Using different rock failure criteria in wellbore stability analysis

• The minimum allowable mud pressure of Mogi–Coulomb is much less than the other two criteria.
• The minimum and maximum allowable mud pressure resulted from Mohr–Coulomb and Hoek–Brown criteria are not significantly different.
• The Hoek–Brown criterion is more conservative than the other two criteria.
• The mud window resulted from Mogi–Coulomb is the broadest and Hoek–Brown is the most limited.

The minimum and the maximum allowable drilling mud pressures for two wellbores are calculated analytically by Mohr–Coulomb, Hoek–Brown and Mogi–Coulomb failure criteria and numerically using a Fish program which is implemented in FLAC. The allowable drilling mud pressures that resulted from these methods are compared with each other and then with the field data: two wellbores in two Iranian oilfields are investigated as case studies to assess the results. Finally the criterion that matches closely field data is identified. It is shown that the minimum allowable drilling mud pressure obtained from the Mogi–Coulomb criterion is close to actual data collected during drilling operation. Hence, this criterion is considered more appropriate for wellbore stability analysis than the other two criteria.