A fundamental wax deposition model for water‐in‐oil dispersed flows in subsea pipelines

Water‐in‐oil dispersions frequently form in subsea oil pipeline transportation and their presence affects the wax deposition rate in subsea pipelines. A fundamental model for wax deposition on the wall of water‐in‐oil dispersed phase flow pipelines has not been developed. Dispersed water droplets can affect the heat and mass transfer characteristics of wax deposition and alter the deposit growth rate. In this study, wax deposition from water‐in‐oil dispersed flows is comprehensively modeled using first principles of heat and mass transfer. The role of the dispersed water phase on the heat and mass transfer aspects of wax deposition is analyzed. The developed model predicts different effects of the water volume fraction and droplet size on the wax deposition rates in laboratory flow loop experiments and in field scale wax deposition processes. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4201–4213, 2017     

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     

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     

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。     

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.     

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.     

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。     

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。     

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。     

管道结蜡层温度分布计算研究

通过对试验环道上测试段相关数据的测试,对比分析测试段管壁有沉积物和无沉积物时测试段管壁内温度分布的不同表达式,根据能量方程建立了无量纲温度分布方程,利用贝赛尔函数推导出原油在层流状态下沉积层表面温度分布、沉积层热流密度、油流温度分布等相关温度场的计算公式,为研究蜡沉积规律,定性分析管路结蜡层厚度和制定合理的清管方案奠定了理论基础.     

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.     

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.     

基于冷指的不同防蜡率计算方法分析

防蜡率的测定对防蜡剂的有效筛选具有重要意义。考虑到标准中推荐的防蜡率计算方法的局限性,利用自行改造的冷指装置对不同温度、剪切强度和作用时间下加剂前后的蜡沉积物进行了测定,并给出了两种不同的防蜡率计算方法。结果表明:防蜡率与防蜡沉积速率随温度区间的变化规律基本一致,油温为47℃、壁温为37℃时的防蜡沉积速率为99.83%,明显高于防蜡率;防蜡沉积速率与防蜡率随剪切强度的变化规律基本一致;作用时间较短时,防蜡沉积速率比防蜡率大,超过4 h后两者基本不再随时间变化;所用防蜡剂对各碳数的防蜡效果各异,对C44之前的碳具有防蜡效果,C44及其以后的碳具有负面作用。在实际使用时应根据具体实际情况合理选取或三种防蜡率计算方法结合起来使用。     

利用掺稀泵压计算掺稀管线结蜡厚度

鲁克沁油田属于超深稠油油藏,原油粘度大、密度大,稠油在井筒中流动困难,需进行井筒降粘才能实现油田开发。鲁克沁油田共有油井126口,95%以上的油井采用掺稀油降粘工艺开采。由于稀油含蜡量较高,管壁容易结蜡,必须定期进行热洗清蜡才能维持管线的正常运行。本文综合考虑掺稀量、管线长度、原油粘度、管线两端的高程差等因素的影响后,利用掺稀泵压和掺稀管线打回流后的井口回压,来计算地面掺稀管线的管壁结蜡厚度,并以此指导掺稀管线的日常热洗维护。     

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.     

高效固体防蜡剂的研制与试验

长庆油田X区块结蜡周期短,蜡质碳数在C10-C51之间,峰值在C39左右,呈现出蜡质碳数较高、蜡分子稳定性强的特点,常规防蜡剂防治困难,存在针对性强、适应性差的问题。针对X区块原油及蜡质特征,实验室合成的3种防蜡剂并进行防蜡率评价,应用气相色谱法对不同碳数范围的蜡样进行了防蜡剂防蜡效率的分析,确定出了固体防蜡剂的主剂B,可以适应C15-C51的蜡质;将低熔点EVA-01和高熔点LD-01的骨架材料复配,测试不同比例下的溶释速率,确定出两者最佳比例为2.5∶1;通过分析主剂B、分散剂FSJ-01加量的影响,确定出了固体防蜡剂的配方:10%B+85%(EVA-5/LD-03(2.5∶1))+5%FSJ-01。该防蜡剂在20mg·L~(-1)时,防蜡率为62.3%,使原油析蜡点降低6.1℃。现场试验表明:固体防蜡剂可以降低油井载荷,延长结蜡周期,取得了较好的防蜡效果。     

Investigation of inhibitors efficacy in wax deposition mitigation using a laboratory scale flow loop

Statistically reliable wax inhibition experimental data was obtained by utilizing the newly built laboratory scale flow loop. The comb‐shaped inhibitors are found more effective in decreasing the thickness compared to the linear inhibitor under the same conditions. Moreover, this becomes more predominant as the chain length of inhibitors increases. Interestingly, even though all the inhibitors decreased the deposit thickness, the wax content increased significantly. Besides, the longer chain length (PI‐B) of the inhibitor results in a higher wax content. Since the combination of growth and aging influenced by the presence of inhibitor significantly, paraffin inhibition efficiency (PIE) based on the wax mass was proposed to quantitatively assess the inhibitors. Based on the PIE, PI‐B, and PI‐C have more inhibition efficiency than PI‐A. Therefore, when selecting wax inhibitor, one should be aware about the strength of the deposit gel in addition to the reduction of the deposit mass. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4131–4139, 2016     

Wax deposition modeling of oil/water stratified channel flow

Wax deposition modeling becomes complicated when multiphase flow is involved. Empirical heat and mass transfer correlations are unreliable for multiphase deposition modeling and full scale computational fluid dynamics calculations require expensive computational intensity. In this work, numerical methods are used to study wax deposition in oil/water stratified flow through a channel. A unidirectional flow analysis is used to calculate the nonisothermal hydrodynamics and mass transfer. It was found that the change in the position of the oil/water interface throughout the channel must be taken into accounted for the mass balance to be valid. Unfortunately, this change has not been accounted for in all previous studies. In addition, the growth of the wax deposit as a function of time along with the effect of oil/water flow rate ratio is discussed. The presence of water significantly reduces the severity of wax deposition by altering the heat and mass transfer characteristics. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

原油管道内蜡沉积速率预测及分析

分别运用灰色预测理论和灰色神经网络理论对原油管道内的蜡沉积速率进行了预测分析;应用灰色人工神经网络理论,考虑剪切应力、温度梯度、粘度以及浓度梯度4个影响因素作为主要因素的对原油管道内的蜡沉积速率进行的预测,与传统的灰色预测方法相比,所得到的预测值更为接近实际值,蜡沉积速率的相对误差绝对值在1．6％以内,灰色神经网络用于管道内蜡沉积速率预测的效果良好,能为原油管道蜡沉积规律的深入研究和制定合理的清蜡周期提供理论依据。     

Evaluating the Oil‐Gelling Properties of Natural Waxes in Rice Bran Oil: Rheological,Thermal, and Microstructural Study

The main objective of this research was to enhance the understanding of the oil‐structuring properties of natural waxes. A number of natural food‐grade waxes were evaluated for their oil‐gelling properties using a combination of techniques, including rheology, differential scanning calorimetry, and polarized light microscopy. Based on the rheological measurements (oscillatory, flow, and thixotropic behavior), we found that rice bran wax, carnauba Brazilian wax and fruit wax showed weak gelling behavior in rice bran oil (prepared at concentrations as high as 5 % w/w), exhibiting relative low elastic moduli that displayed a high frequency dependency. On the contrary, carnauba wild wax, berry wax, candelilla wax, beeswax, and sunflower wax were efficient oleogelators forming strong gels at concentration of <2 % w/w. We attempt to explain these observed differences in gelling behavior by crystal morphology, network formation, and the final amount of crystalline phase.