高温接触应力松弛对特殊螺纹微观动态泄漏的影响机理研究

The contact stress relaxation on sealing surface will directly reduce the long-term sealability of premium connection, while it lacks of relevant investigations on high temperature contact stress relaxation on micro-dynamic leakage mechanism at present. In this project, the same types of sealing pair will be made up of P110-13Cr and same steel grade of titanium alloy, and the contact stress relaxation testing will be carried out under conditions of 100 ℃, 150 ℃, 200 ℃ and 50%σs, 90% initial average contact stress. The curve of contact stress relaxation will be obtained and the leakage rate tested. The law of contact stress relaxation will be analyzed and the relaxation equation matched. Based on the sealing surface fractal characterization with W-M function and thermal elasto-plastic contact mechanics theory, the thermal elasto-plastic fractal normal contact load and stiffness model of sealing asperity will be established respectively with the considerations of high temperature contact stress relaxation. Further, the fractal micro-leakage cross-sectional area will be described and the micro-dynamic leakage model of premium connection will be established and validated by the tested leakage rate. With the proposed model, the effects laws of initial sealing contact stress and temperature on the dynamic leakage rate will be researched comprehensively and the dynamic leakage mechanism caused by contact stress relaxation revealed, also the new methods for sealing material selection and sealing parameters design will be put forward. The research results will provide theoretical basis and technical support for the independent innovation of premium connection key technology and safe production for gas well.

密封面接触应力松弛会直接降低特殊螺纹长期气密封性能，而目前还未见应力松弛对特殊螺纹微观动态泄漏的影响机理研究。本项目选取P110-13Cr和同钢级钛合金制作锥面对锥面密封副，开展100℃、150℃、200℃和50%σs、90%σs初始平均接触应力下的应力松弛实验，获得接触应力松弛曲线并测试动态泄漏速率，弄清应力松弛规律并拟合松弛方程；基于粗糙表面W-M函数分形表征和热弹塑性接触力学理论，建立考虑高温接触应力松弛的密封面微凸体热弹塑性接触法向载荷和刚度分形模型，对密封面泄漏通道进行分形表征从而建立特殊螺纹微观动态泄漏理论模型，并对比实验数据以验证其有效性；基于泄漏模型综合分析温度和初始接触应力对动态泄漏速率的影响规律，揭示高温接触应力松弛对特殊螺纹微观动态泄漏的影响机理，提出控制泄漏的密封材料优选和密封参数优化新方法。预期可为我国特殊螺纹关键技术自主创新和气井安全开采提供理论依据和技术支撑。

密封面接触应力松弛会直接降低特殊螺纹长期气密封性能，研究应力松弛对特殊螺纹微观动态泄漏的影响机理和规律对螺纹密封性能定量评价和密封参数设计具有重要意义。针对L80钢和同钢级钛合金管材开展了密封面50%σs、90%σs初始接触应力和100℃、150℃、200℃温度下的压缩应力松弛正交实验，获得了应力松弛规律和松弛方程。基于密封面正弦微凸体弹塑性接触模拟和应力松弛方程，建立了特殊螺纹微观动态泄漏理论模型并验证其可靠性，分析了温度和密封面初始接触应力对螺纹泄漏的影响机理和规律，提出了控制泄漏的材料优选和密封参数设计新方法。取得的主要认识如下：.（1）井下特殊螺纹密封接触应力随时间增加先快速降低、后缓慢降低最后趋于稳定；温度越高、初始接触应力越大，接触应力松弛越明显；同钢级钛合金应力松弛比L80钢明显。.（2）随密封面接触应力松弛进行，螺纹泄漏速率先快速增加后缓慢增加最终将趋于稳定；密封面初始接触应力一定时，温度越高，L80钢特殊螺纹稳定泄漏速率越大，钛合金特殊螺纹稳定泄漏速率越小；温度一定时，密封面初始接触应力越大，两种管材特殊螺纹稳定泄漏速率均越小；密封面初始接触应力和温度相同时，钛合金比L80管材特殊螺纹稳定泄漏速率明显小。.（3）特殊螺纹密封设计应考虑密封面高温接触应力松弛的影响，应测试管材井下温度的接触应力松弛曲线，按照应力松弛稳定值评估井下特殊螺纹密封性能。为提高螺纹长期密封性能，普通碳钢管材特殊螺纹可考虑对密封面加工低弹性模量合金镀层，增大密封面接触长度、选用锥面对锥面型密封结构；钛合金等低弹性模量合金钢管材特殊螺纹应增大密封面初始接触应力、选用球面型密封结构。.研究成果为保障高温高压气井完井管柱长期可靠气密封性能提供了技术支撑。