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Wellbore Stability Analysis in an Offshore High-Pressure High-Temperature Gas Field Revealed Lost Times Due to Lack of Well Trajectory Optimization


 Wellbore stability (WBS) problems causes excessive lost times and cost during drilling. Drilling 10 development wells in an offshore high pressure high temperature (HPHT) gas field showed different non-productive time (NPT) values due to different severity of WBS issues such as kick flows, lost circulation, tight holes, stuck pipes which are responsible for repeated reaming, fishing and sidetracking. To reveal the reasons for the different severity of WBS problems in the studied wells and enhance future drilling, this work focused its investigation on the geomechanical modeling and WBS analysis.
 The results of the constructed geomechanical model show that well trajectory parameters of azimuth and inclination angle have crucial effects on the safe mud weight window and the consequent WBS problems. The stable mud weight window decreases as the borehole deviation increases, the maximum allowable inclination angle was determined as 50 degrees; otherwise, severe WBS issues are expected during drilling. The well azimuth showed to have trivial effect on the breakout mud weight, whereas the breakdown mud weight is significantly greater in wells drilled in the direction of minimum horizontal stress (NW-SE). Therefore, as safe mud weight windows are broader in wells with NW-SE, it is expected that such wells have greater wellbore stability than wells drilled in other directions. Therefore, the different extent of the actual field WBS issues in the studied wells was attributed to their well trajectories, in accordance with the WBS analysis.
 Optimization of wellbore trajectory parameters while taking into account reservoir targets are recommended for future drilling in HPHT fields. This would contribute to reducing WBS problems and NPT for subsequent drilling jobs and finally contribute to more efficient drilling operations.