The Vertically Moored Platform for Deepwater Drilling and Production
Authors: Berman M.Y. , Blenkarn K.A. , Dixon D.A. 
Published: December 2007

The general configuration, motion characteristics, and basic design principles of the vertically moored platform (VMP) are described. Two principles of the vertically moored platform (VMP) are described. Two example designs are presented with a description of fabrication and installation; cost estimates also are presented. The VMP is a feasible and practical structure for developing deepwater fields and has distinct practical structure for developing deepwater fields and has distinct structural and operational advantages.

Introduction

While the pace of development has not been as rapid as anticipated a few years ago, the oil industry clearly is moving ahead with exploration and production in deepwater offshore areas. Several exploratory wells have been drilled in water deeper than 3,000 ft (914 m), and the need for production facilities will increase. While a number of different systems are being developed for these deepwater areas, the attraction of surface completion stations remains strong. This paper describes such a system, the vertically moored platform (VMP), and stresses the development efforts, system design, fabrication and installation procedures, and estimates of the costs and time.The VMP is basically a semisubmersible-type floating platform that can be used to support drilling and platform that can be used to support drilling and production in deep water. An overall perspective of the production in deep water. An overall perspective of the VMP is shown in Fig. 1; Fig. 2 presents a front elevation. The basic components of the VMP are (1) the deck; (2) the jacket structure, which provides the excess buoyancy to maintain the risers in tension; (3) the structural risers, which serve to keep the platform on station, (4) special riser spacer frames, which mitigate any potential flutter effects of the riser as well as facilitate installation; and (5) the ocean floor template, which is nonstructural in nature and serves as a guide for installation and drilling.The flexibility of the structural risers allows the platform to surge under environmental loadings and thus platform to surge under environmental loadings and thus avoid large structural forces; in essence, the platform resists only mean environmental loads. The surge and sway of the platform are similar to those experienced by floating drilling vessels, however, the structural risers effectively eliminate heave, pitch, and roll motions.The structural riser system is the key element of the VMP. This riser system allows the wells to be drilled and produced through the structural risers. The structural produced through the structural risers. The structural risers themselves are connected to the drive pipe and conductor system. which is cemented into the seafloor formations. After the risers are installed, wells can be drilled with the blowout preventer on the structure. After completion, the Christmas trees are located on the lower deck. The wellheads do not move in relation to the deck structure; constant tensioning devices or flexible piping are not required. Therefore, one main advantage of the VMP is that drilling and production are performed the same way as from a conventional fixed structure.

Background

Studies initiated by Amoco Production Co. and Amoco International Oil Co. in 1966 to define deepwater production concepts identified the VMP as a feasible and production concepts identified the VMP as a feasible and attractive system. Later, the dynamics aspects of the platform were reviewed and a number of wave-basin platform were reviewed and a number of wave-basin model tests also were performed. A computer program was developed to predict platform motions, calibrated against the model tests. Feasibility studies were performed to define fabrication and installation techniques. performed to define fabrication and installation techniques. JPT

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