The Seastar Tension-Leg Platform

ABSTRACT The Seastar Tension-Leg Platform (TLP) family has been developed to unlock the economic potential of discovered, but as yet undeveloped, deepwater fields in the Gulf of Mexico and around the world. This new generation of deepwater platforms combines the well-proven technology of TLP's with industry accepted shallow water marginal field practices. The designs have been developed, over a four-year period under the sponsorship of the U.S. Department of Energy. This paper describes one Seastar platform design and illustrates typical Seastar applications. INTRODUCTION Atlantia conceived the Seastar design, and together with subcontractors, developed this technology under funding received from the U.S. Department of Energy. The primary engineering subcontractors were Han- Padron Associates (HPA) and Offshore Systems Analysis Corporation (OSAC). Other important contributions were made by American Bureau of Shipping, Marine Pipeline Consultants, A13B Vetco Gray, Amfels, Gulf Island Fabrication, Applied Drilling Technology, and OPI. In water depths up to about 300 R, in regions where other oil and gas production operations have been established, successful exploration wells drilled by jack-up drilling rigs are routinely completed and produced. Such completion is often economically attractive because bottom founded structures can be installed to support the conductor pipe left by the jack-up. Moreover, in a region where production operations have already been established, available pipeline capacities are relatively close, making pipeline hook-ups economically viable. Significant hydrocarbon discoveries in water depths over 300 R are typically exploited by means of centralized drilling and production operations that achieve economies of scale. These central facilities are costly and typically require up to five years to plan and construct. To economically justify & such central facilities, sufficient producible reserves must be proven prior to committing to construction. Depending on geological complexity, the presence of commercially exploitable reserves in water depths of 300 R or more is verified by a program of drilling and testing a number of expendable exploration and delineation wells. Conventional deepwater technology is based on achieving economies of scale in which a high "fixed" component of cost-the deepwater platform-enables the unit "variable" component of cost-drilling and completion of wells-to be low. Existing deepwater technology is therefore suitable for fields with many wells, but not for many discovered smaller fields, each of which require few wells. Seastar uses proven components and techniques in a new configuration that reduces the platform cost by an order of magnitude, while keeping total variable cost low. A Seastar platform has application as a full production platform on fields having smaller reserves or as an auxiliary, satellite, or early production platform for larger deepwater discoveries. Specifically, the platform can, 1) help oil companies determine the reservoir characteristics before committing to full field development 2) function as a gathering and control platform for subsea wells distant from a host platform, and 3) add future deck area and payload capacity near an existing platform.