Ayub Valizadeh - Petroleum University of Technology

Wellbore instability is becoming a major concern due to increasing the number of directional wells, deep formations and naturally fractured media. Anappropriate wellbore stability model is desired to correctly calculate the stresses around the wellbore and predict a reasonable safe wellbore pressure.Analytical solutions for wellbore stability study are mainly easy to use but in some cases are time consuming. Thus, numerical ethods, including finite difference and or finite element have been applied to model wellbore stability. In this paper, a finite difference code was used inanalyze the mechanical to determine the optimum mud pressures and the best well trajectories for different wellbore inclinations, azimuth angles and in-situ stress regimes. The results indicated that in normal fault stress regime, the stability in direction parallel to the minimum horizontal stress was morethan the others. Furthermore, vertical well was more stable than the horizontal one in this case. But in strike slip and reverse fault stress regimes, thedirection of maximum horizontal stress was the best drilling direction and in the case of strike slip stress regime, the higher deviated boreholes were more stable.