Hydraulic fracture initiation and propagation: roles of wellbore trajectory, perforation and stress regimes

This paper develops a generic model for predicting hydraulic fracture initiation from arbitrarily oriented wellbores. For a given in-situ stress condition and wellbore orientation parameters, the model predicts the fracture initiation pressure and the orientation and location of fractures on the wellbore wall. The model has been applied in a series of in-situ stress conditions to study the effect of wellbore orientation on fracture initiation using non-dimensional parameters, which have enhanced the applicability of presented results for any stress condition. Closed-form analytical solutions are also obtained for initiation of longitudinal, transverse and complex multiple fractures from vertical and horizontal wellbores with and without perforation. A numerical model is then incorporated in the study to analyze the propagation behavior of initiated fractures. Causes of fracture initiation at non-preferred locations and its effects on fracture propagation pressure and fracture volume due to twist of these initiated fractures during propagation are studied and discussed. Results from the analytical and numerical models used in this study are interpreted with a particular effort to enlighten the causes of abnormally high treating pressures during hydraulic fracture treatments.