Yaser Arjmand - PhD Student, Department of Petroleum Engineering, Amir Kabir University of Technology | National Iranian Oil Company- Exploration Directorate
Mahdi Abolhasani - Geomechanics Related Project Manager, University of Tehran | National Iranian Oil Company- Exploration Directorate
Arash Heydari - Senior Drilling Engineer, Islamic Azad University-Shahrood Branch | National Iranian Oil Company- Exploration Directorate
Mohammad Ebrahimi - PhD Student, Department of Petroleum Engineering, Amir Kabir University of Technology | National Iranian Oil Company- Exploration Directorate

One of the most important challenges during drilling HPHT oil and gas wells is the wellbore instability which is an essential factor for economic analysis of drilling operations. Wellbore instability is usually caused due to inaccurate mud window design. A safe mud weight window is the window between pore pressure and fracture pressure of the formation, and a stable mud weight window is taken from the Mechanical Earth Model (MEM) of the area. In this research, the safe-stable mud weight window for a HPHT exploration well in south of Iran is determined, by superposing safe and stable mud window of the well. For determining safe-stable mud weight window, pore pressure and MEM of the area is estimated. The MEM is obtained using well drilling data, well logging data, and rock mechanics laboratory test results. According to Mohr-Coulomb, and Mogi-Coulomb failure criterions, two different safe-stable mud weight windows are taken from this MEM. Comparing the results, shows that the safe-stable drilling window determined by Mogi-Coulomb failure criterion tends to be more accurate than the other window.

Safe Mud Weight Window, Stable Mud Weight Window, Safe-Stable Mud Weight Window, Mechanical Earth Model (MEM), Wellbore Stability, Mohr- Coulomb Failure Criterion, Mogi- Coulomb Failure Criterion