Interactions of ferro-nanoparticles(hematite and magnetite) with reservoir sandstone: implications for surface adsorption and interfacial tension reduction

There are a few studies on the use of ferro-nanofluids for enhanced oil recovery,despite their magnetic properties;hence,it is needed to study the adsorption of iron oxide(Fe2 O3 and Fe3 O4) nanoparticles(NPs) on rock surfaces.This is important as the colloidal transport of NPs through the reservoir is subject to particle adsorption on the rock surface.Molecular dynamics simulation was used to determine the interfacial energy(strength) and adsorption of Fe2 O3 and Fe3 O4 nanofluids infused in reservoir sandstones.Fourier transform infrared spectroscopy and X-ray photon spectroscopy(XPS) were used to monitor interaction of silicate species with Fe2 O3 and Fe3 O4.The spectral changes show the variation of dominating silicate anions in the solution.Also,the XPS peaks for Si,C and Fe at 190,285 and 700 eV,respectively,are less distinct in the spectra of sandstone aged in the Fe3 O4 nanofluid,suggesting the intense adsorption of the Fe3 O4 with the crude oil.The measured IFT for brine/oil,Fe2 O3/oil and Fe3 O4/oil are 40,36.17 and 31 mN/m,respectively.Fe3 O4 infused with reservoir sandstone exhibits a higher silicate sorption capacity than Fe2 O3,due to their larger number of active surface sites and saturation magnetization,which accounts for the effectiveness of Fe3 O4 in reducing IFT.

Effect of different concentrations of surfactant on the wettability of coal by molecular dynamics simulation

Anionic surfactant sodium dodecyl benzene sulfonate(SDBS)at varying concentrations was selected to investigate the influence on the wettability of Zhaozhuang Coal by molecular dynamics simulation.Six groups of water/surfactant/coal systems with different concentrations were constructed.The influence of surfactant with different concentrations on the wettability of coal was concluded by analyzing various properties from the energetic behaviors to the dynamic characteristics.The results show that the interfacial tension decreases sharply and then rises slowly with the increase of SDBS surfactant concentration,obtaining that surfactants can obviously reduce the interfacial tension.The surfactant molecules could be detected at the water/coal interface through analyzing the system’s relative concentration distribution.In addition,the difference in the wettability of surfactants on coal surfaces is caused by the spatial distribution differences of alkyl chains and the benzene ring of the surfactant molecules.And the negative interaction energy between SDBS and the coal surface indicates that adsorption process is spontaneous.Furthermore,it is of great practical significance for improving the dust reduction effect and reducing the disaster of coal dust by exploring the effects of surfactant molecules on the wettability of coal.

Study on the Mechanism of Asphaltenes Reducing Oil-Water Interfacial Tension

As high polar components of crude oil, asphaltenes play a significant role in reducing oil-water interfacial tension(IFT). In this paper, the effects of asphaltenes on reducing IFT in the presence of surfactant were compared, and the mechanism of asphaltenes reducing the IFT was studied by the dynamic interfacial tension(DIFT) equation. Whether asphaltenes were added to the oil or 2,5-dimethyl-4-(4-dodecyl) benzene sodium sulfonate(p-S14-4) was added to the water phase, either of all results in the IFT reducing and the IFT is related to the coverage and the mass of asphaltenes adsorption at the interface. In the presence of asphaltenes, the adsorption of the active substances to the interface is not entirely dependent on diffusion, and the process can be divided into three regions. Region I: the IFT rapidly reducing, this process is controlled by diffusion of surfactant;Region II: the IFT reducing slowly, resulted from the lower diffusion rate that is limited due to the aggregates formed by the interaction of asphaltene-asphaltene;Region III: the interaction of asphaltene-asphaltene is broken by the interaction of surfactant-asphaltene. The asphaltene aggregates are reduced and adsorbed rapidly at the interface. Furthermore, the results reveal that the asphaltenes concentration affects the coverage rate and adsorption at the interface.

