径向水平井造斜器内钻杆的弯曲状态分析

分析了连续管钻杆弯曲状态的各种影响因素及影响程度。结果表明 ,由于连续管材料变形强化度低 ,钻杆塑性变形有限 ,在分析钻杆反复弯曲应力状态时 ,可不考虑强化和塑性变形的面积效应。采用弹性刚塑性材料模型及平面应力假设 ,建立了内压作用下钻杆弹性层与曲率的关系以及钻杆的极限弯矩、应变中性层与轴向力、内压的关系。分析结果表明 ,钻杆弯曲主体的中性层随弯曲曲率的变化很小 ,但内压和轴向力对中性层的位置有明显影响 ;在内压和沿程阻力作用下 ,钻杆的弯曲表现为横截面变形的压弯特征和轴向弯曲的拉弯特征。这为控制钻杆的截面变形和设计造斜器滑道提供了理论基础。

Bending analysis on drilling string in whipstock of ultrashort turning-radius horizontal well

The affecting factors and degrees on the bending of coiled tubing drill pipe are analyzed. Since the strain hardenability of coiled tubing is low, and the plastic deformation of drill pipe is limited, the hardenability and the change of cross section area of drill pipe effected by plastic deformation can be neglected practically. By using the model of elastic rigid plastic constitutive relation and plane stress model, the correlation of elastic layer in drill pipe with curvature of the drill pipe under an inner pressure is determined, and the relations of limit moment and the middle layer of strain with inner pressure and axial load of drill pipe are also suggested. According to the material of drill pipe and the track of whipstock, it is concluded that the middle layer of the bent drill pipe is less affected by the curvature, but the position of middle layer is quitely affected by the inner pressure and axial load. The bent drill pipe shows a press bending feature on the cross section and a stretch bending feature along the axial direction under the action of inner pressure and the axial resistance during drilling process. This result can provide a theoretical foundation for controlling the deformation of cross secton of drill pipe and for the design of the track of whipstock.