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.     

临邑-濮阳原油管道结蜡层的组成与流变性研究

以临邑-濮阳管道所输原油与临邑-赵寨子(结蜡层1)和赵寨子-莘县(结蜡层2)管段处的结蜡层为研究对象,通过SARA分析、DSC热分析、流变测量、气相色谱分析和宏观、微观形貌观察的方法,研究了管输原油与结蜡层的组成与流变特性。实验结果表明,与管输原油相比,结蜡层的凝点、析蜡点、含蜡量、饱和分含量和沥青质含量均有大幅升高,而芳香组分和胶质含量减少;黏度和屈服值显著增大;低碳数正构烷烃显著减少,高碳数正构烷烃显著增加;蜡晶结构由细小的针状和片状蜡晶变为类球状蜡晶和大针状和片状蜡晶。两种结蜡层相比,结蜡层1的析蜡点更高,蜡含量更少,沥青质含量更多;黏度和屈服值更大;高碳数正构烷烃含量更多;宏观和微观形态上来看,结蜡层1的片状针状蜡晶更多、尺寸更大、结构更为致密。因此,在临邑-濮阳管道的临邑站-赵寨子站管段,清管球卡死的现象更容易发生。     

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(50~200μg·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(400μg·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C_(24)升高到C_(25),但结蜡层底部样与表面样相比低碳数正构烷烃(≤C_(25))有所减少,高碳数正构烷烃(≥C_(26))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。     

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。     

陇东地区油井结蜡机理及蜡沉积动力学研究

陇东地区油井井筒结蜡问题严重影响了油井的正常生产,不同于其他区块多在井筒中部结蜡的情况,LN区块在井筒深部泵口、尾管附近结蜡现象严重,大大制约了该区块油井的正常生产。文中以LN区块蜡样及原油为研究对象,通过蜡样组分、结构、碳数分布、溶蜡点及原油黏温曲线、碳数分布等的测定探索造成该区块结蜡严重的原因;并利用数学模型对该区块井筒结蜡过程进行研究,分析含水率、温度、流速等外因对油井井筒结蜡的影响。研究结果表明:造成该区块在井筒深部泵口、尾管附近结蜡的主要原因为原油中高碳数组分占比大、所结蜡为直链烷烃且碳链较长、蜡样中机械杂质及沥青质含量高;通过动力学分析表明:结蜡速率随含水率的增大而减小,随温度及流速的增大先增大后减小。     

磁力搅拌下离子液体AlCl_3/Et_3NHCl恒电流法电沉积铝

磁力搅拌下,在1.75AlCl3/Et3NHCl离子液体中不锈钢电极片上利用恒电流法电沉积制备金属铝。研究发现,AlCl3/Et3NHCl离子液体的黏度随温度的升高而减小,lnμ与T-1符合线性关系;AlCl3/Et3NHCl离子液体的电导率随温度的升高而增大,符合Arrhenius公式。磁力搅拌下恒电流法电沉积铝实验结果表明,转速低于700 r/min时电流效率和沉积速率随着转速的增大而升高,沉积物表面形貌逐渐平整致密,颗粒细化。温度70℃、电流密度22 mA/cm2、转速700 r/min、电沉积90 min下,沉积铝的表面形貌相对比较平整致密,电流效率达到78%,沉积铝的纯度（质量分数）达到97%。     

基于冷指实验的高含蜡原油蜡沉积规律研究

为解决管道蜡沉积问题,本实验应用冷指法以大庆油田含蜡原油为介质,对其蜡沉积规律因素进行分析,研究了含蜡原油的蜡沉积量随着温度、温差、沉积时间、剪切速率、驱油剂和沥青质含量的变化规律。结果表明,沉积时间8～24h时,沉积速率最大为0.35g·h^-1;在转速为90r·min^-1时速率最大为0.26g·h^-1,沉积量高于最低时3%;与驱油剂含量成正比,速率为0.6g·h^-1,沉积量高于最低30%;在沥青质含量4%时,沉积速率最大为0.26g·h^-1,5%时淤积物降到最低速率为0.22g·h^-1,最高沉积量较最低时高出21.3%。     

蜡、胶质沥青质对易凝原油析蜡特性及凝点影响研究

易凝原油在我国原油中占比较大,一直是我国储运研究者的关注重点,对其凝点、析蜡特性的研究也是提高管输运行经济性的关键.介绍了塔里木油的密度、凝点、黏温关系及四组分,分析其作为胶质沥青质组分来改变人工蜡油配比的可行性.接着通过改变柴油、石蜡、塔里木油的配比获得不同组成比例的人工蜡油.然后以人工蜡油为实验对象,观察了不同蜡、胶质沥青质比例下,析蜡特性及凝点的变化情况.结果表明:随胶质沥青质含量的增加,凝点、析蜡点、析蜡量下降,但下降速率逐渐变缓;随石蜡含量的增加,凝点、析蜡点、析蜡量上升,但上升速率逐渐变缓.最后给出了具体理论分析,并指出了胶质沥青质的降凝重要性.     

