Field Pilot of Subsea Equipment Installation in Deep Water using Fibre Rope in Two-fall Arrangement
Authors: Torben Sverre , Ingeberg Per 
Published: May 2011

This paper gives a summary of the 250Te FRDS (fibre rope deployment system) joint industry project (JIP). The background for the project is the industry's need for lifting capacity of 250Te in 3 000m of water depth as expressed, for instance, by the DISH (deepwater installation of subsea hardware) JIP. The main objective of the 250Te FRDS JIP was to develop a FRDS with an installation capacity of 250Te in 3 000m based upon a 125Te FRDS operation in a two-fall configuration, and to demonstrate through a field pilot that deepwater lifting operations can be executed safely with this system. The project kicked off in September 2006 with conceptual design of the system, based on scaling up the field-proven 46Te ODIM CTCU (cable traction control unit) based FRDS system. Building, testing of the system, installation on the Skandi Santos vessel and execution of the field pilot were conducted from October 2007 to December 2009. The field pilot consisted of a deepwater lifting test in two-fall configuration. Its main purpose was to demonstrate that combining a torque-free fibre rope with a handling system which minimises the introduction of twist in the rope solves the inherent twist problem of a steel wire system. All phases of a subsea installation and recovery operation were demonstrated with 100Te payload and empty hook operations in two-fall configuration to 940m of water depth. The test results were very convincing, with twist levels well within the acceptance criteria established for the test. This proves that combining a torque-free rope with a suitable handling system which does not introduce twist in the rope opens up for using two-fall lifting arrangements in deep water, and that a proven system with the capacity of 250Te in 3 000m is available.

Introduction

The 250Te FRDS JIP aimed to demonstrate that deepwater subsea lifting operations can be performed safely and successfully by using a fibre rope deployment system (FRDS) in two-fall configuration based on the CTCU technology in combination with a torque-free fibre rope instead of steel wire as the lifting line. This opens the way for using smaller construction vessels for heavy deepwater lifts up to 250Te, where the weight of a steel wire system disqualifies the use of this traditional solution.

Participants in the project were:Research Council of Norway/Demo 2000 (sponsShell Technology Norway (sponsStatoil (sponsAker Oilfield Services: owner of the system, and responsible for conduct of the field pODIM: JIP organiser and supplier of products and services for the field pi

The 125Te FRDS designed for two-fall operation with a lifting capacity of 250Te down to more than 3 000m of water depth was the key product for the project. In order to make a field pilot possible, this system had to be mobilised on a vessel with additional equipment for handling the test weight and the two-fall arrangement.

Aker Oilfield Services decided to purchase the 125Te CTCU system in addition to a module handling system from ODIM - Rolls-Royce. This complete system was to be placed on the Skandi Santos newbuilding for operation off Brazil on a five-year contract from Petrobras for installing Xmas trees. This vessel was considered an adequate platform for conducting the field pilot, although some additional equipment had to be provided.