基本工况条件对螺杆钻具硬铬镀层腐蚀影响的研究

发布时间：2018-02-11 09:05

  本文关键词： 腐蚀 螺杆钻具 硬铬镀层 氯离子 正交实验法 动电位扫描　出处：《重庆科技学院》2017年硕士论文　论文类型：学位论文

【摘要】：随着我国油气开发行业的进一步发展和井下油气钻井技术的逐渐成熟,螺杆钻具常被广泛应用到定向井和水平井的钻井过程中。然而,根据油气田的现场应用表明,盐水钻井液常被用在钻井过程中,致使螺旋钻杆表面硬铬镀层发生严重的腐蚀。严重的腐蚀将缩短螺杆钻具使用寿命,直接导致经济成本的增加,还可能造成事故风险增加,甚至有人员伤害的可能。目前,国内外学者研究氯离子腐蚀的课题较多,但是针对螺杆钻具在盐水钻井液工况中腐蚀行为的系统研究较少,制造企业也缺乏充分的参考依据。因此研究实际工况下螺杆钻具硬铬镀层的腐蚀规律具有重要的学术价值和工程应用意义。本文通过收集目前螺杆钻具在井下工作的工况信息,拟定了基本工况条件参数,即温度、压力和氯离子浓度,以及各参数的范围。利用高温高压反应釜模拟螺杆钻具在井下的基本工况条件,对螺杆钻具表面硬铬镀层进行腐蚀和检测,并以常温常压环境镀铬层的腐蚀试验以及电化学参数作为参考,通过正交实验法研究温度、压力和氯离子浓度对硬铬镀层腐蚀的影响,采用开路电位、动电位扫描和失重腐蚀法研究硬铬镀层的电化学参数及腐蚀特征,采用扫描电子显微镜和能谱观察和分析镀层腐蚀前后的微观形貌和表面成分。研究发现,镀层的腐蚀速率随着氯离子浓度的升高而降低,随着温度的升高而升高,随着压力的升高而升高。影响硬铬镀层腐蚀速率最大的因素是氯离子浓度的变化,其次是温度,再次是压力。从基本工况条件可以推断硬铬镀层腐蚀最严重的情况是在温度为180℃、压力为15MPa和氯离子浓度为30g/L的参数附近。从镀层腐蚀前后形貌看,氯离子优先在敏感位置(钝化膜的薄弱点处)引发孔蚀核,在闭塞腐蚀电池催化作用下,镀层表面不断形成孔蚀,腐蚀孔加大形成宏观腐蚀坑;同时裂纹处受到一定程度的腐蚀,裂纹被明显加宽;个别严重的情况下,腐蚀导致少部分区域镀层深孔、剥落,甚至穿透镀层,形成阴极镀层与基体之间的电偶腐蚀。
[Abstract]:With the further development of China's oil and gas development industry and the maturation of downhole oil and gas drilling technology, screw drilling tools are often widely used in the drilling process of directional wells and horizontal wells. However, according to the field application of oil and gas fields, Salt water drilling fluid is often used in drilling process, which results in serious corrosion of hard chromium coating on helical drill pipe surface. Serious corrosion will shorten the service life of screw drill pipe, directly lead to the increase of economic cost, and may also increase the risk of accident. There is even the possibility of human injury. At present, scholars at home and abroad study more topics of chloride ion corrosion, but there are few systematic studies on corrosion behavior of screw drilling tools in brine drilling fluid. Therefore, it has important academic value and engineering application significance to study the corrosion law of hard chromium coating of screw drill tool under actual working condition. The basic operating condition parameters, that is, temperature, pressure and chloride concentration, and the range of the parameters are worked out. The basic working conditions of the screw drilling tool are simulated by using a high temperature and high pressure reactor. The corrosion and detection of hard chromium coating on the surface of screw drill tool were carried out. The corrosion test and electrochemical parameters of chromium plating layer in normal temperature and atmospheric pressure were used as reference, and the temperature was studied by orthogonal test method. The effect of pressure and chloride concentration on the corrosion of hard chromium coating was studied. The electrochemical parameters and corrosion characteristics of hard chromium coating were studied by open-circuit potential, potentiodynamic scanning and weightlessness corrosion. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to observe and analyze the microstructure and surface composition of the coating before and after corrosion. It was found that the corrosion rate of the coating decreased with the increase of chloride concentration and increased with the increase of temperature. The corrosion rate of hard chromium coating increased with the increase of pressure. The change of chloride concentration was the most important factor, followed by temperature. From the basic operating conditions, we can infer that the most serious corrosion of hard chromium coating is near the temperature of 180 鈩，

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