Abstract
A geomechanical study was conducted for one of the drilling platforms in offshore Saudi Arabia, where several highly deviated (well inclination > 80°) development wells were planned. The main objective was to provide safe mud weight ranges and predict possible problematic depths to minimize drilling challenges like pack-off, stuck-pipe, lost in hole, over-pulls etc., which are likely due to wellbore instability. The scope of this work was restricted to the curve section of the planned wells because most of the problematic formations, comprising mainly shale and weak interbedded sand formations, are encountered in the curve section.
The operator's drilling department sought a clear understanding of the geomechanical aspects of these problematic formations to optimize the drilling plan and minimize nonproductive time. A 1D mechanical earth model (MEM) was constructed using openhole log data available from the only exploratory well drilled on this platform. The 1D MEM was further used in conducting post-drilling analyses to validate and history match events related to wellbore instability (like tight spots, pack-off etc.,) that were observed while drilling and stress-related wellbore failure as shown by the calipers.
The developed model was used for analyzing planned well trajectories and providing mud weight window limits to safely drill the highly deviated planned wells. Sensitivity analysis was performed to identify the well inclination limits to drill across the problematic zones whilst minimizing issues related to wellbore instability. The developed geomechanical model was validated using the log data acquired during drilling each of these inclined wells; the predictions from the model were in close agreement with actual observations during drilling.
The outcome of this study helped optimize the well design for upcoming wells in this field. Using the recommendations provided from this study, several highly deviated development wells were successfully drilled and completed. Apart from standard failure analysis, ‘depth of failure’ approach was also taken into account to provide recommendations on optimum drilling mud weight. Utilizing the geomechanical study, extended reach curve sections as long as 5000-ft measured depth (MD) were planned and drilled successfully without any significant nonproductive time (NPT).
