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.     

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.     

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.     

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。     

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。     

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。     

Investigations into asphaltenes in heavy crude oils. I. Effect of temperature on precipitation by alkane solvents

Precipitation of asphaltenes by alkane solvents from the Qaiyarah heavy crude oil resulted in relatively higher yields under both cooling and solvent reflux temperature conditions as compared to room temperature. Resins occlusion in the cold precipitation conditions is suggested. From detailed elemental analysis, molecular weight and spectroscopic measurements, it is suggested that at reflux temperatures a rearrangement of the asphaltene moeity takes place through molecular degradation followed by a reaction with resins to form new modified asphaltic materials. A typical light crude oil behaved differently, the asphaltene yield increasing continuously with temperature of precipitation.     

Phase Transformation and Rheological Behaviour of Highly Paraffinic “Waxy” Mixtures

An experimental investigation was undertaken for the rheology and phase transformation of prepared solutions comprising a paraffin wax dissolved in n‐dodecane or n‐hexadecane. The liquid‐solid phase transformation in wax‐solvent mixtures was investigated through the measurement of wax appearance/disappearance temperature (using cross polar microscopy, differential scanning calorimetry, viscometry and a visual method), pour point temperature and crystallization temperature. The results were utilized to prepare a temperature‐composition phase diagram for the wax+n‐C₁₆H₃₄ pseudo‐binary system. The effects of composition, temperature, cooling rate and shear rate were studied on the rheology of wax‐solvent mixtures. A correlation was developed for the apparent viscosity of wax‐solvent mixtures.     

含蜡原油管道清、防结蜡技术

在管道输送含蜡原油的过程中,由于原油的物性,即原油的内在因素,和外界环境因素的影响,输送过程中会产生操作上的问题,有时会严重影响生产的进行。本文针对目前我国原油输送管道所存在的含蜡问题,分析含蜡原油管线结蜡机理和影响因素,提出了常用于输油管道的清防蜡化学药剂。     

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…     

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。     

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.     

Separation and Analysis of Wax from Egyptian Sugar Cane Filter Press Cake

Waxes from filter press cake of the by-product of the Sugar Cane Industry gained from various Egyptian Cane Sugar Factories were studied. A method for continuous extraction of wax filter cake using different solvent i. e. toluene, naphtha, acetone, fractionated gasoline, denatured and refined alcohol was investigated. The speed and ease of extraction using different solvents were compared. By using toluene as solvent the highest percentage of crude wax was obtained from Edfu, which gave 14.55%, while extraction with refined alcohol produced 12.65% crude wax from Qus. Decolorization of crude wax was carried out by sodium hypochlorite, nitric acid, chlorine, sulphur dioxide and acetone. The pure wax was separated from the fatty oil fraction by fractional crystallization from 70° to 0° C. The greater portion of wax can be obtained at 30° C. Hard, brittle wax was obtained between 45° to 20° C. The crude and refined waxes had properties comparable to carnauba wax and other commercial waxes. The Egyptian cane sugar waxes can be utilized in paper, ink, coating, varnishes, pharmaceuticals, cosmetics and fertilizer industries.     

Optical fiber extrinsic refractometer to measure RI of samples in a high pressure and temperature systems: Application to wax and asphaltene precipitation measurements

An optical fiber extrinsic sensor for measurement of changes in the refractive index of liquids confined in chambers for high pressure and temperature experiments is described. One head sensor composed by two fibers is fixed in front of a high pressure and temperature cell filled with the sample. The operation principle is based in the reflectivity dependence in the refractive index of the glass–liquid interface. Excellent results and a sensitivity of 10⁻⁵ RI were obtained for pure liquids. The applicability of the sensor is demonstrated following the changes in the refractive index for pure liquids at different pressure and temperatures and by measuring the asphaltenes and wax precipitation in crude oils under pressure. The extrinsic probe designed for refractive index measurement proves to be a reliable tool for measuring heavy organics deposition in crude oils under high pressures and temperatures where the sample to be measured is not very accessible.     

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.     

溶剂沉淀法净化萃余酸工艺研究

为了能循环利用湿法磷酸净化的萃余酸，实验研究了溶剂沉淀法净化萃余酸的工艺条件，选择以乙醇和异丙醇体积比为1的混合醇作为溶剂，对不同杂质含量的萃余酸进行了净化除杂。实验结果表明：在溶剂与萃余酸体积比为5：1、反应时间为30min、反应温度为75℃的条件下对萃余酸中的金属离子的去除率达75％以上，达到净化萃余酸循环利用的要求，蒸馏回收溶剂也可循环利用。     

低含蜡原油防蜡剂的研究与应用

春光油田结蜡反常严重,影响生产。通过针对原油和析出蜡的组成研究后,设计了防蜡剂组成及用量优化试验方案,经过试验得到了防蜡剂组合配方。室内试验表明,该配方对春光原油的防蜡率可达70%以上,在最低0.01%的浓度条件下,防蜡率仍达到52.9%。2011年9月在春光油田实施防蜡现场试验3口井,收到良好效果,防蜡后试验井的清蜡周期延长1倍以上,防蜡后与防蜡前的清蜡周期比平均2.26。     

A Simplified Method for Fractionation and Analysis of Waxes and Oils from Sorghum (Sorghum bicolor (L.) Moench) Bran

In the United States, sorghum is primarily used for animal feed and ethanol production but has potential to provide value-added coproducts including waxes and oil. The surface of sorghum contains 0.1–0.4% wax; however, wax extraction from whole kernels before fermentation may not be economical. An alternative method for this extraction could be facilitated through decortication, abrasion of the surface to remove bran. Decortication increases the starch content of decorticated sorghum, potentially improving ethanol yields, while concentrating wax and oil to the bran. Typically, oil (triacylglycerols) and waxes are extracted from bran in one extraction and waxes are precipitated from oil using cold temperatures then filtration. This research compared traditional fractionation (simulated with a two-step, single-temperature extraction) to a two-step, dual-temperature extraction, whereby oil is first extracted at room temperature and then waxes at elevated temperature. Extractions were performed using an accelerated solvent extractor with hexane or ethanol as solvents. Ethanol extraction showed greater yields (~15% w/w) compared to those of hexane (~11% w/w) because polar materials were extracted. Using hexane, the two-step, dual-temperature fractionation separated waxes from oils via the temperature of extraction solvent with similar purity to the traditional method that fractionated via cold precipitation and filtration. For ethanol, the traditional single-step method fractionated with higher wax purity but lower oil purity compared to the two-step, dual-temperature fractionation.     

含蜡原油管道的结蜡规律研究

原油输送中的析蜡问题是影响管道安全运行和管理的重要因素之一。介绍了管壁结蜡影响因素,通过试验,探讨了原油输送温度和管壁温差对管壁蜡沉积速率的影响,得出了输油温度和温差与结蜡层厚度之间的关系,对于预测结蜡规律有一定的参考作用。     

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。