Molikpaq: An Integrated Mobile Arctic Drilling Caisson

Abstract

ABSTRACT The design, installation and performance of Molikpaq, an innovative mobile steel drilling caisson designed to cope with the severe ice conditions in the Beaufort Sea are summarized. The environmenta1 constraints and the rationale for choosing the unique design are briefly discussed. A sub sea berm was constructed and tested prior to placement of the caisson. The caisson was installed in September 1984 by ballasting it down onto the berm and subsequently filling the central core of the caisson with sand for stability against sea ice forces. In the interests of safety, the berm and caisson are instrumented and carefully monitored. The 95-foot high caisson is much higher than any used to date and is so designed to reduce the volume and cost of the sub sea berms. The design of the caisson permits its quick relocate on to a new dri11ing site during the short open water period in summer, since the drilling equipment and accommodation are an integral part of the unit. Molikpaq, the Inuit name for "great wave" can be utilized in water depths ranging from 50 to 130 feet by varying the sub sea berm height. It can be operated in a range of sea bottom conditions by appropriate preparation of the foundation. Since it is designed to withstand multi-year ice features, it is capable of year-round drilling. Valuable performance data being acquired will be very useful in the design of other exploratory drilling units or larger production platforms in the future. INTRODUCTION Permits were issued over the period 1963 to 1969 to explore for oi1 and gas on the majority of the Canadian continental shelf of the Beaufort Sea which extends some 75 to 100 miles to a water depth of 600 feet. Gulf Canada Resources Inc. operates 2.5 million acres mainly in the 60 to 140 ft. water depth range. The Geological Survey of Canada's average expectations of the hydrocarbon potential of the Beaufort Sea-Mackenzie Delta 8.5 billion bbl of oil and 66 TCF of gas till Although many encouraging discoveries have been made offshore, the commercial viability of the reserves will depend on many factors such as pay thickness and other reservoir characteristics, well productivities, reservoir depth, water depth, distance from shore, environmental forces, sea bottom conditions, capital and operating costs, crude oil prices and fiscal regime. Further deli neat ion dri11ing is required for several discoveries including Gulf's recent Amauligak major oil discovery. BEAUFORT SEA ENVIRONMENTAL CONDITIONS Sea ice is the most severe environmental constraint in the Beaufort Sea, with the area of interest usually ice-covered nine months of the year. This sea ice affects operations as well as design of platforms. Freeze-up usually commences in early October, with new ice formation beginning near shore and slowly progressing offshore.