Investigation on the Stability of the Dispersion System of Cross-Linked Polyacrylamide Microspheres

The salt resistance, temperature resistance, and shear stability of a cross-linked polyacrylamide microsphere system are studied by microfiltration, light diffraction analysis, and optical microscopy. The results show that other conditions being equal, the particle diameter of cross-linked polyacrylamide microspheres decreases with increased NaCl concentration. When NaCl concentration is lower than 10,000 mg/L, its effect on the plugging performance of a cross-linked polyacrylamide microsphere system in regard to the nuclear pore membrane is weak in comparison with a linked polymer solution, but the former system has better salt tolerance. Particle diameter decreases with increased swelling temperature. When the swelling temperature is below 90°C, its effect on the plugging performance of the cross-linked polyacrylamide microsphere system in regard to nuclear pore membrane is weak in comparison with the linked polymer solution, but has better temperature tolerance. Particle size shows little change, with shearing rate being increased, while the shape remains about the same and the effect of shearing on the plugging performance of the cross-linked polyacrylamide microsphere dispersion system in regard to the nuclear pore membrane is weak in comparison with the linked polymer solution, but has better shear stability. The salt tolerance, temperature tolerance, and shear stability of microspheres are associated with a particular cross-linked structure.     

Synthesis and plugging effect of inverse emulsion polymerization microspheres (OPME) for oil-based drilling fluids

It is difficult to seal oil-based drilling fluids in the large pore and micro-fracture formation, and there are few suitable materials for the oil phase with good sealing ability at present. In order to solve the problem of the lack of sealing ability of oil-based drilling fluids, acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, and acryloyl morpholine were used as monomers, N'N-methylenebisacrylamide was used as a cross-linking agent, Span-80 and Tween-60 were used as emulsifiers, and 2,2′-azobis(2-methylpropionamidine) dihydrochloride was used as an initiator. Polymer microsphere emulsion OPME was synthesized by inverse emulsion polymerization. The structure of polymer microspheres was characterized by infrared spectroscopy, scanning electron microscopy, electron microscopy, H NMR, laser particle size analysis and thermogravimetric analysis. The optimal synthesis conditions were determined by the control variable method: the monomer ratio of acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, and acryloyl morpholine was 45:20:15, the amount of emulsifier was 8%, and the reaction temperature was 55℃. The synthetic polymer microspheres were added to the oil-based drilling fluids to perform filtration and loss plugging at atmospheric pressure and high-temperature and high-pressure, as well as pore and artificial fracture core plugging evaluation. The evaluation results show that the permeability reduction rate of pore core can reach 82%, and that of fracture core can reach 100% by adding polymer microspheres with 3% dosage. Finally, the pressure transmission experiment proves that the addition of polymer microspheres can slow the pressure transmission and filtrate intrusion, and enhance the stability of wellbore. Therefore, polymer microspheres are a micron-level plugging agent with good compatibility and high performance with oil-based drilling fluids, and the 3% dosage can better seal the formation of large pores and micro-fractures, which has a good potential for field application.     

核壳聚合物微球调驱剂的合成及性能

以油酸改性二氧化硅为核,丙烯酰胺、2-丙烯酰胺-2-甲基丙磺酸为单体,采用反相乳液法合成了核壳聚合物微球调驱剂,其结构、微观形貌和性能经IR, SEM和TGA表征。结果表明：微球呈不规则球形,粒径分布较集中,中值粒径约300 nm;室温下,微球溶胀7 d可达最大膨胀倍率(7.43倍);1%微球可使油水界面张力降至0.028 mN·m^-1。岩心流动实验结果表明：与常规微球相比,核壳微球兼具封堵和洗油双重效果,注入0.5 PV微球,二次水驱升至3.36 MPa,累积采收率达93.86%。     

Pressure driven flow of polymer solutions in nanoscale slit pores

Polymer solutions subject to pressure driven flow and in nanoscale slit pores are systematically investigated using the dissipative particle dynamics approach. The authors investigated the effect of molecular weight, polymer concentration, and flow rate on the profiles across the channel of the fluid and polymer velocities, polymer density, and the three components of the polymers radius of gyration. They found that the mean streaming fluid velocity decreases as the polymer molecular weight and/or polymer concentration is increased, and that the deviation of the velocity profile from the parabolic profile is accentuated with increase in polymer molecular weight or concentration. They also found that the distribution of polymers conformation is highly anisotropic and nonuniform across the channel. The polymer density profile is also found to be nonuniform, exhibiting a local minimum in the center plane followed by two symmetric peaks. They found a migration of the polymer chains either from or toward the walls. For relatively long chains, as compared to the thickness of the slit, a migration toward the walls is observed. However, for relatively short chains, a migration away from the walls is observed.     

