沥青质引发的蜡油体系结蜡层分层现象及分层规律

利用自主研发的Couette结蜡装置,对蜡含量相同的油样1(不含沥青质)和油样2[含0.75%(质量分数)沥青质]进行结蜡实验,并研究其结蜡层的分层现象和分层规律。通过对油样1和油样2结蜡表层和底层的宏观形貌、DSC放热、析蜡量、蜡晶微观形貌的分析发现:油样1结蜡层无明显分层现象,而油样2结蜡层分层现象明显,沥青质的加入导致了结蜡层的分层。与结蜡表层相比,油样2结蜡底层的析蜡点、蜡含量与沥青质含量显著升高,蜡晶形貌发展为致密的类球状大蜡晶。油样2结蜡表层沉积量随壁温的升高、油壁温差和转速的增大而减小;结蜡底层沉积量随壁温升高而减小,随油壁温差和转速的增大而增大;总的蜡沉积量随壁温的升高和转速的增大而减小,随油壁温差的增大先增大后减小。     

原油管道蜡沉积物径向性质研究进展

蜡沉积物性质对原油管道清管方案的制定有重要影响,是原油流动保障领域的研究热点之一。本文回顾了近年来关于管道蜡沉积物径向特性的研究成果,对当前实验研究手段和方法进行了系统的对比分析;从蜡沉积物组成、析蜡特性、宏观形态与微观结构、力学特性四个方面深入阐述了对管道蜡沉积物径向性质的认识与结论,分析了其内在影响因素和作用机理;评述了蜡分子扩散系数及径向含蜡量分布预测模型的理论基础和存在缺陷;提出了未来的研究方向：加快研发更加精确的机械取样装置,深入研究沉积物微观结构特性对宏观流变性的影响机理并建立二者之间的定量关系,建立考虑多孔网状结构中蜡分子扩散动力学的蜡沉积物径向性质预测模型。     

Investigation of thickness and wax content of wax deposits in polyethylene pipe using a flow loop

In this study, the thickness and wax content of wax deposits were found to be thinner and lower in the polyethylene (PE) pipe than in the stainless steel (SS) pipe using a flow loop apparatus. The diffusivity of wax, radial thermal gradient, and wax precipitation rate in the PE and SS pipes were calculated and compared. It was found the diffusivity of wax in the PE pipe was higher and tended to enhance the wax deposition in the PE pipe, while the radial thermal gradient and wax precipitation rate were lower in the PE pipe and had the opposite effects. These factors are shown to be comparable with each other and the effect of the thermal gradient dominates the mass flux of wax from bulk to the oil-deposit interface and into the deposits finally, thus causing differences in thickness and wax content of deposits between the PE and SS pipes.     

A fundamental model of wax deposition in subsea oil pipelines

Wax deposition in subsea pipelines is a significant economic issue in the petroleum industry. A mathematical model has been developed to predict the increase in both the deposit thickness and the wax fraction of the deposit using a fundamental analysis of the heat and mass transfer for laminar and turbulent flow conditions. It was found that the precipitation of wax in the oil is a competing phenomenon with deposition. Two existing approaches consider either no precipitation (the independent heat and mass transfer model) or instantaneous precipitation (the solubility model) and result in either an overprediction or an underprediction of deposit thickness. By accounting for the kinetics of wax precipitation of wax in the oil (the kinetic model), accurate predictions for wax deposition for both lab‐scale and pilot‐scale flow‐loop experiments with three different oils were achieved. Furthermore, this kinetic model for wax precipitation in the oil was used to compare field‐scale deposition predictions for different oils. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

偏光显微法测定含蜡原油析蜡点的影响因素研究

在含蜡原油析蜡点测定和蜡晶特性分析等研究中,偏光显微法以其灵敏度高、接近实际、直观等优点而得到广泛应用。但该方法受测试条件和人为因素的影响较大。以阿赛线某站原油为研究对象,探讨不同热处理温度、偏光显微镜放大倍数和试样盖玻片自身缺陷等因素对含蜡原油析蜡点偏光显微测定的影响。结果表明：热处理温度对原油的析蜡点和蜡晶结构有较大的影响,盖玻片自身缺陷在一定程度上将干扰析蜡点的准确判断。     

Mixture temperature prediction of waxy oil–water two-phase system flowing near wax appearance temperature

