CAJ | 학술논문

在钻井作业过程中，井口附近钻杆受到的拉力和扭矩往往达到整个钻柱的最大值，尤其是在上提钻柱解卡、震击解卡以及蹩钻、卡钻情况发生时，井口附近钻杆受力更为恶劣。针对井口附近钻杆的断裂问题，以某超深直井的实际工况载荷为例，将钻杆外表面的缺陷简化为横向半椭圆裂纹，以30CrMo作为钻杆材料并通过实验拟合得到其Ramberg-Osgood（R-O）本构模型，研究了拉力和扭矩组合作用下裂纹的弹塑性断裂特性。得到钻进工况下钻柱外表面裂纹扩展至不同深度的临界形状比以及塑性成分在J积分中所占的比例；定量分析了拉力波动和扭矩波动对井口附近钻杆弹塑性断裂性能的影响，发现扭矩波动对裂纹扩展的贡献远大于拉力波动，避免钻柱受到扭转冲击对延长钻柱寿命有重要意义。
재찬정작업과정중，정구부근찬간수도적랍력화뉴구왕왕체도정개찬주적최대치，우기시재상제찬주해잡、진격해잡이급별찬、잡찬정황발생시，정구부근찬간수력경위악렬。침대정구부근찬간적단렬문제，이모초심직정적실제공황재하위례，장찬간외표면적결함간화위횡향반타원렬문，이30CrMo작위찬간재료병통과실험의합득도기Ramberg-Osgood（R-O）본구모형，연구료랍력화뉴구조합작용하렬문적탄소성단렬특성。득도찬진공황하찬주외표면렬문확전지불동심도적림계형상비이급소성성분재J적분중소점적비례；정량분석료랍력파동화뉴구파동대정구부근찬간탄소성단렬성능적영향，발현뉴구파동대렬문확전적공헌원대우랍력파동，피면찬주수도뉴전충격대연장찬주수명유중요의의。
The drill pipe near the surface stands the largest tension and torsion in the whole drillstring especially during drill pipe sticking or bit bouncing. As an example,a 5 inch drill pipe made of 30CrMo that was near the well head of an ultra-deep straight well was analyzed here. Simplifying the crack of the drill pipe as circumferential semi-elliptical surface crack and using the fitted Ramberg-Osgood equation as constitutional relation,we simulated elastic-plastic fracture feature of the drill string under combined loading of axial force and torsion corresponding to its drilling behavior. The transition aspect ratios are determined for the given combined loading and the crack shape could be determined approximately corresponding to different crack depths. The contribution of the plastic J-integral is estimated and the effect of material nonlinearity on the crack propagation is described. Variations of J-integral as a function of axial force and torsional moment respectively are compared, and the dangers from tension and torque fluctuation are evaluated quantitatively. Compared with tension,fluctuation in torque contributes much more to crack propagation. It is an important significance for increasing drill string′s service life to avoid the drill string from severe torsion impact.