Thermodynamic Properties of Asphaltenes Through Computer Assisted Structure Elucidation and Atomistic Simulations. 1. Bulk Arabian Light Asphaltenes

This article describes a new method for estimating the thermodynamic properties of asphaltenes. To illustrate this methodology, we used a computer assisted structure elucidation software (SIGNATURE) to generate an ensemble of 10 isomers for Arabian Light (AL) asphaltenes compatible with (i) analytical data from elemental analysis, FT-IR spectroscopy, 1-D ¹H/¹³C solution NMR and vapor pressure osmometry and (ii) literature data on the molecular composition of asphaltenes. The 10 model isomers were packed into a 3-D periodic cell to form the condensed phase model for the fraction of bulk AL asphaltenes with a number average molar mass (M_n) approximately equal to 1280 Dalton. This cell was subsequently used in molecular dynamics (MD) simulations to estimate the molar volume, density, enthalpy, specific heat at constant pressure, solubility parameter, and isothermal compressibility of the AL asphaltene fraction. The results of the MD simulations compare favorably with the available experimental data.     

Abiotic Degradation of Petroleum Asphaltenes

Chemistry and Technology of Fuels and Oils - The literature data on the abiotic degradation of asphaltenes are the subject of a systematic review. Such degradation may proceed under natural...     

Cracking of Maya Crude Asphaltenes

Cracking of Maya crude asphaltenes was carried out in a batch reactor at the following reaction conditions: temperature of 380–410°C, total pressure of 2 MPa, and asphaltenes/catalyst ratio of 5 g/g using NiMo commercial catalyst. n-hexadecane was used to keep asphaltenes dispersed and reaction time ranged from 0 to 60 min. The products were lumped into four fractions: asphaltenes, maltenes, gases, and coke. A kinetic model assuming pseudo–first-order parallel reactions was used to fit the experimental data.     

Microbial and Enzymatic Biotransformations of Asphaltenes

Asphaltenes are considered the most recalcitrant fraction of oils. Nevertheless, there are reports with rigorous experimental procedures that clearly demonstrate the capacity of enzymes and few microorganisms to transform asphaltenes. These microorganisms, fungi and bacteria, may contain a unique or very versatile enzymatic system that allows the transformation and mineralization of the highly complex asphaltene molecules. For enzymatic reactions, the biotransformation may occur only when the asphaltenes and the enzyme are in the same phase, reducing the mass transfer limitations. In this work, literature on the biotransformations of asphaltene fraction is critically reviewed.     

Design of Synthetic Dispersants for Asphaltenes

Synthetic dispersants can greatly increase the solubility of asphaltenes in crude oils at low concentrations. They have one or more head groups that complex with the polynuclear aromatic structures in asphaltenes and long paraffinic tails that promote solubility in the rest of the oil. As a result, synthetic dispersants can be much more effective than the natural dispersants in the oil, the resins. At high concentrations, synthetic dispersants can even make all the asphaltenes soluble in n-heptane and thereby convert asphaltenes to resins. Asphaltene dispersants were optimized according to their ability to reduce the toluene equivalence of 05a crude oil. By synthesizing families of prospective dispersants, one sulfonic acid group was determined to be the most effective head attached to a two ring aromatic structure. As previously reported, a straight chain paraffinic tail is not effective above 16 carbons. We discovered that this was because of decreased solubility in the oil caused by crystallization with other tails and with waxes in the oil. In addition, not previously reported, n-alkyl-aromatic sulfonic acids lose their ability to disperse asphaltenes with time. Both of these problems were solved by using two branched tails of varying length proportions between the two tails. As a result, the effectiveness of the dispersant increases with total tail length, well above 30 carbons and it remains effective with time.     