Temperature sensitivity of waxy crude oils makes it difficult to study their flow behaviour in the presence of water especially near their wax appearance temperature(WAT). In this study a method was proposed and implemented to mitigate such difficulties which was applied in predicting mixture temperatures(Tm) of a typical Malaysian waxy crude oil and water flow in a horizontal pipe. To this end, two analytical models were derived firstly from calorimetry equation which based on developed two correlations for defining crude oil heat capacity actualized from the existed specific heat capacities of crude oils. The models were then applied for a set of experiments to reach the defined three predetermined Tm(26 °C, 28 °C and 30 °C). The comparison between the predicted mixture temperatures(Tm,1and Tm,2) from the two models and the experimental results displayed acceptable absolute average errors(0.80%, 0.62%, 0.53% for model 1; 0.74%, 0.54%, 0.52% for model 2). Moreover,the average errors for both models are in the range of standard error limits(±0.75%) according to ASTM E230.Conclusively, the proposed model showed the ease of obtaining mixture temperatures close to WAT as predetermined with accuracy of ± 0.5 °C approximately for over 84% of the examined cases. The method is seen as a practical reference point to further study the flow behaviour of waxy crudes in oil–water two-phase flow system near sensitive temperatures.     

A new method for the determination of wax precipitation from non-diluted crude oils by fractional precipitation

Wax precipitation is one of the most important flow assurance problems. Unfortunately, experimental data are very scarce to confirm existing models for prediction of such precipitation problem. This work reports a new experimental method. Multistage fractional wax precipitation was carried out by decreasing the temperature of crude oil. No solvent dilution was used, so the effect of solvent on temperature wax precipitation was avoided. The reproducibility of the method was tested with comparable results. The precipitation curve and the wax appearance temperature were obtained for two crude oils with different chemical nature using the reported method.     

Analysis of paraffin precipitation from petroleum mixtures by means of DSC: Iterative procedure considering solid-liquid equilibrium equations

Wax deposition is a well known flow assurance risk in crude oil production due to temperature decrease which depends mainly on the crude oil nature and the type and content of paraffin. The prevention of this problem requires a detailed characterization of the crude oil and the availability of reliable predictive models.The experimental determination and quantification of the precipitation process is quite complex and time consuming and simpler techniques are of interest to carry out such study. Among them, differential scanning calorimetry (DSC) technique is appropriate to develop routine essays and has been extensively applied to determine wax appearance temperature in crude oil and fractions because the simplicity and fast response of the technique.However, the determination of wax precipitation curve from a quantitative DSC interpretation is usually based on pure n-alkane properties and involves some difficulties. In this work, a new procedure has been developed including the effect of the fluid composition on the precipitation temperature and the melting heat. Solid-liquid equilibrium equations were introduced through a simplified thermodynamic model in the integration procedure resulting in an iterative method combining experimental and calculated values. The final method yields the wax appearance temperature (WAT), the full wax precipitation curve and the estimated wax composition.In order to validate the procedure, several crude oil fractions were used as standards due to the advantage of a narrow n-alkane distribution. Experimental characterization for the cloud point temperature, the n-alkane distribution (determined by gas chromatography with mass detector, GCMS) and DSC was carried out. The agreement between experimental results and those obtained from the DSC interpretation is a good check for the proposed procedure.     

原油组成对原油管道结蜡规律的影响

利用旋转式动态结蜡装置,对不同组成的人工油样(胶质和沥青质含量不同或蜡含量不同)进行了不同条件下的实验研究.通过对管壁沉积物取样并利用差式扫描量热法(DSC)和四组分法进行分析,探究了不同原油组成对结蜡的影响规律.结合胶质和沥青质在结蜡过程中的作用机理,发现胶质和沥青质的存在虽然总会削弱蜡分子的迁移动力,阻碍蜡分子的沉积,但在含量较小时会协同蜡分子的沉积作用,而当含量较大时会以粘壁的形式附着于管壁.对蜡含量不同原油的结蜡规律研究发现:原油所含蜡分子的碳数越高,结蜡层中的蜡含量就越少.但由于碳数较高的蜡分子具有相对较长的碳链,更容易与原油中的胶质和沥青质发生共晶作用,故更易与胶质和沥青质一起沉积于壁面.     

