回灌过程中离子强度和水流流速对胶体粒子在多孔介质中堵塞的影响

人工回灌过程中的堵塞问题一直是影响其推广的瓶颈,目前回灌过程中大颗粒悬浮物导致的堵塞机理研究较多,对胶体类颗粒物的堵塞机理研究相对少。采用室内砂柱实验,研究不同离子强度和不同水流流速条件下胶体在饱和多孔介质中的迁移-滞留特征。选择大肠杆菌为实验胶体,设计在不同离子强度、不同水流条件下的砂柱回灌实验;运用Hydrus-1D软件模拟,拟合穿透曲线后得到表征胶体沉积的相关参数。实验结果表明,在相同的离子强度下,流速增大会促进胶体的迁移,穿透曲线峰值增高,胶体的吸附率减小。在中等离子强度条件下(IS=30、50 mmol·L-1)流速对胶体的这种影响比在更低的离子强度(≤10 mmol·L-1)或更高的离子强度(≥300 mmol·L-1)条件下更为显著;相反地,同一流速条件下,离子强度从10 mmol·L-1升高到300 mmol·L-1时,胶体的吸附随着离子强度的增加而迅速增加。从胶体和介质相互作用势能来看,随着离子强度的增加,胶体和砂表面的相互作用增强,有利于胶体吸附在介质表面,增加介质堵塞的概率。但是,在一定的离子强度下,流速的增加产生的水动力剪切力有利于促进胶体的迁移,不利于胶体的吸附或阻塞,减少了微小颗粒堵塞的概率。模拟结果显示吸附速率系数k、最大固相沉积量Smax随着离子强度的增大而增大,随着流速的增大而减小。从整体上来看,回灌过程中胶体微粒的迁移滞留行为主要受控于离子强度,但水流因素会干扰离子强度的控制作用。在实际的人工回灌过程中,有效的预防堵塞需要将化学(降低离子强度)和水动力(增加回灌水流速)手段有效地结合起来。     

回灌过程中离子强度和水流流速对胶体粒子在多孔介质中堵塞的影响

人工回灌过程中的堵塞问题一直是影响其推广的瓶颈,目前回灌过程中大颗粒悬浮物导致的堵塞机理研究较多,对胶体类颗粒物的堵塞机理研究相对少。采用室内砂柱实验,研究不同离子强度和不同水流流速条件下胶体在饱和多孔介质中的迁移-滞留特征。选择大肠杆菌为实验胶体,设计在不同离子强度、不同水流条件下的砂柱回灌实验;运用Hydrus-1D软件模拟,拟合穿透曲线后得到表征胶体沉积的相关参数。实验结果表明,在相同的离子强度下,流速增大会促进胶体的迁移,穿透曲线峰值增高,胶体的吸附率减小。在中等离子强度条件下（IS=30、50 mmol·L^-1）流速对胶体的这种影响比在更低的离子强度（≤10 mmol·L^-1）或更高的离子强度（≥300 mmol·L^-1）条件下更为显著;相反地,同一流速条件下,离子强度从10 mmol·L^-1升高到300 mmol·L^-1时,胶体的吸附随着离子强度的增加而迅速增加。从胶体和介质相互作用势能来看,随着离子强度的增加,胶体和砂表面的相互作用增强,有利于胶体吸附在介质表面,增加介质堵塞的概率。但是,在一定的离子强度下,流速的增加产生的水动力剪切力有利于促进胶体的迁移,不利于胶体的吸附或阻塞,减少了微小颗粒堵塞的概率。模拟结果显示吸附速率系数k、最大固相沉积量S_max随着离子强度的增大而增大,随着流速的增大而减小。从整体上来看,回灌过程中胶体微粒的迁移滞留行为主要受控于离子强度,但水流因素会干扰离子强度的控制作用。在实际的人工回灌过程中,有效的预防堵塞需要将化学（降低离子强度）和水动力（增加回灌水流速）手段有效地结合起来。     