�����ʳ����IJⶨ��ģ�ͻ�

沥青质是一种分子量分布范围非常大的有机分子混合物，根据沥青质沉积为一不可逆过程和沥青质中分子量大的组分比分子量小的组分具有更强的沉积趋势的认识，章首次提出了原油体系沥青质沉积时存在一次沉积和多级沉积两种不同的沉积方式和过程的观点，通过实验室分析，验证了这一观点并建立了可描述多级沉积过程的数学模型，通过模型计算可以很好地拟合多级沉积的实验结果。     

Design of Synthetic Dispersants for Asphaltenes

Abstract

Synthetic dispersants can greatly increase the solubility of asphaltenes in crude oils at low concentrations. They have one or more head groups that complex with the polynuclear aromatic structures in asphaltenes and long paraffinic tails that promote solubility in the rest of the oil. As a result, synthetic dispersants can be much more effective than the natural dispersants in the oil, the resins. At high concentrations, synthetic dispersants can even make all the asphaltenes soluble in n-heptane and thereby convert asphaltenes to resins. Asphaltene dispersants were optimized according to their ability to reduce the toluene equivalence of 05a crude oil. By synthesizing families of prospective dispersants, one sulfonic acid group was determined to be the most effective head attached to a two ring aromatic structure. As previously reported, a straight chain paraffinic tail is not effective above 16 carbons. We discovered that this was because of decreased solubility in the oil caused by crystallization with other tails and with waxes in the oil. In addition, not previously reported, n-alkyl-aromatic sulfonic acids lose their ability to disperse asphaltenes with time. Both of these problems were solved by using two branched tails of varying length proportions between the two tails. As a result, the effectiveness of the dispersant increases with total tail length, well above 30 carbons and it remains effective with time.     

Determining the Particle Size of Asphaltenes

Abstract

Study of heavy organics and their behavior is of great importance while occurrence of their deposition in production and processing of hydrocarbon fluids. The physical properties of heavy organics, especially asphaltenes, have been a subject of controversy for several years. The aim of the present work is to determine and measure particle size of asphaltenes. Several mixtures of crude oil and n-heptane were prepared with various dilution ratios (R_v ). Two different techniques were employed to determine and measure the particle size of asphaltenes. The first was utilizing an OLYMPUS BX60, a polarizing microscope with an appropriate magnification, and the second was using high-resolution scanning electron microscopy (SEM) and X-ray diffraction techniques. The results revealed that the size of asphaltene particles is in the range of 1–4 μm for each mixture, regardless of its n-heptane content. Although the quantity of deposited asphaltene was increased by increasing the concentration of n-heptane in mixture, the particle size of asphaltene was independent of the n-heptane concentration.     

The Solubility and Three-Dimensional Structure of Asphaltenes

The tendency of the asphaltenes to form aggregates in hydrocarbon solution is one of their most characteristic features and has tended to complicate the determination of the structure of petroleum In addition, if the composition and properties of the precipitated asphaltenes reflect those of the micelles in solution, the latter should be considered as mixed micelles. This is a reasonable assumption in view of the large quantities of soluble resins found in the precipitated solid

Empirical observations indicate that the resins play an important role in stabilizing asphaltenes in crude oil and under unfavorable solvent conditions the asphaltene species are prone to further aggregation into clusters that are unstable and precipitate from the crude oil. It is also suggested that the resins and the asphaltenes from a particular crude oil have points of structural similarity relative to the asphaltenes and resins from another crude oil. On a more localized scale, i.e. in one particular crude oil there are also structural differences within the constituents of asphaltenes and structural differences within the constituents of the resins are also anticipated

Therefore, the structure of the micelles within any one crude oil must be expected to be varied and non-homogenous. From the evidence cited herein, it follows that the potential for graphite-type stacking by the asphaltene molecules in the center of a micelle might not be as great as the potential for the micelles forming by asphaltene-resin interactions rather than by asphaltene-asphaltene interactions     

T-C Phase Diagram of Asphaltenes in Solutions

Abstract

Comparative analysis of previously available and new experimental data reveals a complex structure of ambient pressure T-C phase diagram of asphaltenes in solutions, as well as in native petroleum. One of the characteristic properties of the diagram is an apparent series of temperature-controlled transitions between structural states in primary asphaltene nanoaggregates, presumably related to different types of intermolecular bonding. Hence, various earlier models of primary aggregates may be more closely related than conventionally believed.     

