三高气田套管应力腐蚀与防腐设计研究

Stress Corrosion of Casing in “Three high”Gas Field and Anti-corrosion Design

针对三高气田套管腐蚀难题,分析了套管腐蚀失效因素,设计了应力腐蚀试验方法。用TP110TS和TP95S套管试样,模拟现场井下条件进行不同拉应力、无应力和压应力状态下套管腐蚀试验,并根据试验结果对套管应力腐蚀速率的主要影响因素、腐蚀后力学性能、应力腐蚀敏感性和应力腐蚀门槛值及安全性进行研究。研究结果表明,三高气田套管腐蚀不可避免,拉应力对应力腐蚀具有敏感性;随着拉应力、H2S和CO2含量的增大,套管腐蚀速率加快、力学性能退化,导致其服役安全寿命缩短。据此提出了采用组合套管、降低套管拉应力水平和适当提高套管设计安全系数等相应的技术措施,以提高三高气田套管抗腐蚀能力。

In a＂three high＂（ i. e. high pressure,high yield and high sulfur） gas field,casing is usually susceptible to corrosion. In this paper,factors for casing failure due to corrosion are analyzed,and the stress corrosion test method is designed. TP110 TS and TP95 S casing samples were used for corrosion test of casing at different tensile stresses,zero stress and compressive stresses under simulated downhole conditions. Based on the test results,key influencing factors for casing＇s stress corrosion rate,properties of corroded casing,stress corrosion sensitivity / threshold and safety were analyzed. The research results show that casing corrosion is inevitable in＂three high＂gas fields and stress corrosion is sensitive to tensile stress; as the tensile stress and the mass concentrations of H2 S and CO2 increase,the corrosion rate accelerates,and mechanical properties deteriorate,reducing the casing＇s safe service life. Therefore,appropriate technical measures are proposed to improve the casing＇s anti-corrosion capacity,such as adoption of combined casings,reduction of casing＇s tensile stress and proper increase of casing＇s designed safety coefficient.