Determining the occurrence time of different stages of asphaltene aggregation using molecular dynamics simulations

This work presents a framework for future studies to better understand the appropriate time to include chemical inhibitors at different stages of asphaltene aggregation in the oil. For this purpose, molecular dynamics (MD) simulations were performed to study the aggregation of asphaltene molecules in heptane, in terms of strength, dynamics, and the occurrence time of each stage of aggregation from single molecules to a large flocculate. Results indicate that the nucleation of nanoaggregates begins prior to 10?ns, clusters start forming at 98?ns, and flocculation happens after 120?ns. It was also observed that the final flocculate had a globular shape.     

A comprehensive experimental evaluation of asphaltene dispersants for injection under reservoir conditions

As the efficiency of dispersants with different origins is questionable for each typical oil sample, the present study provides a reproducible and reliable method for screening asphaltene dispersants for a typical asphaltenic crude oil. Four different asphaltene dispersants (polyisobutylene succinimide, polyisobutylene succinic ester, nonylphenol-formaldehyde resin modified by polyamines, and rapeseed oil amide) were prepared and their performance on two oils from an Iranian field under laboratory and reservoir conditions was studied. A thorough analysis including ash content and SARA tests was performed on the solid asphaltene particles to characterize the nature of deposits. Then a highly efficient carrier fluid, which is crucial when injecting dispersant into the wells, was selected from a variety of chemicals by comparing their solubility. In the next step, using an optical microscope, a viscometer, and a Turbiscan, the screening of dispersants under laboratory conditions was done on a mixture of dead oil and dispersant to evaluate the onset of asphaltene precipitation and its stability when titrating by a precipitant. Finally, two different mixtures of the efficient dispersants, live oil, and carrier fluid were used with the solid detection system (SDS) and the filtration method to examine their effects on the onset pressure of asphaltene precipitation and the asphaltene content of the crude oil under reservoir conditions. The results show that the combination of experimental methods used in this work could be consistently applied to screening asphaltene dispersants. Among the four different dispersants applied here, the dispersant based on nonylphenol-formaldehyde resin modified by polyamines showed the best performance on the available live oils. This chemical modified the onset pressure of asphaltene precipitation of light oil from 4300 psi to about 3600 psi and decreased the precipitated asphaltene of heavy oil by about 30 %.     

沥青质分子界面行为的耗散粒子动力学

运用耗散粒子动力学(DPD)方法模拟了“孤岛型”沥青质分子和其纳米聚集体在油-水界面的取向性、聚集行为,分析了富氧支链对沥青质分子取向性的影响。结果表明：存在油-水界面时,沥青质分子从油、水相中脱离,吸附在油-水界面处,稠芳环核与油-水界面平行,烷烃支链伸入油相;随着沥青质浓度升高,空间位阻作用使沥青质分子彼此分离,稠芳环核与界面存在夹角,直至部分沥青质被“挤出”界面;在π-π相互作用下,被“挤出”界面的稠芳环核与吸附在油-水界面的稠芳环核平行堆叠,距离约为0.5 nm,烷烃支链将稠芳环核包围;沥青质纳米聚集体由于被烷烃支链包裹,极易脱离油-水界面,溶于油相;富氧支链亲水性强,伸入水相,使稠芳环核与油-水界面产生夹角,甚至垂直;富氧支链会改变沥青质分子的取向性。     

The use of nonylphenol formaldehyde resins for preventing asphaltene precipitation in vacuum residues and hydroprocessed petroleum samples

This work focused on the synthesis and characterization of nonylphenol formaldehyde resins (NPFR) as examples of active molecules for preventing asphaltene precipitation in vacuum residue (VR) and hydroprocessed petroleum samples. The evaluation for the NPFR as asphaltene dispersants was carried out using the on-column filtration technique at room temperature and near process conditions (195°C). The results indicated that NPFR (molecular weight = 900–4800 Da) are active for the reduction of asphaltene content of gravimetrically separated asphaltene solutions and for VR and hydroprocessed samples at room temperature (35°C) and at 195°C. It was found that the activity of NPFR as asphaltene dispersants depends not only on the type of sample (asphaltenes, virgin or processed) but also on the temperature, molecular weight, and concentration.     

