管输高水低油分层流动中原油和无机盐混合沉积研究

With the problem of pipeline fouling quickly developing in many of the oilfields that have entered the high water-cut stage, the formation prediction and prevention of fouling has been of increasing importance to efficient petroleum production. This project, by integrating lab experiments with theoretical analyses, aims to study the mixing deposit of crude and inorganic salts in the stratified flow of high-water-low-oil fluids in the gathering pipelines at normal temperatures. Techniques of experimental loops, microscope camera and SEM are employed to investigate the order, composition, and microstructure of the wall-sticking of gelling oil and the deposit of inorganic salts at the initial depositing time, and to reveal the cooperation mechanism of mixing deposit by comparing it with simple oil fouling and with simple salt fouling respectively. The aging properties and removal features will be explored by studying how the elements, compactness and peel strength of the fouling in the same position change with time going by. The connotation of the induction period of fouling will be defined, through an analysis of the influence of the initial deposit microstructure on the pressure drop of oil-water flow. Size distribution and concentration analyses for the salt crystalline grains and morphological analyses for the oil drops will be made to study how their axial diffusion migration, radial migration and follow ability affect the depositing process under the combined influence of the gravity, the interfacial tension between oil and water, the shear force and the lift force. On this basis, a model for predicting the induction period of mixing deposit and its growth speed will be established, thus providing a theoretical support for the formation prediction of fouling in gathering pipelines and the applications of fouling prevention technologies.

我国很多油田进入高含水期后集输管道结垢问题日益突出, 污垢生成预测及防治对于油气生产的高效运行起着越来越重要的作用。本项目实验研究和理论分析相结合，研究常温管输高水低油分层流动中原油和无机盐混合沉积。拟通过试验环道、显微摄像、扫描电镜等技术，研究初始时刻凝油挂壁和无机盐沉积顺序、成分、结构和形貌，与单一原油沉积和无机盐沉积对比揭示混合沉积的协同机制。研究同层位混合污垢成分、致密性及剥离强度随时间的变化规律，探索其老化和脱除特性。通过对沉积物初始形貌对油水两相分层流动压降的影响，研究管流沉积诱导期的内涵。对无机盐晶粒进行粒径分布及浓度分析，对凝油进行形态分析，综合考虑重力、油水界面张力、剪切力及升力协同作用下，凝油和晶粒轴向弥散运移、径向运移以及跟随性对沉积过程的影响，建立混合沉积诱导期和沉积物生长速度预测模型，为油田集输管道污垢生成预测的发展及防垢技术的应用提供理论支持。

利用超高含水原油混合沉积实验装置，确定了油水温度、含水率、流速对沉积速率及压降的影响规律。对沉积物进行了含水率和碳数分析，表明沉积过程同时存在着原油分子扩散、剪切剥离和胶凝作用，其中胶凝作用占主导地位，随温度的降低，胶凝作用逐渐增强，沉积物质量上升。分子扩散和剪切剥离作用造成沉积物组分变化，硬度增加。含水率降低使沉积物中的高碳数组分增加，促进了沉积层的老化。.利用插槽式多材料表面无机盐动态沉积实验装置，确定了流速、浓度、温度、结垢表面性质对无机盐沉积速率的影响规律。提出基于摩擦磨损测试的无机盐污垢附着强度的定量表征方法。发现污垢在材料表面腐蚀处呈选择性附着，污垢晶体与腐蚀产物之间的化学吸附导致表面污垢附着强度明显提高。为避免集输管道内壁面腐蚀，降低管内污垢沉积速率，提出了以超声波促进采出液中二氧化碳解吸方法，给出了超声功率和频率的最佳组合。确定了材料表面特性对碳酸钙晶体形貌和尺寸的影响。提出了基于污垢显微照片的直接分形表征方法，建立了结垢宏观行为与微观形貌间的关系，发现分形维数越大，污垢晶体形态复杂性和不规则性越高，从几何形态角度揭示了污垢宏观结垢行为存在差异的原因。.建立了原油和无机盐混合污垢屈服应力与无机盐含量、温度之间的关系式，无机盐在凝油壁面上沉积速率小于金属壁面。管道中碳酸钙晶体成核主要是一次成核，粒度频率分布曲线为双峰曲线，表明碳酸钙在管道中的生长机制主要为聚结。对微粒污垢的输运、附着、剥蚀过程的进行了机理分析和模型比选，确定了微粒初始沉积的主控因素，给出了集输管道微粒污垢诱导期的预测模型。集输管道粒子的输运主要被扩散和惯性机制控制，绘制了颗粒临界剥蚀尺寸与流速的关系图板。考虑流动和换热对结垢的影响，基于对污垢沉积质量率、脱出质量率的计算，建立了混合污垢结垢量预测数学模型，编制了集输管道结垢量预测软件，用于超高含水集输管道的结垢预测，预测结果与现场实际吻合良好。