考虑扭矩影响的弯曲井眼内钻柱屈曲特性分析

分析了弯曲井眼内钻柱屈曲特性，推导了考虑扭矩影响下的弯曲井眼内钻柱屈曲微分方程和屈曲临界载荷计算模型。针对?215.9 mm井眼内的?127.0 mm钻杆，建立了增斜和降斜井段钻柱的有限元模型，对比分析了考虑和不考虑扭矩影响时的钻柱屈曲特性。结果表明，钻柱正弦屈曲构型与扭矩无关，而只与钻柱所受轴向载荷有关，扭矩对螺旋屈曲构型影响较大。数值模拟得到的弯曲井段不同造斜率下的钻柱屈曲临界载荷与解析解的相对误差在15%以内，证明了数值模拟的可靠性。弯曲井眼内施加扭矩后，螺旋角位移增大，正弦和螺旋屈曲临界载荷降低。钻柱正弦屈曲形态变化较小，扭矩对螺旋屈曲变形的影响更大。增斜井段钻柱从顶部开始发生正弦和螺旋屈曲，钻柱底部保持平衡状态；在降斜井段，不考虑扭矩时，初始正弦和螺旋屈曲均首先出现在钻柱下部，考虑扭矩影响时，降斜段初始正弦屈曲出现在钻柱上部，初始螺旋屈曲同时出现在钻柱上部和下部。相对于增斜段，降斜段钻柱屈曲临界轴向载荷非常小，说明增斜井段发生屈曲的可能性相对较小，降斜井段则很容易发生屈曲。结果有望为水平井、大位移井弯曲井眼内钻柱设计、屈曲控制与强度校核提供参考。

An Analysis of Drilling Pipe Buckling Characteristics in Curved Hole Under the Effect of Torque

This paper analyzes the buckling characteristics of drilling string in curved wells under the influence of torque. The buckling differential equation and the buckling critical load calculation model of drilling string in a curved wellbore are derived. The finite element models of drilling string in buildup and drop-off sections are established for ?127.0 mm drilling pipes in a ?215.9 mm wellbore, and the buckling characteristics of drilling strings with and without torque are compared and analyzed. The results show that the sinusoidal buckling configuration of drilling string is not related to torque. It is only decided by the axial load on drilling string. Torque has great influence on spiral buckling configuration. The relative error between the critical buckling loads of drilling strings obtained by numerical simulation under different build-up rates and analytical solution is within 15%, which proves the reliability of numerical simulation. When torque is applied in curved wellbore, the helical angular displacement increases, and the corresponding critical sinusoidal and helical buckling loads decrease. Sinusoidal buckling of drilling string does not change much, and torque has more influence on spiral buckling deformation. In the buildup section, sinusoidal and spiral buckling start at the top of the drilling string, while the bottom of the drilling string maintains a balanced state. In the drop-off section, when the torque is not considered, the initial sinusoidal buckling and spiral buckling first appear at the lower part of the drilling string. When the torque is considered, the initial sinusoidal buckling appears at the upper part of the drilling string, while the initial spiral buckling appears at both the upper and lower parts of the drilling string. Compared with the buildup section, the critical axial loads of drilling string buckling in the drop-off section are very small, which indicates that the possibility of buckling in the buildup section is relatively small, while that in the drop-off section is much easer to occur. The results are expected to provide a reference for the design, buckling control, and strength check of drilling strings in horizontal and extended reach wells.