Analysis of Wellbore Stability Conditions During Drilling of Extended Reach Wells in the Agbada Formation, Offshore Lagos, South West Nigeria

Extended reach drilling has become increasingly important in the offshore West Africa context for accessing geologically complex reservoirs from limited platform or semi-submersible locations, and wellbore stability management in these high-inclination wellbores through the Agbada Formation presents specific geomechanical challenges. This study analyses wellbore stability conditions for extended reach well trajectories in the Agbada Formation offshore Lagos State, South West Nigeria. A three-dimensional mechanical earth model was constructed by integrating sonic log data, density logs, drilling-induced fracture observations from image logs, and leak-off test data from seven offset wells. Minimum horizontal stress and maximum horizontal stress orientations were derived from breakout azimuth analysis of image log caliper data. The Mohr-Coulomb and Mogi-Coulomb failure criteria were applied to predict mud weight windows for wellbore inclinations from 0 to 85 degrees along the planned well trajectory azimuth. Results indicate that the stable mud weight window narrows from 1.0 to 0.6 equivalent mud weight pound per gallon units as inclination increases from 60 to 85 degrees, due primarily to increased shear failure risk on weak bedding planes in the high-inclination segment. Wellbore trajectory optimisation recommendations are provided to maintain inclination below 80 degrees through the most critically stressed section, reducing shear failure risk without compromising reservoir access. Keywords: wellbore stability, extended reach drilling, Agbada Formation, offshore Lagos, geomechanics.