Dynamic Stationed - Drilling SEDCO 445
Authors: Williford F.B. , Anderson A.B. 
Published: October 2008

This paper describes the first year's operating experience of the SEDCO 445, which is the first ship equipped for dynamic stationing having the specific requirement for drilling exploratory wells. A summary of the difficulties, solutions, and accomplishments of the dynamic stationing, drilling, and ship's systems are presented.

Particular emphasis is placed on those systems which are unique to dynamic stationed, exploratory drilling. Other systems which have necessarily been modified to accommodate dynamic stationed drilling are discussed. Preliminary conclusions are given with respect to future expectations for the drilling and ship's systems.

INTRODUCTION

The SEDCO 445 is a self-propelled, dynamically stationed deep sea drill ship, which is designed, configured, and equipped to serve as a highly mobile and efficient floating drill platform capable of conducting offshore drilling operations worldwide.

Dynamic Stationing control is provided by a Honeywell automatic station keeping (ASK) system specifically designed for position control of offshore drilling vessels.

Reference 1.

Drilling systems have been operated mostly on conventional guidelines, although the scanning sonar re-entry system has been extensively tested. The authors presume that readers of this paper have at least a basic knowledge of floating drilling and underwater systems.

DRILLING SYSTEMS

Re-entry Techniques and Equipment

Components of the re-entry system were assembly tested during initial testing of well head and subsea BOP stack equipment. Field testing and proving of these components has been carried out during the course of a normal exploration program in water depths ranging from 300 to 1,500 feet. During the initial field trial period, a conventional wire1ine guidance system has been employed for all normal operations, however drilling without guidelines commenced mid-February, 1973.

Apart from occasional incidents of fouling of guidelines on the guide structure, no difficulties have been experienced with the guideline system. These incidents have been caused by inadvertent failure to maintain adequate tension in the guidelines. The requirements of the guide structure are such that streamlining to avoid angular sections on which the guidelines can become caught is precluded. Normally, a minimum bottom tension of 2,000 lbs. is maintained and this has proved adequate.

A universal guide frame has been utilized for all drilling tool and surface casing guidance operations. This ruggedly built frame has performed well, though some changes are planned that will allow the mechanism to be released more quickly from casing strings.

In order to ensure that it would be possible to reattach guidelines following their release, or in the event of their being damaged or broken, provision was made to run conventional guideline tools in conjunction with the acoustic re-entry tools. The latch bumper head (LBH) which is the guidance tool which locates and locks to the wellhead or the lower part of the BOP stack, depending upon whether full stack or upper stack reentry is being undertaken, is integrated with a two-arm guide frame so that the handling string may be held in tension in the correct vertical position while the appropriate orientation with respect to the guidelines may be sought. The guideline tool manipulations are then carried out with guideline winches' and hydraulics (in the case of the cutting tool).