Advanced Deep-water Soil Investigation at the Troll East Field

Abstract

Norsk Hydro, Saga Petroleum and Statoil are operators for the Troll East Field, one of the largest offshore gas fields in the world. The field is situated in the Norwegian Trench in water depths of 300 to 330 m. Figure 1 shows the location of the Troll East Field. This field is planned to come into production in the mid-1990s. The development of Troll East Field in deep water with soft sea-floor sediments presents a new engineering challenge in the North Sea. Because of this, present engineering feasibility studies encompass a wide range of platform concepts, including both gravity-base and piled structures. All concepts require a comprehensive knowledge of the soil conditions to evaluate their feasibility. Norsk Hydro have been responsible for the geotechnical aspects of site investigation and, in 1983, a preliminary soil survey was carried out which served as a basis for detailed planning of a major 1984 soil investigation described in this paper. The Norwegian Geotechnical Institute (NGI) was awarded the main geotechnical contract for this investigation, with McClelland Ltd sub contracted to perform sampling and in situ testing. Anton von der Lippe’s soil survey ship Bucentaur was chartered for drilling. Racal Survey provided positioning services. Stressprobe Ltd performed pressuremeter testing. This paper describes the planning of a technically advanced soil investigation which in several aspects represents the state of the art. Offshore soil investigation equipment and procedures are then described and results of in situ and laboratory tests are presented. Finally, operational performance during the fieldwork is discussed.