Features of the State-of-the-art Deepwater Offshore Basin
Authors: Buchner B. , Wichers J.E.W. , de Wilde J.J. 
Published: October 2008

Reliable model testing for deep water requires the controlled modeling of wind, waves and current in time and space to achieve a realistic and well-defined offshore environment in the model basin. In the paper the development of the new state-of-the-art deepwater Offshore Basin of the Maritime Research Institute Netherlands (MARIN) is discussed as a case study in this field. The results of investigations on the current generation system and wave absorbing beaches are presented in the paper. Solutions for ultra deep water testing (water depth&gt;1000 m/3000 ft) are also discussed. Three main solutions are available: ultra small scale testing (1:&gt;100), passive equivalent mooring systems or active equivalent mooring systems. The last two options are preferred and both are based on an integrated approach of model tests and numerical simulations.

Introduction

With the increased activities in the exploration and production of oil and gas in 1000–3000m water depth, the offshore industry enters a challenging phase. New and adapted concepts for exploration and production systems are to be developed. This brings also new challenges to hydrodynamic offshore research. The aim of this research is to support the hydrodynamics aspects of the design and safe operation of economical offshore structures. These hydrodynamic aspects development are numerous in the different stages of deepwater field: from Dynamic Positioning (DP) during drilling, through complex installation operations, to the behavior of all types of production facilities (FPSOs, TLPs, SPARs) in survival conditions. Hydrodynamic problems relate to the overall system behavior, but also to local effects such as Vortex Induced Vibrations (VIV) of risers. The correct prediction of this type of behavior during the design of the structure is of vital importance for the reliability and operability of the structure. Taking into account the large investments and risks related to deepwater field development, hydrodynamic research has a small, but important, role. This role requires reliable hydrodynamic prediction techniques in the design stage.

With respect to these techniques, there is sometimes a tendency in the offshore industry to present model tests, numerical simulations and full scale measurements as opposite to each other. Some then favor a solution with model tests, whereas others promote the use of numerical simulations or full scale measurements. However, if we consider the problems in offshore hydrodynamics carefully, it will be clear that they are complementary. Model tests, numerical simulations and full scale measurements all give important inputs to the design of offshore structures. They should be used to support each other, rather than to use only one of them or to use their results separately. Deepwater developments require an integrated approach, as discussed extensively in Ref. 1.

The present paper focuses on the requirements for reliable model testing for deep water. The development of the state-of-the-art deepwater offshore basin presently under construction at the Maritime Research Institute Netherlands (MARIN) will be used as a case study. First the main features of this Offshore Basin are presented. Second the requirements for the accurate generation of wind, waves and current are discussed in more detail. In the third part of the paper the results of investigations on the current generation system and wave absorbing beaches will be presented. Finally solutions for ultra deep water (&gt;1000 m/3000 ft), when even the deepest model basins are not deep enough at the usual model scales, will be presented.