深部地质钻探钻遇弱面地层井孔围岩稳定分析

Deep geodrilling borehole stability analysis in anisotropic formations

深部地层地质条件复杂,随钻探向纵深发展,钻遇弱面地层导致井孔围岩失稳将严重影响工程进程。本文总结分析具有弱面地层岩石物理力学特性,探讨强度各向异性孔壁围岩稳定模型的适用性;考虑流体向弱面渗透存在渗透各向异性和传热各向异性,发展了具有弱面地层井孔围岩稳定理论。研究发现,某些强度各向异性模型在特定情况下可能失去其适用性;在深部高温环境下忽略弱面地层渗透和热传的各向异性特征可能会导致井孔围岩压力、破坏区域以及坍塌压力产生较大误差。

The geological conditions in deep formations are very complex,especially in bedding strata.Nowadays,with increase in drilling depth,the instability of the borehole caused by the failure of weak planes will seriously affect the drilling progress.In this paper,the physical and mechanical properties of rocks with weak planes are summarized and analyzed,and the applicability of strength anisotropy models are discussed.Considering the permeability anisotropy and heat transfer anisotropy of the rocks with weak planes,the specific borehole stability theory is further developed for the surrounding rock with weak planes.It is found that some strength anisotropic models may lose their applicability under certain circumstances;furthermore,neglect of the anisotropic characteristics of the permeability and heat transfer of the weak-plane rocks in the deep strata in the high temperature environment may lead to big errors in the calculation of stresses,failure area and collapse pressure of the borehole.