Experimental investigation of dodecylbenzene sulfonic acid and toluene dispersants on asphaltene precipitation of dead and live oil

Asphaltene is the heaviest fraction of oil, and if the thermodynamic conditions of oil change, it can be separated from oil precipitate. Of common methods for preventing asphaltene precipitation, using predictive methods, biological methods and injection of dispersants can be mentioned. In this study, the effect of two dispersants of toluene and dodecylbenzene sulfonic acid on asphaltene precipitation of a dead and a live oil sample has been investigated. According to the results, these dispersants in dead oil create an optimum point for asphaltene precipitation. In live oil, these dispersants reduce asphaltene precipitation down to 70%. In addition, it was observed that as an effect of injecting these dispersants, the average sizes of asphaltene flocculation have reduced.     

Group Composition of Hydrocarbons and Hetero Compounds in Stepwise-Thermolysis Products of Asphaltenes from Usa Oil

The group composition of hydrocarbons (HC) and hetero compounds in the products of stepwise thermolysis of asphaltenes from crude oil of the Usa oilfield at temperatures of 120, 230, 370, 500 and 750°C has been studied. The volatile thermolysis products formed at each step of the process have been studied by gas chromatography–mass spectrometry. It has been found that the main products of stepwise thermolysis of asphaltene molecules are alkylbenzenes (AB) and saturated aliphatic hydrocarbons (SAH), aromatic fragments obtained at 370°C are mainly separate structural blocks of asphaltene molecules, and benzothiophenes (BT) predominate over dibenzothiophenes (DBT) as structural units of asphaltene molecules. It has been shown that with an increase in the process temperature, the alkylbenzenes/saturated aliphatic hydrocarbons ratio (AB/SAH + Alkenes) increases by a factor of 6 to 7; the phenanthrene/alkylbenzenes (PN/AB) ratio and the polycyclic aromatic hydrocarbons/alkylbenzenes (PAH/AB) ratio decrease by ten- and twofold, respectively; and the naphthalenes/alkylbenzenes (NP/AB) ratio increases by two times.     

新型油溶性沥青质分散剂抑制重质原油沥青质沉积的研究

针对新疆重质原油沥青质沉积严重的问题,以聚异丁烯丁二酸酐、苯胺和对氨基苯酚为原料合成了尾部基团为高度枝链化的聚异丁烯基,头部基团分别为苯基及酚羟基的新型油溶性沥青质分散剂PA1和PA2。采用分光光度法与显微镜法评价了所合成分散剂对沥青质沉积的抑制效果。实验结果表明,分散剂PA2抑制沥青质沉积作用效果优于PA1。通过对分散剂PA2抑制沥青质沉积作用效果的评价,确定了最佳合成条件：对氨基苯酚与聚异丁烯丁二酸酐摩尔比为1.2,反应温度为120 ℃,反应时间为6 h。在分散剂PA2加入量为200 mg/L的条件下可以将新疆重质原油的初始絮凝点由-19.87提高到8.63,显著改善了新疆重质原油稳定性。     

NEW TECHNIQUES AND METHODS FOR THE STUDY OF AGGREGATION, ADSORPTION, AND SOLUBILITY OF ASPHALTENES. IMPACT OF THESE PROPERTIES ON COLLOIDAL STRUCTURE AND FLOCCULATION

