Spar Platform Oil Storage and Offloading System Design

Liu, Weiwei (COTEC Offshore Engineering Co., Ltd.) | Wang, Jin (COTEC Offshore Engineering Co., Ltd.) | Huang, Jia (COTEC Offshore Engineering Co., Ltd.) | Liu, Yang (COTEC Offshore Engineering Co., Ltd.) | Li, Yang (COTEC Offshore Engineering Co., Ltd.)



In recent years, Spar platform has become one of the most attractive deepwater development concepts due to its superior stability and strong operability suitable for dry-tree drilling and production in a wide range of water depth from 300m to 3000m. A new concept Spar platform, namely Spar Drilling Production Storage Offloading or SDPSO, combining the advantages of the deep-draft classic Spar configuration with the capability of oil storage, will be studied in this paper. This new concept Spar or SDPSO doesn't rely on a subsea pipeline system for oil export, thus significantly improves the flexibility of technical solutions and decrease the overall cost for deepwater marginal field development. Unlike conventional ship-shaped FPSOs, the SDPSO uses the oil-over-water or oil-water displacement method for oil storage. This paper first will provide an overview of the oil storage and offloading systems of the SDPSO. In general, two methods can be used for offshore oil storage loading and offloading, namely oil-gas displacement method (commonly used in a conventional FPSO) and oil-water displacement method. Due to its economical advantage and efficiency, the oil-water displacement method has been widely used in fixed gravity based structures in the North Sea and offshore Canada. In principle, the oil- water displacement method for oil storage and offloading is simply based on the natural separation of oil and water by gravity as the density of oil is lower than that of sea water. Since the SDPSO is a floating platform, the wave induced motions of the floater may cause certain effects on the oil-water interface mixture and potential pollution risk in the water discharged into the sea when the sea water is displaced out by oil in the storage tank. This paper will discuss typical process flow diagrams (PFD) of the oil storage and offloading systems of the SDPSO and provide a new system design which not only retains the advantages of oil-water displacement method for oil storage and offloading, but also eliminate the potential risk of environmental pollution from the displaced sea water discharged into the sea.