复杂结构井磨损套管连接螺纹的三维力学行为

随着水平井、定向井、大位移井及大斜度井钻井技术在石油钻井工程中的广泛应用,由钻柱与套管间侧向接触力引起的套管连接螺纹磨损问题日益突出,导致了修井周期缩短,开采成本增加,成为制约钻采工程效益的主要因素之一。近年来,不少学者对套管磨损问题进行了大量研究,但均集中于套管非连接部分,而复杂结构井中磨损套管连接螺纹的三维力学行为研究鲜见报道。针对上述问题,基于虚功原理、Von Mises屈服准则以及接触非线性理论,建立了磨损套管连接螺纹的三维数值仿真模型,研究了复杂结构井中套管的上扣特性以及固井条件下磨损深度、磨损开度与井眼曲率对套管连接螺纹的影响。研究结果表明:磨损与井眼曲率对套管连接螺纹的应力状态影响极大,常见的某些工况会导致套管螺纹的连接性能和密封性能降低,考虑到服役后开采时的压力波动,常规的水平井、定向井、大位移井及大斜度井弯曲段套管连接螺纹的设计和选型应着重考虑磨损和井眼曲率的影响;针对设计曲率井眼中的每种待选螺纹类型,都应考虑可预见的磨损进行精细化数值计算,以确保其安全工作。

Three-dimensional mechanical behavior of worn casing connecting thread in complex structural well

With wide application of horizontal well, directional well, extended-reach well and highly-deviated well logging technologies in petroleum drilling engineering, the wear problem of casing connecting thread caused by lateral contact force between the drill stem and casing is increasingly prominent, resulting in the shortening of workover period and the increase of drilling cost. Such problem has become one of the main factors to restrict drilling efficiency. In recent years, massive studies have been carried out on casing wear, but are mainly focused on the non-connecting portion of casing. Rare research has been reported on 3D mechanical behavior of the worn casing connecting thread in complex structural well. In view of the above problem, a 3D numerical simulation model has been established for the worn casing connecting thread based on the principle of virtual work, Von Mises yield criterion and nonlinear contact theory, so as to study the upward-buckling property of casing in complex structural well as well as the influences of wearing depth and opening, and borehole curvature on casing connecting thread during cementing process. Research results have shown that wear and borehole curvature have great influences on the stress state of casing connecting thread. The connection and sealing performance of casing thread will be reduced in some common operating conditions. In consideration of the mining pressure fluctuation after service, the casing connecting thread used for common horizontal well, directional well, extended-reach well and highly deviated well should be designed and selected based on the influences of wear and borehole curvature. For each kind of thread to be selected in the design of borehole curvature, accurate numerical calculation should be conducted on the premise of foreseeable wear to ensure work safety.