Ice and Iceberg Management Plans for Shtokman Field

Abstract

The Shtokman gas condensate field lies in the centre of the shelf zone of the Russian sector of the Barents Sea about 600 kilometers northeast from Murmansk. Shtokman Development AG (SDAG, 51% Gazprom, 25% Total and 24% Statoil) is in charge of the integrated development of the phase 1 of the Shtokman Gas condensate field. Exploitation of the gas field will be done through a floating platform that will export gas and condensate to the shore via pipeline. 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 activities have been planned to support the operations. The ice and iceberg management activities include surveillance, threat assessment and physical management. At this stage, definitions of strategy and philosophies for ice and iceberg management have been developed and preliminary plans for the main tasks have been outlined. The present paper describes the different components of the ice and iceberg management system and the rationales for the main technical choices. 1 INTRODUCTION The Barents Sea is bordered by the cold and icy waters of the Arctic Ocean and the Kara Sea on the North and East sides and by the warm water of the Norwegian Sea on the west side. The Gulf Stream enters the Barents Sea as the North Cape and Spitsbergen branches of the Norwegian current, bringing warm water into the region. The border between warm and cold water varies in location, depending on the oceanographic and meteorological conditions; this change is more sensitive in the Eastern part of the Barents Sea and especially at the Shtokman field. Sea ice does not form at Shtokman (except very thin ice in very cold years) but is exported from the North - Northeast by persistent winds. Thus, the origin of ice which can arrive at Shtokman is North-Eastern Barents Sea and possibly Kara Sea. The presence of drifting sea ice is observed in approximately 40% of the years on the Shtokman field, based on satellite observations from 1974 to 2007. This means that sea ice in the Shtokman area occurs approximately once every 2.6 years. Sea ice arrives rapidly at the Shtokman area and ice concentration may increase from 2/10th to above 8/10th within a few hours. Furthermore, ice may not be continually present at Shtokman throughout any one ice season. Historically, icebergs have been observed near Shtokman (within 75 nm) about once every five years on average. 10% of icebergs observed within 25 nm circle around Shtokman were in ice while 40% of icebergs observed within up to 100 nm north of Shtokman were in ice. With regard to seasonal variation it must be assumed that the probability of encountering icebergs at Shtokman during spring is higher than during late summer / early autumn.

The Effect of Ice Floe on the Strength, Stability, and Fatigue of Hybrid Flexible Risers in the Arctic Sea

“…Those case studies show that the presence of ice floes could have a significant impact on the design and fatigue performance of a riser system. To address this issue and comply with ISO 19906 (2010), the operator considered using a submerged turret riser system (STR) for the project [15]. As seen in Figure 1a, the STR system is a modified version of the free-hanging riser system, in which the turret is extended underwater, reducing the interaction between the risers and the ice floes.…”

“…The metallic structure of the turret must be large in diameter to accommodate all the risers, and, therefore, its weight per metre is substantial, affecting the design and cost of the Floating Production Unit (FPU) [3]. Researchers [15] raised concerns about the limited operational experience in the region and the high uncertainty of the data on ice and icebergs. Some icebergs may become frozen in the drifting ice, making them almost impossible to detect using satellite technology, particularly if they are small.…”

Autonomous Aerial Ice Observation for Ice Defense

“…This is neither economically nor practically feasible, so prioritization of the information gathering is needed. The region surrounding the DP operation is often divided into different zones depending on the estimated time of arrival (ETA) of the drifting ice (Sheykin, 2010;Edmond et al, 2011). In the various zones, distinct monitoring objectives apply with different required level of urgency and detail.…”

Numerical Research on Usage of Podded Propulsors in Ice Management

“…In recent operations, icebreakers have been employed to direct propeller wash towards the ice flow and thereby direct it away from the offshore structure [1]. Podded propulsor can generate thrust in any direction as the propeller azimuths around a central vertical axis.…”