Anisotropic strata are frequently encountered in deep drilling engineering, especially for the rock with fracture structures. The problem of instability in highly deviated well in this kind of rock stratum is prominent as the strength of fractured rocks is weakened and the directions of fractures, in-situ stress and borehole axis can be complex. A model is built in this paper to assess the safety of drilling considering the influences of well trajectory, in-situ stress and fractures. The results show that: the fractures with different dip angles have important influence on the failure area and the collapse pressure. It is quite necessary to select the safe drilling trajectory in fractured formations as this is the economical and convenient approach. For some directional drilling, the determination of safe mud weight should be cautious. The in-situ stress difference, pore pressure and fracture strength parameters have significant effects on well collapse pressure. The above model calculation under specific working conditions can easily evaluate the safety and stability of wells drilling in all directions in fractured formation, so as to provide reference for well trajectory design of highly deviated wells.

各向异性地层在深部钻井工程中经常遇到，特别是对于具有裂缝结构的岩石。这类岩层中大斜度井失稳问题突出，裂隙岩石强度减弱，裂隙方向、地应力和井筒轴线复杂。本文建立了考虑井眼轨迹、地应力和裂缝影响的钻井安全性评估模型。结果表明：不同倾角的裂缝对破坏面积和坍塌压力有重要影响。在裂缝地层中选择安全的钻井轨迹是非常必要的，因为这是一种经济、方便的方法。对于一些定向钻井，安全泥浆重量的确定要谨慎。地应力差、孔隙压力和断裂强度参数对井塌压力有显着影响。上述特定工况下的模型计算可以很容易地评估裂缝地层各方向钻井的安全性和稳定性，为大斜度井的井眼轨迹设计提供参考。