原油正构烷烃沥青质聚沉机理研究及沉淀量测定

用IP 143标准方法测定了我国孤岛和草桥原油正构烷沥青质沉淀量。结果表明两种原油的沥青质沉淀量均随沉淀剂分子量增大而减小、随剂油比增大而增大。在原油沥青质 胶质胶束模型的基础上提出了一种新的沥青质聚沉机理 ,该机理的基本假设是原油中沥青质分子以胶束形式存在 ,其中胶核为沥青质缔合物 ,溶剂化层为胶质和溶剂分子。通过分析沉淀剂性质、剂油比、体系温度和压力等对沥青质 胶质胶束稳定性的影响得出了沥青质沉淀点、沉淀量、沉淀物平均分子量以及沉淀物平均颗粒大小随沉淀剂性质和剂油比等因素变化的规律。经比较说明 ,这些规律与本文及文献实验结果相符     

Changes in structural-group characteristics of resins and asphaltenes of heavy oils in the primary distillation process

Transformations of resins and asphaltenes of chemically different heavy oils during primary distillation have been studied using oils form the Usa (Komi Republic, Russia) and Zuunbayan (Mongolia) oil-fields as an example. The structural-group parameters of resins and asphaltene molecules of the crude oils and oil residues (fuel oils) obtained via atmospheric distillation involving the withdrawal of IBP–350°C fractions have been determined using elemental analysis, molecular weight, and NMR data. Changes in the average structures of molecules in the primary distillation process of crude oils have been revealed, and it has been found that these changes depend on the chemical composition of the original oils.     

ASPHALTENE PRECIPITATION AND SOLVENT PROPERTIES OF CRUDE OILS

Improved prediction of the onset of asphaltene precipitation may be achieved using refractive index (RI) to characterize crude oils and their mixtures with precipitants and solvents. Experimental measurements of RI for mixtures of several crude oils with the precipitant n-heptane, are reported at ambient conditions. Theoretical developments are described that will permit extension of these observations to reservoir conditions

Measurements of RJ at the onset of precipitation have shown that the onset occurs at a characteristic RI for each oil/ precipitant combination, supporting the premise that precipitation is dominated by London dispersion interactions and thus, that RI can be used to predict the onset of precipitation. Reports in the literature showing that the onset of precipitation occurs at constant solvent-to-precipitant ratios provide additional confirmation

The theory is developed on the assumption that London dispersion forces dominate aggregation and precipitation of asphaltenes. The interaction energy of asphaltene molecules or aggregates in a medium of oil can be expressed as a function of the difference between the RI of asphaltene and oil. The RI of live crude oil during pressure depletion can be calculated from the RI of the stock tank oil, the molar refraction of the separator gas, the formation volume factor B_o and the solution gas/ oil ratio R_s     

ON THE MASS BALANCE OF ASPHALTENE PRECIPITATION

In the evaluation of experimental data as well as in calculation of phase equilibria the necessity of the application of mass balances is obvious. In the case of asphaltenes the colloidal nature of these compounds may highly affect the mass balance. In the present paper several experiments are performed in order to check the consistency of mass balances within asphaltene precipitation. Asphaltenes are precipitated in two step processes either by changing temperature or by changes in precipitant with increasing precipitation power. This has been performed for three different oils. The data indicates that in temperature experiments as well as in solvent series experiments the precipitation of heavy asphaltenes affects the following precipitation of lighter asphaltenes. In both cases the mass balance using standard separation techniques cannot be closed, as less material is precipitated in a two step process than in the direct process either at low temperature or by direct precipitation with one precipitant. The different fractions were subject to HPLC size exclusion chromtagraphy showing that the material remaining in solution in the stepwise process was of low molecular weight, and that the material in the second precipitation step was often of higher apparent molecular weight and had an increased overall absorbance coefficient.     

ON THE MASS BALANCE OF ASPHALTENE PRECIPITATION

In the evaluation of experimental data as well as in calculation of phase equilibria the necessity of the application of mass balances is obvious. In the case of asphaltenes the colloidal nature of these compounds may highly affect the mass balance. In the present paper several experiments are performed in order to check the consistency of mass balances within asphaltene precipitation. Asphaltenes are precipitated in two step processes either by changing temperature or by changes in precipitant with increasing precipitation power. This has been performed for three different oils. The data indicates that in temperature experiments as well as in solvent series experiments the precipitation of heavy asphaltenes affects the following precipitation of lighter asphaltenes. In both cases the mass balance using standard separation techniques cannot be closed, as less material is precipitated in a two step process than in the direct process either at low temperature or by direct precipitation with one precipitant. The different fractions were subject to HPLC size exclusion chromtagraphy showing that the material remaining in solution in the stepwise process was of low molecular weight, and that the material in the second precipitation step was often of higher apparent molecular weight and had an increased overall absorbance coefficient.     

