Evaluation of Canadian arctic artificial islands

Abstract

In the early seventies the hydrocarbon development of the Beaufort Sea - McKenzie delta region started with the search for oil. To determine if hydrocarbon reserves were to be found a number of artificial exploration-islands were designed and built between 1973 and 1986. Artificial islands were chosen to function as drilling platforms because the easy construction method and the high resistance against ice loads. From the different islands several oil discoveries were made and islands design was found to be sufficient for the exploration purpose. To anticipate future development of the offshore area of the Beaufort Sea when present reserves become depleted a study is made of the artificial island designs. A research is conducted in developing the designs from exploration islands to production facilities. In this thesis report a study is made of the artificial islands designs in the severe circumstances of the Beaufort Sea, the extreme climate posting special design considerations and construction techniques. In this research the question is stated: "Can exploration artificial island design be used as a design for permanent production islands in the extreme environment of the Beaufort Sea - McKenzie delta region?" Production islands have to function much longer and therefore have to withstand higher forces. Exploration designs were designed with a boundary condition of a ten-year return period, for production islands a return period of 100 years has to be taken into account. Complicating factor in the design is the absence of heavy armour layer materials to protect island slopes. Common protection methods for island slopes and other slopes are not available. Purpose of this thesis study is to determine what the maximal lifetime expectancy is of the artificial exploration island designs. Furthermore a number of production island considerations are studied and evaluated. To be able to give a correct overview of the islands that were built between 1973 and 1986 first a thorough literature study has been completed. This to gather as much information available as possible and acquire knowledge of the design practice to date. The islands considered are islands with a granular fill material. Therefore other island types such as caissons are not discussed in this study. The side slopes of these granular fill artificial islands are under the influence of waves and ice. Especially the waves, present for two to three months per year, result in erosion of the fill material. The morphological changes of the slopes are evaluated using a computer simulation model. The evaluation of the slope designs is done with a numerical model developed by Delft Hydraulics called UNIBEST-TC. Note that the model was designed for cross-shore beach-morphology of mildly sloped beaches. To be able to give a conclusion of slope designs on production islands the application in larger water depths and under higher ice loads also is taken into account. With the information from the literature study the thesis problem is defined in the following two parts. 1. Research and summarise all present knowledge of exploration artificial islands in the Beaufort Sea and evaluate exploration island designs in respect to long-term production application. 2. Evaluate production island slope designs with a numerical morphological simulation model to determine erosion and morphological changes. This to postulate new design considerations in respect to the applicability of the available exploration island designs on artificial production islands.