掌握不同地应力条件下地层坍塌压力随井斜角和方位角变化的规律，对于定向井井壁稳定和安全钻井至关重要。采用数值模拟手段对三向地应力的4种大小顺序关系情况下地层坍塌压力当量泥浆密度与井斜角和方位角之间的相互关系进行了系统分析，弄清了定向井中地层坍塌压力的变化规律。其研究成果可为定向井钻井安全泥浆密度的确定提供一定的参考依据。

It′s very important for the directional well drilling stability and security, to know the changes of the formation collapse pressure with the well deviation and azimuth angle under different formation stress conditions. Here we analyze the relationship among equivalent mud density of formation collapse pressure, well deviation and azimuth angle, by numerical simulation of formation stress for four cases. And the changes of formation collapse pressure in the directional wells are also discussed. The result will provide a reference to determine the security mud density in directional well drilling.