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.     

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。     

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.     

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.     

EVA/纳米蒙脱土复合降凝剂对长庆含蜡原油的作用规律

利用纳米蒙脱土(MMT)特殊的带电性,使用含长烷基侧链的季铵盐对其插层改性得到有机改性蒙脱土(O-MMT)。采用熔融共混法制备O-MMT与EVA(聚乙烯醋酸乙烯酯)降凝剂的复合产物EVA/O-MMT,以国内典型含蜡长庆原油为研究对象,通过流变实验从宏观上评价EVA/O-MMT对长庆油的作用效果,并与EVA降凝剂进行对比,利用DSC和偏光显微镜考察加剂前后原油的结晶特性和蜡晶形貌的变化。结果表明:与纯EVA降凝剂相比较,EVA/O-MMT在最优加剂浓度50 mg·kg^-1下使长庆原油胶凝点、黏度、屈服值进一步降低(胶凝点降低2.5℃,5℃下的平均降黏率为25%,3℃下的屈服值下降55.5 %),从而大幅改善长庆原油的低温流变性。DSC放热特性表明O-MMT的引入可以提升EVA的初始结晶温度,拓宽EVA结晶放热区间,降低原油析蜡点。显微结果表明添加EVA/O-MMT的原油在低温下蜡晶结构更致密。     

Surface tension as a limiting factor for aerobic n-alkane biodegradation

A new mathematical model for n-alkane biodegradation in crude oil, heavy oil and paraffinic mixtures is described. The pattern of n-alkane degradation as a function of the inverse of hydrocarbon chain length reported in this paper can be considered as general behaviour for many aerobic n-alkane biodegradation processes. A new interpretation of n-alkane biodegradation as a function of surface tension, is given. A mathematical expression was obtained starting from the degradation values of n-alkane and relative surface tension, which is a parameter independent of fermentation conditions. An interesting parameter, b, was identified which represented the accelerating conversion factor for n-alkane biodegradation. The findings suggested that the n-alkane biodegradation. The findings suggested that he n-alkane biodegradation rate may be affected by the fermentation condition (agitation, aeration, etc.) and by the strain of microorganism, while the behaviour pattern of n-alkane degradation was essentially linked to the substrate characteristics (molecular structure, molecular weight and density).     

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…     

含蜡原油含蜡量与凝点关系的实验研究

实验主要是通过测定不同含蜡量的模拟油与现场提供的高凝原油的凝点,经过实验数据分析,拟合出含蜡量与凝点的关系曲线,并对此进行讨论,得出一个相对符合实际的结果,进而演绎原油含蜡量与凝点的关系。在实际现场中,可以通过测定原油的凝点来估测其含蜡量。     

A油田油井结蜡机理及清防蜡对策研究

针对A油田油井全井段结蜡的特殊性,从影响结蜡的主要因素入手,分析了原油组分、原油含蜡量,蜡样成分;同时考虑压力与气油比对析蜡温度的影响,采用高温高压釜与石蜡沉积激光检测仪分析了不同压力、不同气油比下析蜡点,掌握了A油田全井段结蜡的主要原因,得出了原油析出蜡主要以微晶蜡为主,而且熔点较高,不宜采用热洗方法清蜡。针对这一点,现场开展了防蜡防垢降粘增油器、声波防蜡器、空化防蜡器三种防蜡工艺对比试验;室内评价了长庆油田目前在用的五种清蜡剂对A油田的适应性。优选出适合A油田的防蜡工具和化学清蜡剂,对该油田清防蜡工作的开展有一定的技术指导意义。     