钻井工程系统仿真技术

阐述了钻井工程系统仿真技术的特点及开展仿真技术的重要意义，综述了国内外钻井仿真技术的发展历史、现状及发展趋势，叙述了钻井工程仿真技术的主要内容及应达到的目的，对我国开展钻井工程系统仿真技术研究提出了几点建议。     

T-C Phase Diagram of Asphaltenes in Solutions

Comparative analysis of previously available and new experimental data reveals a complex structure of ambient pressure T-C phase diagram of asphaltenes in solutions, as well as in native petroleum. One of the characteristic properties of the diagram is an apparent series of temperature-controlled transitions between structural states in primary asphaltene nanoaggregates, presumably related to different types of intermolecular bonding. Hence, various earlier models of primary aggregates may be more closely related than conventionally believed.     

Variation in Composition of Subfractions of Petroleum Asphaltenes

ABSTRACT

Boscan asphaltenes were precipitated from the crude oil using mixtures of toluene and heptane at temperatures of 24, 50, and 80°C. Another process of extracting solid n-heptane asphaltenes (24°C) using the same solvent systems and temperatures was also investigated. Asphaltene yield is different by the two processes at similar conditions although both increases in temperature or toluene content lead to lower solid yield. This way the asphaltene continuum was investigated from incipient flocculation to total n-heptane precipitated asphaltenes. The asphaltenes were analyzed using elemental analysis, fluorescence spectroscopy, vapor pressure osmometry, and HPLC size exclusion chromatography. The distribution of porphyrins was also measured using absor-bance spectroscopy. The asphaltenes were found to follow a regular trend in elemental ratios, H/C and N/C, indicating increased aromaticity and nitrogen content as the solid yield decreases. Also the molecular weight was seen to increase. Size exclusion chro-matograms and fluorescence spectra were found to be different comparing solids from the two separation processes. This indicates that the asphaltene fractions obtained by extraction of solid asphaltenes are altered relative to asphaltenes obtained by ordinary precipitation. The porphyrin concentration was found to diminish rapidly with solid yield decrease in both precipitation and extraction experiments, the latter fractions, however, containing significantly less asphaltenes indicating an adsorption step in the coprecipitation of porphyrins. Soluble fractions were found to exhibit relatively low molecular weights and an apparent lack of indications of association up to a point of solubles exceeding 50 % of the total asphaltenes. The-latter have implications for the further understanding and experimental investigation. of the associating nature of asphaltenes such as concentration effects during analytical characterization.     

Variation in Composition of Subfractions of Petroleum Asphaltenes

Boscan asphaltenes were precipitated from the crude oil using mixtures of toluene and heptane at temperatures of 24, 50, and 80°C. Another process of extracting solid n-heptane asphaltenes (24°C) using the same solvent systems and temperatures was also investigated. Asphaltene yield is different by the two processes at similar conditions although both increases in temperature or toluene content lead to lower solid yield. This way the asphaltene continuum was investigated from incipient flocculation to total n-heptane precipitated asphaltenes. The asphaltenes were analyzed using elemental analysis, fluorescence spectroscopy, vapor pressure osmometry, and HPLC size exclusion chromatography. The distribution of porphyrins was also measured using absor-bance spectroscopy. The asphaltenes were found to follow a regular trend in elemental ratios, H/C and N/C, indicating increased aromaticity and nitrogen content as the solid yield decreases. Also the molecular weight was seen to increase. Size exclusion chro-matograms and fluorescence spectra were found to be different comparing solids from the two separation processes. This indicates that the asphaltene fractions obtained by extraction of solid asphaltenes are altered relative to asphaltenes obtained by ordinary precipitation. The porphyrin concentration was found to diminish rapidly with solid yield decrease in both precipitation and extraction experiments, the latter fractions, however, containing significantly less asphaltenes indicating an adsorption step in the coprecipitation of porphyrins. Soluble fractions were found to exhibit relatively low molecular weights and an apparent lack of indications of association up to a point of solubles exceeding 50 % of the total asphaltenes. The-latter have implications for the further understanding and experimental investigation. of the associating nature of asphaltenes such as concentration effects during analytical characterization.     