Characterization of the wax precipitation in Mexican crude oils

This paper reports the rheological and thermodynamic characterization of the wax formation phenomenon in three Mexican crude oils where the effect of waxes and asphaltenes content on wax precipitation and rheological behavior of crude oils is evaluated and discussed. Wax appearance temperature is measured by using differential scanning calorimetry, rheometry and densitometry. The wax precipitation curves were obtained by fourier transform infrared spectroscopy. Pour point temperatures were evaluated according to the ASTM-D97 method, whereas gelation temperatures were determined by rheological experiments made with a controlled-stress rheometer. Waxes of the crude oils were separated and characterized by gas chromatography/mass spectrometry and differential scanning calorimetry. The methods used in this work for the wax appearance temperature determination showed to be sensitive to the crude oil composition. Results showed that the presence of asphaltenes impacts significantly the liquid–solid equilibrium and rheological behavior of the crude oils studied whereas the wax melting temperature was a key factor to evaluate the propensity of crude oils to present wax precipitation problems.     

A thermodynamic model for wax deposition phenomena

Wax precipitation is a serious problem in the petroleum industry because it may cause obstruction in well bores, production facilities and transportation pipelines during oil/gas production. To avoid this problem it is necessary to predict the wax appearance temperature (WAT) accurately. Consequently, a reliable thermodynamic model for predicting WAT is crucial in the design of production and transportation facilities. In this work, a thermodynamic model, based on multi-solid phase theory, has been developed. In this model the vapor and liquid phase fugacities are calculated using the Modified Peng Robinson (MPR) equation of state. The solid phase fugacities of pure components are evaluated indirectly from equation of state by the fugacity ratio. Fraction properties are estimated by using PNA analysis, and a correlation is developed for evaluating enthalpy of fusion. The major aim for performing this research was to develop a thermodynamic-computerized model for predicting WAT and the amount of precipitated wax in petroleum mixtures. The model has been applied to calculate wax appearance temperature and the amount of precipitated wax for some North Sea and synthetic oils. The predicted results are in a very good agreement with experimental data.     

An aging theory-based mathematic model for estimating the wax content of wax deposits using the Fick's second law

In this study, a mathematic model is proposed for estimating the wax content of wax deposits. The proposed model was built based on the diffusion of wax molecules and counter-diffusion of oil molecules and described using the Fick's second law, allowing for the stacking fraction and orientational order of precipitated wax crystals and the tortuosity of diffusion path of de-waxed oil molecules during the counter-diffusion. The calculated results were verified by comparing with the flow-loop wax deposition experimental results. Dependence of radial position, deposition duration, bulk temperature, and wall temperature were investigated. These factors significantly affected the wax content during wax deposition. Good agreements were observed between the predictions and experimental results. The variation trends of wax content affected by various aspects are consistent with the existing studies.     

Effect of polyethylene pipe on wax deposition under different temperature and flow rate conditions

Wax deposition is an important but troublesome boulder in petroleum industry that has always plagued pipeline engineering operators. In this study, wax deposition in the polyethylene pipes has different behaviors comparing wax deposition in stainless steel pipes such as smaller weight of wax deposits and lower wax content. After wax deposition experiments, some important parameters, including diffusivity and temperature gradient, were measured and calculated to explore the differences between two material pipes. Moreover, those factors can make a significant impact on radial mass flux. A series of results in polyethylene pipes suggests that higher diffusivity enhances diffusion flux of wax in the radial direction. But it was found that radial concentration gradient accounted for a larger proportion. These factors are the relationship of competition and cooperation and the combination of them results in different performances of wax deposition between polyethylene and stainless steel pipes.     

不同加热温度和降温速率对含蜡原油析蜡点的影响

利用差示扫描量热法(DSC)对原油的析蜡特性进行分析,并得到了析蜡过程的热谱图和dh/d T-T曲线。以大庆原油为研究对象,对dh/d T-T曲线进行分析,探讨了加热理温度、温降速率对析蜡点的影响。结果表明:加热温度高于溶蜡点温度时,析蜡点随温变化小;加热温度低于溶蜡点温度,析蜡点随温度的降低先增大后减小。温降速率越大,析蜡点越低。     

Modelling wax deposition of diesel in sequential transportation of product oil pipeline using optimized back propagation neural network

Contamination of gasoline by wax deposit of diesel is a severe problem in sequential transportation of product oil pipelines in cold areas. However, most works on wax deposition are focused on crude oil. In response, this paper aims to investigate wax deposition from a unique perspective of diesel oil in sequential transportation. To this end, a cold finger apparatus was designed and constructed. It is found that the wax deposition rate of diesel oil increases with oil temperature and wax content, and decreases with cold finger temperature. A non-monotonic variation trend is observed against shear stress. To predict diesel wax deposition rate, a back propagation (BP) neural network optimized by bald eagle search (BES) algorithm is proposed. Grey relational analysis (GRA) is employed to get the highly relevant factors as input parameters of the developed model. Prediction accuracy and generalization ability of the BES-BP model is experimentally verified. This work will be helpful to schedule the transportation program of product oil to avoid contamination of gasoline by diesel wax deposit.     

