Modeling Poroelastic Effect on Borehole Stability for Under-balanced and Over-balanced Drilling Conditions

Since rock formations are always saturated by fluids, the coupled poroelastic models were developed for improved wellbore stability analysis. Poroelastic models allow to consider phenomena such as well communication with rock formation and pore pressure redistribution. This paper presents the analytical solution of one coupled poroelastic model and then departs to consider two common drilling scenarios, under-balanced and over-balanced drilling. Obtained results show that time-dependent delayed failure and failure initiation taking place inside the formation rather than at the wellbore wall can be predicted by virtue of the coupled model. Moreover, these two phenomena are different for the two drilling scenarios mentioned above. For the under-balanced drilling borehole stability will get enhanced with time due to poroelastic effect in the formation. On the contrary, the borehole stability status will get worse and time-delayed failure may happen for the over-balanced drilling.