Icebreaking Drillship for Offshore Exploratory Drilling in the Arctic
Authors: Jones Klemme M. , Schaff James C. 
Published: December 2007

An offshore drilling system designed expressly for the unique environment of the Arctic must take into account many parameters. This paper discusses design considerations for a drillship intended for extended offshore operation in the Arctic areas. Discussion of environmental protection and safety features for icebreakers, shipping rules, and icebreaking capability are included.

Introduction

About 3 years ago it became apparent that the offshore oil potential in the Beaufort Sea and Canadian Arctic Islands areas was sufficient to give serious consideration to practically and economically providing a system capable of performing the needed exploratory drilling service. The practical approach was to use proven drilling techniques, systems, and equipment, proven drilling techniques, systems, and equipment, but to apply them to an environment not previously considered in their design, using imagination to accept opposing precepts to conceive a workable compromise. Economics dictate that the results must be reasonably capable of profitable application. A preference for ship-shaped units for exploratory drilling and the existing technology for breaking navigable ice channels with ships afforded a marriageable pair of disciplines. The only total unknown was how pair of disciplines. The only total unknown was how to maintain a drilling station in a slowly moving ice sheet.

Design Considerations

Combining a drillship with an icebreaker provided the basis for the design considerations (Fig. 1). Throughout the design of the vessel, safety was the over-riding criterion - safety not only for the personnel, vessel, and equipment, but also safety personnel, vessel, and equipment, but also safety in terms of environmental protection. The design evolved around considerations of environmental parameters such as climatic conditions and their parameters such as climatic conditions and their impact; crew, equipment, and vessel safety; regulatory parameters; and icebreaking and operational requirements.

Environmental Parameters

Experience with ship-shaped drilling vessels was a starting point for the design. This experience was adapted to the hostile climate of the Arctic. Where interfacing problems between the drillship and the icebreaker were encountered, the solution was normally an adaptation of drilling equipment or systems to the environment. The winters of the Beaufort Sea and Canadian Arctic Islands are long and severe. Although temperatures do not fall as far below zero as they do in the southern continental belt of the Arctic, the cold is persistent. The chill factor, coupled with the strong prevailing winds, makes this a very hostile region during the winter months. The long period of total darkness further complicates operations period of total darkness further complicates operations in the Arctic during this season. The summers in this area are cool and short. Cloudiness is prevalent along the coast because of the open water and abundant moisture, The clouds are always low and their formation lasts longer where open water and ice coexist. Snow occurs during every month of the year in the Beaufort Sea region. On the other hand, rain has never been recorded from October through May at most Arctic weather stations. During the summer months (June through September), rain accounts for more than 75 percent of the precipitation. The water equivalent of the mean annual precipitation is about 8 in., divided almost equally between rain and snow.

JPT

P. 433