The era of the low oil price makes all key players to establish the distinct business and technical strategies from the past successful models of offshore plant for better construction and operation. This paper describes design features of a single deck topside and wide beam hull concept for large new-build FPSOs in West Africa. The single deck topside is a common concept in the platform of small production capacity, while it is not applied to large new-build FPSOs. Generally, multiple deck topside has been introduced to large FPSOs to carry a lot more equipment within allowed footprint area. But, it has caused heavy structural reinforcement and complicated layout in topside. To overcome this shortcoming in Large FPSOs, our approach increases the hull deck area, mainly by the breadth more than conventional vessel. Equipment is grouped by the functional similarities and arranged on larger main deck. Other fitting and less heavy equipment may be located on the self-supporting structure. The major piping route, valve location and topside structure are also verified. Combination with mega-block modules could enhance the benefits of this concept, especially in saving the execution time and obtaining the design flexibility. Further, it creates more value of the maintainability by open overhead access to the main equipment, not compromising the safety. Initial hull sizing is carried out in terms of optimizing weight and motion characteristics. Several barriers are reviewed for realizing the single deck topside and wide beam hull, based on the previous experience. Finally, the benefit of this concept is validated by the 3D modeling. In this paper, the main findings and further discussion points from the study are addressed.
Standardization of offshore platforms is refocused to reduce costs and accelerate project delivery times. Some components or modules of offshore platforms are tried to be standardized in industry. There are also applications to use a standard platform itself. This paper describes the standardization of FPSO hull with 2MMbbls storage capacity for West Africa. The FPSO hull in West Africa is better to be standardized than ones in other sites, for most of new-build FPSOs in the world are in West Africa and many of their storage capacities are 2MMbbls. In design procedures, we focus on the selection of design basis and the design of hull configuration, tank arrangement and midship section. As a result, a standard model of FPSO hull is presented. For the standard model of FPSO hull to be competitive in West Africa, it could satisfy the requirements of this region. The past new-build FPSO projects in West Africa are investigated to premise the design basis such as the environmental conditions, topside weight and module layout, storage capacity, motion criteria, etc. Systematic procedures for each design items are presented in this paper. Firstly, the generic topside modules and their weight distributions are suggested. Initial hull sizing is carried out in terms of hull weight and motion characteristics. Hull bow and stern shapes are designed to achieve the towing performance for resistance and directional stability. Tank capacity plan, intact/damage stability and rule scantling for midship are checked for the design of hull configuration. The design procedure for hull sizing is automated with an optimization tool which provides Pareto-solutions to designers. Final standard FPSO hull has less weight and satisfies the general requirements in West Africa. The design procedures in this paper are applicable to early stage of field development and could correspond flexibly to various offshore fields.
The purpose of a gravity anchor is to moor the installation barge affected by the environmental condition during installation at the offshore site. It is important to obtain the sufficient holding capacity to prevent the anchor from dragging. There are several methods to enhance the holding capacity such as increasing its self-weight or attaching the shear key at the bottom of the gravity anchor. However, increasing the self-weight of gravity anchor is a constrained approach due to the limitation of handling equipment capacity. Therefore, it is necessary that the shear key design should be optimized to maximize the holding capacity under limited handling equipment. In this paper, reduced scale model tests simulating rock condition mixed by sand, cement, and water are performed. The actual offshore mooring condition is simulated by using towing carriage. Five types of gravity anchor models which have different shear keys are assessed to examine what type of the shear key is the optimum design. The optimum shape and the number of shear keys for maximizing the holding capacity are assessed through this study. The results of this study can be utilized to design the shear key of gravity anchor.
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