ABSTRACT: Drilling Structures in Arctic Environment

Devinder S. Sodhi

In the last two decades, major offshore exploration for hydrocarbon resources has been taken along the southern coast of the Beaufort Sea. The ice cover in that region presents hazardous to normal offshore operations and is an impediment to navigation. However, an ice cover when it is stable enough can be used as a working platform or for transportation.

The sea ice in the southern Beaufort Sea can be broadly subdivided into three zones: the fast ice zone, the seasonal pack-ice zone, and the polar pack-ice zone. Further, the sea ice can be classified as first-year or multiyear according to its age. A third classification is based on the deformation of ice during its existence: undeformed and deformed. In the presentation, characteristics of each type of ice will be discussed and illustrated with photographs.

An interaction between an ice feature and an exploration drilling structure results in development of forces that may threaten the structural stability and safety. These forces depend to a large extent on the size, speed, and properties of an impacting ice feature, the environmental condition, and the mode of ice failure, if any.

Arctic drilling structures are evolving rapidly to adapt to different offshore environments characterized by water depth and ice conditions. Arctic structures are of two types: exploration and production. All structures placed in the Arctic so far have been designed for exploration. Existing arctic drilling systems fall into two broad categories: bottom-founded systems and floating systems. Starting with artificial gravel islands in shallow water, drilling structures have evolved to integrated caisson structures, which can be moved to different locations. In deeper water depths, active floating drilling systems have been used during summer months because of their limited capacity to resist ice forces. The passive floating system makes use of the floating sea ice in areas of land-fast ce zones where ice movements are small. Examples of each type of drilling structure system will be given in a slide presentation.

The development of hydrocarbon resources in the Arctic presents great challenges to engineers. Arctic structures are required to operate safely under various conditions as well as to survive possible extreme events without major catastrophic consequences.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990