Contact angle and stability of interfacial nanobubble supported by gas monolayer

Since solid-liquid interfacial nanobubbles(INBs)were first imaged,their long-term stability and large contact angle have been perplexing scientists.This study aimed to investigate the influence of internal gas density and external gas monolayers on the contact angle and stability of INB using molecular dynamics simulations.First,the contact angle of a water droplet was simulated at different nitrogen densities.The results showed that the contact angle increased sharply with an increase in nitrogen density,which was mainly caused by the decrease in solid-gas interfacial tension.However,when the nitrogen density reached 2.57 nm^(-3),an intervening gas monolayer(GML)was formed between the solid and water.After the formation of GML,the contact angle slightly increased with increasing gas density.The contact angle increased to 180°when the nitrogen density reached 11.38 nm^(-3),indicating that INBs transformed into a gas layer when they were too small.For substrates with different hydrophobicities,the contact angle after the formation of GML was always larger than 140°and it was weakly correlated with substrate hydrophobicity.The increase in contact angle with gas density represents the evolution of contact angle from macro-to nano-bubble,while the formation of GML may correspond to stable INBs.The potential of mean force curves demonstrated that the substrate with GML could attract gas molecules from a longer distance without the existence of a potential barrier compared with the bare substrate,indicating the potential of GML to act as a gas-collecting panel.Further research indicated that GML can function as a channel to transport gas molecules to INBs,which favors stability of INBs.This research may shed new light on the mechanisms underlying abnormal contact angle and long-term stability of INBs.

页岩油-CO_(2)、CH_(4)、N_(2)混合物界面性质的分子动力学模拟研究

油气界面张力是气驱提高采收率过程中分析油气两相混合程度、影响油气最小混相压力和注气开发效果的重要参数。针对页岩油的主要成分正辛烷(C8),通过分子动力学模拟方法研究了纯CO_(2)和混合气体(CO_(2)、CH_(4)、N_(2))与C8的界面张力及界面微观特征变化规律,并考虑了温度、压力和气体组分等外界因素对界面特征的影响。结果表明,随着气相压力的增大,气体与C8混合程度增大,界面厚度、粗糙度、相对吸附量等微观特征增强,导致油气界面张力逐渐减小。界面张力随温度在不同压力区间表现出相反的变化趋势:在低压时温度越高,界面张力越小;在高压时温度越高,界面张力反而越大。相较于纯CO_(2)、CH_(4)和N_(2)的加入会增大混合气体与油相的界面张力,其中N_(2)对油气界面张力的影响更大;同时CH_(4)和N_(2)会使得油气界面厚度、相对吸附量等微观特征减弱。在三元CO_(2)+CH_(4)+N_(2)/C8体系中,CO_(2)的相对吸附量最大,CH_(4)次之,N_(2)最小,证明了3种气体与油的相互作用由强到弱为CO_(2)>CH_(4)>N_(2)。此外,所有体系相对吸附量均大于0,吸附量越大,界面张力随压力的增大下降得越快,这与吉布斯吸附理论相一致。

基于分子动力学方法的致密砂岩储层CO_(2)驱油研究进展

随着致密砂岩储层CO_(2)-EOR项目的不断增加,亟需对CO_(2)与致密砂岩储层流体在孔隙介质中的相互作用机理进行研究,但室内实验难以观察到CO_(2)与流体在孔隙通道中的动态过程,而分子动力学模拟则可以弥补传统实验和数值方法的不足。为此,围绕该方法在CO_(2)-EOR研究中的2大重点——界面行为与受限空间运移行为,对包括萃取、溶胀、降黏、降低界面张力、最小混相压力、润湿性等6个方面界面行为的相关研究成果进行了系统梳理,结合前人对CO_(2)与致密砂岩储层流体在受限空间中运移行为的研究成果,提出了分子动力学在致密砂岩储层CO_(2)-EOR研究中的关键科学问题。研究结果表明:①分子动力学能够很好地将CO_(2)萃取原油中—轻烃组分的过程进行可视化,建议根据原油实际组分构成分析CO_(2)的萃取能力,从而弄清CO_(2)萃取原油中各组分的优先顺序及效率;②有关CO_(2)分子对原油溶胀降黏作用的研究,大多数成果中的原油组分体系较为单一,建议根据实际储层的原油组分,系统探讨高温高压条件下CO_(2)的溶胀降黏作用;③对于CO_(2)与油水两相之间界面张力的研究更多是在体相中进行展开,而在纳米受限空间界面行为的研究还有待完善;④有关地层水在孔隙壁面的润湿性研究,对不同因素之间的协同效应影响润湿性的机理尚不明确。结论认为,随着量子力学研究的不断深入以及计算性能的日益强大,该方法可以在更大尺度上进行复杂体系的计算,以其为基础的油藏、页岩油气藏CO_(2)-EOR机理等研究将会取得较大的突破。

