A micromechanical model to estimate borehole collapse pressure

Abstract

Borehole collapse is predicted by common rock failure criteria despite they give conservative results due to some simplification of rock behavior. It is the source of many difficulties in implementation of oil well, underground structures and foundations. Utilizing damage theory could improve the conservancy of rock failure criterion. Damage theory considers loss of function rather than loss of strength. Unlike criteria which were derived from plasticity that assume yielding point as the limit of functionality of rock, damage theory uses a state between failure and yielding in stress-strain diagram as the limit of the rock applicability. In this study, a new model is proposed to predict minimum borehole pressure based on rock damage theory. The model is verified by actual wellbore data. The proposed model predicts minimum borehole pressure close to actual data and more accurate than Mohr-coulomb and Mogi-Coulomb criteria.