In the present phase of the Shell ETAP (Eastern Trough Area Project) development, all pipelines and umbilicals are routed in parallel along a corridor from the Heron subsea manifold via the Egret and Skua manifolds to Marnock CPF (Central Processing Facility). They consist of two 10" pipe-in-pipe lines for production transport to the CPF, one 6" pipeline for transporting wash water for well annulus injection from the CPF, and one (sectional) umbilical for control and communication, electrical power and hydraulics and chemical injection. The product pressure (CITHP) is 613 barg and the temperature is up to 160°C at the wellhead. Due to the arrival temperature and cool down criteria, the pipelines need to be thermally insulated. A pipe-in-pipe system was selected as the preferred insulation for the design of the Heron Cluster, due to the limitations of traditional insulation coatings. The pipe-in-pipe system incorporates a 10" diameter production pipeline insulated inside a 16" jacket (outer) pipe. The Shell ETAP Project carried out extensive analytical work and research and development in order to validate the design, develop specifications for purchasing, fabrication and installation. The insulation and pipeline design in some respects go beyond previously established technology. This paper discusses in detail critical aspects of the design and construction of these pipelines, but in particular, the production pipelines that are designed to cater for high pressures and temperatures.
ETAP is a UK Central North Sea development comprising up to seven oil fields, as shown in Figure 1. Shell/Esso are the licence owners of three of the satellite fields, Heron, Egret and Skua, which collectively make up the Heron Cluster fields, located in a water depth of approximately 95m. The development of the Heron Cluster fields is through completion of up to 10 wells.