Analytical Failure Prediction of Inclined Boreholes

Abstract

Predicting when, where, and how pressure-induced borehole failures occur is of fundamental importance in borehole stability analysis and hydraulic fracture design. Numerical and statistical methods are not suited for system analysis, while existing analytical solutions depend on failure location, neglect shear stresses, or only consider vertical boreholes. This paper derives explicit analytical relations between far-field stresses and when, where, and how borehole failures occur in arbitrarily oriented boreholes. These relations reveal that when, where, and how failures occur varies characteristically with the borehole orientation. Further, the optimal drilling- and optimal hydraulic fracturing orientations are determined, together with two simple methods for determining the stress regime based on where or how failures occur. It was also found that failure prediction is more sensitive to noise when the formation is more anisotropic and/or closer to failure.