BP Marlin: First Flexible Pipelay With Newbuild Deepwater Pipelay Vessel
Authors: Lecomte Hubert , Hogben Stan , Smith Jim , Bednar John , Day Jon , Palmer Mike 
Published: October 2008

This paper describes the design and installation of two 6" high pressure / high temperature flexible pipes in the Marlin field, Gulf of Mexico. These flexible pipes connect the Marlin subsea development to the Marlin TLP one mile away, in 3,400' of water. The new build pipelay vessel CSO Deep Blue performed its first flexible pipe installation on this project.

Introduction

The Marlin field consists of two wells, located approximately one mile from the Marlin TLP (see figure 1) in 1,000 m (3,400') of water, located in block Viosca Knoll 915.

As shown on figure 2, "General Arrangement" and figure 3, "Subsea Field Layout", two 6" flexible pipes connect the TLP to the Marlin field. Each flexible pipe is fitted with a Pipe Line End Termination (PLET). Rigid spool pieces, with vertical collet connectors, link each PLET to one Xmas tree, and provide a pigging loop between the two PLETs. Both trees are controlled from the TLP through a single umbilical.

At the platform end, the dynamic risers follow a free hanging catenary configuration. The riser top is hung off in a retrofitted cassette at the upper deck level.

The installation of the flexible pipes was scheduled in two separate installation campaigns (phase 1 and 2), with the first pipe installed and commissioned in November 2001, and the second scheduled for April 2002.

Both campaigns were performed or planned with the new build pipelay vessel, CSO Deep Blue. Therfore, all installation procedures had to be fully engineered, and were extensively tested before actual installation.

The first campaign was to be performed as a flyby, with the vessel returning from working in another GoM field upon completion of one of its rigid pipelay trips. As such, vessel availability was dependent on the schedule of this other major project.

This paper describes the challenges specific to this project, combining the use of a new vessel spread with a fast track schedule, and how they were safely met. These were:Stringent pipe specifications, with high temperature, high pressure service.A two month period for the entire preparation of the offshore work for the first campaign.A two day notice for vessel mobilization.Use of a new build vessel, with all new installation equipment and machinery, for the first campaign.

Flexible Pipe Design

Each line is composed of a 1,000 m (3,300') static flowline section, and a 1,350m (4,400') dynamic riser section of a different construction, which accounts for dynamic effects and ensures the required service life in operation. The flexible pipes for phase 1 and 2 were designed and built by two different flexible pipe manufacturers. Specifications for the design of the pipe for phase 2 were more stringent than those for phase 1.

Specifications (phase 2).

The pipe for phase 2 was designed according to the specifications shown in Table 1:

Table 1: Pipe Specifications(Available in full paper)

The design was performed per API 17J 2nd edition, with allowable stresses and strains in accordance with the more stringent requirements of API 17J 1st edition.