改性聚丙烯酰胺降低油水界面张力行为的分子动力学模拟

采用分子动力学模拟方法,从原子分子层次考察部分水解聚丙烯酰胺(HPAM)以及改性HPAM的界面活性。结果表明:HPAM降低油水界面张力能力极其有限,而引入疏水基团后的HPAM具有较好的降低界面张力效果;改性HPAM的疏水基团增强与油相的作用,并在界面处形成致密的聚合物膜,增加油水界面层厚度,隔离油水相接触,从而降低油水接触形成的界面张力;盐离子的存在增加油水界面张力,改性HPAM引入的磺酸基团具有较好的抗盐能力,可以降低界面处盐离子的聚集,从而减弱盐离子对界面张力的影响。

驱油剂对无碱三元复合驱采出液乳化稳定性影响

为探究无碱三元驱油剂对于采出液乳化稳定的机理,为采出液处理提供依据。对游离水中含油量、油水动态界面张力、液滴界面寿命与油滴粒径分布状态及粒径随驱油剂含量的变化进行了研究。加入低浓度表面活性剂(100 mg/L)时,动态界面张力、界面寿命、油滴粒径均显著降低,水中含油量显著增加,随着表面活性剂浓度增加,动态界面张力、界面寿命、粒径、含油量变化均不明显;随着NaCl浓度上升,动态界面张力与界面寿命变化不明显,油滴粒径变大,水中含油量增加;随着聚合物浓度增加,动态界面张力与界面寿命变化不明显,对于油滴粒径与含油量出现双重作用。这表明表面活性剂与NaCl有利于乳化稳定,但表面活性剂作用远大于NaCl;低浓度聚合物不利于乳化稳定,随着浓度增加,有利于乳化稳定。

HPAM聚合物与离子型表面活性剂协同稳定CO_(2)泡沫的分子模拟研究

CO_(2)泡沫驱可以有效地控制CO_(2)相的流度从而提高波及效率,同时它还能够进行CO_(2)地质封存,减少碳排放以应对全球气候变暖的挑战。表面活性剂能降低CO_(2)泡和水相液膜之间的界面张力(IFT),从而增加因拉普拉斯毛细管自吸效应导致的泡沫液膜中液体析出的阻力。聚合物可以提高泡沫液膜黏度,也可以减缓液膜中的液体析出并缓解气泡聚并现象。二者同时被用作提高泡沫稳定性的化学试剂,然而表面活性剂分子根据亲水头基电荷正负属性不同会具有不同的界面行为,在微观尺度下不同类型表面活性剂和聚合物分子之间的协同作用还不明确。本研究采用分子动力学模拟的方法,研究了油藏条件下阴离子型(SDS)和阳离子型(CTAB)表面活性剂分别与水解聚丙烯酰胺(HPAM,水解度25%)在CO_(2)与水相界面处的相互作用。研究结果表明,CTAB比SDS具有更强的降低CO_(2)与水之间IFT的能力,IFT的大小与界面宽度和界面覆盖率呈正相关性。具有相同电性的HPAM与平衡离子Br-在CTAB界面膜上形成竞争吸附关系;而带有相反电性的HPAM与平衡离子Na+在SDS界面膜附近形成盐桥结构。前者更有利于降低气—液界面处IFT和增大液膜厚度,两种模式对泡沫液膜剪切黏度的提高程度差别不大。本研究揭示了阴/阳离子型表面活性剂分别与水解聚合物分子协同作用稳定CO_(2)泡沫的微观机制。

