中间主应力对垂直井井壁坍塌压力的影响

运用线弹性本构模型来分析垂直井井壁应力分布,并分别用Mohr-Coulomb准则、Drucker-Prager准则和Mogi-Coulomb准则3个强度准则来计算平谷地应力测量与监测钻孔维持井壁稳定所需的最小钻井液液柱压力。通过对比分析得出考虑中间主应力的作用,会使岩石强度得到加强,使得维持井壁稳定所需的最小液柱压力降低;3个准则得出的最小液柱压力在与深度的对应图中表现出一致的变化趋势,说明3个准则有各自的适用性;比较而言Mohr-Coulomb准则偏于保守,Drucker-Prager准则偏于危险,而Mogi-Coulomb准则要优于前两个准则。

Effect of Intermediate Principal Stress on the Wall Collapsing Pressure of Vertical Wellbore

Linear elastic constitutive model was used to analyze the stress distribution in the vertical wellbore;Mohr-Coulomb criterion,Drucker-Prager criterion and Mogi-Coulomb strength criterion were respectively applied to calculate the minimum fluid column pressure required to maintain stable wellbore for the crustal stress measurement and monitoring borehole in Pinggu.By the contractive analysis,because of the intermediate principal stress,the minimum fluid column pressure required to maintain wellbore stable could be reduced.The minimum fluid column pressure derived from three criteria show the consistent variation trend with the depth in corresponding diagraph,which indicates that three criteria have their own applicability： Mohr-Coulomb criterion is conservative,Drucker-Prager criteria is somewhat dangerous and Mogi-Coulomb criterion is superior to the first two.