A Micromechanical Model to Estimate Borehole Collapse Pressure

Borehole collapse is predicted by common rock failure criteriadespite they give conservative results due to some simplificationof rock behavior. It is the source of many difficulties in implementationof oil well, underground structures and foundations.Utilizing damage theory could improve the conservancy of rockfailure criterion. Damage theory considers loss of functionrather than loss of strength. Unlike criteria which were derivedfrom plasticity that assume yielding point as the limit of functionalityof rock, damage theory uses a state between failureand yielding in stress-strain diagram as the limit of the rockapplicability. In this study, a new model is proposed to predictminimum borehole pressure based on rock damage theory. Themodel is verified by actual wellbore data. The proposed modelpredicts minimum borehole pressure close to actual data andmore accurate than Mohr-coulomb and Mogi-Coulomb criteria.