THE TOP DOWN RISK MANAGEMENT SYSTEM OF THE OFFSHORE OPERATIONS OF THE EKOFISK PROTECTIVE BARRIER

摘要

The Ekofisk Field in the centre of the North Sea is a very important junction in the oil producing and transporting North Sea network. In 1987, the wave loads on the Ekofisk Installations had become unacceptable, due to a significant seabed subsidence. In order to cope with the increased wave loads, it was decided to build a Protective Barrier around the central Ekofisk Storage Tank. This barrier was to be installed in two separate half units, which were to be brought to the Ekofisk Field in floating condition. After installation, the two halves were to be structurally connected. The paper deals with the overall risk management of the total offshore operations, including tow-out, installation, coupling and completion. The operations were governed by conflicting requirements with respect to relevant aspects like stability, strength, stiffness, weight, geometry and were perceived to be extremely risky due to the marginal resistance against the expected load cases. The operations were weather dependent, thus dominated by changing stochastic boundary conditions. Most of the processes were irreversible, non-linear, and determined by a large number of variables. A top down risk management system was developed for control purposes. The system provided a continuous insight right from the very start of the project till the end of the project in the percentage of failure in the most relevant failure modes as a function of tow out date. The system allowed for strategic, tactical and operational interventions in case critical criteria were exceeded. This in particular makes that the approach - even 10 years after completion of the project - is still a new development in risk management and an interesting basis of further research on control of the design, construction and installation of complex Civil Engineering and other Systems.