Infrared Study of Hydrogen Bond Types in Asphaltenes

The structural characteristics of asphaltenes are important to refiners for determining the yields from the residual fraction of crude oils and the operating parameters of the process units for deep conversion processes. In this article, we studied the hydrogen bonding distribution of four Saudi Arabian crude-oil-derived asphaltenes against the phenol solutions of various concentrations in carbon tetrachloride. In an attempt to explain relative hydrogen bonding capabilities of asphaltenes, OH peak intensity of phenol and enthalpies of hydrogen bond formation were used in combination with the content of heteroatoms (N, O, and S) in asphaltenes. The OH peak intensity of phenol depends on the presence of acidic and basic moieties or functional groups on the surface of asphaltenes. The results obtained show that the asphaltenes with high oxygen and low nitrogen contents have poor interaction with phenol, which indicates that oxygen might be incorporated as acidic hydroxyl groups in asphaltenes. In a similar way, asphaltenes with low oxygen and high nitrogen contents give high phenol interaction values. Piperidine was also tried to evaluate the hydrogen bonding capabilities of NH group with the asphaltenes. The trace metal and GPC molecular weight measurements showed that the Arab heavy asphaltenes possess highest molecular weights and maximum V and Ni contents.     

Correlation Between Properties of Asphaltenes and Precipitation Conditions

Abstract

Asphaltenes from three crude oils were precipitated by using a pressurized system. Different conditions during the precipitation of asphaltenes were studied: pressure was varied between 15 and 45 kg/cm² and temperature between 40°C and 100°C. The effect of contact time and solvent-to-oil ratio was also studied in the range of 0.5–6 hr and 2:1 to 5:1 mL/g, respectively. Asphaltenes properties were analyzed as a function of pressure and temperature. It was found that in a deeper way temperature influences the asphaltenes properties than pressure in the range studied in this work. Asphaltenes properties were highly dependent on the nature of crude oil. Various correlations were developed and experimental and calculated asphaltenes contents and properties were in good agreement with absolute error less than 0.2%.     

Correlation Between Properties of Asphaltenes and Precipitation Conditions

Asphaltenes from three crude oils were precipitated by using a pressurized system. Different conditions during the precipitation of asphaltenes were studied: pressure was varied between 15 and 45 kg/cm² and temperature between 40°C and 100°C. The effect of contact time and solvent-to-oil ratio was also studied in the range of 0.5-6 hr and 2:1 to 5:1 mL/g, respectively. Asphaltenes properties were analyzed as a function of pressure and temperature. It was found that in a deeper way temperature influences the asphaltenes properties than pressure in the range studied in this work. Asphaltenes properties were highly dependent on the nature of crude oil. Various correlations were developed and experimental and calculated asphaltenes contents and properties were in good agreement with absolute error less than 0.2%.     

浮式起重船吊装过程的计算机仿真

研究浮式起重船吊装过程的计算机仿真技术。从安全性上分析,对吊装过程进行理论建模、优化选择,并确定起重船的工作参数。利用计算机软件对吊装过程进行运动干涉检验和仿真,防止重物与障碍物的碰撞。该软件采用通用数据库技术,系统具有开放性和可扩展性,具有普遍的意义。     

录井技术与钻井计算机仿真

该文探讨了钻井计算机仿真技术与现代录井技术的关系,认为钻井仿真技术是现代录井技术拓展其功能的有力工具,其一是可以促使综合录井更准确地预报井下事故,通过模拟正常情况下的“理论曲线”与“实测曲线”的对比分析来做出事故预报;其二是为录井的中长期预报创造了条件;其三是可以提供多项服务,便于钻井设计方案的选优和对录井技术人员进行训练和培训。文章还简介了钻井计算机仿真技术的现状,这一研究的定义、内容及发展趋势,探讨了该项技术的应用前景。