气体钻井中预弯底部钻具组合控斜的非线性动力学机制

The deviation control in gas drilling is difficult, but it is more difficult in thicker conglomerate. The experimental of deviation control in gas drilling in thicker conglomerate achieved initial successful in Tarim oilfield by using the bottomhole assembly with prebent section (prebent BHA). This attracted much attention, but the extension effect was not good because the deviation control mechanism has not been proved yet. The nonlinear dynamic characteristics of prebent BHA in gas drilling will be studied deeply in this application. And the deviation control mechanism will be analyzed. First, taking the specific characteristics of prebent BHA, the nonlinear stiffness, and contact friction between drill collar and borehole wall into consider, the total kinetic energy and virtual work will be derived. The governing nonlinear equations will be established by using a Lagrangian approach. Second, the boundary condition based on practice will be presented. Taking the strongly nonlinear and coupling feature of the dynamic model into consider the Runge-Kutta algorithm will be applied to decouple and solve the dimensionless nonlinear dynamic model with iterative method. The nonlinear dynamic characteristics of prebent BHA in gas drilling will be deeply analyzed. The dynamic side force and axial force of bit and motion stability will be studied, and the nonlinear dynamic deviation control mechanism of prebent BHA in gas drilling will be proved. Finally, the design basis of the parameter of structure and construction of prebent BHA in gas drilling will be proposed. These offering a theory support for popularization and application of a low cost and effective deviation control method in gas drilling.

气体钻井井斜控制困难，巨厚砾岩层气体钻井控斜更难。基于带预弯结构的底部钻具组合（预弯BHA）控斜方法在塔里木巨厚砾岩层气体钻井实验中取得初步成功，倍受关注，但推广效果不佳，原因在于其控斜机理还未探明。本项目针对气体钻井中预弯BHA的非线性动力学特性进行攻关，研究其控斜机制。首先，考虑气体钻井中预弯BHA所特有的非线性刚度及其与井壁碰摩特征，推导系统总动能和虚功，利用Lagrange方程建立预弯BHA动力学模型。其次，结合实际提出边界条件，考虑模型的强非线性及耦合特征，基于Runge-Kutta法，对无量纲化的二元高阶非线性动力学模型进行解耦和迭代求解，深入研究气体钻井中预弯BHA的非线性动力学特性及其对钻头动态侧向力、轴向力及BHA运动稳定性的影响规律，探明气体钻井预弯BHA的非线性动力学控斜机制。最后，提出结构和施工参数设计依据，为气体钻井中低成本动力学控斜方法的推广应用提供理论支持。

气体钻井是一项极具潜力的新型实用钻井技术，它利用可压缩的空气或其它气体作为循环介质进行钻进，具有大幅度提高钻速，有效避免地层漏失、油藏污染的技术优势，但气体钻井直井井斜控制困难一直是影响气体钻井技术发展的难题之一。塔里木巨厚砾岩层气体钻井实验表明，利用带预弯结构的底部钻具组合（预弯BHA）控制井斜是一种有效可行的方法，但其机理尚不明确，影响了推广应用。本项目针对上述问题开展了以下研究：首先基于变形势能理论推导了预弯BHA的非线性刚度，通过虚功原理及Lagrange方程建立了充分考虑BHA与井壁碰摩特征的气体钻井预弯BHA的非线性动力学模型及钻头上动态载荷计算模型。其次，基于四阶Runge-Kutta法，研究了无量纲化的二元高阶非线性动力学模型的迭代求解方法，编制了计算程序。在此基础上研究了气体钻井预弯BHA的运动特征及钻头动态侧向力、轴向力的变化规律，探明了气体钻井预弯BHA的非线性动力学控斜机制，并进行了现场实例的应用分析。最后，研究了不同预弯结构弯角、不同钻压、转速对预弯BHA的运动特征及钻头动态载荷的影响规律。结合参数影响规律分析，通过评价气体钻井中预弯BHA的动态侧向力和运动稳定性提出了其结构参数和钻井作业参数的优化设计依据。项目研究成果为气体钻井低成本动力学控斜方法的推广应用提供了理论支持。