Experience With Alert and Evacuation, Tarsiut Island, Summer 1982

ABSTRACT The original concept for Tarsiut Island considered that drilling operations in the Beaufort Sea would be done under ice covered conditions. Extension of drilling to summer open water conditions necessitated two major changes. Upgrading construction would be required to reduce the potential for scour at the base of the concrete caissons, and to increase freeboard protection from waves and spray. The Island Alert and Evacuation Manual also had to be changed. Depending upon the position of the permanent ice pack, the fetch for waves can change drastically. Weather changes are sudden. The principle changes in the alert system had to recognize that local direct decisions as well as short term forecasts would be needed. Warning was needed which recognized the influence of high winds upon helicopter operations. During the summer of 1982, two successful total evacuations of the Island were necessary due to the forecasted and observed weather by conditions. There was minimal damage and no personal injury. The paper indicates the role of the Island Design Engineer in the co-ordination of monitoring activities, the various alert 1evel s which were estab1ished for summer conditions, and summarizes the procedures carried out for the two successful operations. INTRODUCTION Tarsiut Island was primarily designed as a winter drilling platform for Gulf et al East Tarsiut Well N-44 (Stenning and Fitzpatrick (1983)). The island would have a relatively short 1ife before the caissons could be moved elsewhere for other exploratory work. Due to the short life, engineering judgment had to be used in establishing the design standards for island performance and personnel safety. The final design had to provide a safe and long enough time to complete drilling operations with a minimum of interruptions due to physical environmental conditions. The design could obviously not incorporate protection against all statistically possible physical events. No precedent existed for the design of fixed structures in an area where massive ice features are often in motion. The design incorporated assumptions about the prototype ice loads which could be verified by direct measurement. To provide a warning system in the event that the design loads were approached, instrumentation was installed on the caissons and within the sandfill berm. This provided the basis for a portion of the original(winter) alert system. In the event that ice loads or other forces approached the design 1imit, an evacuation procedure was established for island personnel. The adoption of an "abandon in extreme conditions" procedure appeared to be the most cost effective for drilling operations. To forewarn of approaching conditions, an alert system was developed. In the event of deteriorating physical environmental conditions or adverse well operations, personnel could be evacuated to an ice relief pad which was constructed to the north of the island.