悬浮微粒在被加热多孔介质内的沉积与运移特性

通过建立沿管壁恒热流加热的渗流实验系统,实验研究了悬浮颗粒在饱和多孔介质内以及入口界面处的沉积和运移特性。着重研究了有无加热条件,以及不同加热温差,相同多孔介质和进口悬浮液浓度情况下,实验段入口界面处与内部的颗粒沉积量变化,以及沿程不同位置处的压力变化。并对实验过程中的渗流稳定性及各测点温度和多孔介质段渗透系数进行了分析。结果表明:相对渗透率k_t/k₀在不同温差下有明显不同;多孔介质与进口流体界面处的沉积量随温差的增大而增加,沉积结构的稳定性降低;多孔介质段颗粒沉积强度随温差的增大而增大,实验结果可为今后的理论分析提供验证依据。     

颗粒直径对吸附分离影响的数值模拟

基于Fluent的多孔介质模型,建立了变压吸附制氧发生器的立式填充床模型。采用用户自定义函数功能,以反映吸附传质、传热,并将多孔介质单相模型整合为更精确的气固两相耦合模型。在此基础上,模拟了吸附颗粒直径对气相压力、速度、床层压降以及氧气分离浓度、回收率等参数的影响情况。结果表明：床层压降随颗粒直径的增大而减小;床层对入口急流的抗穿透性能随颗粒直径的增大而减小;相同条件下,采用较小颗粒直径能够提高氧气分离浓度、回收率,原因在于小颗粒直径降低了床层内气体的流速,增加了吸附时间,促进了吸附的进行。     

阴离子聚丙烯酰胺在多孔介质中的流变特性

本文研究了阴离子聚丙烯酰胺溶液流经多孔介质的流变性及滞留在多孔介质中聚合物与注水速度的关系．聚合物溶液通过多孔介质的流动特点和由滞留在多孔介质中的聚合物引起注入水的流动特点有相似的流变特性，然而由作用机制引起的效应是不同的．本文根据分子间相互作用力的改变和应力与分子的反应变化解释了不同流速范围内的流变特征．     

木质素磺酸钠在活性炭/水界面的吸附机理

为了探究木质素磺酸钠在活性炭/水界面的吸附机理,研究了温度、pH 值、无机盐、脲以及直链醇对其吸附动力学及吸附等温线的影响.吸附动力学结果表明,木质素磺酸钠在活性炭/水界面的吸附约在10 min 内快速达到平衡;随着离子强度的增加及脲的加入吸附速率常数增大,pH值增加,吸附速率常数先增大后减小.不同pH值条件下的木质素磺酸钠在活性炭/水界面的吸附等温线符合 Langmuir 方程;随着离子强度增大、脲或直链醇的加入,吸附过程更符合 Freundlich 模型.增加离子强度、降低 pH 值及加入直链醇都可显著提高木质素磺酸钠的平衡吸附量,而脲的加入降低平衡吸附量.在中性条件下木质素磺酸钠主要通过疏水作用和氢键作用吸附在活性炭/水界面,疏水作用有利于加快吸附速率及增加吸附量,该吸附过程不受温度的影响.     

粘土矿物对聚合物的静态吸附研究

聚合物在流经多孔介质过程中,由于表面吸附和聚合物分子间的相互作用而产生滞留,影响驱油效果。本文采用淀粉-碘化镉法测得了绥中36-1油田不同粘土矿物对疏水聚合物AP-P4的吸附量,分析了聚合物在浓度、温度发生变化时对粘土矿物吸附量的影响,并得出单位质量粘土矿物对聚合物吸附的变化规律:粘土矿物随聚合物AP-P4浓度的增加单位质量吸附量逐渐增大,随着水浴温度的增加单位质量吸附量逐渐下降。     

岩心中粘土含量对聚合物滞留与捕集的影响

聚合物在流经多孔介质的过程中,由于表面吸附、机械捕集、水动力学捕集和聚合物分子间的相互作用而产生滞留,影响驱油效果。本文通过物质平衡法测得了张家口不同粘土含量的岩心中聚丙烯酰胺的滞留量与捕集量,分析了岩心中的粘土含量对聚合物滞留与捕集的影响,并得出了吸附量、滞留量与捕集量的关系。     