浅析岩石热解五峰分析法在渤海X油田的首次应用

渤海X油田目前已进入高含水和高采出程度的“双高”开发阶段,水淹问题突出,主力层内部剩余油分布明显不均。原油性质为重质油,具有含蜡量、胶质沥青质高的特征。地化录井技术通过定量描述储集层含油气丰度、烃组分分布,分析储集层原油性质的变化、原油遭受破坏的程度来实现井场实时水淹层评价。一般随水淹程度的增加,汽油、煤油及柴油等轻组分占比降低,而蜡、胶质沥青质等重组分占比升高。常规地化录井中岩石热解为三峰分析法,对于蜡、胶质沥青质等裂解烃细分不足,因此本次在M井首次引入岩石热解五峰分析法探索各成分与水淹程度的相关性。     

Study on wax precipitation characteristics of wax deposit in pipes

Wax deposit properties are a significant concern in pipeline pigging during waxy crude oil transportation. In the present work, the impacts of flow conditions and oil properties on the wax precipitation characteristics of wax deposits are investigated. A flow loop apparatus was developed to conduct wax deposition experiments using four crude oils collected from different field pipes. The differential scanning calorimetry (DSC) technique was employed to observe the wax precipitation characteristics of crude oil and wax deposit. The results show that the wax content and the wax appearance temperature (WAT) of the deposits increase with shear stress and radial temperature gradient, and decrease with radial wax molecule concentration gradient near the pipe wall. The DSC tests on the wax deposits revealed that the deposit wax content is strongly correlated to the oil wax content. Furthermore, an empirical correlation was developed to predict the wax content and the WAT of the wax deposit. Verification of the empirical correlation using the different oils indicated that the average relative error of the wax content prediction and average absolute error of WAT prediction were 13.2% and 3.6°C, respectively.     

蜡沉积物对现场管道运行影响研究

蜡沉积是流动保障关键问题之一,前人主要研究了温度、流速等因素对沉积物厚度的影响,而关于蜡沉积物进入原油后,对管道运行影响研究报道较少。通过现场测试储罐内原油和管输原油物性,研究了储罐蜡沉积物和管道蜡沉积物进入原油后,对管道运行的影响。研究表明:加热输送含有蜡沉积物的原油,导致原油凝点显著升高,给管道安全运行带来潜在风险,应慎用加热输送方式;升高输油温度,使管道内较松软的蜡沉积物融化,蜡沉积物厚度减小,但由于蜡沉积物进入原油,导致原油凝点升高。     

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.     

Modeling of asphaltene deposition in a production tubing

Asphaltene deposition phenomena are investigated both theoretically and experimentally. A Couette device, where the inner cylinder rotates and particles deposit on the outer wall, is used for deposition laboratory studies. A deposition modeling approach, recently proposed by the authors is improved. Empirical parameters of the model are obtained from Couette device experiments. The deposition mechanism peculiarities are explained based on an analogy between the deposition and water in oil emulsion stabilization by asphaltenes, and on an analysis of interaction of asphaltene molecules. The model performance is illustrated by modeling oil production, accompanied with asphaltene deposition, from a cylindrical reservoir through vertical tubing. The computations, performed for a reservoir depleting over time, demonstrate a good qualitative agreement with the field data reported in literature. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

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     

Deposition from waxy mixtures in a flow‐loop apparatus under turbulent conditions: Investigating the effect of suspended wax crystals in cold flow regime

The effect of suspended wax crystals in wax‐solvent mixtures on the solid deposition process in the cold flow regime was investigated experimentally and analyzed with a steady‐state heat transfer model. A bench‐scale flow‐loop apparatus, incorporating a concentric‐cylinder heat exchanger, was used to measure solid deposition, in the cold flow and hot flow regimes, from wax‐solvent mixtures under turbulent flow conditions. The deposition experiments were performed with two wax‐solvent mixtures, at two flow rates, with two coolant temperatures, at 8 wax‐solvent mixture temperatures, and for several deposition times. The role of wax crystals on the deposition process was investigated by repeating some of the deposition experiments with a pre‐filtered wax‐solvent mixture. In all experiments, the deposit was formed rapidly such that a thermal steady‐state was attained within 30 min. The deposit mass increased with decreasing the mixture temperature in the hot flow regime, reached a maximum as the mixture temperature became equal to the WAT, and then decreased linearly to zero in the cold flow regime as the mixture temperature approached the coolant temperature. Also, the deposit mass decreased with an increase in the Reynolds number and the coolant temperature. The data and predictions confirmed the solid deposition to be a thermally‐driven process. The experimental deposit mass results in the cold flow regime, supported by model predictions, were identical for the unfiltered and filtered mixtures, which showed that the suspended wax crystals do not affect the deposit mass or thickness.     

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.     

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