This paper reports on extensive experiments on nonlinear wave groups that evolve in a hydrodynamic laboratory over long distances (200 m) from the generation of simple bichromatic waves. The deepwater experiments show large deformations of the wave group, with large increase of wave heights, depending on the value for the quotient of wave amplitude and frequency difference. The experimental results show little dissipation and reflections are virtually absent. A very efficient and accurate numerical code based on the full nonlinear surface wave equations, which has been developed for this purpose, reconstructs the experiments and enables one to investigate the evolution over much longer distances (reported here until 1,200 m) than in the laboratory.

No abstract

For a range of offshore fields, a Dynamically Positioned (DP) Floating Production Storage & Offloading (FPSO) unit can be utilized as a first stage field development unit. The DP-FPSO design is based on a monohull floating production system with a single production riser system. The DP-FPSO can significantly reduce the time to first production, generate early sales revenues and provide valuable reservoir and production data. By utilizing a DP-FPSO during the initial development phase, subsurface risks can be reduced and a permanent production facility can be optimally designed with minimum capital investments. Compared to a conventional mooring system, a DP system provides a flexible and cost-effective station keeping solution, especially in case of deepwater applications and/or when frequent relocations of the floating facility are foreseen. Combining the best practices of designing and operating the latest generation DP drillships and FPSO's, a DP-FPSO has been developed for relatively mild environments. Results from engineering studies have shown the technical feasibility of an FPSO positioned by a DP system for relatively mild environments. This paper will present the general DP-FPSO concept and address both technical design aspects and economic issues related to the DP-FPSO. Introduction Recent advances in drilling and completion techniques have resulted in improved well system design and completion reliability. Extended reach wells, multi-laterals, smart wells producing from multiple pay-zones and a range of completion methods provide high well production rates and significant recoverable reserves per well. During the initial phase of a field development, limited or no production data is available concerning the hydrocarbon reservoir. An extended well test facility or early production facility can provide additional high-quality data related to properties of the recovered hydrocarbons, reservoir drive mechanism, reservoir pressure and temperature, etc. Based on the information provided by the early production facility, geological, technical and commercial risks related to the field development can be re-assessed and used in the decision making process when planning the full field development. With exploration and production operations in deeper water, the cost for traditional (passive) station keeping systems of floating offshore structures has increased accordingly. Hardware and offshore installation costs for a passive mooring system can be significant, especially in case of frequent relocations. A DP system provides a cost-effective and proven means of station keeping and has been extensively applied to deepwater drilling units [Ref 1]. Operating as a first-stage field development unit, the DPFPSO will enable a cost-effective means to gain valuable reservoir and production data, while generating early sales revenues. Concept Description General The DP-FPSO (Figure 1) provides a flexible and highly mobile floating production solution, suitable for a range of applications. In a remote deepwater area the floating facility allows for a stand-alone field development. The DP-FPSO is intended for extended well tests and full production operations, which might not be economic with traditional floating production systems or drillships. By obtaining critical reservoir and production data during the initial project phase, overall field development costs can be reduced significantly. The design of the DP-FPSO has been optimized with the purpose to provide maximum operational flexibility.

No abstract