Experimental Evaluation of the Inhibitors Performance on the Kinetics of Asphaltene Flocculation

The kinetics of asphaltene flocculation are studied on two types of Iranian crude oil. Kinetic studies are conducted by applying near infrared spectrophotometry. The presence of inhibitors in the sample reduces the amount of light absorption of crude oil sample. The effect of these inhibitors according to the initial changes in the light absorption of crude oil samples is studied. The obtained results indicate that the asphaltenes are the highest stabilized in presence of the vegetable oil types (hazelnut and walnut) and chemical compound (4-dodecylresorcinol).     

Investigation of Asphaltene Aggregate Size Distribution Under Aggregation and Breakage Phenomena Using Monte Carlo Simulation

In this article, the aggregation and breakage processes are simulated through Monte Carlo method for asphaltene aggregates under shear-induced petroleum mixtures. The simulation results are verified by the aggregate size distributions of two types of asphaltenes having different fractal dimensions extracted from Iranian crude oil types. The obtained aggregate size distributions are affected by shear rate, toluene to heptane ratios and the oil type. The dynamic evolution of asphaltene aggregates shows an ascendant trend with time until they reach a maximum average diameter and then descent to a steady-state size. The asphaltene fractal dimension affects the aggregation process.     

Smart Determination of Difference Index for Asphaltene Stability Evaluation

Precipitation and deposition of asphaltene during different stages of petroleum production is recognized as problematic in oil industry because of the increase in production cost and the inhibition of a consistent flow of crude oil in different medium. Numerous correlations have been developed to determine asphaltene stability in crude oil. In this study, a novel ONN method was used to estimate difference index from SARA fraction data for rapid, accurate, and cost-effective determination of asphaltene stability. Neural networks are highly in danger of trapping in local minima. To eliminate this flaw, a hybrid genetic algorithm-pattern search technique was used instead of common back-propagation algorithm for training the employed neural network. A comparison between neural network and optimized neural network indicated superiority of optimized neural network.      

DPD Molecular Simulations of Asphaltene Adsorption on Hydrophilic Substrates: Effects of Polar Groups and Solubility

Adsorption of asphaltenes onto a polar substrate (e.g., a mineral) was modeled with dissipative particle dynamics (DPD) simulations, using continental asphaltene models. The adsorption mechanisms in 10–20% wt, of asphaltene in toluene/ heptane solutions were studied (well above the solubility limit). The structure in the adsorbed layer was highly sensitive to the presence of polar groups in the alkyl side chains and heteroatom content in the aromatic ring structure. Four types of asphaltene models were used: completely apolar (zero adsorption), apolar chains and polar heteroatoms, polar chains and no heteroatoms, and polar chains and heteroatoms (maximum adsorption). One hundred asphaltene monomers were distributed homogeneously in the solvent initially, in a ～(10 nm)³ domain.

Asphaltene monomers adsorbed irreversibly on the substrate via the polar group in the side chains, resulting in an average perpendicular orientation of the aromatic rings relative to the substrate. More frequent π–π stacking of the aromatic rings occurred for less solubility (more heptane), as in aggregates. With apolar side chains, only the heteroatoms in the aromatic ring structure had affinity to the substrate, but the ring plane did not have any preferred direction.

An important finding is that the aromatic ring assemblies “shielded” the substrate and polar groups that were anchored to the substrate, resulting in an effective non-polar surface layer seen by asphaltenes in the bulk, leading to much lower adsorption probability of the remaining asphaltenes. This “adsorption termination” effect leads to mono-layer formation. Continued adsorption with multilayering and reversible nanoaggregate adsorption occurred when both side chains in the model asphaltene (located on opposite sides of the aromatic sheet) contained polar groups, with a higher probability of exposing further polar groups to the bulk asphaltene. The general conclusion is that the number and position of the polar groups in side chains determine to a large degree the adsorption and aggregation behavior/efficiency of (continental) asphaltenes, in line with experimental evidence. The heteroatoms in the aromatic ring structure plays a more passive role in this context, only by providing organization via more π–π stacking in the adsorbed layer, and in aggregates.     