The solubility of Furrial asphaltene in toluene was 57g L^-1. However, using a new technique, based on the precipitation of this sample by the phenol PNP, we found that a fraction [2], comprising 47% of the asphaltene, is of low solubility. This suggested that this material constitutes the colloidal phase, and the rest acts as the dispersing fraction. This technique allowed the fractionation of asphaltenes in fractions A₁, A₂, and A₃ according to solubility, going from practically insoluble (A₁) to low (A₂, 1 g L^-1) to high (A₃, around 57 g L^-1). The adsorption isotherms of asphaltenes on glass and silica in toluene consist of a sequence of steps or step-wise adsorption. The first layer or first step is formed by the adsorption of free asphaltene molecules and by small aggregates (aggregation number between 3 and 6) which saturate the glass or silica surface in the usual manner (L-type or H-type isotherms). However, we suggest that the second, third, and other asphaltene layers adsorb sequentially according to the above differences in solubility. The very slow changes with time and the negligible desorption from the surface measured for the above isotherms were interpreted as the effect of packing or the building up of a well packed layer. This would be achieved by the slow formation and rupture of bonds between neighboring molecules at the surface. Thus, molecules with difficulties to pack, adsorbed by a kinetically controlled process, are either rejected or relocated in a thermodynamic controlled process. The above results and ideas were used to improve the models for asphaltene and petroleum colloids and to underscore the importance of surfaces and colloid dispersants in asphaltene precipitation during the production of crude oils. For instance, the results described below suggest that colloids are constituted by a well packed and insoluble asphaltene core, impervious to the solvent, and by a loose packed periphery which, by allowing solvent penetration, keep the colloid in solution. According to this model, desorption of compounds in the above loosely packed periphery, such as the one promoted by a surface, would be the main cause of asphaltene precipitation from crude oils. In this case, solubility reductions caused by pressure drops during oil production would have a minor effect. Also, preliminary number average molecular weights M_n for four asphaltenes, obtained using a new procedure, are presented here. The M_n values obtained ranged from 780 to 1150 g/mol.     

Effect of dispersants on the kinetics of asphaltene settling using turbidity measurement method

Organic deposition especially asphaltenes in reservoirs, wells, and equipment has a detrimental effect on petroleum economy. Generally, for chemically control of asphaltene precipitation using dispersants and inhibitors of precipitation or solvents of asphaltene is very common. Although asphaltene in crude oil is stable under specific conditions, but there is no assurance that the system will be stable and asphaltenes could be remaining in suspension state. In this study, the kinetic effects of three dispersants on stabilization of asphaltene aggregates were investigated by turbidity measurement method. Turbidity measurement showed as the dispersant strength rises, the turbidity of unstable sample containing dispersant less declines versus time. In order to carry out further studies on dispersants, the effect of dispersant on asphaltene particle size distribution was investigated. The results of asphaltene particle size distribution measurements showed that adding dispersant cause to decrease the volume percent of particles with medium diameter.     

Tetraalkylammonium and phosphonium salt for asphaltene dispersion; experimental studies on interaction mechanisms

Asphaltenes deposition is one of the most severe problems in the petroleum industry, imposing high costs on oil producer companies. The use of chemical dispersants reduces the risk of asphaltene deposition. For this purpose, a variety of chemicals with different structures and functional groups were designed and synthesized. Organic quaternary salts, such as ionic liquids, have been widely used to control asphaltene deposition over the last two decades, but the mechanism of their interaction with asphaltene has not been studied in detail. In this study, the interaction of ten commercial quaternary ammonium and phosphonium salts with asphaltene molecules was investigated using ultraviolet-visible (UV-Vis) spectroscopy. It was observed that the size, shape, and hydrophobicity of their cations or anions play an essential role in the dispersion of asphaltene aggregations. The results showed that the interaction of these quaternary salts is strongly influenced by the hydrophobic nature of the salt, and salts with more hydrophobic cations and anions, such as tetrabutylammonium iodide, tetrabutylammonium hexafluorophosphate, and cetyltrimethylammonium bromide, can better disperse asphaltene aggregations. The results also revealed that the role of anions such as iodide, and hexafluorophosphate in the dispersion of asphaltene aggregates is more important than cations. In addition, the results showed that except for tetramethylammonium bromide, the efficiency of the salts was increased with increasing concentration.     