交联聚丙烯酰胺微球的形状与大小及封堵特性研究

采用流变、扫描电镜(SEM)、动态光散射(DLS)、核孔膜过滤和填充砂管驱替实验,研究了纳米级水溶胀交联聚丙烯酰胺微球的性能.结果表明,在一定的剪切速率范围内,微球浓度为100～900 mg/L的分散体系的黏度随剪切速率增加而增大,表现出较明显的剪切增稠的胀流体特性,微球浓度为50 mg/L的分散体系的黏度随着剪切速率...     

Flow Mechanism of Partially Cross-Linked Polyacrylamide in Porous Media

Partially cross-linked polyacrylamides (PCPAM) were prepared, and their rheological property, gel content, swelling property, and suspension property in saline solution were analyzed in laboratory. The goal of the research was to study the flow mechanism of PCPAM as a novel oil displacement agent in porous media. The migration behaviors of PCPAM were studied by single and series connection of double-tube sandpacked core flow experiments. The results showed that there was a critical pressure existing in the migration of PCPAM particles in porous media, and the migration was a dynamic process of plugging and flooding at the same time. When the pressure reached the critical pressure, the PCPAM particles would deform to pass through the pore throat and go ahead. Besides, the profile control experiments were conducted using a parallel connection of double-tube sandpacked core models, and the results revealed that PCPAM could generate “fluid diversion” and enlarge the swept volume of the lower permeable core. Moreover, micro-visualization displacement experiments were also carried out and proved that PCPAM could plug the high permeable pore throat to enlarge the swept volume, leading to an enhancement in oil recovery.     

具有光导性的磁性高分子微球——反应性铁酞菁与苯乙烯共聚

合成出了带有反应性基团的铁酞菁单体 ,并实现了与苯乙烯单体在磁流体存在下的分散聚合而得磁性高分子微球 .研究了微球结构、组成 ,测定了其磁响应性和光导性     

Gel kinetic characteristics and creep behavior of polymer microspheres based on bulk gel

Abstract

Deep profile control technology of polymer microspheres has become a widely used new method in improving oil recovery in heterogeneous reservoirs. The viscoelastic property of polymer microspheres plays an important role in the deformable migration behavior. In this study, a new method of measuring the viscoelastic properties of polymer microspheres based on bulk gel was proposed. Using mechanical rheometer and microrheometer, the effects on the storage modulus and gel performance were systematically researched. The creep-recovery test was applied to characterize the creep behavior of different polymer microsphere bulk gel. The results show that the storage modulus of polymer microspheres could be controlled by adjusting the agent concentration in the synthetic reaction. Moreover, the kinetic equation of gel time of polymer microspheres bulk gel and reaction temperature was established: ln(GT)?=?3289.18(1/T)-9.33. Elastic strain index was put forward as a new parameter to characterize the viscoelasticity of polymer microsphere in creep-recovery test. Finally, relationship between elastic strain index and storage modulus was constructed and a classification criterion of polymer microspheres with different viscoelasticity was proposed based on a large number of creep-recovery results. The research could provide a good theoretical guidance and technical support for the understanding of viscoelasticity of polymer microspheres.     

Effective velocity and effective dispersion coefficient for finite-sized particles flowing in a uniform fracture

In this work we derive expressions for the effective velocity and effective dispersion coefficient for finite-sized spherical particles with neutral buoyancy flowing within a water saturated fracture. We considered the miscible displacement of a fluid initially free of particles by another fluid containing particles of finite size in suspension within a fracture formed by two semi-infinite parallel plates. Particle spreading occurs due to the combined actions of molecular diffusion and the dispersive effect of the Poiseuille velocity profile. Unlike Taylor dispersion, here the finite size of the particles is taken into account. It is shown that because the finite size of a particle excludes it from the slowest moving portion of the velocity profile, the effective particle velocity is increased, while the overall particle dispersion is reduced. A similar derivation applied to particles flowing in uniform tubes yields analogous results. The effective velocity and dispersion coefficient derived in this work for particle transport in fractures with uniform aperture are unique and ideally suited for use in particle tracking models.     

