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     

Liquid wall friction in two-phase turbulent gas laminar liquid stratified pipe flow

The main result of the present work is an analytic expression for the mean liquid wall shear stress in two-phase turbulent gas/laminar liquid stratified pipe flow. The Navier-Stokes equations are solved assuming a flat fluid-fluid interface subject to a constant interfacial shear — approximating the interfacial drag exerted by the gas. The effect of a pipe inclination is accounted for, thereby retaining the interesting two-phase phenomenon of backflow in upwardly inclined pipes. The corresponding expression for the wall shear stress distribution is obtained by formal differentiation. Its limiting behaviour in the triple points, where the fluid-fluid interface meets the pipe wall, is determined by residue calculus. The expression for the mean wall shear stress is given by integration. It is found to be a linear combination of two terms. The first term accounts for the free surface liquid flow in the absence of the gas. The corresponding approximate hydraulic diameter model is found to be in surprisingly good agreement with this term. The second term represents the shear flow associated with the interfacial drag exerted by the gas (not accounted for by the hydraulic diameter approximation). The shear flow increases the flow rate near the interface on behalf of the flow rate near the pipe wall, thus reducing the wall shear stress below the free surface flow value. Expedient evaluation of the expression for the mean wall shear stress, suitable for use in a 1-D multiphase pipe flow simulator, is facilitated by replacing certain one-parameter integrals with highly accurate rational approximations.     

油水两相流蜡沉积研究进展

蜡沉积研究中,油水两相蜡沉积的研究已成为研究重点,但对此领域的研究还处于起步阶段。本文系统阐述了国内外蜡沉积研究的发展现况,对近些年蜡沉积机理研究的新进展--剪切剥离以及老化机理作了分析。介绍了冷板、冷指实验装置和环道实验装置,对国内外学者进行的蜡沉积实验情况作了概述。介绍了国内外单相原油与油水两相蜡沉积动力学模型的研究现状,在单相模型基础上对Couto油水两相模型和Bruno改进模型进行了描述。今后的研究应以蜡沉积机理与预测模型为重点,分析油水两相流蜡沉积的影响因素,这对于缓解输油管道蜡沉积问题,增强管道输送能力具有现实意义。     

水平管气液两相变质量流流型从分层流向非分层流的转变

基于文献中提出的针对常规管中气液两相流分层流稳定性的分析,考虑管壁入流对流型的影响,通过公式推导和分析得出了水平管中气液两相变质量流流型从分层流向非分层流转变的准则。通过室内实验研究和预测计算,分析了3种不同的流型转变准则中多个入流流量下管壁入流对流型转变的影响。研究结果表明,实际水平井筒的单位入流流量通常较小,对本地管道单元流型预测的影响可以忽略不计,但是通过不断累积,使得下游管道中流动参数发生变化,从而影响了下游管道单元中气液流动的流型。因此水平孔缝管中气液两相变质量流的流型判别可以采用常规管流型判别准则,但要分段进行。     

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     

Effect of polyethylene pipe on wax deposition under different temperature and flow rate conditions

Wax deposition is an important but troublesome boulder in petroleum industry that has always plagued pipeline engineering operators. In this study, wax deposition in the polyethylene pipes has different behaviors comparing wax deposition in stainless steel pipes such as smaller weight of wax deposits and lower wax content. After wax deposition experiments, some important parameters, including diffusivity and temperature gradient, were measured and calculated to explore the differences between two material pipes. Moreover, those factors can make a significant impact on radial mass flux. A series of results in polyethylene pipes suggests that higher diffusivity enhances diffusion flux of wax in the radial direction. But it was found that radial concentration gradient accounted for a larger proportion. These factors are the relationship of competition and cooperation and the combination of them results in different performances of wax deposition between polyethylene and stainless steel pipes.     

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.     

An explicit approximation for the wetted angle in two-Phase stratified pipe flow

In two-phase stratified pipe flow the wetted angle relates the flow geometry to the holdup. The relation linking the holdup to the wetted angle does not, however, have a simple explicit solution and is therefore often solved numerically. This analysis yields simple explicit approximations for the wetted angle for a given holdup, which constitute a convenient alternative to a numerical solution.     

苏嵯输油管道蜡沉积规律研究

采用差压法设计安装了一个室内环道管流设备,并以此设备对苏嵯管道的不同工况进行了室内结蜡实验。参照苏嵯输油管线现场运行数据,在通过计算得到管壁剪切率、蜡晶溶解度、油品粘度以及径向温度梯度等参数的基础上,采用最小二乘法回归确立了适用于苏嵯输油管线的管道蜡沉积模型。在数据分析和模拟实验结果的基础上,分析了流速、油温以及壁温等因素对苏嵯输油管道结蜡的影响,得出了该条管道的蜡沉积规律,为苏嵯输油管道的实际生产运行提供了参考依据。     

An experimentally validated heat and mass transfer model for wax deposition from flowing oil onto a cold surface

A transport model is proposed for wax deposition onto a cold finger from flowing wax-containing oils. The model solves transient energy and mass balances simultaneously for a reversible first-order kinetic rate for precipitation of pseudo-single-component wax, and the effects of yield stress using a critical solid wax concentration to withstand flow-induced stress at the deposit-fluid interface. The model can predict the time evolution of the deposit thickness, and the spatial and temporal evolution of temperature and wax concentration as validated using cold finger experiments. It was found that for high wax content oils, deposit thickness growth is dominated by heat transfer. For low wax content oils that are unable to gel, the thickness growth is slow and accompanied by occasional sloughing. Regardless of the mechanism controlling the growth, mass transfer cannot be neglected as wax diffusion into the deposit continues to take place after the deposit has stopped growing.     