Study of asphaltene dispersion and removal for high-asphaltene oil wells

Many wellbores are blocked by asphaltene deposits,which lead to production problems in the oilfield development process.In this paper,methods such as elemental analysis,and solvent extraction are adopted for the study of wellbore blockages.The content of organic matter in blockages is higher than 96% and asphaltene is the main component of the organic matter with n-heptane asphaltene content of 38%.Based on the above analyses,an agent for asphaltene dispersion and removal(named as SDJ) was developed.The performance of the SDJ agent was evaluated,and it was found that the dissolution rate of asphaltene can reach 2.9 mg.mL-1.min-1 at 60 oC.SDJ agent(1wt%) was added to crude oil with a colloid instability index greater than 0.9 can effectively inhibit asphaltene deposition in the wellbore.By the viscosity method,the dissolution amount of SDJ agent was calculated,and it was found that when the viscosity of the system is around 2,000 mPa.s(the common viscosity of crude oil),the amount of SDJ agent added to the blockage was at least 96 g per 100 g blockages.Therefore,SDJ agent has promising application for dispersion and removal of asphaltene deposition in high-asphaltene wells.     

Asphaltene aggregation onset during high-salinity waterflooding of reservoirs (a molecular dynamic study)

Abstract

The primary objective of this study is to establish an understanding of the role of high-salinity brine on the intensity of asphaltene aggregation onset during waterflooding of petroleum reservoirs. We already have shown that asphaltenes have a high tendency to form aggregates during waterflooding process when pure- and low salinity-water are injected into reservoirs. To fulfill the present objective, molecular dynamic simulations are performed on asphaltenic-oil/aqueous systems at 550 K-200?bar. The oil phase consists of asphaltenes (10?wt.%) and ortho-xylene, in which asphaltene molecules are completely soluble. Our simulations results reveal that the “salt-in effect” of high-salinity brine (25 wt.% NaCl) on seven different model asphaltenic oils causes a significant reduction of the onset of asphaltene aggregation as compared with pure-water. Such “salt-in effect” is primarily due to a considerable reduction of water miscibility in the oil phase at high pressure and temperature.     

沥青质分子聚集体中氢键作用力的研究

为研究沥青质分子聚集体中的氢键作用,用量子力学与分子动力学相结合的方法对形成沥青质分子聚集体中的氢键进行了研究。结果发现,沥青质分子中含有的N、S、O等杂原子是沥青质分子形成氢键的必要条件;沥青质分子聚集体形成单个氢键的键能较小,但聚集体中含有多个氢键时,其分子间的作用力会大幅增加。沥青质分子形成氢键的本质是由于H原子与杂原子的价层轨道电子进行叠加形成的,沥青质分子间有极少量的电子转移,导致形成弱的次级键; 在氢键作用中,起主要作用的是轨道相互作用能和色散作用能。     

劣质渣油清洁高效加工技术开发

基于对渣油中沥青质存在形态和反应机理的深入研究,开发了渣油改质的高活性催化剂,提出了沥青质脱金属和高效轻质化的工艺技术。劣质渣油催化临氢热转化技术（RMX）利用高效传质的高压临氢鼓泡浆态床反应器和高活性催化剂,使劣质渣油在相对稳定的浆液体系中转化为轻质组分,其渣油轻质化率大于95%,沥青质轻质化率大于90%,金属脱除率大于99%。RMX技术作为劣质渣油改质平台技术,可与现有固定床加氢和催化裂化工艺组合;与现有的延迟焦化加工路线相比,RMX组合工艺的轻质油品或化工原料收率增加33.13百分点。RMX技术是适应炼油厂向化工转型发展、产品提质增效和结构调整的优选技术。     

沥青质组分轻质化转化的分子结构基础探索

渣油资源高效轻质化转化为轻、中质馏分原料,化工轻油,甚至直接产化学品,是提高渣油资源利用率的重要途径。渣油及沥青质组分的轻质化转化,实质是要大幅降低渣油的馏程范围使其从重变轻,以及降低沥青质沉淀析出倾向使体系相容性提高。研究发现,降芳环反应无论是对降低原料分子的沸点还是对减少原料分子的聚集倾向都具有显著正向效果。基于此,对沥青质组分的多环芳烃体系开展分子表征。结果表明：所研究的减压渣油沥青质分子以孤岛型结构为主,含有多个噻吩环且噻吩环主要处在分子结构内部位置,而噻吩环位于结构外围位置及湾型的含硫沥青质分子相对较少。基于分子表征结果探讨比较不同结构类型沥青质分子的降芳环反应路径,提出具有桥键或内部杂环的沥青质分子(群岛型Ⅰ、群岛型Ⅱ、群岛型Ⅲ和孤岛型Ⅰ)通过断桥键及加氢脱内部杂环反应可大幅度降低芳环数,从而显著降低沸点和聚集活性,实现轻质化目标,并且需要的氢耗较低。     

