泥岩地层软化对反井扩孔井帮稳定影响分析

Influence of Mudstone Formation Softening on Shaft Wall Stability of Raise Boring Enlarging

反井钻井法扩孔施工过程中,井帮缩径和井帮围岩失稳是反井钻井法发展的重难点问题。当扩孔穿过以遇水软化性岩石为主构成的地层时,水对井帮围岩的影响十分突出。以具有遇水软化特性的泥岩为研究对象,首先,通过浸水软化实验,得到不同浸水时间下泥岩的弹性模量和泊松比,再拟合出这两种参数与浸水时间的定量关系,并建立考虑软化效应的参数方程。然后,基于弹塑性模型塑性区位移解,得出扩孔井帮围岩无支护状态下的位移公式,再在此公式中代入考虑软化效应的参数。最后,建立考虑边界效应的井帮围岩位移与浸水时间解析模型,用来评价反井钻井法扩孔施工过程中井帮缩径和井帮围岩失稳的安全性,为反井钻井法的工程应用提供参考。

During the enlarging construction process of the raise boring method,the well reduction diameter and the instability of the surrounding rock are the major difficulty in the development.When the enlarging passes through a stratum mainly composed of water-softening rocks,the influence of water on the surrounding rock of the well is very prominent.The mudstone with water softening characteristics is taken as the research object.Firstly,the elastic modulus and Poisson's ratio of mudstone under different water immersion time are obtained by water immersion softening experiment,and the quantitative relationship between the two parameters and water immersion time is fitted,and the parameter equation considering softening effect is established.Then,based on the displacement of the plastic zone of the elastoplastic model,the displacement formula of the surrounding rock in the unsupported state is obtained,and then the parameters of the softening effect are substituted into this formula.Finally,an analytical model of the displacement and immersion time of the surrounding rock considering the boundary effect is established to evaluate the safety of the wellbore reduction and the instability of the surrounding rock during the enlarging construction of the raise boring method.The study can provide references for engineering applications of raise boring method.