Influence of polymeric additives on paraffin wax crystallization in model oils

Wax deposition, precipitation, and gelation make the transport of crude oil in pipelines challenging. The effect of several ethylene copolymers, and small molecules with a long alkyl chain, on wax formation was investigated for n-C₃₂H₆₆ in decane and de-aromatized white oil. Addition of a small amount of EVA (ethylene-co-vinyl acetate) copolymers delayed nucleation by reducing the onset temperature and the wax appearance temperature. They modified the wax crystal-structure and morphology from large plates to tiny particles by adsorbing to the wax surfaces and inhibiting growth. Viscosity and the pour-point were improved by inhibiting the formation of large aggregates. It was demonstrated that the content of vinyl acetate groups in EVA copolymers affected wax crystallization. The small molecules, propylene copolymers, and ethylene copolymers with ethyl acrylate, maleic anhydride, and ethylene glycol showed a weak inhibiting effect. The effect of wax inhibitors was determined by the content and by the type of structure-disturbing groups in the copolymers.     

高压注气条件下沥青质沉淀的实验研究

引　言注ＣＯ2 三次采油技术的实施容易引发原油中沥青质沉淀 ,并使岩芯渗透率降低、润湿性反转 ,甚至造成永久性油藏损害[1] .此外 ,还会导致设备的堵塞 ,使生产效率严重降低 .为了配合我国注ＣＯ2 三采技术的实施 ,本文首次测定了国产原油 (草桥原油 )注气过程中沥青质的沉淀量 .现有描述沥青质沉淀的理论模型都涉及沥青质物性数据 ,且待定参数多、预测性较差[2 ] .标度方程[3] 不涉及此物性数据 ,且待定参数少 ,预测性较高 ,但迄今仍限于常压正构烷烃 /原油体系 .因此 ,本文将其拓展应用至高压注气体系 ,并与本文及文献数据进行了比较 .1…     

Designing maleic anhydride-α-olifin copolymeric combs as wax crystal growth nucleators

Modification of the wax crystal habit is of great practical interest during transportation and processing of crude oil at low temperature. Various pour point depressant (PPD) additives can facilitate this modification by different mechanisms. Comb shaped polymer additives are known to depress the pour point of crude oil by providing different nucleation sites for the precipitation of wax. This paper describes performance based design, synthesis, characterization and evaluation of comb shaped polymeric diesters. Copolymers of maleic anhydride with different unsaturated C₂₂ esters were synthesized and copolymers then reacted with two unsaturated fatty alcohols. All products were characterized by Fourier Transform Infra Red (FTIR) spectroscopy and Gel Permeation Chromatography (GPC). Rheological properties of crude (with and without additive) were studied by Advance Rheometer AR-500. In this study the additive based on oleic acid was evaluated as good PPD and rheology modifier.     

Effect of aromatics and iso-alkanes on the pour point of different types of lube oils

In this work, we have studied the quantitative composition of seven lube oils obtained from different refineries by Nuclear Magnetic Resonance (NMR) spectroscopy and Gas Chromatography (GC) methods. A trend of low temperature flow behavior of these lube oils has been correlated with the composition, i.e. n-alkane, iso-alkanes and aromatics. The pour point of these lube oils does not depend only on distribution of n-alkanes, rather with quantity and types of other molecules like iso-alkanes and aromatics. Two alkylacrylate co-polymers with different mole fractions of co-monomers synthesized by free radical mechanism are used as pour point depressant (PPD) additives. Effectiveness of additive is dependent on polar aromatic type molecules along with iso-alkane type molecules in lube oil.     

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。     

Effect of ultrasound on the viscosity-temperature properties of crude oils of various compositions

The effect of ultrasonic treatment on the viscosity-temperature properties of crude oils of various component compositions has been studied. The efficiency of ultrasonication depends on the group composition of oil and treatment time. The ultrasonic treatment of low-paraffinic oils with a high tar and asphaltene content leads to a substantial decrease in viscosity and the pour point, and the efficiency of ultrasonication increases with an increase in the treatment time. For crude oils with a high n-alkane content, ultrasonic treatment is not effective, which is due to the intensification of crystallization of high-molecular n-alkanes. Calculations that evaluate the effect of ultrasonic treatment on variations in the viscosity of oils are performed based on the fatigue mechanism, which have shown that experimental data are in agreement with the calculated values.     

