Drilling Challenges in the North Atlantic Margin

Abstract

Chevron and its Partners are facing several challenges in the North Atlantic Margin exploration and development. These challenges affect drilling design and operations, which should take in account several important factors occurring concurrently in this area: deepwater conditions;complex lithological sequence and target imaging uncertainty;geomechanical conditions. Hole section design is strongly affected by the uncertainty of the subsurface data, in particular the seismic data, where the presence of thick basalt flows, as strong reflectors, induce relatively poor seismic imaging of intra–basalt or sub–basalt drilling targets. This issue is mitigated with contingency plans for final hole section size and casing string setting depths. The complex lithological sequence, geomechanical conditions and lithological uncertainty also affect drilling fluid design and bit/bottom hole assembly (BHA) selection. The consideration of some of these factors had the outcome of using thixotropic muds to counter serious lost circulation events. A further successful outcome was the design and implemention of riserless drilling techniques, a first for Chevron Upstream Europe and Halliburton Baroid UK, to counter the threat of shallow water flows in the top hole sections. The paper demonstrates how a multi – disciplinary approach in both drilling design and operations is beneficial to successful drilling optimization in the North Atlantic Margin, a geographically and geologically challenging area.