Arthit Field Development: Float-over Hardware Design and Issues

Abstract

Abstract The 17,500 metric ton Arthit PP topsides was successfully installed in December of 2007 in the Gulf of Thailand after a short voyage from Batam Island, Indonesia, where the topsides was fabricated. The topsides was installed in one piece using the float-over method. Three types of hardware components were designed and fabricated to facilitate the float-over. One type supported the topsides during the loadout, transport and float-over. The second type provided the interface between the topsides legs and the jacket. The third type was mounted on the pile tops and provided landing receivers for the topsides legs and final leveling and joining features. The design, fabrication, and operation of these three components will be discussed in this paper. The float-over hardware components are designed to suit the " loose slot method?? of topsides float-over installation and rapid ballasting system of the transport barge. Arthit PP topsides float-over experience shows that float-over hardware components can be designed and implemented for offshore installation of large topsides. Introduction The installation of single piece, large-sized topsides by float-over method is a cost effective alternative since it minimizes offshore hook-up and commissioning. Various float-over methods and associated challenges are described in paper OTC 19072 by Seji and de Groot (2007). Installation of large topsides tends to produce large mating forces and relative displacements; thus placing high design requirements on sub-structure and topsides. A means of facilitating rapid separation of transportation vessel from underside of the topsides was vital for a successful float-over. The float-over hardware is essentially provided to reduce mating forces, accommodate large relative displacements, provide effective cone capture mechanism, and facilitate rapid separation of transport vessel and topsides. During recent float-over installation of Arthit topsides, the transport barge was not guided by bumpers mounted on the jacket during the barge entry and exit from the jacket " slot??, or during the actual float-over operation. The mean position of the barge was controlled by a primary mooring system fixed to the sea floor plus a tug during entry and exit. In the float-over position a secondary mooring system of soft lines was designed to connect the barge to the jacket. The barge orbited in the slot without touching the jacket. This float-over concept is called the " loose slot method?? and is described in paper OTC 19230 by Kocaman and Kim (2008). This concept is the preferred method at J. Ray McDermott (J. Ray) since it minimizes barge contact with the jacket during slot entry and exit. A rapid ballasting system was installed in the transport barge Inermac 650 during a dry-dock. The system is designed to separate the barge from the topsides in less than twenty minutes (OTC 19231, Kim et al, 2008). The rapidity of the ballasting reduces risk level during the float-over operation.