Stability analysis and trajectory optimization of vertical and deviated boreholes using the extended-Mogi-Coulomb criterion and poly-axial test data

Abstract The wellbore instability costs the drilling of oil and gas wells billions of dollars, yearly. This might happen when the strength and resistance of the surrounded rock become exceeded by local stresses around the borehole. In order to keep the borehole stable, an appropriate density for the drilling mud must be determined based on the rock failure analysis which includes the identification of the rock strength, selection of the constitutive model, and chosen the accurate rock failure criterion. In this study, we used the nonlinear forms of Mogi Failure Criterion and Polyaxial Test Data to estimate the collapse and fracture pressures required to stabilize the wellbore in different well trajectories and in-situ stress regimes. The results reveal that in various in-situ stress regimes, the inclination and azimuth of the borehole have an important role in wellbore stability during drilling operation. It was identified that the Extended Mogi-Coulomb (EMC) and Mogi-Coulomb (MC) parameters in Well A (EMC = 257 psi and MC = 374 psi) are higher compared with Well B (EMC = 0.84 psi and MC = 0.54 psi). Also, the field case studies indicate that the nonlinear forms of Mogi Failure Criterion are greatly close to the real mud weight used to successfully drill the borehole in the field. This kind of borehole stability analysis plays a significant role in designing the drilling plan for oil and gas wells in order to minimize and eliminate the instability problems.