Abstract

This paper deals with the design parameters, fabrication and sea trials of the first ship equipped for dynamic stationing having the specific requirements for drilling exploratory wells in open ocean environment.

Design criteria are reviewed with regard to sea state, environment, propulsion requirements and drilling performance, including automatic control and sensing systems. Model studies and dynamic simulation analyses are presented and compared with the results of early sea trials. Operating systems are summarized, and performance expectations are related to prospective utilization of the vessel in specific ocean areas. Preliminary conclusions are given with respect to vessel response to control and propulsion parameters.

Introduction

The trend in offshore exploration clearly indicates that the Oil Industry must extend its search for oil and gas into water depths beyond the continental shelf. The need for additional oil and gas reserves; and the belief that sizable reserves could indeed exist in greater water depths have encouraged interest in deepwater exploration. This deepwater exploration has resulted in the need for new techniques and tools for water depths of 2,000 feet and greater.

Royal Dutch/Shell Group, with their established world-wide interest in offshore exploration and production and their technological achievements in the offshore environment, has taken a natural step to undertake early development of drilling techniques and tools to explore in the deeper waters.

Extensive study of exploration objectives and research into the means of achieving these culminated in Royal Dutch/Shell engineers drawing up comprehensive engineering specifications for a highly mobile drill ship. Early in 1970, the drilling contractor, SEDCO, Inc., was engaged to design, construct and operate the drilling unit, now known as the "SEDCO 445." At the same time, Royal Dutch/Shell and SEDCO engineers undertook detailed final development of advanced forms of dynamic stationing and underwater drilling equipment. The major limiting factors to existing offshore exploration drilling are the anchoring capability and the underwater drilling equipment system.

A specially designed ship equipped with dynamic stationing has the capability of anchoring in unlimited water depths. The use of new techniques such as Electro-Hydraulic BOP controls; acoustical re-entry; and riser buoyancy increase the capability of the underwater drilling equipment system to something greater than 3,000 feet.

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