交联聚合物溶液突破性能

交联聚合物溶液（LPS）是由低浓度部分水解聚丙稀酰胺和交联剂柠檬酸铝形成的交联聚合物线团（LPC）在水中的分散体系。采用毛玻璃模型驱油实验和核孔膜过滤实验研究了LPS的突破性能以及再封堵特性。实验结果表明,LPS在多孔介质吸附滞留封堵后可以产生突破,突破后还具有再次封堵特性,能够起到更好的深部调剖效果;LPS封堵后突破压力与封堵强度有关,在缓慢升压的情况下,LPC不断的滞留、聚集,形成‘滤饼’,封堵强度越来越大,需要很高的压力才能够使封堵的LPC克服LPC与多孔介质的吸附力以及LPC分子间力产生突破,在封堵强度较低的情况下必须有一个较高的冲击力才能使封堵的LPC发生突破;形成LPS聚合物相对分子质量越高或者封堵的多孔介质孔径越小则其突破压力越大。     

羧甲基纤维素钠改性零价铁在石英砂中的迁移能力

利用羧甲基纤维素钠（CMC）对零价铁进行改性,通过Zeta电位、粒型粒度和沉降曲线的变化探讨改性剂添加量影响零价铁分散的机理,同时考察改性剂添加量、流速和多孔介质类型对零价铁迁移的影响。结果表明,CMC对零价铁的分散机理符合DLVO模型,静电空间位阻带来的势垒增加量与CMC添加量成正相关,能促进零价铁的分散;经500%CMC（CMC与零价铁的质量比）改性的零价铁分散性能最好,成颗粒状、吸光度在90 min下降31%。受零价铁与石英砂作用能、填充介质的吸附位点和剪切力的影响,零价铁的迁移能力随着CMC添加量的增多,填充介质粒径的增大和流速的增加而增强。     

Transport and retention of polymer-stabilized zero-valent iron nanoparticles in saturated porous media: Effects of initial particle concentration and ionic strength

This study investigated the transport and retention of polyacrylic acid and polyvinylpyrrolidone stabilized zero-valent iron nanoparticles (PAA-ZVIN and PVP-ZVIN) in saturated porous media. The transport experiments were conducted in sand packed columns. The breakthrough curves (BTCs) and retention curves of ZVIN were analyzed. Results of transport experiments showed that increasing initial particle concentration and ionic strength led to a decrease in ZVIN transport. The zeta potentials and hydrodynamic diameters of PAA-ZVIN were apparently more negative compared to PVP-ZVIN. Results indicated that some mechanisms such as aggregation, ripening, and surface roughness had considerable impact on ZVIN retention in porous media.     

Role of Interfacial Interactions in the Deposition of Colloidal Clay Particles in Porous Media

Colloidal clay particle transport under saturated conditions is believed to be controlled by its interactions with the surrounding environment. The dominating forces among these interactions are electrostatic forces that are determined by colloidal clay particle and porous medium surface charge density and Lifshitz–van der Waals forces that are determined by colloidal clay particle and porous medium surface thermodynamic properties. Electrostatic forces are greatly affected by solution chemistry in terms of solution ionic strength and pH. In this research, electrostatic and Lifshitz–van der Waals forces of natural colloidal clay particles with a model porous medium of silica sand were quantified at different ionic strength and pH conditions. At the same time, colloidal clay particle transport in the model medium of silica sand was conducted in a laboratory column. The maximum electrostatic forces, F ^EL (max), which occurred when the separation distance between colloidal clay particles and the porous medium was in the range of the sum of the double layer thicknesses of the colloidal clay particles and the porous medium, was found to be the determinant factor for colloidal clay particle deposition in the porous medium. Colloidal clay particle desorption in the porous media was related to the net effect of attractive Lifshitz–van der Waals forces and repulsive electrostatic forces, evaluated at the equilibrium distance where physical contact between the colloidal clay particle and silica sand actually occurred (i.e., affix force). Higher colloidal clay particle desorption was found to coincide with smaller affix force values.     

