Numerical analysis of wellbore stability based on thermal-fluid-solid coupling in deep well drilling

ABSTRACT: As oil and gas exploration and development extend into deeper layers and more complex geological conditions, deep and ultra-deep drilling operations are increasingly facing wellbore instability due to high temperature and high pressure. Therefore, it is crucial to consider the impact of formation temperature changes on wellbore stability. This paper, based on heat transfer control equations and the porous medium thermoelastic theory, establishes a numerical model for formation heat transfer and wellbore stability under thermo-hydro-mechanical coupling conditions. The model investigates the time-dependent temperature changes in the wellbore rock, the additional thermal stresses induced by variations in bottom hole temperature, the deformations of wellbore rock, and the changes in wellbore stress under thermo-hydro-mechanical coupling conditions. The results indicate that with the prolongation of drilling fluid circulation time, the temperature of the wellbore rock exhibits a nonlinear decay pattern, with the temperature field gradually stabilizing. The increase in bottom hole temperature significantly reduces the thermal stresses and displacements of the wellbore rock, showing a negative correlation between the two. The thermo-hydro-mechanical coupling effect is primarily concentrated around the wellbore, with the far-field formation stress being more influenced by the original formation stress field. This model can simulate temperature changes and stress distribution under different drilling conditions, providing valuable insights for wellbore stability analysis and safe drilling cycles in deep high-temperature drilling operations.