Graded regulation technology for enhanced oil recovery and water shutoff in pore-cavity-fracture carbonate reservoirs

Although a single type of chemical agent (eg, gels, microspheres, surfactants, etc.) has achieved some effects in enhanced oil recovery of carbonate reservoirs, for pore-cavity-fracture carbonate reservoirs, the use of a single type of chemical agent does not perform well. The main objective of this study is to study the effect of different types of chemical agents in enhanced oil recovery of complex carbonate reservoirs. In order to determine the screening principle of chemical agents, the types of water channeling in the North Troyes reservoir were analyzed. For complex fractures, step by step plugging, multi-agent and multi-slug comprehensive intervention is carried out to ensure the plugging of high-permeability channels and inhibit the seepage of large channels. It can plug channeling fracture channel, adjust secondary dominant channel and reduce matrix flow resistance, so as to expand macroscopic swept volume and improve microscopic water flooding efficiency. The results show that it is difficult to comprehensively control water channeling in pore-cave-fracture carbonate reservoir, and the reservoir heterogeneity in the test area can be improved by mixing different types of control and flooding agents and carrying out deep profile control. The plugging rate of gel is 97.18 %, and the oil–water selection ratio is 0.45 in fractured core; the expansion rate of nano - microspheres is more than 3 times; the wetting modifier can improve the imbibition oil displacement efficiency by 14.76%, and the test result shown that nano - microspheres and wetting modifier have good synergistic oil displacement effect. The field application result shown that daily oil production of oil well in the test area increased by 5.0 m³/d and the daily water rate decreased by 19.0% compared with that before the control flooding. The findings of this study can help for better understanding of enhanced oil recovery in pore-cave-fracture carbonate reservoir.     

Graft copolymers having hydrophobic backbone and hydrophilic branches. XI. Preparation and thermosensitive properties of polystyrene microspheres having poly (N-isopropylacrylamide) branches on their surfaces

Thermosensitive microspheres with 0.4–1.2 μm diameter consisting of a polystyrene core and poly(N-isopropylacrylamide) (polyNIPAAm) branches on their surfaces were prepared by the free radical polymerization of a polyNIPAAm macromonomer and styrene in ethanol. Electron spectroscopy for chemical analysis (ESCA) of the microsphere surface suggested that polyNIPAAm chains were favorably located on the surface of the microspheres. The morphology of the microspheres was observed by transmission electron micrograph (TEM) and the particle size of was estimated by submicron particle analyzer. The molecular weight of the polyNIPAAm macromonomer, the ratio of the macromonomer and styrene, and the polymerization temperature affected the particle size. Thermosensitive properties of polyNIPAAm-coated polystyrene microspheres were evaluated by the turbidity of their dispersion solutions and the hydrodynamic size of the miocrospheres. The transmittance in dispersion solutions changed clearly, similar to oligoNIPAAm and polyNIPAAm macromonomers. In addition, the particle size of microspheres decreased with rising temperature. These results were explained by the thermosensitivity of polyNIPAAm branches on the microsphere surface. © 1996 John Wiley & Sons, Inc.     

Study on the Plugging Ability of Polymer Gel Particle for the Profile Control in Reservoir

Polymer gel particle is a widely used deep profile control agent to plug the water breakthrough channel in reservoir. However, there is still no theoretical model to describe its plugging ability available when it is applicated. Based on the Hertz contact theory and force analysis, the plugging model of polymer gel particle is established at the view of pore throat, and the parameters in the model are achieved by the pore throat experiments. The plugging model is verified by the core experiments. The results show that the plugging strength of polymer gel particle keeps rise with the increasing of the ratio between particle diameter and pore throat size, and then it will stay at a stable value because of the limitation of material strength. The material strength is 0.32 MPa and the particle will be broken when the size ratio is over 3. The plugging strength of the polymer gel particles with the diameters of 30–40 µm and 60–80 µm is 0.12 and 0.31 MPa in the cores with the permeability of 2989.6 × 10^?3 and 3014.7 × 10^?3 µm², respectively, which is consistent perfectly with the theoretical calculation. The plugging model of polymer gel particle is verified to be correct and can be applied to the profile control in reservoir.     

