During the drilling process, wellbore instability leads to a complex wellbore morphology. Thus, serious drilling accidents, such as leakage and sticking, can occur. Therefore, it is important to choose different failure criteria for different geological engineering conditions to calculate the safe density window of the drilling fluid to prevent borehole wall instability. In this study, the applicability of three different rock failure criteria, Mohr–Coulomb, Mogi–Coulomb, and Drucker–Prager, was examined under five different fault mechanisms, and the variation in borehole collapse pressure with the trajectory of the borehole under different fault mechanisms was investigated. The results provided a scientific basis for the selection of failure criteria under different geological engineering conditions. The relevant theory provides a reference for well trajectory design, well location selection, and drilling directions.
Article highlights: The paper analyzes the change trend of the collapse pressure of the well wall with the azimuth angle of the well slope under different failure criteria. Then compared with the actual drilling fluid density on site to obtain the optimal results of failure criteria under different fault mechanisms. The results can optimize the failure criteria for different stratum conditions in the subsequent collapse of the wellboreThe best drilling direction can be obtained by analyzing the results of the stability calculation of the wellbore trajectory under five fault mechanismsThe conclusion provides a more specific scientific basis for the selection of failure criteria and the calculation of drilling fluid safety density window under different formation conditions in actual drilling