超深井油套管螺纹接头三维力学特性分析及密封机理研究

The threaded connection is the weakness of the tubing and casing string in ultra-deep well, which has the complex stress characteristic in the severe working condition. Thus, the sealing integrity of the threaded connection is increasingly concerned. The 2D axisymmetric analysis and the experiment method can hardly describe the triaxial stress state of the threaded connection, while 3D analysis method can describe the real stress characteristics of the threaded connection. However, the complex contact states between pin and box make the calculation difficult. This project will develop the efficient contact algorithm for 3D spiral surface based on ABAQUS user subroutine. Combined with the full scale experiments, the effective analysis method of 3D mechanical properties of the threaded connection under complex loads will be achieved, and the contact pressure distribution on sealing surface will be calculated. In order to reveal the sealing mechanism of the threaded connection under the complex loads, the elastic-plastic finite element model of the sealing surface based on the initial actual 3D surface topography will be established. Then, the deformation characteristics of the sealing surface under the specific contact pressure will be studied, and the micro leakage channel of the sealing surface will be constructed. On this basis, the flow characteristics of the fluid in micro leakage channel will be simulated by lattice Boltzmann method, and the seal leakage criterion of the metal to metal contact under non-uniform contact condition will be determined. Finally, the micro leakage mechanism of the threaded connection under complex loads will be revealed.

油套管螺纹接头是超深井油套管柱的薄弱环节，服役条件恶劣，受力状态复杂，其密封完整性问题日益突出。目前常用的二维轴对称分析和实物实验很难描述复杂载荷作用下接头的三轴应力状态，而三维分析方法虽能很好地研究螺纹接头的受力，但公扣、母扣间复杂的接触关系使得计算十分困难。本项目基于ABAQUS用户子程序开发适用于三维空间螺旋啮合曲面计算的高效、稳定接触算法，结合实物试验，实现油套管螺纹接头高效三维力学计算，同时研究密封面接触压力分布特征。为了揭示复杂载荷条件下油套管螺纹接头密封失效的微观机理，基于密封面初始真实三维形貌特征建立其弹塑性有限元模型，研究特定接触力作用下密封面变形特征，重构密封啮合面三维微观泄漏通道。在此基础上，采用格子Boltzmann方法研究三维微观泄漏通道内流体流动特征，确定非均匀接触条件下金属-金属接触密封泄漏判据，明确复杂载荷条件下油套管螺纹接头金属-金属接触密封微观泄漏机理。

本项目围绕油套管螺纹接头密封完整性问题，深入研究复杂载荷条件下油套管螺纹接头三维力学计算方法和密封完整性评价依据，重点开展了以下研究：首先，基于ABAQUS用户子程序开发了适用于三维空间螺旋啮合曲面计算的高效、稳定接触算法，实现了油套管螺纹接头高效三维力学计算。其次，通过复杂载荷条件下油套管螺纹接头的三维力学计算，深入研究了密封面接触压力分布特征，并基于密封面初始真实三维形貌特征建立了密封啮合面微观弹塑性有限元模型，重构出密封啮合面三维微观泄漏通道，形成了基于密封面初始真实表面形貌的三维微观泄漏通道构建方法。最后，采用格子Boltzmann方法研究了三维微观泄漏通道内流体流动特征，模拟了气体驱替液体致气体漏失的过程，得到不同压力梯度条件下微观通道中液相流体的体积分数随时间的变化规律，深入研究了不同条件下密封面三维微观泄漏通道内流体的速度、压力分布特征，结合相关理论和试验数据，确定了非均匀接触条件下金属-金属接触密封泄漏判据。项目研究成果为复杂载荷条件下油套管螺纹接头密封完整性评价提供了理论支持。