A new philosophy for design and installation of lightweight satellite wellhead platforms has resulted in the development of a new and simple platform concept designed for installation by a conventional North Sea jack-up rig and a stepwise extension of the topside module depending on the reservoir requirements.
In the continuing effort to reduce overall capital cost and keep the operational cost of remotely operated satellite platforms at a minimum, various platform alternatives are available depending on the environment and infrastructure in which these satellite platforms have to be installed.
In a previous paper (ref. 1), we discussed in detail the concept and design consideration for a mono-tower platform.
Based on the ideas developed for the mono-tower, the concept of a simple and cost effective platform has since then been further expanded such that both the substructure and deck can be installed by a jack-up drilling rig instead of the more expensive derrick barges.
The first STAR (Slim Tripod Adapted to Rig) of this new generation of satellite platforms was successfully installed in August 1990, with more to come in 1991/1992.
This paper will describe the platform concept, the basis for the design, the feasibility studies and the advanced dynamic structural and lift analyses. The installation by a jack-up rig was carried out by the Engineering Department within Marsk Olie og Gas AS and the preinstalled work in connection herewith included model tests with the transportation barge, 3-dimensional maneuvering simulation and lift studies, which are all described in the paper.
The STAR concept has been developed in order to meet the requirements for a small, simple platform type suitable for shallow water in the Danish North Sea, especially for marginal fields where a stepwise development approach is desirable due to e.g. reservoir uncertainties. As the number of crane barge contractors available on the market is limited, the aim was to develop a platform concept, which apart from conventional installation methods also would allow for installation by a medium size North Sea drilling rig in connection with drilling of the wells.
The conceptual studies concluded with a tripod substructure, which consist of a center column brace supported by 3 battered skirt pile sleeves suitable for water depths in the range of 30-50 m with a total weight ranging from 450-550 tons (fig. 1).
A major design parameter for the STAR substructure was to develop a light-weight jacket with a configuration, such that the piles could be stabbed within the skidding area of the jack-up drilling rig. The problem was solved by introducing a guide system on the top bracings to guide the pile tip into the pile sleeves allowing the top of the pile to remain within the skidding area of the drill floor during the stabbing operation.
The diameter of the center column was given by minimizing the weight and the wave exposed area against the environmental loads, opposed to the structural resistance against ship impact and the maximum number of slots to be installed.
