Wellbore instability management using geomechanical modeling and wellbore stability analysis for Zubair shale formation in Southern Iraq

Abstract Wellbore instability problems cause nonproductive time, especially during drilling operations in the shale formations. These include stuck pipe, caving, lost circulation, and tight hole, requiring more time to treat therefore additional costs. The extensive hole collapse problem is considered one of main challenges experienced when Zubair formation. In turn, it caused by increasing well expenditure. this study, geomechanical modeling was used determine a suitable mud weight window overpass these improve performance for development. Three failure criteria, including Mohr–Coulomb, modified Lade, Mogi–Coulomb, were predict safe window. model constructed using offset log data, formation micro-imager (FMI) logs, acoustic compressional wave, shear gamma ray, bulk density, sonic porosity, events. calibrated image data interpretation, modular dynamics tester (MDT), leak-off test (LOT), integrity (FIT). Furthermore, comparison between predicted wellbore actual performed examine model's accuracy. results showed that Mogi–Coulomb Lade criterion most criteria given good match with field observations. contrast, Mohr–Coulomb improper because does not from caliper log. addition, obtained inappropriate (10.6 ppg) behind optimum should apply ranges 11.5 14 ppg. Moreover, inclination angle be less than 25 degrees, azimuth 115 120 degrees northwest-southeast (NE–SW) can presented risk. NE–SW direction, parallel minimum horizontal stress (Shmin), will provide best stability This study's findings help understand root causes Thus, research applied as expenditure effectiveness tools designing future neighboring directional wells get high reducing expenses.