A Deepwater Actively Frozen Seabed (OAFS) Drilling/Production Structure for the Beaufort Sea
Authors: Padron D.V. , Joneidi F. , Nixon J.F. 
Published: October 2008

The development of concepts for drilling and production facilities in the Beaufort Sea in water depths exceeding twenty-five meters poses major engineering problems. A drilling/production structure concept based on the utilization of the sustained low temperatures of the Arctic has been developed. It consists of a pre-assembled, fully equipped steel caisson, towed to the Beaufort Sea and ballasted with seawater to rest on the seabed. The seabed is subsequently froze, utilizing active thermal piles, to provide the required foundation strength.

The Deepwater Actively Frozen Seabed (OAFS) drilling/production structure is suitable for water depths ranging from approximately twenty-five meters to fifty meters or more. Due to the fact that it re 1ies on the frozen seabed soil mass for its stability, it is relatively lightweight and suitable for installation on virtually any seabed soi1 conditions that may be encountered. Since it does not require ballast other than seawater, it can be completely installed in a matter of weeks an d ca n be re 1ocated if necessary. Storage space for more than 1,000,000 barrels of crude oil is available within the structure.

INTRODUCTION

The construction of a permanent drilling and production facility in the Beaufort Sea in water depths of twenty-five to fifty meters or more poses major engineering problems. A concept has been developed to solve these problems in a unique fashion.

The key problem areas can be summarized as:Harsh environmental conditions and a very brief open water window for construction.Substantial ice impact forces threatening any structure or island concept.Poor soil conditions for structure foundation or island construction in many areas.Existence of soft overburden which varies substantially in thickness and which could pose significant dredging problems.Difficulty of on-site construction of conventional islands due to short season, unavailability of adjacent fill material and slope protection. The substantial low temperatures result in ice conditions which subject marine structures to forces that are orders of magnitude above those in less hostile environments. The OAFS drilling/production structure described in this paper is based on the concept of utilizing this same sustained low temperature as a valuable construction material for resisting the forces which it causes to be imposed. The proposed concept thus tends to take advantage of the severe environment rather than simply opposing it.

The concept is illustrated in the artist's rendering shown in Figure 1. It consists of a preassembled steel caisson structure fully completed with its topsides equipment, towed to the Beaufort Sea site and ballasted to rest on the seabed with a predetermined bearing pressure. The seabed is subsequently frozen through the use of thermal piles.The concept is adaptable to a wide range of Beaufort Sea conditions, particularly regarding water depth, seabed soil characteristics and ice forces.The concept is based on adaptations of available technology and does not rely on unproven construction materials or techniques.