The Hutton TLP: A Preliminary Design

Abstract

Summary This paper presents a preliminary design for a tension leg platform (TLP) to develop the U.K. Hutton field. A platform (TLP) to develop the U.K. Hutton field. A structural design is described with results of performance analyses and model tests. Designs of the facilities, the tension leg system, the foundations, and the well systems also are included. Introduction The TLP that is being designed for the U. K. Hutton field will support all functional requirements for drilling, oil production, personnel accommodation, and ancillary production, personnel accommodation, and ancillary services. The Hutton field lies 144.8 km (90 miles) northeast of the Shetland Islands in 147-m (482-ft) water depth.The TLP is a floating structure connected to anchors fixed in the seabed by vertical mooring lines (tension legs) at each corner of the platform (Fig. 1). These vertical mooring lines virtually eliminate the vertical plane motions of heave, pitch, and roll, while the lateral movements in surge, sway, and yaw are compliantly restrained. Buoyancy is provided by the vertical columns and the horizontal pontoons connecting the bottoms of these columns. An excess of buoyancy greater than the platform weight keeps the mooring lines in tension for all platform weight keeps the mooring lines in tension for all weather and all loading conditions. Column height is sufficient to support the deck above the wave crest elevations for all tide and wave conditions when the TLP is fixed to the seabed foundations by the tension legs.The TLP is installed permanently in the sense that it can resist the effects of extreme environmental conditions and continue operations in the same manner as conventional fixed platforms. The fabrication, outfitting, hookup, and commissioning of the facilities can be completed in onshore fabrication yards and/or inshore completion sites. All components are designed for a minimum of 20 years' service life. Key components such as tension legs and well riser tensioners are simple and intrinsically reliable, have backups, and are replaceable for inspection and maintenance. Individual well risers connect each well to the TLP. These individually tensioned risers safely and reliably withstand the effects of extreme environmental conditions without the need to be disconnected.In the early 1970's, a team of Conoco engineers analyzed subsea production systems for deep water. As a result, they recommended that designs be developed to provide above-water platform space to accommodate provide above-water platform space to accommodate drilling and production facilities in deep water. The tension leg platform was recognized as a potential system with a cost that should be relatively insensitive to water depth. An intensive study concluded that this concept was feasible and could be designed to be reliable.As a consequence of these studies, another in-depth design study was carried out in 1977 on the application of a TLP for development of the Hutton field. In addition, the application of a semisubmersible early production system was investigated. Following a production system was investigated. Following a comprehensive investigation of alternative development methods, including a steel jacket structure, the team recommended the use of a TLP to develop Hutton. The development plan calls for nine wells to be drilled with a plan calls for nine wells to be drilled with a semisubmersible drilling rig before TLP installation. The remaining wells will be drilled from the TLP while previously completed wells are being produced.The development of new technology is greatly enhanced by application to a specific, real project. TLP development studies prior to the Hutton field design study necessarily included numerous alternative solutions. For example, the TLP could be anchored by a gravity base, driven piles, or drilled and grouted piles. Specific environmental conditions, water depth, and soil characteristics can minimize the consideration of certain alternatives before detailed and costly studies are made. The most feasible or preferred solution can be selected early and designers can proceed directly to detailed engineering studies. Vendor support is obtained more easily for a specific real project for which there is a visible and timely application of their effort.This paper describes a preliminary design for the Hutton TLP. JPT P. 208