基于节理塑性模型的页岩地层水平井井壁稳定性分析*

为研究层理页岩地层中水平井井壁失稳机理，基于流固耦合理论，考虑地层渗透率和强度各向异性，运用节理材料模型对水平井井周塑性失稳区域分布规律进行数值分析。结果表明:钻井液流体侵入导致井周孔隙压力分布呈各向异性，页岩水平井井周破坏形态为四角形状，且随时间增加逐渐向地层内部延伸形成剪切带；在考虑井壁渗透情况下，增大钻井液密度并不能显著改善页岩井壁失稳状况，加强钻井液封堵性对维护井壁稳定具有重要作用。

Borehole wall stability analysis of horizontal well in shale formation based on jointed plastic model

In order to study the borehole wall instability mechanism of horizontal well in the bedding shale formation,the fluid-solid coupling theory was applied,considering the anisotropy of formation permeability and strength,,the numerical analysis on the distribution laws of plastic instability area around the horizontal well was conducted based on the jointed material model.The results showed that the pore pressure distribution around the well presented the anisotropy.The failure form around the shale horizontal well was the quadrangular shape,which would extend into the formation over time to form a shear zone.Considering the permeation of borehole wall,increasing the density of drilling fluid could not significantly improve the instability of the shale borehole wall.Strengthening the plugging of drilling fluid had an important role in maintaining the stability of borehole wall.