Abstract

In the Upper Assam Basin, areas specifically near the Naga thrust belt are challenging for oil and gas exploration due to its complex geological settings, leading to high costs and risks associated with drilling. The Oligocene formation in this area is the main reservoir and is mainly composed of thick and highly compacted reservoir sandstone with some interbedded shale layers. The reservoir is sealed by overlain (Upper Oligocene formation) shale layer which contains a few strikes of sandstone and coal seams. The Upper Oligocene formation generally poses significant drilling challenges, viz. over-gauged borehole, tight pull, pipe stuck etc. Also, few drilling challenges have been observed in the overlying Miocene formation. These complications in turn increases Non-Productive Time (NPT) while drilling. Moreover, the over-gauged borehole and severe down-hole drilling complications result in poor logging condition and uncertainty in reservoir evaluation. In this study, a Mechanical Earth Model (MEM) has been generated, and wellbore stability analysis has been carried out using industry standard Geomechanics workflow to optimize mud weight in future wells, in order to reduce drilling complexities and also to reduce NPT.