基于支持向量机方法的HERG钾离子通道抑制剂分类模型

对human ether-a-gō-gō related genes(HERG)钾离子通道(钾通道)抑制剂,计算了表征分子组成、电荷分布、拓扑、几何结构及物理化学性质等特征的1559个分子描述符.采用Fischer Score(F-Score)排序过滤和Monte Carlo模拟退火法相结合从中筛选与HERG钾通道抑制剂分类相关的分子描述符.采用支持向量机(SVM)方法,分别以IC50=1.0、10.0μmol·L-1为分类标准,建立了三个分类预测模型.对367个训练集分子,用五重交叉验证.得到正、负样本的平均预测精度分别为84.8%-96.6%、80.7%-97.7%,其总的平均预测精度为87.1%-97.2%,优于其它文献报道结果.对97个外部测试集分子,所建三个模型的总样本预测精度在67.0%-90.1%之间,接近或优于其它文献报道结果.     

Generation of Asphaltene Deposition Envelope Using Artificial Neural Network

The usefulness of the asphaltene deposition envelope (ADE) is that no asphaltene flocculation occurs at conditions outside the envelope. Since artificial neural network (ANN) is best at identifying patterns or trends in data, it is well suited for prediction or forecasting needs. ANN is also capable of addressing case specific problems that may be encountered in the field such as deposition of asphaltene. In this article, the high pressure, high temperature setup used to perform pressure depletion experiments at three different temperatures on one the Iranian live oils and the ADE generated using ANN.     

Asphaltene Precipitation Modeling Using Fuzzy Tuning of Scaling Equations

A major concern in the petroleum industry is asphaltene precipitation, which has negative impacts on production costs and recovery. The scaling equation is the most popular approach for modeling asphaltene precipitated out of solution in crude oils. Due to different values assigned for involved coefficients in scaling equations, they might overestimate or underestimate in some region relative to each other. This study proposes an improved strategy for tuning scaling equations and compensating effects of overestimation and underestimation through fuzzy rules. This strategy, called fuzzy tuning of scaling equations (FTSE), has a parallel framework, which gains outputs of different scaling equations and then introduces them to a fuzzy model as inputs. The fuzzy model breaks down the problem into subspaces through fuzzy membership functions and solves each region separately using fuzzy rules. Aggregating results of each subspace produces final model's output (i.e., FTSE output). Results indicated that FTSE performed more satisfyingly compared with individual scaling equations performing alone.      

Polarization of Fluorescence of Asphaltene Containing Systems

Formation of supermolecular structures in petroleum disperse systems is determined by interactions of asphaltenes. Petroleum systems are lyophilic oleocolloids with low polar dispersive media which is in dynamic balance with elements of disperse structure. Supermolecular scale of organization is most important for determining the macroscopic parameters. Levshin-Perrin equation for depolarization of fluorescence was modified for polydispersed systems. Interfacial tension coefficient of model asphaltene solution was calculated in a case of Volmer's function. For technogenic mixtures the temperature dependences of the sizes near the point of phase transition are presented. Enthalpy of asphaltene association per one molecule was calculated. Polarization degree together with macroscopic parameters correlates with appearance of asphaltene dispersed phase in system.     

用紫外-可见分光光度计测定油样中沥青质含量

介绍了一种用分光光度法测定油品中的沥青质含量的方法。通过测定样品悬浮液在７５０ｎｍ、８００ｎｍ下的吸光度而获得样品中正庚烷沥青质含量,阐述了方法的测量原理,讨论了取样量范围、沥青地方法的影响。结果表明,该法可应用于各种油品（如原油、重质馏分油、渣油和沥青等）的分析,具有简单、快速的优点,相对标准偏差小于３％。     

The Effect of Sample Age and Neutron Radiation to Dynamic Nuclear Polarization Parameters in Some Asphaltene Suspensions

