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弱面地层在较小的钻井液柱压力下先于岩石本体破坏，引起井壁垮塌，甚至在高密度钻井液情况下也难以维持井壁稳定。我国西部钻井中常遇此类问题。本文从弱面模型出发建立大倾角地层的井壁稳定力学模型，详细分析倾角地层的倾角和走向对井壁稳定性的影响，认为弱面地层的坍塌方位主要集中在走向与水平最小地应力夹角在90±20度范围内，在钻遇此地层时，若维持井壁稳定所需的钻井液密度过高，可采用合理的井眼轨迹进行大斜度井钻井。
The weak-surface formation destroys before the rock mass at a lower pressure of the drilling fluid column, causing the collapse of the borehole wall. It is difficult to maintain the stability of the borehole even in the case of high-density drilling fluid. This type of problem is often encountered in drilling in western China. In this paper, the stability model of wellbore with large dip angle is established from the model of weak face, and the effect of dip angle and strike direction on the stability of wellbore is analyzed in detail. It is considered that the collapse orientation of weak face mainly lies in the direction and the minimum level of earth- When the angle is within 90 ± 20 degrees, a reasonable well trajectory can be used to drill a high-skewed well when drilling this formation, if the density of drilling fluid needed to maintain stability of the borehole is too high.