聚丙烯酸十八酯降凝剂对合成蜡油结蜡特性影响的研究

采用自主研发的Couette结蜡装置研究了聚丙烯酸十八酯（POA）降凝剂对合成蜡油体系结蜡特性的影响。通过对结蜡层表面样（远离结蜡筒）和底部样（靠近结蜡筒）的宏观观察、DSC放热、气相色谱及蜡晶微观结构的分析发现：POA的加入降低了蜡油体系的结蜡速率,加快了蜡油体系的老化速率,且在一定浓度范围内（50～200 μg·g^-1）导致了径向不均质蜡沉积结构的形成,从结蜡层表面到底部含蜡量逐渐升高,但在较高加剂浓度（400 μg·g^-1）时径向不均质蜡沉积结构消失;POA的加入使得结蜡层表面样和底部样的临界碳数（CCN）都由C₂₄升高到C₂₅,但结蜡层底部样与表面样相比低碳数正构烷烃（≤ C₂₅）有所减少,高碳数正构烷烃（≥ C₂₆）有所增加;随着油样中POA浓度的增大,结蜡层表面样与底部样的蜡晶形貌由针状蜡晶逐渐转变为片状蜡晶,且蜡晶尺寸逐渐变大,结构更为致密。     

An experimentally validated heat and mass transfer model for wax deposition from flowing oil onto a cold surface

A transport model is proposed for wax deposition onto a cold finger from flowing wax-containing oils. The model solves transient energy and mass balances simultaneously for a reversible first-order kinetic rate for precipitation of pseudo-single-component wax, and the effects of yield stress using a critical solid wax concentration to withstand flow-induced stress at the deposit-fluid interface. The model can predict the time evolution of the deposit thickness, and the spatial and temporal evolution of temperature and wax concentration as validated using cold finger experiments. It was found that for high wax content oils, deposit thickness growth is dominated by heat transfer. For low wax content oils that are unable to gel, the thickness growth is slow and accompanied by occasional sloughing. Regardless of the mechanism controlling the growth, mass transfer cannot be neglected as wax diffusion into the deposit continues to take place after the deposit has stopped growing.     

利用NIRS和RI技术测试石油流体析蜡温度新方法

析蜡温度是重要的石油流体性质参数，得到准确的析蜡温度是保证含蜡原油管道安全输送的前提。提出了近红外光谱温度扫描测试法和折射率测试法，改进了近红外光谱波长扫描测试法，并从可靠性、灵敏性和稳定性等方面与常用的偏光显微镜法和差示扫描量热法进行比较。结果表明，近红外光谱法和折射率法可以得到可靠的测试结果，并具有较高的灵敏性和稳定性；实验操作和数据分析方法简单，测试结果不易受到制样过程影响，尤其适合挥发性较强的油样。此外，近红外光谱法测试时油样处于运动状态，可有效减小过冷度的影响，但与实际管输条件仍存在一定差别。     

原油中石蜡沉积的热力学模型

1 INTRODUCTION Crude oils are mixture of light and heavy hydro-carbons. The components in crude oils can be classi-fied into paraffin, naphthene and aromatic compo-nents[1]. Though the non-n-alkane components in crude oils are minor, it is essential to consider the in-fluence of non-alkane components in the model since their properties, such as fusion temperature and fusion enthalpy, are much different from paraffin. The solu-bility of each component of crude oils depends on the temperatu…     

Wax deposition modeling of oil/gas stratified smooth pipe flow

Wax deposition modeling is complicated under oil/gas two‐phase pipe flow and therefore remains poorly understood. One‐dimensional empirical heat and mass transfer correlations are unreliably for deposition modeling in stratified flow, due to non‐uniform deposit across the pipe circumference. A mathematical model has been developed to predict the deposit thickness and the wax fraction of deposit in oil/gas stratified pipe flow using a unidirectional flow analysis of non‐isothermal hydrodynamics and heat/mass transfer. The predictions for wax deposition are found to compare satisfactorily with experimental data with three different oils for single phase and oil/gas stratified pipe flow. In particular, the reason that the deposit forming a crescent shape at the cross section of pipe observed in different experiments is revealed, based on the non‐uniform circumferential distributions of two most important parameters for the wax deposition, diffusivity at oil–deposit interface, and the solubility gradient at the oil–deposit interface at different time. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2550–2562, 2016