological risks. The retention/transport features of MPs in porous media govern the fate and risks of MPs in subsurface environments. Polystyrene (PS) microspheres are employed as representative MPs to explore the migration behaviors in water-saturated quartz sand columns. The hydrodynamic size mainly determines the deposition and size exclusion straining of MPs in porous media, and further the attachment efficiency. PS50 (PS with 50 nm diameter) shows a total migration rate greater than 85% in each of the studied conditions. In contrast, PS500 commonly exhibits slower migration velocities and higher attachment efficiencies than those of PS50 and PS100. The ionic strength, pH, and dissolved organic matter content of the solution show obvious effects on the retention/transport of PS MPs. The influences of solution chemical properties are consistent with the prediction of Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The results in this study clarify the size-dependent migration characteristics of MPs in porous media and provide a basis for risk assessment of MPs in terrestrial environments.

Effect of fracture roughness on transport of suspended particles in fracture during drilling

Fractures with different roughness are important permeable channels in oil and gas reservoirs. However, the drilling fluid is prone to leakage through fractures, resulting in formation damage. Study on the migration behavior of suspended particles with drilling fluid loss is the basis for finding the damage mechanism of solid invasion and drilling fluid loss control measures. From a comprehensive review of the previous studies, the transport behavior of suspended particles considering particle-fluid-fracture interaction hasn't been fully understood and quantified. In this study, we examined flow behavior of the particle-fluid mixture by the unresolved CFD-DEM approach. The effects of particle concentration, particle size, fracture width, drilling fluid loss rate, drilling fluid viscosity and cohesive force on particle transport in different rough fractures were studied. The research suggests that: (1) Increase of particle concentration will not only result in significant increase in fluid-particle velocity, but will also increase the wall mechanical retardation. (2) Particle aggregation near the fracture walls is more serious than in the fracture center. The shape of the agglomeration particle clusters is mainly elongated, with the long axis direction consistent with the flow direction. (3) Rough fracture walls will not only lead to more energy loss due to frequent particle-particle and particle-fracture contact, but also cause more particles to migrate in the fracture center.

Experimental Study of Transport Behavior of Swellable Microgel Particles in Superpermeable Channels for Conformance Control

SummaryGel treatment is an effective way to attack excessive water production during oil development. The transport behavior of gel materials in reservoirs is of crucial importance to the effectiveness of gel treatments. The aim of this paper is investigating the transport behavior of swellable micrometer-sized preformed particle gels (PPGs, or microgels) through superpermeable (super-K) channels. Sandpacks with permeabilities ranging from 27 to 221 darcies were used to mimic the super-K channels. Multiple pressure sensors were applied along the sandpack models to monitor the propagation behavior of the microgels. The tested microgel particles could transport through the super-K channels, and a higher driving pressure gradient was required when the particle/pore size ratio was larger. The pressure gradient distribution along the super-K channels was relatively uniform when the particle/pore ratio was low (less than 1.3). However, the inlet section would show increasingly higher pressure gradients as the particle/pore ratio was increased, indicating increased difficulty in propagation. The propagation of the gel particles was significantly slower compared with the carrying fluid. The delayed propagation behavior was more pronounced when the particle/pore ratio was higher. The injection pressure was much less sensitive to the injection flow rate compared with a Newtonian fluid. The gel dispersion exhibited an apparent shear thinning (pseudoplastic) behavior when transporting through the porous channels. Breakage of the gel particles was observed especially at high superficial velocities. The particle breakage was partially responsible for the apparent shear thinning behavior. The breakage phenomenon was in favor of deep placement of the gel particles. The channel permeabilities were significantly reduced by the microgels, bringing sufficient resistance to subsequent waterflooding (more than 99.5%). At given matching size conditions, softer gels were more likely to establish in-depth placement and uniform water blocking capacity in the channels. The microgel particles exhibited salinity-responsive behavior to the post-brine flush. The gel particles could shrink and reswell according to the salinity of the injected water. Possibilities were discussed to use this salinity-responsive behavior. Also, the microgels exhibited a particular disproportionate permeability reduction (DPR) effect. After gel injection, the channel permeability to water flow was reduced by more than 20 to 92 times of the permeability to oil flow. This work provides important support to understand the transport behavior of gel particles in super-K channels. The achievements are helpful for gel product selection and gel treatment design.

Numerical simulation of reactive particle transport in a randomly-orientated rough fracture with reversible and irreversible surface attachments

A novel and robust methodology has been developed to simulate reactive, dense, and polydisperse particle transport behavior in a randomly-orientated rough fracture by applying particle tracking algorithms and the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. More specifically, particle attachment onto an aperture surface is described by both reversible and irreversible adsorptions, which are respectively controlled by the energy barrier and the dominant forces at the secondary minimum on the DLVO interaction profiles. After the simulation model is validated, a number of simulation scenarios are conducted to examine the effect of dominant factors on the particle transport behavior subject to aperture surface attachment. It is found from the simulated results that a large spreading of particle plume is induced with the presence of particle gravity settling and surface attachment. Particle attachment is positively affected by particle size, fracture heterogeneity (i.e., σln(2b)2) and particle density (i.e., ρp) but negatively affected by hydraulic gradient (i.e., ∂h/∂x), fracture inclination (i.e., θ), and the ratio (i.e., λx/λy) of the x-directional to the y-directional correlation length scales of an aperture field. The sensitivity of particle attachment follows a strong-to-weak order for the non-DLVO parameters as ∂h/∂x > θ ≈ ρp > σln(2b)2 > λx/λy. Inconsistencies are also found between mass and number attachments for the associated quantities as well as sensitivities to the dominant factors. Among the non-DLVO factors, reversible attachment is more sensitively affected by ∂h/∂x, σln(2b)2, and λx/λy as they are capable of influencing the velocity field. An increased Hamaker constant (i.e., A123), particle surface potential (i.e., Ψp), and ionic strength (i.e., Is) respectively enhances, reduces, and enhances the overall particle attachment, while the irreversible attachment can be mildly mitigated by the increased A123 and Is when a deep secondary minimum appears on the DLVO profile. This study technically improves the previous work by jointly incorporating fracture orientation, particle gravity settling, and the reversible/irreversible surface attachment into the original particle transport models through a scientific manner. Also, this work further reduces the deviation between the existing theoretical modeling and the real particle transport/filtration behavior in fractured media, while the associated findings in this study provide better understanding and significance on this research topic.