Effect of inhibitors on asphaltene precipitation for Marrat Kuwaiti reservoirs

The main objective of this paper is to investigate the asphaltene precipitation problem and the performance of some asphaltene inhibitors for some of the Marrat Jurassic wells located in producing areas in West Kuwait and South East Kuwait. Kuwait Oil Company (KOC) is currently facing the problem of asphaltene deposition in oil well tubing which has a severe detrimental effect on the economics of oil production. Therefore, this paper summarizes the results obtained on the inhibition effect of three commercial and three non-commercial inhibitors. The effect of these inhibitors was investigated on four crude oil samples by a series of titration tests using the PVT cell with the laser technique. The four crude oils and inhibitors were evaluated for their physical properties and chemical composition. The asphaltene and resin fractions were characterized for their elemental compositions. It was found that all asphaltene fractions have low H/C ratios indicating high instability. Furthermore, the solubility class of the asphaltene fractions was evaluated as part of the asphaltene precipitation remedy study. The inhibitors screening tests revealed that the base-based inhibitors are more effective with most crude oils because of the inhibitor's high resins content of 75%. On the other hand, acid-based inhibitors are more effective with some other crudes because of their high polarity and compatibility with the asphaltene fraction.Therefore, from scientific and economic points of view, it is recommended to use low dose of commercial inhibitors (0.8%–1%) rather than high dose of non commercial inhibitors (30–50%) in order to have the same degree of inhibition (85%).     

The study of the composition of oils and structure of their components during the preliminary refining of oil feedstock with metal powders

The results of elemental analysis, determination of molecular masses, IR and ¹H NMR studies of the resin—asphaltene components, and gas chromatographic—mass spectrometric analysis of lube oils from a blend of West Siberian crude oil and the liquid products of its treatment with powders of iron and copper modified with nickel and cobalt ions are presented. The structural—group analysis has been performed and the structural fragments of the average asphaltene and resin molecules have been described. The changes in the structural parameters of their molecules under the treatment conditions and in the composition of hydrocarbons and hetero compounds of lube oils have been revealed. It has been shown that the preliminary upgrading of the petroleum feedstock decreases the concentration of heteroatoms in the composition of the resin—asphaltene components and the concentration of heteroatoms and aromatic hydrocarbons the lube oils.     

ASPHALTENE PRECIPITATION AND SOLVENT PROPERTIES OF CRUDE OILS

ABSTRACT

Improved prediction of the onset of asphaltene precipitation may be achieved using refractive index (RI) to characterize crude oils and their mixtures with precipitants and solvents. Experimental measurements of RI for mixtures of several crude oils with the precipitant n-heptane, are reported at ambient conditions. Theoretical developments are described that will permit extension of these observations to reservoir conditions

Measurements of RJ at the onset of precipitation have shown that the onset occurs at a characteristic RI for each oil/ precipitant combination, supporting the premise that precipitation is dominated by London dispersion interactions and thus, that RI can be used to predict the onset of precipitation. Reports in the literature showing that the onset of precipitation occurs at constant solvent-to-precipitant ratios provide additional confirmation

The theory is developed on the assumption that London dispersion forces dominate aggregation and precipitation of asphaltenes. The interaction energy of asphaltene molecules or aggregates in a medium of oil can be expressed as a function of the difference between the RI of asphaltene and oil. The RI of live crude oil during pressure depletion can be calculated from the RI of the stock tank oil, the molar refraction of the separator gas, the formation volume factor B_o and the solution gas/ oil ratio R_s     

FLOCCULATION OF ASPHALTENES AT HIGH PRESSURE. II. CALCULATION OF THE ONSET OF FLOCCULATION

The influence of pressure on the onset of flocculation of asphaltenes was calculated in the region from 1 to 300 bar and from 50 to 100°C. These calculations are the counterpart to our experimental data which, recently, have been reported in part 1 of an equally titled article [9]. As gas component methane and as precipitant i-octane were used. The asphaltene flocculation was considered to be a liquid-liquid equilibrium. For modelling the van der Waals equation of state (vdW-EOS) in the framework of continuous thermodynamics was applied. The composition of the crude oil was described by a continuous distribution function with respect to the solubility parameter δ of the Scatchard-Hildebrand theory. Within the distribution the asphaltenes represent the species with the highest δ-values. For oils with a very low content of asphaltenes the model developed describes the experimental flocculation data reasonably. In accordance to the experimental data the model predicts that, in the considered pressure range, without addition of i-octane asphaltene flocculation does not occur. However, on contrary to the experimental results, the model predicts the asphaltenes to show a higher flocculation tendency with increasing asphaltene content of the crude oil. For very high asphaltene contents the model even completely fails. Probably, the reason of this lack is the disregarding of asphaltene association.     