疏水界面上的NaCl液滴蒸发过程内环流调控机制研究

盐水微液滴蒸发结晶在海水淡化、晶体制备、药物预混合和颗粒筛选中具有非常重要的作用。通过计算流体动力学模型,对不同疏水界面传热系数和不同直径疏水平台上的NaCl盐水液滴蒸发过程开展模拟研究,主要通过模拟预测了液滴内流体在温度和浓度差作用下的环流演变机制。模拟结果通过光学可视化和红外热成像仪进行了验证。结果表明,常温蒸发下,NaCl液滴内部的环流主要由Rayleigh对流和溶质Marangoni效应主导。不同的固液界面传热系数会影响液滴的升温速率和温度分布,当温差大于一定值时,热Marangoni效应可以主导液滴内部环流。基于Rayleigh数和Marangoni数的调控区间制得了流场演变相图,有效地预测液滴内部的环流状态。盐水液滴内环流方向和持续时间可以通过调整热Marangoni效应来控制,从而影响最终蒸发结晶的晶体形貌和沉积分布。这项工作可以为蒸发界面设计、蒸发结晶的过程控制等提供理论依据。

透明质酸体系与水界面稳定性的分子动力学模拟

为考察仿生黏液透明质酸体系与水相界面行为随时间的变化规律,结合Forcite模块,采用Nose扩展系统控温法、Atom based计算方法和Ewald计算方法,通过分子动力学研究,探讨仿生黏液-水界面的分子之间的变化。以透明质酸的水溶液为代表,模拟生物黏液,从微观层面探讨界面稳定性:从界面张力、界面相互作用能、径向分布函数和均方根位移等方面分析影响界面稳定性的因素。结果表明:仿生黏液在透明质酸高分子多聚体和水分子在质量比为1∶10时的界面张力最小为61.33 mN/m,此时的单位界面能最低为242.67 kJ/(mol·nm^(2)),界面最稳定。根据MSD曲线和RDF(径向分布函数),从水分子和透明质酸分子相互作用的强弱和水分子的移动也间接地表明在质量比为1∶10时,体系界面稳定性最高。模拟结果与实验的稳定性结果一致,从微观层面解释了透明质酸体系和水界面的一些规律。

熔渣中金属液滴沉降过程流体力学模拟

建立熔炼渣中金属液滴沉降过程的数学模型,研究不同粘性模型下金属/熔渣界面张力对液滴沉降速度以及拖曳力的影响。结果表明:对于较小直径的液滴,Laminar模型和RNG k-ε湍流模型能够准确预测液滴最终沉降速度;界面张力对液滴沉降速度有影响,且影响作用随着液滴尺寸增大而逐渐增大;“RNG+CSS”模型可以准确描述液滴沉降过程和液滴沉降速度的变化。结合数学模型和实验数据,推导出耦合界面张力作用下拖曳力系数计算公式。该模型揭示熔炼渣中金属液滴沉降过程机理,为实际生产中降低渣中有价金属含量提供理论指导。

表面活性剂亲水-亲油能力对动态界面张力的影响

The dynamic interfacial tensions between hydrocarbons and solutions of surfactants having different hydrophilic- lipophilic ability are measured.The effects of ionic strength and alkyl chain carbon- number on dynamic interfacial tensions are also studied.It is found that adsorption- desorption barriers are connected with the hydrophilic- lipophilic ability of surfactants.There exists a large or small adsorption- desorption barrier to the transfer of surfactant having strong hydrophilic or lipophilic ability from water to oil.The influences of ionic strength and alkyl chain carbon- number on adsorption- desorption barriers are discussed.

Triton X-100/甲苯/水三元体系界面张力的耗散颗粒动力学模拟

采用耗散颗粒动力学方法在介观层次上模拟了非离子表面活性剂TritonX-100在油/水界面上的分布行为,并把用于油/水二元体系界面张力的计算方法拓展到含表面活性剂的三元体系.利用该方法可以得到与实验数值吻合的界面张力数据.另外,模拟结果直观展示了表面活性剂界面张力与界面密度的关系,为表面活性剂复配增效理论提供了依据.该模拟方法给出的微观信息可以为驱油体系配方筛选和表面活性剂有效应用提供指导.

