The Heidrun Field:Oil Offtake System

Abstract

Off take of oil from the Heidrun field is achieved through a Direct Shuttle Loading (DSL) system. This approach eliminates the need for an intermediate storage facility, allowing continuous production and transfer of oil directly from the Heidrun TLP to shuttle tankers. Purpose-built or appropriately converted tankers with an integral bow turret locate and connect to a Submerged Turret Loading (STL) buoy which functions both as a tanker mooring point and a termination for the flexible offloading line. The system is designed to permit the tankers to remain connected during loading and to disengage km the STL buy on completion of loading in all weather conditions up to and including the 100 year storm. This paper describe a implementation of the Heidrun DSL system from conception to first oil. It gives the background for choosing the DSL system and information on the data generated to support the selection process. Design, fabrication and installation of various components are explained to give an sight into the challenges that had to be overcome for realization of this 'first-of-its-kind' system in a record time of about one year Installation of the complete DSL system in the summer of 1994, approximately one year ahead of the original plans, mabled full scale in situ testing of the system with a purpose modified shuttle tanker. The two-month program provided the equivalent of one year of operational experience with the system before first oil. The paper addresses data obtained during the full scale testing, and comparison with analytical results. The operation of the Heidrun DSL system is also described, These data together with the experience gained during realization of this bold concept will give key information on how such a concept can be effectively applied to any major or marginal field development scenario either as an off take system or in conjunction with an FPSO/FSO. Introduction The DSL represented a method of offloading oil which required a bold decision for its implementation for a major development like Heidrun. When in summer of 1992 Conoco decided to use this concept for Heidrun, the STL technology was still in it a infancy and had not advanced beyond the preliminary design stage. Nevertheless, the idea was promising and offered potentially substantial cost savings when compared with other alternatives. However, the 'first-of-its-kind' and uninvolved nature of the STL technology, combined with the extremely tight schedule for its implementation, presented the Conoco Project Team with a formidable challenge. An STL system was used for the first time in October 1993, albeit in a permanent connection mode, for the UK Fulmar field. Some Fulmar experience was useful, including the marine operation aspects, in service data, etc. which led Conoca to adopt a modified approach to marine operations and very rigorous testing and trial programs for implementation of the Heidrun DSL system.