等井径膨胀套管螺纹接头的结构完整性研究

Monohole expandable tubulars technology is the revolution in well drilling and completion, which can realize the drilling without inner diameter loss. It can be used for the drlling in the deep sea water or other complicated process and to reduce the cost of well drilling effectively. However, the affect of 30% expansion ratio on the formation process and bear capacity is not clear, which is the challenge to the material properties, geomerty, and formation process of threaded connection. The structural integrity of the twinning-induced plasticity steel threaded connection of monohole expandable tubulars will be studied. The mechaincal properties revolution due to the large plastic deformation will be tested, and the hybid consitutive model including Bauschinger effect will be obtained. The nonlinear finite analysis model for the formation process of the threaded connection will be established, which can be used for calculating the stress and deformation of the thread during the expanding process. The deformation incoordination and residual stress distribution of the post-expansion threaded connection will also be obtained. The ultimate bearing capacity under the combinded tensile force, inner pressure, and outer pressure of the formed threaded connection will be investigated base on the twin shear strength theory. The effects of material properties revolution, deformation incoordination, and residual stress on the ultimate bearing capacity will be inlluminated. Accroding to the formation process and ultimate bearing capacity, the two-step structural integrity evaluation criterion including multi-parameter will be proposed. The effect of material properties, geomerty, and formation process on the structural integrity will be studied, which can be used to optimize the threaded connection. The basic mechanical problems of threaded connection of monohole expandable tubulars can be solved, and the study will lay a theoretical foundation of further application and development of monohole expandable tubulars technology.

等井径膨胀管技术可实现无内径损失钻井，能应对海洋深水等复杂地层并降低开发成本，是钻井领域的一项革命性技术。然而高达30%的膨胀率对螺纹接头成形和承载的影响机理尚未明确，给接头材质、结构及成形工艺带来了新的挑战。本项目以孪生诱发塑性钢等井径膨胀套管螺纹接头的结构完整性为研究对象，研究材料在塑性大变形中的力学性能演化规律，建立包含包辛格效应的混合强化本构模型；利用非线性有限元数值模型，研究接头成形过程中应力应变演变规律和成形后的变形失调及残余应力分布规律；基于双剪强度理论，研究接头在拉伸、内压和外压等组合载荷下的承载性能，阐明材质性能演化、变形失调和残余应力对接头承载极限的影响规律；综合成形过程和承载性能，提出两级多参数结构完整性评价准则，并揭示接头形状、材质和膨胀工艺对结构完整性的影响规律。该研究有助于认识等井径膨胀管螺纹接头成形和承载中的力学问题，为该技术的发展和应用奠定坚实的理论基础。

膨胀管螺纹接头结构完整性是等井径膨胀管技术发展的主要难点。项目研究了孪生诱发塑性钢（TWIP钢）膨胀管及其螺纹接头结构完整性问题。通过力学性能实验，研究了退火温度和预变形处理对TWIP钢力学性能的影响规律；通过有限元模拟，研究了不同材料和不同温度下膨胀管成形过程中的应力演化规律。利用实验和数值模拟，研究了膨胀锥结构和膨胀工艺对膨胀管变形、残余应力和力学性能的影响规律，并确定出优化的膨胀锥尺寸。基于塑性力学模型，推导了TWIP膨胀推力的计算公式，并研究了膨胀率、摩擦系数和膨胀锥尺寸对膨胀推力的影响规律。利用有限元方法，研究了不同强化模型下TWIP钢膨胀管成形性能和承载性能的差别。研究结果对于膨胀套管的材质和膨胀工艺的选择具有重要的指导意义。