Performance, Operability, and Risk Assessment of the Shtokman Floating Platform in Ice

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper OTC 22100, ’Approach to Performance, Operability, and Risk Assessment of the Shtokman Floating Platform in Ice,’ by Pavel Liferov, Guillaume Le Marechal, Marc-Marie Albertini, Michel Metge, and Erik ter Brake, Shtokman Development A.G., prepared for the 2011 Arctic Technology Conference, Houston, 7-9 February 2011. The paper has not been peer reviewed. Copyright 2011 Offshore Technology Conference. Reproduced by permission. The Shtokman gas/condensate field (SGCF) is 610 km from Murmansk, Russia, in the Barents Sea. The water depth is approximately 340 m. The offshore facilities of the SGCF Phase-1 development will include an ice-resistant ship-shaped disconnectable-turret-moored floating platform (FP). Significant sea-ice invasions occur at Shtokman approximately 3 out of every 10 years. Icebergs also may occur in the SGCF area. Ice and iceberg management is planned to support the FP operations. The performance, operability, and risk of the FP in waters where occasional invasion of sea and glacial ice is anticipated were assessed. Introduction The main challenge was to achieve an appropriate reliability level at acceptable costs, while minimizing operational downtime. The main ice-related challenges identified in the prefront-end engineering and design (FEED) and updated during the FEED included FP loss of station keeping because of actions from sea ice, FP loss of station keeping because of actions from icebergs, and underhull ice interaction in the riser-connection area. It was decided early on to establish challenging but realistic design targets for the main systems (e.g., hull, mooring, and disconnection system) and, in parallel, work on design of operational measures, including assessment of efficiency and reliability. Further, quantitative operability and risk assessments of the entire system were performed to evaluate potential optimization needs. Ice-Related Design and Operating Philosophy The FP was designed as an ice-resistant disconnectable production unit, able to withstand independently almost all ice and iceberg actions expected to occur at Shtokman. The following conditions are the design limits, and acceptable response criteria under these conditions and interaction scenarios must be satisfied. Ultimate-limit-state (ULS) mooring safety factor under: Head-on interaction with unmanaged 100-year-return-period (YRP) ice ridge (with corresponding companion environmental actions) Ice vaning in unmanaged 100-YRP level ice (with corresponding companion environmental actions) Interaction with 10,000-YRP iceberg in open water (for demonstration purpose, not for use in operations) 5000-t horizontal load (as practically achievable value, on the basis of results from initial studies)