Wellbore stability analysis in transversely isotropic rock The occurrence of weakness planes in rock formations poses significant challenges to borehole stability. The drilling stability is closely related to the inclination angle of the rock formation, the mud pressure, the stress of the surrounding rock, and the mechanical characteristics of the surrounding rock. In order to reveal the mechanism of drilling stability instability. This paper uses the kirsch theory, Mohr Coulomb criterion, Hoek and Brown criterion to establish the drilling instability equation, and analyzes the influence of rock formation dip angle, mud pressure, and surrounding rock stress on the drilling stability,and obtains different rock formations.