Effect of sample’s length on flow properties of open-cell metal foam and pressure-drop correlations

Many applications require fluid flow through the open pores of metal foam. The foam is usually treated as a porous medium for which the Darcy law and the Hazen-Dupuit-Darcy (or Forchheimer) equation are used to describe the pressure drop, and for obtaining the two important flow properties, i.e., the permeability and the form drag coefficient. Little or no attention is paid to the length (or thickness) of the porous medium in the flow direction. This paper establishes a minimum length necessary for the foam to have length-independent (or bulk) permeability and form drag coefficient. This minimum length is obtained experimentally for various types of open-cell aluminum foam subjected to airflow in the Forchheimer regime. Below this thickness values of the two key flow properties are not constant, and they include entrance/exit effects, which may explain some of the discrepancies in the reported values in the literature. The Forchheimer equation was recast in two different manners, which resulted in new non-dimensional numbers- one representing the form drag and the other the viscous drag. These numbers correlated very well with the thickness of the porous medium. The obtained correlations allow for determining the pressure drop given only the velocity and the thickness of an aluminum foam sample.     

Creeping motions of a composite sphere in a concentric spherical cavity

An analytical study is presented for the quasisteady translation and steady rotation of a spherically symmetric composite particle composed of a solid core and a surrounding porous shell located at the center of a spherical cavity filled with an incompressible Newtonian fluid. In the fluid-permeable porous shell, idealized hydrodynamic frictional segments are assumed to distribute uniformly. In the limit of small Reynolds number, the Stokes and Brinkman equations are solved for the flow field of the system, and the hydrodynamic drag force and torque exerted by the fluid on the particle which is proportional to the translational and angular velocities, respectively, are obtained in closed forms. For a given geometry, the normalized wall-corrected translational and rotational mobilities of the particle decrease monotonically with a decrease in the permeability of its porous shell. The boundary effects of the cavity wall on the creeping motions of a composite sphere can be quite significant in appropriate situations. In the limiting cases, the analytical solutions describing the drag force and torque or mobilities for a composite sphere in the cavity reduce to those for a solid sphere and for a porous sphere.     

不同pH环境下CMS改性纳米铁在异质多孔介质中的迁移

纳米铁在污染土壤和地下水的修复中受到广泛关注。为进一步探究其在多孔介质的迁移行为,本研究采用羧甲基淀粉钠（CMS）对纳米零价铁（nZVI）进行包覆,进行了改性纳米零价铁的沉降试验,测量zeta电位与粒径分布探究其分散性;进行了不同pH条件下改性纳米零价铁在酸洗砂与水洗砂的柱实验,分析了化学异质性与pH对纳米铁在多孔介质迁移的影响。结果表明,CMS包覆纳米铁不仅使纳米颗粒本身稳定,而且还减少其在多孔介质表面沉积,大大提高了迁移性。pH=6～8时,nZVI的zeta电位由18.3mV减小到2.9mV,有效粒径由685nm增大到880nm,稳定性变差;而CMS-nZVI的zeta电位值由-19.7mV增大到-53.5mV,颗粒间静电排斥力增强稳定性变好。经能量色散X射线光谱（EDS）分析,水洗砂表面存在碳、铝、铁等氧化物杂质,这些杂质带有正电荷,会增强与带负电的CMS-nZVI的吸附作用,不利于其迁移;而经过酸洗后的石英砂,其表面杂质大大减少,在pH=8时,CMS-nZVI在酸洗砂最大迁移率为77.0%要好于水洗砂的63.0%。此外较高pH环境有助于增加石英砂介质的表面负电荷,减少颗粒与介质的吸附,促进纳米颗粒的迁移。     

Flow of nanodispersed catalyst particles through porous media: Effect of permeability and temperature

The proposed in situ catalytic upgrading of heavy oil to achieve an environmentally sustainable method for heavy oil recovery requires the placement of nanodispersed catalyst particles deep into the formation where it can accelerate the high‐temperature upgrading reactions. In continuation of the previous work [Zamani et al., Energy Fuels 24, 4980‐4988 (2010)], this paper presents results of several new experiments carried out to examine the effects of other parameters, including the connate brine salinity, absolute permeability, sand‐bed temperature and particle concentration on the propagation of nanoparticles in porous media. The results show that lower permeability, increased operating temperature and higher particle concentration did not significantly affect the propagation of nanodispersed catalyst suspension through the sand‐bed. Virtually the same filtration behaviour, displaying a rapid increase of effluent concentration at 1 pore volume injected to a steady concentration close to the inlet concentration was seen in all experiments. A classical phenomenological approach was used to model the macroscopic propagation behaviour of suspended particles in the porous medium. The model was successful in history matching the effluent composition profile observed in the experiments and the deposition profile obtained from post‐test analysis of the sand‐bed. © 2011 Canadian Society for Chemical Engineering     

