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Buckling characteristics research of drill strings in vertical well based on co-rotational coordinate method

DOI：

 作者 单位 邮编 王雨妹 中国石油大学（北京） 102200 顾继俊* 中国石油大学（北京） 郭华 中海油研究总院有限责任公司 黄晨 中国石油大学（北京） 王树江 中国石油大学（北京）

为了研究钻杆在套管径向约束下的变形问题，用Julia编写了EndoBeams.jl包。在共旋坐标基础公式与隐式接触动力学相结合的基础上，建立空间钻杆有限元接触模型，通过离散符号距离场(SDF)对套管表面的隐式描述，采用HHT-α方法对系统进行时间积分。通过共旋方法对轴向力压缩作用下的钻杆进行后屈曲特性研究，分析不同载荷下的屈曲形态，得到正弦屈曲和螺旋屈曲的无量纲临界载荷，讨论不同摩擦系数以及间隙对钻杆后屈曲特性的影响。研究指出，轴向力的增加使得钻杆从正弦屈曲向空间屈曲的转变是一个突变的过程，钻杆屈曲模态构型包括平面正弦屈曲、空间屈曲和螺旋屈曲。该结论为基于共旋坐标法所建立的钻杆接触动力学模型能够有效解决几何接触双重非线性收敛困难的问题，降低时间计算成本，研究成果对于钻杆工艺参数的选择以及垂直井的延伸提供了理论依据。

To study the deformation problem of drill strings under radial constraint of casing, EndoBeams.jl package was written in Julia. Based on the combination of the co-rotational coordinate formulation and implicit contact dynamics, a finite element contact model of the spatial drill string is established, the casing surface is implicitly described by the discrete signed distance field (SDF), and the time integration of the system is carried out by the HHT-α method. The post-buckling characteristics of drill string under axial force compression are investigated by the co-rotational method, and the buckling patterns under different loads are derived to obtain the dimensionless critical loads for sinusoidal and helical buckling, and the post-buckling characteristics effects of different friction coefficients and gaps are discussed. It is pointed out that the increase of axial force makes the transition from sinusoidal buckling to spatial buckling of drill string an abrupt process, and the buckling mode configurations include planar sinusoidal buckling, spatial buckling and helical buckling. The conclusion is that the contact dynamics model of drill string established based on the co-rotational coordinate method can effectively solve the problem of difficult convergence of geometric contact double nonlinearity and reduce the time computation cost, and the research results provide a theoretical basis for the selection of the process parameters of drill strings as well as the extension of vertical wells.
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