Characterization of Doba-Chad heavy crude oil in relation with the feasibility of pipeline transportation

A heavy crude oil was characterized in view of the recent commercial exploitation of Doba oilfield in landlocked Chad from where the crude oil is extracted and expected to be routed to the Atlantic shore through pipeline transportation. The elemental composition of Doba feedstocks is 86.25% C, 12.10% H, 0.25% N, 0.14% S and 1.16% O. Atmospheric distillation indicated an initial boiling point at 85 °C, a 10 vol% fraction distilling before 250 °C and an onset of crude thermal cracking at 300 °C. Crude API gravity is 18.8° API, corresponding to a specific gravity of 0.94 at 15.6 °C. The Doba crude oil was found to exhibit non-elastic purely viscous Newtonian behavior over the temperature range typical of crude transportation by pipeline. The crude was fractionated into 97.4% maltenes (n-pentane solubles), 1.8% asphaltenes (n-pentane insolubles), and 0.1% toluene insolubles. The maltenes were subsequently split into four sub-fractions: 45.0±1.2% saturates (MF1), 11.0±0.3% mono and diaromatics (MF2), 26.8±1.2% polyaromatics (MF3), and 12.8±0.8% polars (MF4). FT-IR characterization and proton nuclear magnetic resonance identification of the maltenic and asphaltenic fractions provided evidence of the chemical nature of the different fractions. The high values of the kinematic viscosity of crude oil (184.4cSt at 50 °C) and deasphalted crude oil (152.4cSt at 50 °C) suggest that partially upgrading the oil would be necessary to comply with the viscosity specifications recommended for crude transportation by pipeline.     

埋地含蜡原油管道停输温降最新进展

梳理了我国含蜡原油停输温降的最新研究进展,强调了停输过程中析蜡潜热对原油温度场的影响以及合理处理凝固潜热的必要性;在传热学的理论基础之上,研究了用显热容法建立的新的数学模型。热油管道停输温降过程是输油管道中常见的现象,研究含蜡原油管道停输过程的温度变化规律,为原油输送管道的科学设计和安全、经济运行提供了一定的理论参考。     

The interaction of waxes with pour point depressants

Paraffin wax deposition from crude oils at low temperature is one of the serious and long-standing problems in petroleum industry. Addition of pour point depressants (PPD) has been proved to be an efficient way to inhibit wax deposition. The influence of PPD on wax precipitation at low temperature was investigated. The amount and composition of wax precipitated from paraffin solutions with and without PPD at different temperatures were studied by high speed centrifuge and gas chromatography (GC), respectively. The interactions between waxes and PPD were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed that PPD do not completely prevent the wax from precipitating, but just shift the precipitation toward a lower temperature. This conclusion was identified from the analysis of the amount and composition of precipitated wax as well as the transition temperatures and energies of wax. It was shown that this effect is due to the structure of wax is partly transformed from orthorhombic into hexagonal form by PPD.     

Settling and re‐entrainment of wax particles in near‐gelling systems

Under near‐gelling conditions, the precipitated wax particles can settle down due to gravity and form a bed at the bottom of the pipeline. During restart, the settled waxy bed can increase the pressure drop significantly, and the necessity for pigging and/or addition of chemicals has to be determined to re‐entrain settled wax particles. A laboratory‐scale flow loop, first of its kind, has been built and used to understand the settling and re‐entrainment behavior. The experimental results confirmed the settling of precipitated wax in a pipe under quiescent conditions when the oil temperature falls between wax appearance temperature and pour point. During restart, complete re‐entrainment was attained after reaching a critical flow rate. Solid transport models were able to predict reasonably good results in agreement with experiments. This work emphasizes the importance of understanding the behavior of waxy crude oil during production shutdown and design appropriate startup strategies. © 2017 American Institute of Chemical Engineers AIChE J, 64: 765–772, 2018