净水功能型透水混凝土的组成设计研究

为净化雨水和补充地下水,设计了一类净水功能型偏高岭土基地聚合物透水混凝土。通过研究壳聚糖掺量、碱激发剂模数与碱当量对偏高岭土基地聚合物浆体力学、吸附特性的影响,制备了一种可用于透水混凝土的高吸附性浆体材料。基于此,进一步探讨了透水混凝土骨料堆积孔隙率、浆集比(P/A)等体积结构参数对其净水、透水与力学性能的影响。结果表明:随着壳聚糖掺量的增加,偏高岭土基地聚合物的强度呈先提高后降低的趋势,Pb²⁺的吸附量呈增大趋势;随着骨料堆积孔隙率的增大,透水混凝土的力学和净水性能均减弱,透水性增强;随着浆集比的增大,透水混凝土力学与净水性能增大,透水性减小。最终设计出净水、透水与力学性能协调的透水混凝土,其28 d抗压强度、透水系数和Pb²⁺去除率分别为20.1 MPa、0.67 cm/s和90.5%。     

Pore‐network modeling of particle retention in porous media

Transport and filtration of micron and submicron particles in porous media is important in applications such as water purification, contaminants dispersion, and drilling mud invasion. Existing macroscopic models often fail to be predictive without empirical adjustments and a more fundamental approach may be required. We develop a physically‐representative, 3D pore network model based on a particle tracking method to simulate particle retention and permeability impairment in polydisperse particle systems. The model includes the effect of hydraulic drag, gravity, electrostatic and van der Waals forces, as well as Brownian motion. A converging‐diverging pore throat geometry is used to capture the mechanism of interception. With the analytical solution of fluid velocity within a pore throat, the trajectory of each particle is calculated explicitly. We also incorporate surface roughness and particle–surface interaction to determine particle attachment and detachment. Pore throat structure and conductivity are updated dynamically to account for the effect of deposited particles. Predictions of effluent concentration and macroscopic filtration coefficient are in good agreement with published experimental data. We find that the filtration coefficient is dependent on the relative angle between fluid flow and gravity. Particle deposition by interception is significant for large particle/grain size ratios. Brownian diffusion is the primary cause of retention at low Peclet numbers, especially for small gravity numbers. Particle size distribution is found to be a cause of hyperexponential deposition often observed in experiments. Permeability reduction was small for strong repulsive forces because particles only deposited in paths of slow velocity. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3118–3131, 2017     

多孔介质内颗粒流动特性的格子Boltzmann模拟

地下岩石孔隙中小颗粒的运移和沉积会使得储层渗透性能降低,影响石油开发。为了探究悬浮颗粒在多孔介质中的流动过程,采用格子Boltzmann方法对三维多孔介质内流体和颗粒的运动过程进行了数值模拟,采用有限体积颗粒法构建多孔介质中骨架颗粒和悬浮颗粒。通过Half-Way反弹格式实现流体与颗粒间的相互作用,考虑孔隙结构、入口流速、孔隙率和颗粒直径对颗粒流动特性的影响,探究颗粒的运移和沉积规律。结果表明,入口速度对不同孔隙结构下颗粒的运动作用显著。随着入口速度增大,颗粒与颗粒、孔隙壁面以及流体之间的动量和能量交换作用增强,缩短了颗粒的运移路径,颗粒沉积率逐渐变小,颗粒拟温度增大。孔隙率的下降强化了颗粒间的碰撞,孔隙率由0.581降低至0.400,使得颗粒拟温度提升至9倍。颗粒拟温度随颗粒直径的增加而增加。但随着孔隙率增加,颗粒轴向速度增加,颗粒最高轴向速度可达入口流速的11倍,而颗粒接触力降低。