CHARACTERIZATION OF ASPHALTENES AND RESINS FROM PROBLEMATIC MEXICAN CRUDE OILS

Asphaltenes and resins have been separated from four mexican oils suffering from the deposition of asphaltenic material during recovery operations. A SARA separation of the oils was performed and the resins and asphaltenes further analyzed. Characterization methods employed were FTIR, elemental composition both of CHNSO, and trace metals and molecular weight determination using size exclusion chromatography. NMR techniques were applied to two asphaltene samples. The overall scope of the work was to get a better understanding of the nature of the asphaltene stability at a molecular level in these problematic oils. Separation of resin in two fractions indicates that there is no long alkyl chains in these as given by FTIR, which may be the cause of the lack of stability along with the large difference in bubble point and reservoir pressure.     

CHARACTERIZATION OF ASPHALTENES AND RESINS FROM PROBLEMATIC MEXICAN CRUDE OILS

Asphaltenes and resins have been separated from four mexican oils suffering from the deposition of asphaltenic material during recovery operations. A SARA separation of the oils was performed and the resins and asphaltenes further analyzed. Characterization methods employed were FTIR, elemental composition both of CHNSO, and trace metals and molecular weight determination using size exclusion chromatography. NMR techniques were applied to two asphaltene samples. The overall scope of the work was to get a better understanding of the nature of the asphaltene stability at a molecular level in these problematic oils. Separation of resin in two fractions indicates that there is no long alkyl chains in these as given by FTIR, which may be the cause of the lack of stability along with the large difference in bubble point and reservoir pressure.

     

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 %.     

严重生物降解稠油沥青质包裹体中生标的研究

对孤岛原油中的可溶有机质生物标志化合物进行了气相色谱—质谱分析,结果表明,该原油受到了严重的生物降解,部分用于对比的生物标志物受到了破坏,致使有关参数值发生了变化,给油—油对比、油—源对比带来了困难。采用超声萃取技术,分离出沥青质包裹体中抗生物降解的生物标志物,并与原油中的生物标志物进行对比。其结果显示沥青质包裹体组分与原油组分的甾、萜烷非常相似,C27,C28,C29规则甾烷类分布均呈"L"型,而与生物降解程度无关,表明此方法可完全用于强烈生物降解原油的油—油对比和油—源对比研究,在有机地球化学领域的研究中具有重要的指导意义。     

Investigation into mechanisms and kinetics of asphaltene aggregation in toluene/n-hexane mixtures

Determining the rate of asphaltene particle growth is one of the main problems in modeling of asphaltene precipitation and deposition.In this paper,the kinetics of asphaltene aggregation under different precipitant concentrations have been studied.The image processing method was performed on the digital photographs that were taken by a microscope as a function of time to determine the asphaltene aggregation growth mechanisms.The results of image processing by MATLAB software revealed that the growth of asphaltene aggregates is strongly a function of time.Different regions could be recognized during asphaltene particle growth including reaction-and diffusion-limited aggregation followed by reaching the maximum asphaltene aggregate size and start of asphaltene settling and the final equilibrium.Modeling has been carried out to predict the growth of asphaltene particle size based on the fractal theory.General equations have been developed for kinetics of asphaltene aggregation for reaction-limited aggregation and diffusion-limited aggregation.The maximum size of asphaltene aggregates and settling time were modeled by using force balance,acting on asphaltene particles.Results of modeling show a good agreement between laboratory measurements and model calculations.     

