Protection Barrier for Shallow Arctic Waters

Abstract

Hydrocarbon discoveries in the shallow waters of the Northern Caspian Sea have caused intensive drilling activities to be carried out to explore the potentials. Experience with mobile drilling units in the seasonally ice infested waters hitherto originates from the drilling campaigns of the Sunkar drilling barge at Kashagan and Kalamkas. However, with increased drilling activities upcoming, innovative drilling concepts are desirable due to the objective of maintaining drilling operations (of production wells) also during the ice period with the use of conventional non-ice-resistant drilling platforms. The employment of external Shoulder Ice Barriers (SIBs) to protect a conventional jack-up drilling rig from the hazards of drifting ice in shallow water is discussed. Model tests on the SIB were performed in the large ice tank of the Hamburg Ship Model Basin (HSVA) during July 2007. These tests were performed to investigate the conceptual design under ice impact. The characteristic shoulder sections' inclination was varied to investigate the shoulder’s contribution towards stabilizing broken ice and to prevent ice from over-riding. Ice up-riding onto the barrier contributes towards increased vertical forces. The global vertical forces showed to be higher than the global horizontal forces, and in particular when ice grounding was observed. Even under extreme rubble heights of up to 9.4 m (full scale), ice overtopping the structure was effectively prevented. The SIB showed the potential to be utilized as ice protection structure for future shallow water developments. Finally, the stability on the sea bottom was investigated. The conclusion being that the concept will perform well on average to strong soils but needs to have a larger foot print area in very soft soils condition. This paper thus documents, on a feasibility level, the concept of ice protection in shallow water by means of the SIB. This paper presents a summary study of the design and verification work performed with regard to the feasibility of an innovative design.