RIO OIL & GAS 2014 - Mooring System for a Semi-Submersible Rig in Ultra-Deepwater and Under Severe Currents

In the nearby future, deepwater and ultra-deepwater Exploration and Production activities will represent most of the Oil and Gas Industry operations in Brazil, West Africa and Gulf of Mexico. This paper consist of the mooring analysis in water depth of 2,000m, 2,500m and 3,000m on Basins of North and Northeast of Brazil with severe current, wind and wave conditions using a standard anchor handling tug and supply vessel (AHTS). Alternatives in mooring systems are evaluated based on the rig preferable mooring spread, fairlead angle limitation and proposed mooring components. Due to increase of water depth in Mobile Offshore Drilling Unit (MODU) mooring, the development of different types of mooring system configuration in order to meet mooring line safety factor and rig offset requirements is becoming crucial. The case study presented in this paper considered different types of mooring systems: Wire-Chain system (catenary) and Chain-Polyester-Chain system (taut-leg). The mooring analysis was done with the rig Noble Clyde Boudreaux (NCB) that has capacity to be moored at 3,048m of water depth and to drill until 10,668m depth. The results show that it is possible to moor a semi-submersible rig in ultra-deepwater fields under extreme environmental conditions, considering the premises and methodology described in this paper.

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