静载、振动与腐蚀作用下H2S/CO2气井完井管柱螺纹密封面的力化学损伤机制研究

Recently, the problem of well integrity of H2S/CO2 gas well has been particularly acute. Annular abnormal pressure usually occurs in most wells, which may be caused by the sealing failures of screw thread. Therefore, one of the basic theoretical problems in well integrity field is to study the failure mechanism of thread seals. The project intends to establish a thread contact mechanical model based on the contour characteristics of sealing surface, studying the influence of static load and vibration load on the contact area stress and deformation of thread sealing surface, and revealing the mechanical mechanism of reducing the sealing ability of sealing surface of thread under the action of vibration load. In addition，the project, adopting the dynamic sealing experiment method, studies the influence law of different load types on thread seal performance, microstructure of sealing surface and tissue evolution, which reveals the micro mechanism of thread sealing surface damage. In addition, damage law of sealing surface and its influence on sealing performance under the combined action of corrosion and stress would be studied using the HPHT circulation flow simulation, electrochemical measurement and full-sized structural components test so as to clarify the interaction mechanisms among microstructure damage, stress state and corrosion. The results would break the evaluation criterion of API /ISO only with statics index, and further complete the existing thread evaluating system, thus providing theoretical reference for the optimal design, manufacture and application of premium thread sealing structure.

当前高温高压H2S/CO2气井井筒完整性问题尤为突出，大量气井出现环空带压，其原因多为完井管柱螺纹的密封失效，弄清螺纹密封失效的机理是井筒完整性研究领域寇待解决的基础理论问题之一。项目拟建立基于密封面表面轮廓特征的螺纹接触力学模型，研究静载和振动载荷对螺纹密封面接触区域应力和形变的影响规律，揭示振动载荷作用下螺纹密封面密封能力降低的力学机理；采用动态密封实验方法研究不同载荷类型对螺纹密封性能、密封面微观形貌及组织演变的影响规律，揭示螺纹密封面损伤的微观机制；利用高温高压腐蚀模拟、电化学测试和全尺寸构件实验方法研究应力和腐蚀共同作用下密封面的损伤规律及其对密封性能的影响，揭示应力状态、腐蚀和组织损伤的交互作用机制，打破API/ISO标准仅从静力学角度评估螺纹密封性的作法，完善现有螺纹密封性能评价指标，为气密封螺纹密封结构的优化设计、制造和使用提供新的理论依据。

当前高温高压H2S/CO2气井井筒完整性问题尤为突出，大量气井出现环空带压，原因多为完井管柱螺纹的密封失效，其与密封面结构、承受载荷、腐蚀环境和材质因素密切相关。项目主要从应力状态、组织演变、腐蚀损伤等方面研究了完井管柱螺纹接头密封面的损伤机理，主要内容包括：①基于典型气密封螺纹密封面微观轮廓特征和分形几何原理，建立了螺纹接头密封特性分析的有限元力学模型，研究了静载和振动载荷下的螺纹密封面接触力学行为，分析了拉伸、内压、弯曲等载荷对螺纹密封面接触区域应力和形变的影响规律；②创建了载荷与腐蚀环境耦合工况下油井管螺纹接头密封面腐蚀和密封性能评价装置及方法，实验研究了应力状态、接头材质、缝隙对螺纹密封面材料组织演变、损伤及密封性能的影响规律，分析了内压、拉伸等载荷作用下螺纹密封面失效的力学机理；③设计专用夹具，采用电化学法和高温高压釜测试，研究了弹塑性应力、螺纹缝隙、CO2/H2S服役环境（氢渗透、温度、H2S含量）耦合条件下螺纹密封面失重腐蚀和电化学腐蚀动力学规律，在介观尺度下观测了密封面腐蚀的微观形貌变化和损伤特征；④研究了螺纹密封面应力状态、缝隙和腐蚀的交互作用规律，分析了应力和腐蚀共同作用下密封面组织损伤特征及其对螺纹接头密封性能的影响。项目揭示了H2S/CO2气井完井管柱螺纹密封面的力化学损伤机制，为气密封螺纹密封结构的优化设计、制造和使用提供新的理论依据。