Innovative Concept of a Drilling and/or Production Platform for Operating in Arctic and Deep Water

摘要

A concept of an innovative floating platform using a conical structure was originally developed for operation in arctic region. It is called as MCAD (MonoCone Arctic Drilling Platform). The conical structure is used to reduce ice-loading as it facilitates ice to break in flexure while riding the slope of the conical surface. For supporting the weight of the platform, equipment, and ballast, a base structure with sufficient buoyancy is added at the base of conical structure. To ensure the platform with adequate stability, a heavy (solid) ballasting system that can be lowered to adjust thevertical center of gravity of the platform is incorporated in the system. The conceptual platform configuration has been analyzed for a large payload of more than 25,000 ST operating in approximately 125 feet of water depth. In the winter season, the platform is subjected to more than 12,000 ST of ice load. For warmer season the platform has been designed to survive a 45 feet significant wave height with 80 knots wind, and a very strong current of 6 knots. To withstand such magnitude of ice forces, mooring system using 32 lines was designed. For lower ice loads in a milder environment, the number of mooring lines can be reduced considerably. For operating in the warmer season, the platform was analyzed for design environments of operating and survival conditions. The motion responses in these conditions were found to be excellent in comparison to other deepwater concepts in use. With the promising motion response results of the conceptual platform with such a high payload, the concept is expected to provide operating company an alternative for deepwater application as well. Since the concept has been developed for a very large payload, the excess payload may be utilized as storages of produced oil. Mooring system for operating in deep water has been developed, and has been compared with that of the system for arctic condition. This paper describes the concept identifying the salient features. The effects of various features on the design and platform performance are also described. The ballast system with its lowering system makes this concept attractive foreasy installation without the assistance of a large derrick vessel, a significant reduction of installation time is also expected. Results of stability, motion and mooring analyses is presented in the paper as well. Preliminary structural analyses were carried out to confirm the viability of the concept in operational, installation and survival conditions.