油井管接头密封方法及机理综述

高温高压天然气井的管柱密封性至今无法完全保障。油井管最常用的四种密封方法是螺纹密封、台肩密封、弹性密封环密封和金属接触密封。大部分特殊螺纹接头采用金属接触密封,密封面接触压力决定了密封能力。正确的金属接触密封会显示出一种压力激发效应。将密封面设计在远离螺纹端部的位置,螺纹端部刚性增强了密封接触力。金属接触密封的泄漏概率为10^-2,泄漏速度取决于密封面的接触应力宽度、粗糙度、损伤程度、密封脂、涂层等。特殊螺纹接头在振动后,即使产生疲劳裂纹,也不发生泄漏。一些接头台肩刻槽后作密封性试验,结果发生泄漏。很多气井管柱扭矩台肩发生了腐蚀,证明金属接触密封存在泄漏通道,即扭矩台肩起密封作用。接触压应力设计法无法完全解决特殊螺纹接头的密封问题,发展全新的设计理论和制造技术,是保障特殊螺纹接头密封性的重要发展方向。

Review on the Thread Connection Seal Method and Mechanism of Oil Country Tubular Goods

Seal integrity of tubular string in HTHP well has not been well guaranteed.Four kinds of seal system for oil country tubular goods(OCTG)are thread seal,shoulder seal,resilient seal and radial metal contact seal.Most gas tight premium connections utilize radial metal seal,and the seal contact pressure in excess of the expected well pressure determines the sealing performance of the connection.A properly designed metal-to-metal radial seal exhibits a pressure energization effect.An innovative feature can amplify the seal contact force using the stiffness of the pin extension,instead of using the reaction force provided by the negative shoulder angle.The leak probability of metal gas seal is 10^-2.the leak rate dependents on the effective width of the contact stress band,surface roughness,surface damage,sealing compound and the type of coating.Leakage did not occurred even fatigue cracks appeared in the premium connections due to vibration.Some premium connections leaked after the shoulders were notched.Shoulders of many tube strings in HTHP well have been corroded,which proves that the radial metal seal surface has leakage path,and the shoulder plays seal role actually.It is concluded that the contact stress design method can not resolve the seal ability of premium connections thoroughly.Other design and manufacture methods should be innovated.