深部地质环境对井壁稳定性的影响

The Impact of Geological Environment on Wellhole Stability

井壁失稳是制约深井、超深井快速钻进的重要因素,在综合考虑深部井周应力、井周温度扰动以及孔隙压力等因素的条件下,建立了深部地质环境条件下的井壁稳定性力学评价模型。基于该评价模型,定量分析了深部复杂地质条件下地应力状态、地层温度及地层孔隙压力对井壁稳定性的影响。结果表明:(1)原地应力状态对井壁稳定性有决定性的影响,原地三个主应力差异增大,将加剧井壁失稳;(2)井壁温度升高将加剧井壁的剪切破坏失稳,而有利于减弱破裂失稳;相反,井壁温度降低,将有利于抑制井壁剪切失稳,而增大井壁张性破坏的可能性。(3)其他条件相同的情况下,地层孔隙压力升高将加剧井壁失稳。

Wellbore instability is an important constraint for improving the drilling speed of ultra-deep wells. Engineering geological environment including high confine pressure, high temperature and high pore pressure is the key cause of bore- hole instability. Borehole stability evaluation model is derived from stress condition, temperature perturbation and pore pres- sure around well under the deep geological conditions. The effect of stress state, formation temperature and pore pressure on borehole stability is quantitatively analyzed base on the model. The following conclusions have been drawn： （1） in-situ stress has significant impact on borehole stability, and the increase of difference between three principal stresses will aggravate wellbore instability. （2） The increase of temperature will increase the possibility of Shear failure, but weaken the tensile instability. （3） High oore oressure will aggravate wellbore instability.