Preliminary Study of the Effect of Pressure on Asphaltene Disassociation by Molecular Dynamics

Abstract

Preliminary studies of the effect of pressure on a system composed of 32 asphaltene molecules immersed in a solvent (pentane or toluene) were carried out. In this case, this system was randomly distributed into a cubic box of 49430.9 Å³ of volume. The NPT simulations showed spontaneous asphaltene disassociation when an asphaltene aggregate was immersed in toluene as a function of the pressure. Among the main configurations found, offset π-stacked geometry was the most frequently observed stacking form. Calculation of the radial distribution function on the system also revealed that the nearest asphaltene molecules have an average separation distance around 3.8 Å. This is a value in agreement with the classical model for asphaltene aggregates developed almost 40 years ago. Some possible asphaltene micelle formation and phase transitions will be described.     

Investigation of Molecular Weight and Aggregation of Asphaltenes in Organic Solvents Using Surface Tension Measurements

The physico-chemical behavior of asphaltene is very useful to assist prediction and control the mechanisms of asphaltene deposition during the production of petroleum fluids. It has been realized that the first step in the formation of precipitated asphaltene particles is the self-aggregation mechanism to form colloidal particles or pseudo-micelles in several solvents. In this work, the critical micelle concentration (CMC) of two asphaltene fractions extracted from vacuum residues (VR) were obtained by surface tension measurements, using aromatic solvents. The molecular weight (1094-565 g/mol), calculated from average radii of the asphaltene molecules adsorbed at the air-solvent interface, are also in agreement with the values for small aggregates reported using small angle X-ray scattering.     

PREDICTION OF THE PHASE BEHAVIOR OF ASPHALTENE MICELLE / AROMATIC HYDROCARBON SYSTEMS

Asphaltene particles can be dissolved in an organic molecular system, and they may form micelles in the presence of excess amounts of aromatic molecules. The existent thermodynamic theory of phase separations in micellar solutions, developed for water/ amphiphile solutions, it is generalized and applied to the prediction of the phase separation in micellar solutions of aromatic/ asphaltene at various temperatures and normal pressure, in this paper. Three forms for asphaltene micelle formation are proposed. The calculations performed are indicative of the existence of one new phase in the asphaltene micelle formation region. The results obtained are compared with the available critical micelle concentration data.     

Investigation of Molecular Weight and Aggregation of Asphaltenes in Organic Solvents Using Surface Tension Measurements

Abstract

The physico-chemical behavior of asphaltene is very useful to assist prediction and control the mechanisms of asphaltene deposition during the production of petroleum fluids. It has been realized that the first step in the formation of precipitated asphaltene particles is the self-aggregation mechanism to form colloidal particles or pseudo-micelles in several solvents. In this work, the critical micelle concentration (CMC) of two asphaltene fractions extracted from vacuum residues (VR) were obtained by surface tension measurements, using aromatic solvents. The molecular weight (1094-565 g/mol), calculated from average radii of the asphaltene molecules adsorbed at the air–solvent interface, are also in agreement with the values for small aggregates reported using small angle X-ray scattering.     

PREDICTION OF THE PHASE BEHAVIOR OF ASPHALTENE MICELLE / AROMATIC HYDROCARBON SYSTEMS

ABSTRACT

Asphaltene particles can be dissolved in an organic molecular system, and they may form micelles in the presence of excess amounts of aromatic molecules. The existent thermodynamic theory of phase separations in micellar solutions, developed for water/ amphiphile solutions, it is generalized and applied to the prediction of the phase separation in micellar solutions of aromatic/ asphaltene at various temperatures and normal pressure, in this paper. Three forms for asphaltene micelle formation are proposed. The calculations performed are indicative of the existence of one new phase in the asphaltene micelle formation region. The results obtained are compared with the available critical micelle concentration data.