Geomechanical Assessment of Wellbore Stability in the Deep Offshore Niger Delta

Wellbore instability events including stuck pipe, hole collapse, and lost circulation in deep offshore Niger Delta wells represent a major source of non-productive drilling time with associated cost implications that motivated this investigation of the geomechanical conditions controlling well bore stability at depths exceeding three kilometres below sea floor. This study constructs a one-dimensional mechanical earth model for a deep offshore well in the Niger Delta, integrating wireline log data with core strength measurements and regional stress orientation information. Pore pressure was estimated from seismic velocity data calibrated to measured formation pressures at permeable intervals, identifying transitions from hydrostatic to overpressured conditions within the Agbada and Akata formations. Overburden stress was calculated by vertical integration of the density log. Minimum horizontal stress was estimated from leak-off test data and formation integrity tests at selected casing shoe depths. Maximum horizontal stress orientation was inferred from breakout analysis of image log data. Rock strength parameters were estimated from multivariate correlations with sonic and density log values calibrated against triaxial core test results. A mud weight window analysis was performed to define the safe drilling fluid density range preventing both shear failure and hydraulic fracturing at each depth interval. Recommended mud weight schedules and casing setting depths are presented for future well design. Keywords: geomechanics, wellbore stability, mechanical earth model, Niger Delta, mud weight window.