W/O型含蜡原油乳状液触变特性及其微观机理研究

Most oils produced in the China’s offshore oilfields are the waxy crudes, which are of high pour point and viscosity. Nowadays, the mixed transportation of oil-gas-water has become a major way for long distance offshore pipelines. Crude oil emulsion is one of the statesinwhich crude oil and water coexist inmixed transportation pipeline. Therefore, the thixotropic of waxy crude oil emulsion is important basic material for the flow assurance research of oil-water mixed transportation.In this study, based on the needs of numerical simulation of the shutdown and restart of subsea pipelines,the thixotropic of the water-in-oil emulsion for waxy crude oilwas studied, which aims to reveal the macro-rheological laws and its micro-mechanismsunder different loading conditions. Then, based on the ideas of the structural dynamics model and the relative viscosity in dispersed system, a mathematical model was establishedto describe the thixotropic behaviorsatmultipleloading modes. Meanwhile, the influence rules of water cut on the thixotropic of the water-in-oil emulsion for waxy crude oil were discussed.On this basis, with the analysis of related factors of the macro-thixotropic, a forecasting method wasestablished, which could predict the thixotropic of the water-in-oil emulsion for waxy crude oil at any water cut and different loading modes by using only few experimental data. The research results will provide important basic information for the pressure prediction of the shutdown and restart of mixed transportation pipelines,and promote the advance of rheological study on waxy crude oil.

我国海上油田所产大多为易凝高粘的含蜡原油，油气水混输已成为较长距离海上油田集输管道主要的输送方式，原油乳状液是原油和水在混输管道中共存的状态之一。因此，含蜡原油乳状液触变性是原油—水混输管道流动安全保障研究的重要基础资料。本课题针对W/O型含蜡原油乳状液触变特性开展研究，揭示不同加载条件下W/O型含蜡原油乳状液触变性宏观流变特性规律及微观机理；基于结构动力学模型和分散体系相对粘度的构想，建立适合描述多种加载模式下W/O型含蜡原油乳状液触变特性的数学模型；探知含水率对W/O型含蜡原油乳状液触变特性的影响规律；在此基础上，结合宏观触变特性关联因素分析，建立基于少量实验数据准确预测任意含水率、多种剪切加载模型的W/O型含蜡原油乳状液触变特性预测方法。研究成果将为油水混输管道停输再启动压力预测提供重要基础资料，推动含蜡原油流变学研究的进展。

海上油田的开发是世界能源发展的趋势，油气水混输已成为较长距离海上油田集输管道主要的输送方式，W/O型含蜡原油乳状液触变性是原油—水混输管道流动安全保障研究的重要基础资料。本课题研究内容包括：W/O型含蜡原油乳状液实验样品制备条件研究，多种加载模式下W/O型含蜡原油乳状液触变特性及其微观机理研究，适合描述多种加载模式下W/O型含蜡原油乳状液触变特性的数学模型及任意含水率条件下触变特性的预测方法研究。课题组通过理论研究、实验研究等手段，取得了以下研究成果：.基于热力学和粘性流体力学的理论，建立了以粘性流动熵产描述乳状液配制过程的条件参数关系式；建立定量描述乳状液配制条件与平衡表观粘度关系的数学模型，为实验室基于平衡表观粘度量化表征的原油乳状液的配制提供理论。.表征了W/O型含蜡原油乳状液在恒定剪切速率加载、恒定剪切应力加载、阶跃增加剪切速率加载、阶跃增加剪切应力加载、剪切速率线性变化加载、剪切应力线性变化加载六种加载模式下的触变特征；总结分析了含水率对胶凝体系触变特性及结构恢复特性的影响规律；结合显微图像分析提出，W/O型含蜡原油乳状液的触变特性是剪切作用下蜡晶结构的裂解和液滴直径的增加两者共同作用的结果；建立了能够很好描述W/O型含蜡原油乳状液触变性基本特征的数学模型，其能力好于Houska模型，与赵晓东模型相当。但表达式均为显示方程，而且模型参数相对较少，只有7个，数学形式上比赵晓东模型简单很多。从工程应用角度讲，本模型更实用。.提出了基于3个含水率的W/O型含蜡原油乳状液和脱水原油的触变性实验数据，即可预测其它含水率下W/O型含蜡原油乳状液触变特性的方法。用所预测的结果对描述触变性的数学模型进行拟合获取触变模型参数，即可为输送W/O型含蜡原油乳状液的管道停输再启动数值计算提供触变性基础数据。.本次研究完成了既定目标，成果为油水混输管道停输再启动压力预测提供重要基础资料，一定程度上推动含蜡原油流变学研究的进展。