带有酰胺侧基的中空手性高分子微球的合成及其分离性能

合成了带有手性基团的多孔高分子微球, 并将其作为高效液相色谱手性固定相用于分离制备盐酸贝那普利的一个重要中间体(R)-α-羟基苯丁酸乙酯.     

Experimental Study of Microscopic Displacement Efficiency of Polymer Microspheres Using Low-Field NMR

For reservoirs in high water cut exploitation period, profile control and water plugging is one of the important ways to improve oil recovery. Cores with different permeability were flooded to analyze the displacement results and displacement mechanisms for different grain size of polymer microspheres. Fluid distribution in cores was measured by NMR spectroscopy after water flooding, polymer microspheres flooding, and subsequent water flooding. The range of pore sizes from which oil was swept out was also calculated. The results showed that microspheres can effectively sweep remaining oil in different pore size of the cores. The suitability of different grain size of polymer microspheres with cores is different, microspheres with micron size are suitable for high-permeability cores, and microspheres with nanometer size are suitable for low-permeability cores.     

Efficient synthesis of monodisperse,highly crosslinked,and “living” functional polymer microspheres by the ambient temperature iniferter‐induced “living” radical precipitation polymerization

The facile and efficient one‐pot synthesis of monodisperse, highly crosslinked, and “living” functional copolymer microspheres by the ambient temperature iniferter‐induced “living” radical precipitation polymerization (ILRPP) is described for the first time. The simple introduction of iniferter‐induced “living” radical polymerization (ILRP) mechanism into precipitation polymerization system, together with the use of ethanol solvent, allows the direct generation of such uniform functional copolymer microspheres. The polymerization parameters (including monomer loading, iniferter concentration, molar ratio of crosslinker to monovinyl comonomer, and polymerization time and scale) showed much influence on the morphologies of the resulting copolymer microspheres, thus permitting the convenient tailoring of the particle sizes by easily tuning the reaction conditions. In particular, monodisperse poly(4‐vinylpyridine‐co‐ethylene glycol dimethacrylate) microspheres were prepared by the ambient temperature ILRPP even at a high monomer loading of 18 vol %. The general applicability of the ambient temperature ILRPP was confirmed by the preparation of uniform copolymer microspheres with incorporated glycidyl methacrylate. Moreover, the “livingness” of the resulting polymer microspheres was verified by their direct grafting of hydrophilic polymer brushes via surface‐initiated ILRP. Furthermore, a “grafting from” particle growth mechanism was proposed for ILRPP, which is considerably different from the “grafting to” particle growth mechanism in the traditional precipitation polymerization. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Effect of asymmetrical flow field-flow fractionation channel geometry on separation efficiency

The separation efficiencies of three different asymmetrical flow field-flow fractionation (AF4) channel designs were evaluated using polystyrene latex standards. Channel breadth was held constant for one channel (rectangular profile), and was reduced either linearly (trapezoidal profile) or exponentially (exponential profile) along the length for the other two. The effective void volumes of the three channel types were designed to be equivalent. Theoretically, under certain flow conditions, the mean channel flow velocity of the exponential channel could be arranged to remain constant along the channel length, thereby improving separation in AF4. Particle separation obtained with the exponential channel was compared with particle separation obtained with the trapezoidal and rectangular channels. We demonstrated that at a certain flow rate condition (outflow/inflow rate = 0.2), the exponential channel design indeed provided better performance with respect to the separation of polystyrene nanoparticles in terms of reducing band broadening. While the trapezoidal channel exhibited a little poorer performance than the exponential, the strongly decreasing mean flow velocity in the rectangular channel resulted in serious band broadening, a delay in retention time, and even failure of larger particles to elute.     

