基于OLGA软件的海底管道蜡沉积规律模拟研究

油田高含蜡油在管道输送过程中会在管壁析蜡,对管线安全运行构成一定的威胁。利用OLGA 5.3软件某输油管道蜡沉积规律及其影响因素进行了数值模拟分析。对于输油管道,管道中途某一温度范围内是蜡沉积高峰区,过了高峰区后蜡沉积层又逐渐减薄。采取适当提高油温、减小原油与管壁的温差、减小管道粗糙度等措施,可在一定程度上减弱蜡在管壁上的沉积。     

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。     

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。     

蜡沉积层特性参数随时间的变化规律研究

蜡沉积层的形成机理对于管道进行防蜡清蜡作业具有重要意义。基于分子扩散理论,建立了蜡沉积层形成模型。以扩散指数取值2.5、3.5,平均孔隙度取值0.75、0.90为例,计算得到沉积质量、沉积层厚度和平均孔隙度随时间的变化规律。结果表明,扩散指数越小,蜡沉积质量增加的越快。沉积层越厚,孔隙度级别降低的越慢。扩散指数较大时,沉积层厚度初始增速较大,但是一定时间后厚度逐渐平稳。在整个沉积层形成期间,尽管孔隙度级别会显著的减少,但初始线性孔隙度分布还是会保持线性。     

基于颗粒堆积理论的管壁水合物沉积层力学特性研究

管壁水合物沉积层的稳定性与管壁水合物沉积层的力学特性密切相关,研究管壁水合物沉积层的力学特性对深水流动安全保障具有重要意义。为研究管壁水合物沉积层的力学特性,假设沉积层内所有水合物均为大小相同的球形颗粒,且沉积层是由多层水合物颗粒相互堆积而成。根据水合物颗粒堆积方式的不同,将管壁水合物沉积层分为简单立方堆积型、六方堆积型、复六方堆积型、四面体堆积型、角锥堆积型和随意堆积型6类。不同类型的水合物沉积层对应有不同的空隙率和层间受力特性,以此为基础,分别计算分析了各类水合物沉积层的压缩波速、剪切波速、泊松比、弹性模量、抗拉强度,并依据摩尔--库仑强度准则给出了各类管壁水合物沉积层的抗剪强度。同时,计算分析了退火作用对管壁水合物沉积层抗拉强度和抗剪强度的影响。本文研究成果可为油气管道水合物防治技术的发展提供理论支持。     

考虑肋片与内外管壁辐射换热时肋片温度与散热量计算

建立了肋片与内外管壁的辐射换热方程及肋片的温度分布计算方程 ,分析了它们之间的辐射换热对肋片温度、散热量和外壁温度的影响     

管道蜡沉积物抗剪切强度研究进展

对蜡沉积物抗剪切强度的了解,有助于制定合理的清管方案,防止清管过程中发生卡堵事故,但目前关于蜡沉积物性质的研究很少。确定了影响蜡沉积物抗剪切强度的主要因素,包括固相蜡浓度、蜡的碳数分布、胶质沥青质和管流剪切。并从宏观和微观机理的角度,介绍了各因素对蜡沉积物抗剪切强度影响的研究进展。指出定量确定蜡沉积物抗剪切强度亟待解决的主要问题。     

热油管道结蜡对管线运行的影响分析

原油管道输送过程中,随着油流所携带的热量不断地向管外散失,当温度降低到析蜡点以下时会导致蜡质的析出,在管壁内壁上会逐渐沉积一定厚度的石蜡、胶质等混合物,结蜡会对输油管道内油流的传热和流动造成影响;通过分析结蜡前后管线运行状况,建立管道运行的数学模型,对结蜡前后输油管线的温度和压力变化进行计算;结果表明,管壁结蜡会增加管壁热阻,减少原油向地层的热量损失;但足结蜡管壁使管道流通截面减小,会增大管内摩阻。     

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。     

考虑肋片下内外管壁辐射换热时肋片温度与散热量计算

建立了肋片与内外管壁的辐射换热方程及肋片的温度分布计算方程，分析了它们之间的辐射换热对肋片温度，散热量和外壁温度的影响。     

热油管道最佳蜡沉积厚度研究

热油管道输送含蜡油在管壁出现蜡沉积时,往往频繁使用清防蜡剂或者清管器清管手段予以清除。但是在管道建设初期和运营后期,实际输量小于设计输量,在管壁形成一定厚度的蜡沉积反而有益于提升输送效益。通过分析热油管道蜡沉积前后总传热系数和轴向温降的变化,给出了蜡沉积前后温降计算、经济效益评估、允许最小输量计算等公式。为定量分析蜡沉积最优厚度提供了理论依据,对不同管道确定蜡沉积厚度具有指导意义。     

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     

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.     

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.     

Deposition of paraffin wax from kerosene in cooled heat exchanger tubes

Studies of the deposition of wax from wax/kerosene mixtures onto cooled simulated heat transfer tubes has demonstrated that, following an initial deposition taking a relatively short period of time, the heat transfer resistance fluctuates with time. Theoretical estimates of temperature distribution in the experimental flowing wax/kerosene system suggest that the cloud point temperature of the mixture falls within the laminar boundary layer. Since the cloud point is considered the temperature at which particles of wax appear, the conditions within the boundary layer will influence deposition. Increased flowrate and temperature decrease the number of particles able to deposit while the number is increased by greater wax concentration in the bulk solution.     

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。     

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     

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