A Conceptual Study of Deepwater Arctic Floater for Year-Round Drilling and Production

摘要

The Arctic offshore may hold the largest undiscovered oil deposits which could account for up to 25% of the world's undiscovered hydrocarbons based on Gautier et al (2009). Access to the deepwater deposits in the Arctic Ocean presents a special challenge. In the past four decades only shallow water drilling campaigns have been executed in relatively mild ice environments and have accumulated valuable drilling experience. To drill an exploratory well at a deepwater Arctic location, a floating drilling platform is required. Floating platform design poses significant challenges given the harsh ice loading conditions and the demand on the hull and mooring system strengths. In most of the deep water Arctic regions, the winter season is characterized by the presence of first-year ice, multi-year ice, and in some areas ice islands and icebergs. Compared to the environmental loads due to waves, winds and currents, ice actions (both forces and moments) are considerably higher and are the governing loads for deepwater Arctic systems. The capability of a floater mooring system to withstand ice loads is limited as compared to gravity based structures. One of the solutions is a disconnectable system utilizing the ability to disconnect the floater from the mooring system and move off site when the ice loads are forecasted to approach the design limit. As of today, several disconnectable floating system concepts have been proposed, such as disconnectable FPSO, non ship-shaped circular FPSO, Arctic Spar and semi-rigid floater. These concepts are either intended for relatively mild Arctic ice conditions or require long durations for disconnection and re-connection. This paper presents an innovative disconnectable floating platform concept for deepwater Arctic, which can perform exploratory, development drilling and potentially year-round production in various deep water Arctic locations. This design, like many other similar concepts, by limiting the design ice loads to a pre-defined level, enables reasonable hull and mooring system configurations within existing technology limits for an environment where the environmental loading seems to approach infinity in practical terms, if unmanaged. In the event of an excessive ice feature approaching, the innovative platform can be quickly disconnected and towed away, and can then be quickly re-connected once the ice feature has passed.