Abstract
The Cooper Basin of Australia is challenged by high deviatory stress conditions in the strike-slip to reverse stress regimes, which increase borehole breakout during drilling. This paper studies the applicability of failure criteria such as Mohr-Coulomb, Mogi-Coulomb, and Drucker-Prager for wellbore collapse in a low permeability sandstone well in the Cooper Basin, Australia. The influences of well conditions and rock mechanical properties on the wellbore collapse modeling are also investigated. The 1D mechanical earth model (MEM) from well Tamarama-1 is compiled and extracted to provide four sections of data with borehole breakouts. First, the stresses around the borehole are calculated using the Kirsch equations. Then, different failure criteria (i.e., Mohr-Coulomb, Mogi-Coulomb, and Drucker-Prager) are used to evaluate the areas of borehole breakout. Finally, a parametric analysis is presented to show the influences of well conditions and rock mechanical properties on the prediction of borehole breakouts.
The results show that the Mogi-Coulomb criterion and Drucker-Prager criterion have a good match with borehole breakouts from field observations. The Mohr-Coulomb criterion overestimates the wellbore collapse pressure and breakout areas because it ignores the strengthening effect of the intermediate principal stress. The parametric study shows that the maximum horizontal stress, azimuth, inclination, and friction angle can affect borehole breakouts in terms of magnitude and orientation. Rock mechanical properties such as Young's Modulus do not affect the borehole breakout, and Poisson's ratio has a minor effect on the borehole breakout. A better understanding of borehole stability is crucial and beneficial to drilling and completions of oil and gas wells. This paper provides an integrated workflow to determine which failure criterion is most applicable for given conditions and provides a framework for a more detailed sensitivity analysis on borehole breakout. It has applicability for the numerous strike-slip regimes being appraised with deviated and horizontal wellbores in the Eastern Hemisphere.
