复杂结构井钻压值的有限元数值计算

Finite element numerical calculation on axial force along drilling tube for complex wells with finite element method

通常,钻井过程中钻杆自重生成的钻杆轴向力即钻压的计算是通过解析方法计算的.由于接触条件复杂,钻杆与井壁及套管接触产生的摩擦力一般通过简化的经验系数计入.随着水平井等复杂结构井的普及,解析方法得到的钻杆轴向力的结果误差逐渐明显,不能满足实际需要.因此,采用三维有限元法计算钻杆自重生成的钻杆轴向力即钻压值.模型采用管单元模拟套管和钻柱,并在钻杆与井壁之间设置专门模拟管-管相互作用的ITT摩擦接触单元,判断钻柱与套管和井壁的接触状态,可以准确计算钻杆全长沿井轴方向的轴向力、轴向摩擦力及其引起的钻压变化.在钻杆全长的整体力学行为的有限元计算中,还可以考虑钻杆的屈曲问题.结果表明:有限元法是正确设计钻压的有效理论工具.该数值结果为正确设计钻杆尺寸、得到理想的钻压值提供成功的例子.

Usually, the gravity resulted axial force along drilling tube is calculated by analytical methods. Due to the complicated contact condition of drilling tube with casing and borehole, the frictional force along drilling tube can only be taken into account through the simple empirical manner. With more and more application of complex wells, the analytical solution of axial force of drilling tube can not meet the accuracy requirement of the complex well design. The finite element method is used to calculate the distribution of axial force along the whole length of drilling tube. The model uses pipe element to simulate drilling tube and casing, as well as wellbore. It also uses ITT element to simulate the interaction between tube and casing and/or wellbore. This model can be used to calculate the axial force along the drilling tube and the axial frictional force and variation of pressure at drilling bit. The buckling of the drilling tube can also be calculated with the model. The numerical results indicate that finite element method is an efficient and practical tool for analysis on axial force of drilling tube. The results can be taken as a best practice of analysis of axial force in the design of drilling tube for complex wells.