Heidrun TLP Titanium Drilling Riser System

Abstract

Abstract The Heidrun TLP drilling riser system has been designed and fabricated using a titanium alloy for the riser pipe body arid flanges, the booster line and the fasteners. This is the first use of this material in this application. The process described in this paper includes several engineering stages, a materials qualification and testing stage and the fabrication stage, all of which took place over a four and one half year period. The use of titanium for the riser allowed the optimization of associated components of the system; the tensionless, the sub sea wellhead and drilling connector and the surface handling systems which resulted in considerable weight and cost savings to the Heidrun Project. At the time of this writing the riser has not been used in service from the TLP, but has been used in both factory acceptance testing of the various components and through an extensive system integration testing program which involved both surface and sub sea trials. This paper describes these processes and highlights several design innovations and key leanings about the use of titanium in an offshore drilling environment. Introduction The Heidrun field was discovered in 1985 and is located in the Norwegian continental shelf, blocks 6507/7 and 6507/8 of the Haltenbenken area. These blocks were awarded to the operators, Conoco Norway Inc. and Statoil in 1984 and 1986, respectively, in the license rounds for production licenses numbers 095 and 124. The Tension Leg Platform (TLP) location is 65 19'33" North, 0719'03" East in a mean water depth of 1132 ft. (345 m) re. Figure 1. The Heidrun field consists of three main producing reservoirs with total estimated recoverable oil reserves of more than 750 million barrels (120 million m') and around 1,800 billion standard cubic feet (50 billion Sm') of gas. The Heidrun Field is currently the most northerly development on the Norwegian continental shelf and weather conditions are extremely hostile. During design and development of the Heidrun TLP, Conoco Norway Inc. utilized previous experience and expertise gained from the Hutton TLP in the UK sector, located in a water depth of 482 ft, (147m) and the worlds first TLP, and the Jolliet Tension Leg Wellhead Platform (TLWP) in the Gulf of Mexico, located in a water depth of 1759 R. (536m). The Heidrun TLP is the worlds first concrete TLP and has a total displacement of 290,621 T. The Heidrun drilling and production template has 56 well slots, 8 export-import riser tie-in porches, 8 dual-purpose slots, measures 176 × 125 × 20 fl. (51 × 38 × 6m) and weighs 2290 tones, re. Figures 2 and 3. Well slots are positioned at 9.84 ft. (3m) centers minimum and the overall system is designed for simultaneous drilling and production. Ten TLP wells were pre-drilled and partially completed prior to installation of the TLP, the drilling of the remaining 46 wells requires a high pressure drilling riser and are being performed subsequent to the TLP installation. The 7" (177.8 mm) well completions are performed through the 10-3/4" (273 mm) OD production riser.