A Simulator for Minimizing Openhole Breakdown Pressure through Notch Shape Optimization

Abstract

Wellbore breakdown pressure is an important parameter utilized in hydraulic fracturing stimulation design. Because of the stress concentration around wellbore and formation strength, the borehole breakdown pressure is often much higher than the minimum confining stress plus tensile strength. To overcome the barrier of the stress concentration and locate the fracture initiation spot, well is often perforated or notched before the hydraulic fracturing treatment. Qualitatively, it is well observed and accepted that perforations and notches can reduce the breakdown pressure; quantitatively, however, there is a demand for reliable and accurate method to predict how much various perforating or notching configurations can help reduce the breakdown pressure. In this paper, a computational mechanics simulator is developed to predict the breakdown pressure inside a notched wellbore subjected to loading of in-situ stresses. The simulator can predict the breakdown pressure for a well with a given notch stimulated with fluid injection. It can also be used to optimize the design of a notching tool which can minimize the breakdown pressure during hydraulic fracturing. The simulator is applicable to cases of both longitudinal and transverse notches.