Nuclear magnetic resonance and the Overhauser effect type dynamic nuclear polarization experiments were performed to study suspensions of asphaltene in the xylene isomers at a low magnetic field of 1.44 mT at room temperature. Intermolecular spin-spin interactions occur between nuclear spins of hydrogen in the solvent medium and the free electron spins in the asphaltene micelles. The samples were prepared in three different asphaltene concentrations at vacuum. The samples were waited for four years and dynamic nuclear polarization parameters were found via dynamic nuclear polarization experiments performed again. Thus, it was investigated the effect of sample age to dynamic nuclear polarization parameters. In addition, the medium concentrations of each sample were exposed to radiation for 48 hours and neutron radiation effects to the dynamic nuclear polarization parameters were investigated. The results are discussed.     

Influence of Asphaltene Concentration on the Interfacial Properties of Two Typical Demulsifiers

Oil-in-water emulsion is an innovate manner by which heavy crude oil can be transported from producing sites to transforming sites through pipelines. The effect of emulsifier on the interfacial properties and demulsification performance of demulsifier for heavy crude oil–in-water emulsion has been studied by many researchers. However, the influence of asphaltene in heavy crude oil on the interfacial properties of demulsifier has not been investigated yet. In this article, the influence of asphaltene concentration of two typical demulsifiers (straight-chained SP-1 and branch-chained AE-1) was systematically studied in terms of absorption thermodynamics, absorption kinetics, and coalescence kinetics. The results revealed that the demulsifier adsorption was a ΔS controlled spontaneous process. The absolute value of ΔG of SP-1 adsorption was found to decrease with asphaltene concentration, whilst the asphaltene concentration had no significant influence on that of AE-1. With the increase of asphaltene concentration, the demulsifiers’ adsorption rates increased, but the reorganization rates on the interface decreased. Coalescence speed of asphaltene droplet decreased with asphaltene concentration in spite of demulsifier type. Additionally, AE-1 had higher absolute value of ΔG, adsorption speed, and coalescence speed than that of SP-1 at the same condition.     

Asphaltene Instability Trends of Light and Heavy Crude Oils

In this work, two Iranian crude oils diluted in 1-methylnaphthalene (1-MN) were titrated with selected n-alkanes. Subsequently, samples were observed microscopically to determine the onset of asphaltene precipitation. A series of micrographs from de-asphaltening were used to show visible changes of the asphaltene sizes, shapes, and frequencies by addition the n-heptane to the subsamples after 5, 6, 11, and 24 hour lag times. The refractive indices (RI) of the titrated mixtures at different temperatures below and above the onset conditions were measured aiming to establish the asphaltene instability trend. Results show that for the diluted light and heavy crude oils, the onset of asphaltene precipitation is rather a gradual process with an almost constant slope of RI decrease due to the separation of asphaltene clusters from the mixture. This is a kinetically controlled process. Furthermore, the nature of the precipitant is likely to play a notable role. The rate of RI decreasing with temperature was approximately 0.0004/°C for both tested crude oils.     

Patchy粒子聚集的统计力学研究

应用统计力学原理对A_aB_b型Patchy粒子的聚集过程进行研究, 考察了典型平均物理量在聚集过程中的变化情况. 首先基于配分函数导出体系的平衡自由能及描述Patchy粒子之间联接作用的质量作用定律, 进而获得团簇的数量分布函数. 进一步给出Patchy团簇的数均和重均聚合度以及物理凝胶化条件, 探讨了凝胶化区域与Patchy粒子数之间的依赖关系. 同时给出Patchy团簇生长的微分动力学方程, 并进行了相应的Monte Carlo模拟. 本文旨在揭示Patchy粒子的内在和外在因素对体系聚集态结构的影响, 为实现对Patchy粒子体系的有效调控提供理论依据.     

Effect of Crude Oil Aging on Asphaltene Inhibitor Product Recommendation

Aging refers to the deterioration of hydrocarbon fluids that manifests as changes in the physicochemical characteristics of the fluid upon exposure to ambient conditions. In order to understand the effect of aging of crude oils on asphaltene inhibitor product recommendation, simulated aging studies were performed on a crude oil from Wyoming with known asphaltene issues. The results clearly show that aging of crude oil affects the stability of the oil with respect to asphaltenes and caution must be exercised when recommending asphaltene inhibitor if the evaluations were performed on fluids after long-term storage. A real case study where ambient storage in the lab adversely affects the stability of the crude oil and renders asphaltene inhibitor ineffective further confirms results from simulated aging.     

