Development of a New Self-Stable Dry-Tree GoM TLP With Full Drilling Capabilities

SBM Atlantia has developed a Dry-Tree FourStar TLP with full drilling capability for GoM applications. This paper focuses on the unique features of the Dry-Tree FourStar by considering a typical design example. The Dry-Tree FourStar TLP considered is a 100,000 ton displacement structure with a payload of approximately 40,000 tons, designed for 4300 ft water depth. Like its wet-tree predecessor, the hull geometry follows the battered column form, which leads to increased stability for quayside integration, wet tow of the integrated system, and self-supported installation. Furthermore, the large keel footprint of the hull maximizes the efficiency of the tendon system, resulting in a more economical solution. In order to enable quay side integration of the 22,000 ton topsides onto the FourStar hull, the deck is designed as three separate interconnecting modules. The Dry-Tree FourStar hull is structurally optimized for effective load transfer through the outer-shell of the structure, resulting in significantly lower hull steel densities when compared to industry standards. The design was confirmed through a comprehensive wave basin model test campaign performed at the Offshore Technology Research Center at Texas A&M University. The model tests were performed at 1:52 scale, and utilized the latest GoM MetOcean criteria. The top-tensioned risers were included in the physical model in order to provide more realistic estimates of the hydrodynamic behavior of the TLP. The model tests confirmed the performance of the GoM Dry-Tree FourStar as a stable drilling and production platform. This paper presents the development of this TLP with emphasis on the hydrodynamic and structural aspects that are unique to the concept. It discusses the observations from the wave basin model tests, including the results of a comparison with a theoretical global performance analysis.