Morpeth SeaStar Installation
Authors: Redfern I.J. , Calkins D.E. , Matten R.B. 
Published: October 2008

The Morpeth project included a first of its kind installation of a mini-TLP in 1670 feet of water, from the J. Ray McDermott (JRM) DB50, a dynamically positioned derrick barge. The installation made maximum use of existing equipment and was performed using conventional techniques. Large diameter, single-piece piles were upended, free-stabbed and driven to precise tolerances. Multi-section tendons were installed onto the piles in advance of the TLP hull and held in tension using temporary buoyancy modules. The TLP hull was loaded out and dry towed to site on a standard cargo barge. The hull was lifted and stabbed over the pre-installed tendons by a derrick barge. Trim adjustment of the TLP during ballasting and tendon lock-off was achieved using the hull ballast tanks and a system of control winches. Systems were used that allowed remote control of the hull ballasting and tendon tension monitoring systems from the construction vessel. The platform topsides installation was a conventional Gulf of Mexico integrated deck lift.

Introduction

Installation of the Atlantia designed and built Morpeth SeaStar TLP was performed by J. Ray McDermott under contract to British-Borneo Exploration, Inc. (BBEI).

The platform is located in Ewing Banks, Block 921, in approximately 1700 feet water depth. The production wells are located 1500 feet to the south of the platform and are tied in using flexible flowlines and control umbilicals. Steel catenary risers (SCRs) to the export pipelines leave the platform in a north-westerly direction. Fig. 1 shows a generic SeaStar TLP configuration.

The Morpeth SeaStar was installed in two phases. During the fall of 1997, the first phase pile installation was completed. Accurate water depth measurements were taken to enable the tendons to be fabricated to suit their final placement, accounting for the slight seafloor slope across the site and the final installed elevations of the piles.

The TLP tendons, hull and deck were installed during the second installation phase, in the summer of 1998. Prior to mobilizing for the TLP installation, the export pipelines and SCR sections were laid and abandoned on the sea floor. These SCRs were recovered and landed on the TLP hull, in a interim period between installing the hull and the permanent production deck.

This paper describes the TLP structure installation in detail, however, there are some key features of the process to be emphasized, namely:The installation was performed in small steps, each of short duration. This minimized weather related risks to the permanent structure(s) and installation equipment. Table 1 shows a summary of the installation durations.Minimal specialist equipment was needed to perform the installation. With few exceptions, use was made of traditional equipment and installation techniques.Unlike other (larger) TLP installations, the attendant derrick barge provided a more comprehensive range of support services. There was no permanent manning and little equipment on the TLP hull. Instead, most of the installation utilities and personnel accommodations were provided onboard DB50.Most of the specialized equipment that was developed for the Morpeth project was also configured for re-use on the Allegheny installation and other similar sized SeaStar installation projects.