The Effect of Number of Arms on the Aggregation Behavior of Thermoresponsive Poly(N-isopropylacrylamide) Star Polymers

The thermoresponsive nature of aqueous solutions of poly(N-isopropylacrylamide) (PNIPAAM) star polymers containing 2, 3, 4, and 6 arms has been investigated by turbidity, dynamic light scattering, rheology, and rheo-SALS. Simulations of the thermosensitive nature of the single star polymers have also been conducted. Some of the samples form aggregates even at temperatures significantly below the lower critical solution temperature (LCST) of PNIPAAM. Increasing concentration and number of arms promotes associations at low temperatures. When the temperature is raised, there is a competition between size increase due to enhanced aggregation and a size reduction caused by contraction. Monte Carlo simulations show that the single stars contract with increasing temperature, and that this contraction is more pronounced when the number of arms is increased. Some samples exhibit a minimum in the turbidity data after the initial increase at the cloud point. The combined rheology and rheo-SALS data suggest that this is due to a fragmentation of the aggregates followed by re-aggregation at even higher temperatures. Although the 6-arm star polymer aggregates more than the other stars at low temperatures, the more compact structure renders it less prone to aggregation at temperatures above the cloud point.     

Morphology and Size Distribution Characterization of Precipitated Asphaltene from Live Oil During Pressure Depletion

The size and morphology of asphaltene aggregates, precipitated from live oil by pressure depletion at the reservoir temperature was studied using scanning electron microscopy and atomic force microscopy. The experimental studies showed that the mean size of aggregates increased when pressure decreased. The results indicate that the morphology of aggregates was changed from amorphous spherical and elliptical shapes to irregular. A bimodal distribution function was able to describe the size distribution in pressure range of 500 to 3500 psi. At higher pressure, the unimodel was able to represent the size distribution. The results showed reduction in live oil stability and asphaltene aggregation with pressure drop.     

Effect of Asphaltenes and Resins on Asphaltene Aggregation Inhibition,Rheological Behaviour and Waterflood Oil-Recovery

This study presents an investigation about the influence of resins and asphaltenes, extracted from two Mexican crude oils (light and heavy oil samples), on the asphaltene aggregation inhibition, rheological behavior, and waterflood oil-recovery. Resins and asphaltenes were characterized by means of elemental analysis, metals analysis by atomic absorption, ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, and electrospray ionization mass spectrometry (ESI-MS) in order to evaluate the effect of their structural parameters on the phenomena studied. Efficiency of the resins fraction as natural inhibitors of asphaltene aggregation was evaluated trough ultraviolet–visible (UV–vis) spectroscopy. Results showed better efficiencies of resins on asphaltene aggregation inhibition at resin/asphaltene (R/A) ratios close to unity and at high temperature. In addition, efficiencies were influenced by structural characteristics of the asphaltene–resin system. Rheological behavior of the heavy crude oil sample was significantly influenced by the presence of asphaltenes and resins. Finally, asphaltenes and resins played an important role on wettability and waterflood oil-recovery.     

胶粒分形粒子簇反应控制聚集动态行为位垒影响的Monte Carlo模拟

通过对反应控制聚集过程的MonteCarlo模拟,从微观及介观层次上探讨了胶粒间相互作用位能曲线上位垒高度的变化对胶粒分形粒子簇大小分布和动态标度函数及聚集动力学行为的影响规律。     

布朗扩散系数对胶体分形粒子簇扩散控制聚集动力学影响的Monte Carlo模拟

使用表征粒子簇结构的几何形状因子,通过对扩散控制聚集过程的模拟,从微观或介观层次研究了粒子簇结构对粒子簇增长速率和速率常数的影响规律,并与实验结果进行了对比分析.