结合图像数字化技术用悬滴法测动态界面张力——动态界面张力与表面活性剂浓度的关系

A pendant drop tensiometry apparatus aided by video-image digitization technology was established, by which static interface or surface tension of some liquids was measured with satisfactory results.In order to study the effect of emulsifier concentration on emulsion stability, dynamic interfacial tension was measured between toluene and water against concentration of Tween 60(Polyoxyethylene(20) stearyl-sorbitanate). As expected, higher concentration is the Tween 60 solution in toluene injected into the toluene phase, faster falls the interface tension between toluene and water.Furthermore, it reveals interestingly that two steps of diffusion occur in the system, i.e ., at low and high concentration, after the surfactant solution is injected.The characteristic process of dynamic interface tension can be ascribed to diffusion control because of linearity between interface tension and the minus second root of aging time.The discovery is correlated to the fact that much higher concentration of surfactant above its critical micelle concentration is often required when a stable emulsion is planned to prepare.

油相性质对水相中混合表面活性剂协同效应的影响

通过不同碳链长度的正构烷烃与石油磺酸盐 非离子表面活性剂和石油磺酸盐 十二烷基苯磺酸钠体系之间动态界面张力的研究 ,发现混合表面活性剂在降低界面张力能力方面的协同效应不仅与表面活性剂分子之间的相互作用有关 ,而且与油相性质密切相关。

复合驱油体系与胜利原油间的动态界面张力特性

本文系统研究了不同离子强度和碱浓度条件下胜利原油 碱水体系的动态界面张力特性 ,考察了复合驱体系各组分对界面张力的影响。发现胜利原油与碱水间的界面张力在适宜的离子强度和碱浓度条件下达到最低 ,碱与表面活性剂之间在降低界面张力方面存在明显的协同效应 ,而表面活性剂与聚合物之间不存在明显的协同效应。

碱/烷基硫酸盐、烷基磺酸盐体系与原油间的动态界面张力的研究

合成了一系列高纯度的表面活性剂。在碱溶液中添加单一的表面活性剂 ,简化了驱油体系。考察了表面活性剂的结构、浓度与动态界面张力的关系。结果表明 ,只有当表面活性剂在两相的分配系数适当时 。

渤海油田聚合物驱采出液的破乳研究

采用室内模拟的聚合物驱采出液,研究了聚合物含量对渤海油田聚驱采出液破乳效果的影响,通过油水界面动态界面张力的测定,对破乳机理进行了探讨。结果表明,油溶性高分支破乳剂ICO-89针对模拟聚驱采出液具有较好的破乳效果,对于ρ(聚)=50 mg/L的模拟采出液,破乳2 h脱水率达到85%,随着聚合物含量的增加,脱水率呈下降趋势,当ρ(聚)=300 mg/L时,破乳2 h脱水率降至81%。破乳剂的分子结构与油水界面吸附能力的强弱是影响破乳脱水的两个重要因素。

十二烷基甜菜碱/十二烷基硫酸钠复配体系与原油间的界面张力

通过界面张力测定 ,研究了两性表面活性剂十二烷基甜菜碱 (C12 BE)与阴离子表面活性剂十二烷基硫酸钠 (SDS)复配体系的界面活性 .结果表明 ,C12 BE与SDS复配 ,其界面活性产生较强烈的增效作用 ,C12 BE/SDS =6 ∶ 4 (摩尔比 )时增效作用最显著 .以此配比的C12 BE/SDS作为复配表面活性剂FS ,采用旋滴法探讨了FS/碱 /聚乙二醇PEG2 0 0 0 0与孤东原油体系的动态界面张力(IFT) ,并考察了离子强度和烷醇酰胺对体系IFT的影响 .发现了碱与外加表面活性剂FS之间存在明显的协同效应 ,使界面张力达到超低的条件 :适宜的离子强度及烷醇酰胺加量 .而聚乙二醇PEG2 0 0 0 0的加入既改善了体系的流度 ,又可延长低界面张力状态稳定存在的时间 。