RIASSUNTO
Abstract
The Penguins Field is located in the most northern waters of the United Kingdom Sector of the North Sea, approx. 250km NE of the Shetland Isles, Scotland. The pipeline comprises 66km of Pipe-in-Pipe (PIP) in water depths peaking at 170m. The HT/HP pipeline navigates a sinuous route through boulder fields, isolated rock embedment and clay outcrops, around subsea facilities and over several crossings, in regions subject to moderate fish trawling activity.
The highly insulated PIP system was installed in a snaked configuration to achieve significant CAPEX reduction over the very few viable alternatives, such as trench and rockdump. The snakelay design pre-determines a lateral buckling response that relieves the high expansion forces in the operational pipeline, whilst controlling the level of combined loading the PIP system experiences.
The DNV 2000 Limit State design code was utilized in conjunction with the HOTPIPE Guideline to demonstrate pipeline system robustness. The HOTPIPE Guideline is not currently in the public domain, but the principles adopted therein are described in public domain papers.
This paper describes the Detailed Design process for the PIP system, and outlines the associated testing programs. The main emphasis will be given to the application of snaked lay technology, which enabled accurate pre-setting of the lateral buckle initiation sites, as evidenced by the post-operational surveys of the pipeline.
This successful application of PIP snaked lay will help bolster industry confidence at a time when the number of potential subsea applications of this technology is increasing.
Introduction
Field Description and Layout. The Penguins field is a subsea satellite that is 66km north of its host, the Brent Charlie (Brent C) platform, in the Northern North Sea. Its location relative Scotland and Norway, is shown in Figure 1.
The cluster of four fields was developed using five subsea drilling centers (DCs). Manifolds are positioned at four of them. A single production pipeline is used to tieback the DCs in a ""daisy-chain"" to the BC platform, crossing two umbilicals, three operational pipelines and one decommissioned pipeline. The pipeline consists of two PIP sizes: 10.75""/16"" between DC2 & DC3, and 16""/22"" from DC3 to BC, via DC4 & DC5.
Figure 1 Penguin Field Location (Available in full paper)
An Overall Heat Transfer Coefficient (OHTC) of 0.7 W/m2K was specified as a target for the 66km PIP System. This was part of the flow assurance strategy for management of field shutdown and start-ups to limit temperature decay for a given shutdown period. It was also related to wax (which may become a concern towards the end of the field life) and hydrates (the formation region is approached during the last few years of production).
As well as providing electrical and hydraulic power, the 6"" umbilical routed from Brent C to the subsea manifolds has provision for methanol, corrosion, scale, wax, and asphaltene inhibitors, to meet whatever needs may arise for field flow assurance.