Float over topside installation has become a cost effective alternative for offshore construction over the past 25-30 years, as ever-increasing integrated topside weight constantly exceeds the lifting capacity of installation vessel cranes.
The basic concept of float over installation is to transport the topside on a vessel in one piece, position the vessel over the substructure, and lower the topside onto the substructure while maintaining the position of the vessel.
While this basic principle of loadout and transportation remains the same, methods and systems used to execute the concept vary significantly, and pose numerous technical and operational challenges.
PETRONAS Carigali Sdn. Bhd. (PCSB) undertook the development of BARDEGG-2 and Baronia EOR project located offshore Sarawak, Malaysia within South China Sea. Baronia B Central Processing Platform (BNCPP-B) was installed in May 2017 and was the first PCSB's float over installation by a portable Dynamic Positioning 2 (DP2) vessel.
A Deck Transportation Vessel (DTV) was upgraded with DP2 capability by adding two portable azimuth thrusters to allow safe and efficient installation of the topside. Sea trials and annual DP trials were conducted in ensuring DP functionality and performance in compliance to Class requirement. Float over engineering was performed including float over design criteria, hydrodynamic analysis and mating analysis. All outfitting, secondary steel works and grillage structures were installed on the vessel before mobilization for transportation and installation of BNCPP-B Topside.
The operation required high precision engineering and execution considering the close proximity between BNCPP-B Topside and existing BNQ-B platform during the vessel approach towards BNCPP-B Jacket. Additional control measures were taken for safe execution. DP checks were conducted at certain intervals while approaching the jacket. BNCPP-B Topside installation commenced at first daylight on 22 May 2017 and successfully completed by noon.
It has again proven that float over installation by portable DP2 vessel was technically feasible and would be an example for future projects undertaking the same approach. Having a vessel with portable DP2 system will help to optimize the vessel utilization and improve overall project cost.
This paper aims to highlight the float over methodology for BNCPP-B topside 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.