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ABSTRACT Worldwide, operators are focusing efforts on deep water prospects in their search for new oil and gas discoveries. In the US Gulf of Mexico, Tension Leg Platforms (TLP) are drilling and producing in 800 meters water depth and developments in even deeper water are underway. Current TLP technology can be extended to approximately 1,500 meters, but in order to make developments at such water depths (and deeper) economical, new and innovative solutions are required to reduce costs and shorten development schedules. The 3 column TLP design described in this paper satisfied such requirements. The concept features a simplified and cost effective tendon system and a modularized deck design utilizing a ‘splash zone truss’. INTRODUCTION The concept presented is based on approx, 10,000 man hours of conceptual study work carried out over the last two years in close cooperation with Saga Petroleum. The work was focused on an 800 meters water depth Norwegian North Sea harsh environment case (ref. Table 1), but the feather of the 3 column TLP discussed in this paper are generic and applicable to almost any deepwater region worldwide. The first half of the paper gives a general description of the 3 column TLP concept, including deck structure, hull and tendon system. Comparisons to conventional 4 column TLPs arc made, where relevant and advantages and savings quantified. The second half of the paper discusses the global performance and hydrodynamic aspects of the 3 column TLP including major findings of a recently completed model test. Lastly, the relevance and validity of the main features of the 3 column TX-Pis discussed for application in other geographical regions. Cost Drivers. In an attempt to few the attention and effort in areas where the largest cost savings could be achieve the development work initially concentrated on identifying the main deep water TLP cost drivers;The hull size is a primary cost driver as it governs both the tendon system design and hull structural weight, The hull size is dependent on the topside load, tendon pretension and hull weights.The TLP tendon system cost increase with water depth, so hull optimization with respect to tendon responses and tendon pretension becomes important.For the TLPs installed in the Norwegian North Sea to date (Snorre and Heidnm), the tendon top/bottom connectors and installation teds represents approx. 70 % of the total tendon system cost. This percentage decreases for deep water, but a simplified tendon design still has a significant potential for cost savings.Important cost drivers for the TLP installation are the requirement for heavy lift barges with deep water station keeping capability, the tendon deployment duration, and the need for specialized tendon installation aid. |
