A theoretical model of borehole failure has been developed which predicts the conditions for pressure-induced lost circulation (hydraulic fracturing) and borehole collapse. The model can be used to calculate the conditions of borehole failure in vertical and directional wells under normal and tectonic in-situ stress conditions. The results show that deviation and hole direction can significantly influence both lost circulation and borehole collapse. The paper concludes with an illustration on how this theoretical model can be used to select proper mud weights to prevent borehole failure.

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