Design Challenge of the West Nile Delta Gas Development: The Rosetta Channel Crossing

Abstract

Raven is the third stage of the West Nile Delta development (following Taurus / Libra and Giza / Fayoum) from two BP-operated offshore concession blocks, North Alexandria and West Mediterranean Deepwater. The Raven project included the design of various rigid pipelines, of which one specifically is the subject of this paper. The 16" RSM to RP in-field flowline is approximately 4.8 km long, connecting a manifold (RSM) to a PLEM (RP) through a route that crosses a prominent geological feature identified as the Rosetta Channel, a submerged canyon that extends for about 30 km. The Rosetta Channel is about 2.5 km wide at the location of the 16" flowline route crossing, with steep slopes going down for approx. 40m (in height) on the RSM side, and then climbing up approx. 150m (in height) towards the RP side. Although it is typically preferred to avoid very rough geophysical features, this is not always possible or practicable and it is not uncommon to come across challenging seabed features that demand complex engineering solutions in order to minimise risks and associated costs. This paper addresses the numerous technical challenges involved in the design of the 16" flowline that crosses the Rosetta Channel. Following close collaboration between all involved stakeholders, a robust, reliable and cost-effective solution was achieved after a detailed engineering process, where the final design required a unique combination of mitigations including seabed excavation, pre-lay rock carpets, post-lay rock berms, cable jetting, curve bollards and sleepers.