Interpretation of the Scale Effect in Perforation Failure

Abstract

In this paper we examine a borehole failure model which is based on fracture mechanics and layer buckling theories in the light of experimental data. The model assumes that the main mechanism of borehole collapse takes place in the form of (pre-existing or formed) layers buckling [1]. The model introduces a combination of fracture mechanics parameters with length dimension that scale the size of the holes allowing for size effect predictions. We present and compare the model predictions with available experimental data. For the model predictions as well the experimental data we found a strong correlation between hole strength normalized by the uniaxial compressive strength and hole size normalized by the square of the division of rock fracture toughness over its tensile strength. These findings can be used for constructing mechanical models to predict failure in small size holes such as perforations.