科学超深井铝合金钻杆的腐蚀防护机制研究

As the increasingly higher dependence of the development of earth sciences on the deep exploration data, the scientific ultra-deep drilling, known as “the telescope into the crust”, becomes an indispensable method for research of deep geology. Compared with the steel drill pipe, the aluminum alloy drill pipe with its unique superiority (lighter weight, higher specific strength, deeper drilling depth and less energy consumption) is the essential scheme of the drill string design used in scientific ultra-deep well. However, the low anti-corrosion performance in the complex working environment is the main weakness of aluminum alloy drill pipe, which has greatly affected the application of aluminum alloy drill pipe under the scientific ultra-deep well. Therefore, further knowledge of the corrosion failure and anti-corrosion protection mechanisms for the aluminum alloy drill pipe under complex working environment would be essential to ultra-deep drilling engineering. In this project, based on the application of ultra-deep drilling, the corrosion behaviors of the aluminum alloy drill pipe in the complex working environment will be investigated, and the corrosion failure and anti-wear mechanisms will be revealed and deeply discussed. It aims to build relationships among the corrosion failures, micro-structures, corrosion performances and anti-corrosion protection methods under the working environment. The results would be expected that it would provide a theoretical and practical guidance to the application of aluminum alloy drill pipe technology under complex working environment in the scientific deep drilling.

地球科学的发展对地球深部数据的依赖程度越来越高,作为“入地”重要手段的科学超深井工程是研究深部地质学的重要方法，被誉为是“伸入地壳的望远镜”。与钢钻杆相比，铝合金钻杆以其独特的优越性(重量轻、比强度高、钻进深度大、所需能耗少)，已成为万米以深科学超深井钻柱设计的必备方案。然而，复杂的服役工况条件致使铝合金钻杆极易发生腐蚀失效，极大的影响了其在科学超深井中的应用。因此，深入认知腐蚀失效及防护机制是科学超深井铝合金钻杆技术应用的核心与关键。本项目以铝合金钻杆超深井工程应用为背景，通过“高温-高压-力学-化学”多因素协同作用下腐蚀性能和防护方法实验的设计与实施，分析并建立铝合金钻杆的失效方式、组织结构、腐蚀性能、防护方法之间的关系，实现服役条件下铝合金钻杆腐蚀防护的作用规律的理论预测与实验调控，为我国未来的万米科学钻探工程的谋划与实施提供基础实验数据和技术支撑。

“高温-高压-力学-化学”多因素协同作用服役条件致使铝合金钻杆极易发生腐蚀失效，极大的影响了其在科学超深井中的应用。本课题综合考虑科学超深井井内工况因素和钻杆性能因素，开展了铝合金钻杆材质选择和评价，支撑后续铝合金钻杆腐蚀防护基材优选。探究了科学超深井“松科二井”复杂服役条件下铝合金钻杆腐蚀机理，运用COMSOL软件建立了多物理场腐蚀分析模型，揭示了铝合金钻杆“应力-温度-电化学”作用下的腐蚀规律与失效机理，指导后续铝合金钻杆的腐蚀防护涂层制造工艺试验参数优化。同时，选用耐热铝合金钻杆材料，对比研究了微弧氧化、电镀镍/氧化石墨烯、微弧氧化/超声表面冷锻等复合强化层多因素条件作用下的抗腐蚀作用机理。试验测试等结果表明：腐蚀体系达到平衡时，铝合金电极一侧的电解质电位偏高，钢接头电极一侧电解质电位偏低，靠近钢接头电极一侧铝杆体电流密度高，最高为5.5 A/m2；离电偶腐蚀处越近，铝合金钻杆的界面电流密度越大，并成指数关系，外壁强影响区域大约在距电偶腐蚀处0~200mm，内壁为0~110mm；MAO涂层对与其耦合的合金钢起到较好的保护作用。随着钻杆所受应力、温度的增加，腐蚀速率加快，相对于温度的影响，载荷对腐蚀影响较小；在300 MPa的弹性拉应力作用下，经UCFT+MAO处理的铝合金仍能维持较低的腐蚀速率（0.02mm/a），并且耐蚀性能仍高于未经UCFT+MAO处理的；当试验温度增长超过125℃时，经UCFT+MAO处理的铝合金的腐蚀速率随温度的增加而显著上升。综上所述，经UCFT和MAO处理形成的细晶层和微弧氧化膜层能够有效保护铝合金基体，提升铝合金的耐腐蚀性能，研究成果对我国未来的万米科学钻探工程的谋划与实施可提供基础实验数据和技术支撑。