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

Abstract

The Shtokman Gas Condensate Field (SGCF) is located 610 km from Murmansk in the Barents Sea. The water depth at location is around 340 m. The offshore facilities of the SGCF Phase 1 development will include ice-resistant ship shape disconnectable turret moored floating platform (FP). Significant sea ice invasions occur at Shtokman in approximately 3 out of 10 years, on average. Icebergs may also occur in the SCGF area. Ice and iceberg management are planned to support the FP operations. The present paper describes the methodology to assess performance, operability and risk of the FP in waters where occasional invasion of sea and glacial ice is anticipated. Introduction Challenges with ice-related design and operating philosophy for the Shtokman FP have been described in [Ref. 1]. In brief, the main challenge is to achieve an appropriate reliability level and at the same time minimize operational downtime at acceptable costs. Table 1 summarizes the main ice-related challenges as identified in the pre-FEED and updated during the FEED, categorized by the accidental scenarios. Actions have been taken in order to address the challenges and quantitatively assess the risks. It shall be emphasised that no attempt was made to target the design of individual components to achieve the target reliability level for the entire system, i.e. floating platform with respect to ice actions. This is simply because it would have been too speculative given all the uncertainties involved. On the contrary, it was decided early 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 the operational measures, including assessment of their efficiency and reliability. Further, quantitative operability and risk assessments of the entire system have been performed to evaluate potential needs for optimisation. The objective of this paper is to present the approach developed and used for assessing performance, operability and risk of the Shtokman Floating Platform with regard to sea and glacial ice. The content of this paper is based on numerous studies performed to provide input for the Final Investment Decision.

Iceberg disconnect criteria for floating production systems

“…In the future, disconnectable FPSOs will likely be used to develop discoveries to the north and east of the Grand Banks. Disconnectable FPSOs could also be used in the Barents Sea north of Norway and Russia, where icebergs also occur (Liferov et al 2011). To be able to optimally design FPSOs for more challenging ice environments (higher iceberg areal densities, higher drift velocities and greater water depths), it is advantageous to continue to improve our knowledge and modelling capabilities regarding iceberg impact loads.…”