Modelling Borehole Collapse with Capability of Predicting the Radius Size Effect

We present a borehole failure model which is based on fracture mechanics and layer buckling theories and compare its prediction with experimental data. The model assumes that the main mechanism of borehole collapse takes place in the form of layers buckling near the borehole surface. The model introduces a combination of fracture mechanics parameters with dimension of length that scale the size of the holes allowing for size effect to be predicted. We present and compare the model predictions with available experimental data. For the model predictions as well for the experimental data we found a strong correlation between the borehole failure load normalized by the uniaxial compressive strength and the hole size normalized by the square of the division of rock fracture toughness over its tensile strength. The model can be used for constructing practical mechanical models for predicting failure and avoiding sanding from small size holes such as perforations.