Summary Borehole instability is primarily a rock mechanics problem. Regional earth stresses and typical rock strengths are used to explain the widespread nature of irregularly shaped, fragile boreholes in the western Canadian Overthrust Belt (foothills). Drilling fluids and practices are investigated with a rock mechanics model of borehole failure. Although drilling practices can significantly affect problems associated with borehole wall failure, they are not the primary cause.
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D. Woodland (1990) studied this question.
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