Preparation of core-shell microporous organic polymer-coated silica microspheres for chromatographic separation and N-glycopeptides enrichment

Through a “one-pot” strategy, a layer of microporous organic polymer was coated onto the surface of monodisperse amino-functionalized silica microsphere via amino-aldehyde condensation reaction with core-shell structure. The change in chemical structure of material before and after modification was determined by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Due to existence of a large number of amino and aldehyde groups in microporous organic polymer shell, the water contact angle decreased from 56.8° (silica microspheres) to 34.7° (microporous organic polymer-coated silica microspheres). Based on these properties, microporous organic polymer-coated silica microspheres were employed as the stationary phase for capillary liquid chromatography and successfully offered baseline separation of polar small molecules. Additionally, the material could also be served as the sorbent of hydrophilic interaction chromatography to enrich glycopeptides from human serum digest. A total of 470 unique N-glycopeptides and 342 N-glycosylation sites mapped to 112 N-glycosylated proteins were unambiguously identified from 2 μL of human serum, exhibiting a promising application prospect of microporous organic polymer-coated silica microspheres in the pretreatment of proteomics samples.     

Electrorotation of leaky-dielectric and conducting microspheres in asymmetric electrolytes and angular velocity reversal

We consider the central problem of polarizable and leaky-dielectric uncharged spherical particle freely suspended in an unbounded nonsymmetric binary electrolyte, which is forced by an ambient time-harmonic uniform electric field. Under the assumption of a “weak field,” we employ the linearized standard electrokinetic model of binary electrolytes to account for such anion/cation asymmetry. A simplified generalized asymmetric dipole-term approximation, valid for a dielectric/conducting microsphere, is analytically derived for an arbitrary Debye scale and for any mismatch between ion diffusivities and valances. A two-peak unified dispersion spectrum covering all range of practical frequencies (KHz to MHz), is found for the case of a rotating electric field (ROT). The angular velocity of a free polarized particle is composed of dielectrophoretic contribution, resulting from the electrical torque (dipole term) as well as from the induced electroosmotic (ICEO) flow field. The two effects usually act in opposite directions. Under ROT excitation, we obtain a cofield rotation at high frequencies (MHz) and a counter-field behavior at low frequencies (KHz). The low-frequency dispersion is generally governed by electric double-layer charging and the high frequency by a Maxwell–Wagner relaxation process. ICEO generally dominates the low-frequency cofield response; however, it can be shown that depending on the electrolyte asymmetry, yet another dielectrophoretic related switching (reversal) point might exist. Furthermore, for large frequencies and depending on the complex permittivity ratio between the particle and electrolyte, we find a second switching point. Explicit expressions for the above two frequency reversal values are obtained in terms of the problem physical parameters and are compared against experimental results. Finally, we provide an analytical solution for the ROT ICEO velocity field of a microsphere as a function of electrolyte asymmetry and Debye length and compare it with numerical simulations.     

Determination of individual microsphere properties by capillary electrophoresis with laser-induced fluorescence detection

Capillary electrophoresis with postcolumn laser-induced fluorescence detection was used to individually detect 6.0, 1.0, 0.5, and 0.2 num diameter polystyrene microspheres and individually measure their electrophoretic mobility. The analysis of a nanoliter-size volume from a microsphere suspension results in an electropherogram characterized by several narrow spikes in a well-defined migration time window. Each spike is associated with one microsphere because, when one single microsphere is introduced into the capillary by micromanipulation, the electropherogram has only one spike in the same migration time window. The distributions of individual measurements resulting from an electropherogram were used to evaluate the reproducibility from run to run, observe the effect of sodium dodecyl sulfate (SDS) added to the running buffer, and to investigate the origin of electrophoretic dispersion. As expected from the interactions between microspheres and SDS, the addition of this surfactant to the running buffer narrowed the range and shifted the average electrophoretic mobility to more negative values. After evaluating common sources of broadening in capillary electrophoresis, electrophoretic dispersion was attributed to microsphere heterogeneity. Unlike electropherograms displaying Gaussian-like profiles, the two-dimensional representations of the individual measurements provide a new alternative to evaluate and study electrophoretic-related properties of microspheres.     

Continuous flow separation of particles within an asymmetric microfluidic device

A microfluidic based device has been developed for the continuous separation of polymer microspheres, taking advantage of the flow characteristics of systems. The chip consists of an asymmetric cavity with variable channel width which enables continuous amplification of the particle separation for different size particles within the laminar flow profile. The process has been examined by varying the sample inlet position, the sample to media flow rate ratio, and the total flow rate. This technique can be applied for manipulating both microscale biological and colloidal particles within microfluidic systems.