Application of Dynamic Positioning Float-Over Technology to HZ25-8 DPP Topside Installation

Xu, Nan (Offshore Oil Engineering Co. Ltd.) | Qin, Licheng (Offshore Oil Engineering Co. Ltd.) | Wang, Yisheng (Peking University)

OnePetro 

ABSTRACT

This paper presents the nonlinear time-domain mating simulations and their major findings successfully applied in designing the installation devices and selecting the dominant design parameters, thus ensuring the successful execution of the DP floatover installation for the HZ25-8 DPP integrated topsides. It is essential to correctly and accurately model the jacket flexibility, fender gaps, nonlinear fender stiffness, as well as the contact mechanism and high nonlinearities of the elastomeric elements in LMUs and DSUs, etc., and therefore obtain reliable and repeatable design maxima. The analysis of the results meet the design requirements, and successfully completed in May 21, 2014.

INTRODUCTION

Float-over is an offshore installation method which describes the operation of transferring the integrated topside onto a pre-installed jacket by float-over vessel’s ballasting system and tidal change, it’s first introduced in year 1983 and applied on the installation of topside of Phillips Maureen Project. Refer to He et al. (2011) for details. Since then many float-over concepts have been successfully applied on fixed platform even floating platform. DP float-over describes the float-over operation by maneuvering the DP vessel entering the jacket slot and holding station during weight transfer without the aid of moorings. Refer to Brink et al. (2011) for details.

Dynamic positioning float-over technology is a new type of float-over installation technology combined with dynamic positioning system and float-over installation technology. Refer to Johan et al. (2011) for details. It uses barge transport platform topside into the jacket slot installed, implements barge loading adjustment, tide level and other ways to transfer the topside weight during the installation process. In the meantime, it is supplemented by fender components to complete installation technology of topside and jacket docking operation. But the biggest difference is that does not require the mooring system positioning and auxiliary tug traction, which saves costs and preparation time of manufacturing, installation and use of these devices and structures, and it does not need the large floating crane and cooperation of professional personnel when installation. The main advantage of the differences are: (1) DP float-over installation can resist worse offshore work condition and increase weather window of construction operation, which can effectively guarantee the time limit of topside installation schedule requirements. (2) DP float-over installation operation eliminates the arrangement and connection of mooring system, and its cost will not increase with the increase of water depth. (3) The DP vessel in the installation process has good ballasting ability and precise docking ability, which is easier to meet the weather window needed, especially suitable for the South Chinese sea under harsh environmental conditions. (4) The DP vessel has the ability of self-propulsion, which saves the ship sailing days and is higher safety. During the installation process of float-over, there is no need of the assistance of tugboats, which saves the cost of ship. Analysis of DP float-over installation is complex, which needs to design a docking fender system to analyze the DP capability. Refer to Xu et al. (2011) for details.