The best failure criteria with an analytical model for underbalanced drilling

摘要

One of the important issues in borehole instability assessments is choosing proper failure criteria. In this paper, four different failure criteria are used. These failure criteria are Mohr-Coulomb, Hoek-Brown, Modified Lade and Mogi-Coulomb failure criterion.A poroelastic model is used for calculating collapse pressure. A MATLAB code is generated for this purpose. These failure criteria are presented in the following sections briefly. The two first failure criteria ignore the effect of intermediate stress but two other failure criteria are polyaxial failure criteria and take into account the effect of intermediate stress. Collapse pressures for different inclination and azimuth which are calculated with different failure criteria are presented here.It is concluded that the failure criteria which ignore intermediate principle stress causes to overestimate collapse pressure. Modified Lade and Mogi-Coulomb criteria give the more realistic collapse pressures