Stability analysis of deviated boreholes using the Mogi-Coulomb failure criterion, with applications to some oil and gas reservoirs

Borehole collapse is the commonly encountered wellbore stability problem during drilling. The precursor of such borehole failure can be often eliminated by a proper determination of the critical mud pressure. Recently, Al-Ajmi and Zimmerman developed a new 3D analytical model to estimate the mud pressure required to avoid shear failure (i.e., borehole collapse) at the wall of arbitrary oriented boreholes. This had been achieved by using linear elasticity theory to calculate the stresses around the borehole, in conjunction with the fully-polyaxial Mogi-Coulomb criterion to predict failure. The developed model has been used to study the behaviour of the collapse pressure under different in situ stress regimes. We have found that the optimum drilling trajectory is directly related to the principal in situ stresses. Accordingly, we have developed a new analytical solution to optimize well path. The stability model has been applied to several field cases, and the new model in each case is consistent with the field experience. It has been concluded that the optimum wellbore profile can be ensured by employing the developed analytical stability model.