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     

硬球-拟颗粒模拟高超声速稀薄气体流动

发展了适应高超声速稀薄流动的硬球-拟颗粒模拟(HS-PPM),并分别采用硬球分子动力学模拟(HS)、HS-PPM和直接模拟蒙特卡洛(DSMC)对马赫数为5、努森数为0.8的圆球绕流进行模拟,证明了HS-PPM可以得到更接近HS的模拟结果。对雷诺数100、马赫数5~19的三维圆球绕流,采用HS-PPM模拟得到了填充率0.01~0.08、完全热边界和完全滑移边界条件下的曳力系数,与HS模拟结果的一致性较好;模拟了马赫数24、努森数0.11~4.55的零攻角三维尖锥绕流,结果与文献中DSMC的模拟结果相符。研究验证了HS-PPM处理高超声速稀薄气体流动的可行性。     

原油集输管线结蜡机理分析及动态结蜡实验研究

本文首先分析总结了输油管线的结蜡机理以及影响结蜡的常见因素。然后介绍了采用JLY-2型原油动态结蜡仪进行模拟的结蜡实验,实验过程中采取了对结蜡管进行表面改性技术处理,从而来实现防蜡效果。实验结果显示,对于不同含水率的原油,防蜡率可以达到80%以上,十分具有应用价值。     

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     

基于独立成分分析的水平管气液两相流分相信息提取

基于独立成分分析(ICA)方法分析水平管气液两相流的电阻成像（ERT）所获取数据,提取水平管气液两相流流动特征,获取分相信息。通过分析比较ICA所得的独立分量以及ERT侧视、俯视成像时间序列和摄像仪记录的流动状态图像,并经过实验表明,对水平管气液两相流中的弹状流、分层流、波状流,电阻层析成像方法结合ICA方法可有效地获取水平管气液两相流流动特征参数,提取的独立分量反映了物理上相互独立的分相的变化情况,具有明确的物理意义;对水平管气液两相流中的塞状/泡状流,ICA方法结合多尺度分析方法可获得更为有效的信息。     

上倾管高黏油气两相流型及压降特性

利用室内实验装置,对上倾管内高黏油气两相流的流型和压降特性进行了实验研究。实验中观测到7种流型,得到了不同工况下的压力波动信号及压降值。实验结果表明,由于液相黏度的影响,上倾管内大部分流型的过渡边界向流型图的左侧偏移,且黏度越大偏移程度越大。将流型数据与Barnea流型判断模型进行对比,发现在高黏度时两者误差较大。根据压降数据得出,由于高黏度时液滴的附着作用增强,在气液表观速度均较小时,会出现黏度增加而压降却减小的现象。验证了OLGA模型和Zhang模型对于压降的计算精度,发现高黏度时模型的计算误差远大于低黏度情况。通过高黏度闭合关系式对Zhang模型进行修正,结果表明可以显著地提高其计算精度。     

Numerical modeling of three-phase stratified flow in pipes

The simultaneous flow of water, oil and gas is of practical importance for the oil and gas industry. These three phases are present in varying degrees of concentration in many oil and gas pipelines. In this work, a model has been developed to predict the values of the hold-up and pressure gradient for three-phase stratified flow prevailing in a horizontal pipeline. This information is usually the first step for analyzing the stability of stratified flow and developing transition criteria. The concept of extended velocity has been applied to compute the wall shear stresses in three-phase flow. The effect of process variables such as gas to liquid ratio, pipe diameter, oil viscosity and non-Newtonian character of oil on hold-up and pressure gradient has been studied to simulate the oil well conditions. Structural stability analysis was also carried out to check for the sensitivity of the model.     

槽式孔板的湿气分层流差压预测模型

槽式孔板是一种新型的气液两相流测量元件,与标准孔板相比,槽式孔板具有前后直管段要求低、差压信号平稳、上游液相无累积等优点。通过对槽式孔板的局部阻力进行分析,槽式孔板总压降主要由摩阻压降和加速压降两部分组成。基于气液两相流体流经槽式孔板的流动机理,利用动量守恒关系式和能量守恒关系式计算摩阻压降和加速压降,建立了槽式孔板的分层流差压预测模型。以空气/水为介质,进行了一系列实验,实验结果表明,孔径比为0.75、0.6、0.5的槽式孔板的平均相对误差分别为6.45%、11.06%、12.52%,为湿气计量算法的完善提供了参考。     

油水混合物在水平管中的二相流动特性研究

对内径40mm的钢管和有机玻璃管内油水二相水平流动时的流型、摩擦压降特性进行了详细的实验研究,结果表明:油包水向水包油的转变发生在含水体积分数约0. 4时。随含水体积分数的增大,油水二相流的摩擦压降先是急剧减小,其后在含水体积分数大于0. 4时压降变化趋于平缓。油水二相流的摩擦压降受含水体积分数、管壁润湿特性、管壁粗糙度以及混合物流速的影响,当二相流体处于水包油状态时,钢管内的摩擦压降比有机玻璃管内的大;而当处于油包水时,有机玻璃管内的摩擦压降则比钢管内的摩擦压降大。