Abstract

Topsides float-over installation is not new in the industry but the method and technology in executing the float-over operation varies and keep improving to increase project efficiency and cost effectiveness. Each method comes with own technical and operational challenges which determine its feasibility and suitability for the project.

A Deck Transportation Vessel (DTV) was upgraded with DP2 capability by adding two portable azimuth thrusters to allow safe and efficient topsides float-over installation. Sea trials and annual DP trials were conducted in ensuring DP functionality and performance in compliance to Class requirement.

The operation required high precision engineering and execution considering the close proximity between topsides and existing living quarters platform during the vessel approach towards the Jacket. Additional control measures were taken for safe execution. DP checks were conducted based on certain intervals while approaching the jacket. The topsides installation commenced at first daylight on the 22 May 2017 and successfully completed by noon.

This paper aims to highlight the float-over methodology for the topsides using portable DP2 vessel and the technical challenges for offshore execution. The activities during the float-over operation, analysis and simulation methods are also presented in this document. This paper should be an interest to those who will perform the offshore installation via float-over method utilizing Portable DP Vessel.

Introduction

PETRONAS Carigali Sdn. Bhd. (PCSB) undertook the development project located offshore Sarawak, Malaysia within South China Sea. Transportation & installation scope of the Central Processing Platform (CPP) topsides include transportation of the topsides weighing approximately 15,500 MT by Deck Transportation Vessel (DTV) from fabrication yard in Korea to offshore Sarawak and performing topsides installation onto the pre-installed substructure.

The platform location is within a field complex, which limit the operation if an anchored barge is used. Avoiding mooring system barge is essential due to limited gap of only 5m between topsides and existing nearby platform for the operation. There are also other marine vessels within neighboring platforms performing simultaneous activities, which potentially introducing risk of vessel clashing should anchored barge is being used. Float-over is a weather restricted operation, hence option with shorter duration float-over method is required. Considering the above constraint, a DP2 vessel was proposed for the float-over installation of the topsides.

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