气体钻井井底应力场数值模拟研究

通过分析气体钻井井底岩石边界条件,建立了轴对称井底岩石物理模型。利用有限元方法求解,对1 000～3 000 m井深条件下的井底岩石应力场进行数值模拟计算,并对井眼轴线、井底面、井壁进行岩石力学特性分析。分析结果表明,井轴最大主应力在1.6～2.8倍井径距离后,应力逐渐低至水平地应力,破岩难度增加;井底面0.0～0.8倍井径区域存在低应力区,有利于岩石破碎;在井底面向上0.0～0.2 m井壁范围内出现拉应力增加趋势,易出现井壁失稳现象。

Numerical Simulation Study of the Bottomhole Stress Field in Gas Drilling

The axial symmetry physical model for bottomhole rock was established by analyzing the boundary conditions of bottom rock in gas drilling.The finite element method was used for solution.The numerical simulation and calculation of the stress field of bottomhole rock in the well depth of 1 000 ~ 3 000 m were conducted.A mechanical property analysis of borehole axis,hole undersurface and well wall was carried out.The findings show that the maximum principal stress of the axis gradually decreases to the horizontal ground stress when it is beyond 1.6 ~2.8 times the length of well diameter,and the rock-breaking difficulty increases.There exists the low-stress zone in the area of 0.0~0.8 times the length of well diameter in hole undersurface,which is favorable to rock breaking.The tensile stress increases on the well wall which is 0.0~0.2 m upward the hole undersurface and it is easy for well wall instability to take place here.