大庆、辽河催化油浆窄馏分受热相分离行为的研究

利用石油大学（北京）重质油加工国家重点实验室开发的超临界体萃取分馏技术将大庆,辽河催化油浆分离得到多个窄馏分。从中间选出族组成（饱和分,芳香分,胶质＋沥青质）有代表性的6个窄馏分,3个选自大庆催化油浆,3个选自辽河催化浆,利用热台显微镜考察了它们的受热相分离行为,实验结果表明,高温时催化油浆中的芳香分有缩合生焦的倾向,较低温度下由于芳香分的强胶溶能力使得油浆生焦倾向减缓,在芳香分含量相同条件下,胶质沥青质含量高,油浆的生焦倾向就会增大。     

On prediction of asphaltene precipitation in different operational conditions utilization of LSSVM algorithm

Asphaltene which is known as one of the fractions of oil, can cause the important problems during production of crude oil in reservoir, tubing and surface facilities so these problems can influence the production cost and time. In order to predicting and solving asphaltene problems, a powerful Least squares support vector machine (LSSVM) algorithm were developed for asphaltene precipitation estimation as function of dilution ratio, temperature, precipitant carbon number, asphaltene content and API of oil. A total number of 428 measured data were utilized to train and test of LSSVM algorithm. The average absolute relative deviation (AARD), the coefficient of determination (R²) and root mean square error (RMSE) were determined as 7.7569, 0.98552 and 0.26312 respectively. Based on these statistical parameters and graphical analysis it can be concluded that the predicting algorithm has enough reliability and accuracy in prediction of asphaltene precipitation.     

Modeling the Onset of Asphaltene Flocculation at High Pressure by an Association Model

A new thermodynamic model was developed to calculate the onset of flocculation in crude oil systems similarly to the liquid-liquid equilibrium of polymer solutions. The key concept of the model is that asphaltene self-association leads to a polydisperse system of associates characterized by a size distribution function. Using continuous thermodynamics the mass action law is applied to the association equilibrium and an analytical expression for the size distribution function is derived. In contrast to polymer thermodynamics this distribution function depends on temperature, pressure, and concentration. For modeling the high pressure equilibrium the Sako-Wu-Prausnitz equation of state is applied. The model was tested on existing flocculation data for three systems of the type methane + i-octane + maltene + asphaltene with crude oils of different asphaltene contents. The amount of precipitant necessary to provoke flocculation was calculated in good agreement with the experimental data for all three systems up to a pressure of 15 MPa.     

Methodology for Predicting the Phase Envelope of a Heavy Crude Oil and Its Asphaltene Deposition Onset

Abstract

We have presented general ideas to develop a new theoretical methodology, based on molecular simulation and equations of state, for obtaining the phase envelope and to predict pressure, volume, temperature (PVT) conditions of asphaltene precipitation by only taking into account the composition of the heavy crude oil and an asphaltene average molecular structure. Those results show that asphaltene precipitation is a reversible thermodynamic process. The precipitated phase is a liquid phase which consists of mainly asphaltene and some heavy fractions from the crude. This methodology can be applied to find complete phase diagrams of different crude oils based on an asphaltene average molecular structure and the composition of crude oil.     

SOLID ORGANIC DEPOSITION DURING GAS INJECTION STUDIES

Recently a series of first contact miscibility (swelling) experiments have been performed on undersaturated light and heavy oils using LPG rich and methane rich injection gases, in which solid organic deposition was observed. A compositional gradient in the oils during the gas injection process was also evident as oil fractions expelled from the top to bottom of the PVT cell were observed to vary in density, molecular weight, as well as darkness of color. The change in stability of the oil samples before and after the contact with gas was analyzed using flocculation threshold titration. The asphaltene content of the different oil samples were determined by the IP 143 method. The standard asphaltenes and the solid organic deposit recovered from the swelling tests were analyzed using FTIR, HPLC-SEC and ¹H NMR. The aim of these analyses is to reveal the molecular nature of the deposits formed during the gas injection process in comparison with the standard asphaltenes in order to understand the mechanisms involved in asphaltene deposition.     

辽河超稠油的化学组成特征及其致黏因素探讨

 基于对辽河油田2个超稠油化学组成的系统剖析,研究了辽河油田超稠油的致黏因素,以及化学成分的结构类型、极性和相对分子质量大小对稠油黏度的影响。结果表明,辽河盆地曙光油田超稠油具有成熟度低,胶质、沥青质含量特别高,低相对分子质量组分特别少,并且遭受过严重生物降解等特征。胶质和沥青质的总质量分数接近70%,尤其是沥青质质量分数在40％以上,明显高于国内一般稠油。气相色谱可检测物的总质量分数在饱和烃、芳烃馏分中低于22%,在酸性非烃和中性非烃馏分中分别低于15%和1%。饱和烃中正构烷烃及支链、开链烷烃接近消耗殆尽,GC-MS检测到的几乎全部是孕甾烷、重排甾烷和降藿烷系列化合物。低成熟度和强烈的次生降解作用是其形成的石油地球化学条件,极高含量的大分子组分和极性非烃组分是其具有高黏度的化学组成基础。