Lntroduction to the Troll Project

Abstract

Abstract This paper sets the scene for six other papers to be presented at the joint Shell-Statoil session at the 1997 OTC Conference. The subject for this session is the Troll Phase I Gas ExportProject, for which A/S Norske Shell was the Development Operator, and Statoil is the Production Operator. The Troll gas development consists of an offshore platform standing in 303 metres of water connected by twomulti-phase pipelines to an onshore gas processing facility, which can export up to 100 MM Sm3 and 3500 m3 condensate per day. The paper briefly traces the history of the Troll field development from the discovery of the field in 1979, through to the establishment of the major design solutions. The first crucial development decision was to utilise on-shore gas processing, and the background to this decision is examined. In particular, the concept of utilising carbon steel multi-phase pipelines to transport the wet, untreated gas, is described. Anticipated benefits, relating to safety and environmental considerations, as compared to an integrated offshore facility, and the realisation or otherwise of these, are discussed. The offshore and onshore facilities are described, and the major design decisions that they represent are highlighted. In particular: the satisfying of the offshore power requirements from the national electrical grid and the use of variable speed electric motors for driving the gas export compressors (subjects covered more comprehensively in another paper); the provision of the necessary fibre optic link from the platform to the onshore central control room to enable the offshore facilities to be operated from onshore; the use of air to satisfy process cooling requirements and hot oil for process heating needs; the use of a High Integrity Pressure Protection System (HIPPS); the use of an semi-automated, packaged drilling rig; and the extensive use of composite materials. These features represent design decisions which, are at least to some degree, counter-intuitive, and are reviewed specifically with respect to their contribution to overall environmental and safety objectives. Introduction The Field. The Troll field is located about 85 km north west of Bergen on the west coast of Norway, (fig. 1) in the Norwegian Trench, at a water depth of 303.4m MSL. The field was discovered in 1979 by AlS Norske Shell, operatorfor Production Licence 054 covering Block 31/2. In 1983 this Block was declared commercial. Also in 1983, the adjoining blocks 31/3, 31/5 and 31/6 were awarded under Production Licence 085. Subsequent drilling ascertained that Troll extended into all four blocks (fig. 2). This initiated a process of unitisation of the two licences. By the end of 1986 the individual shares of the various companies with interests in the four blocks were recalculated for Troll as one single field. The shares of the Troll Partners were established as follows: (available in full paper)