油套管丝扣塑性变形促进腐蚀加速机理和控制措施研究

With the development of ultra-deep, ultra high temperature and ultra-corrosion oil and gas exploitation, the joint of screw thread connection of casing and tubing shows the weakest point under the corrosion environment combined with stress concentration. The complex corrosion behavior around screw thread of casing and tubing induced by plastic deformation will be investigated in this project based on both mechanical and electrochemical driving forces. The two important forces lead to localized corrosion are considered as mechanical driving force induced by plastic deformation and electrochemical driving force induced by galvanic corrosion between elastic zone and plastic zone. This project will focus on the effect of plastic deformation on corrosion acceleration and influence mechanism, and promoting mechanism induced by galvanic effect between elastic zone and plastic zone under high temperature and high pressure CO2 corrosion environments. High temperature high pressure corrosion simulation and electrochemical experiments will be used to research the acceleration mechanisms of localized corrosion induced by plastic deformation and elastic zone and plastic zone galvanic corrosion. Based on the detailed researches, quantitative relationship between corrosion rate and plastic deformation effect and galvanic effect can be established. The methods decreasing screw thread corrosion will also be investigated. Thereby it will lay the foundation for leaking failure induced by screw thread corrosion during safety production of oil and gas field.

针对油套管丝扣连接处塑性变形导致腐蚀穿孔这一油气开发过程中频繁发生的腐蚀现象和工程难题，分别从力学和电化学两个学科角度出发，提炼出导致局部腐蚀发生的两个重要驱动力：塑性变形引起的力学驱动力和弹变区/塑变区腐蚀电偶引起的电化学驱动力。围绕高温高压CO2服役环境中塑性变形对腐蚀的加速效应与影响机制，弹变区/塑变区电偶效应对腐蚀的促进机制，利用高温高压腐蚀和电化学方法，研究塑性变形和弹变区/塑变区腐蚀电偶导致局部腐蚀的复合加速机理，建立腐蚀速率与塑性变形和腐蚀电偶的定量关系，探索消减塑性变形导致丝扣腐蚀的控制措施，为探求油气田安全生产所遇到的丝扣腐蚀泄漏这一难题的解决方法奠定基础。

本项目针对我国超深、超高温、超高腐蚀油气田开发过程中日益多发的油套管柱丝扣连接部分由于应力集中和腐蚀环境耦合造成的腐蚀断裂实际问题和需求，重点研究塑性应变及其电偶效应促进腐蚀机理。分别从力学和电化学两个学科角度出发，围绕塑性变形引起的力学驱动力和弹变区/塑变区腐蚀电偶引起的电化学驱动力开展研究工作。利用高温高压腐蚀模拟和带载荷条件下的高温高压原位电化学和微区电化学等方法，研究了高温高压CO2服役环境中塑性变形对腐蚀的加速效应与影响机制，弹变区/塑变区电偶效应对腐蚀的促进机制，建立腐蚀与塑性变形效应和电偶效应的定量关系，探索了通过合金化和环境控制消减腐蚀的方法。开展了大量现场实际油套管螺纹丝扣失效案例分析，明确了丝扣腐蚀失效过程；建立了可进行弹/塑性区腐蚀实验研究的高温高压电化学测试和电偶腐蚀测试方法与装置。通过大量实验工作，分别针对N80油管钢为代表的碳钢活化体系和13Cr不锈钢为代表的钝化体系，研究阐明了高温高压CO2腐蚀环境下变形对腐蚀热力学和动力学机制的影响，明确了弹变区/塑变区电偶效应对腐蚀的加速效应，阐明了塑性变形促进腐蚀的机制。在SCI/EI刊物上已发表篇高水平论文10篇，专利授权1项，出版专著1部，培养研究生10人。并与我国西北地区石油天然气开发现场的失效案例与控制应用相结合，基于低Cr合金化、井下工况介质控制、油管表面变形损伤控制等，探索了消减塑性变形导致丝扣腐蚀的控制方法，为油气田井下油套管腐蚀控制和我国大型钢厂油套管耐蚀产品开发提供了理论和方法支撑。