Abstract

This paper discusses the upgrade of the Discoverer 534, from a turret moored 3500 ft [1100 m] rated drillship, to a fully dynamic positioned vessel rated at 6000 ft [1830 m] water depth. After the upgrade, the vessel commenced drilling in 3730 ft [1137 m] water depth which will be followed by a well in 5900 ft [1800 m] waters during the first quarter of 1991. This will be a world water depth record for a vessel with a 18-3/4 in. [476 mm] BOP stack and a 21 in. [533 mm] drilling riser.

Introduction

During the third quarter of 1989, BP Exploration set out to select a drilling vessel to explore its large deep water lease holdings in the Gulf of Mexico. It was necessary to acquire a drilling vessel that was capable of drilling in up to 6000 ft [1830 m] water depth to allow exploration of all the geological prospects in BP Exploration's inventory.

An assessment of the global deep water drilling fleet was performed during the third and fourth quarter of 1989. This was done to identify the vessel best suited for BP's program and to assess required modifications to take it into the 6000 ft [1830 m] water depth.

This paper discusses the primary systems installed or modified, procedures in effect, and challenges of the upgrade. It also lists the numerous other technical modifications that were carried out.

RIG SELECTION

Table 1 shows the global drilling fleet that was considered in the selection of a rig for the deep water program. In addition to considering availability and cost, an extensive technical evaluation was carried out to assess these rigs deep water capability including: station keeping, past performance, mooring capability, load carrying performance, mooring capability, load carrying capacity, vessel stability with drilling consumables and 6000 ft riser onboard, type of drilling riser, and riser hang-off and disconnect system. Additionally, the drilling contractor's safety program, safety record, engineering and operational support were evaluated.

Based on the above assessments, the Discoverer 534 was selected for BP Exploration's deep water drilling program.

ENGINEERING OF THE UPGRADE

The major modifications, to qualify the Discover 534 for 6000 ft [1830 m] water depth, were decided upon prior to contracting the rig. Due to the extensive effort of upgrading and modifying the rig, and the short time available, many of the projects were performed right up until the vessel projects were performed right up until the vessel left the shipyard for sea trials. Sonat Offshore Drilling, in conjunction with BP Exploration and outside engineering resources, identified and designed the necessary modifications. Due to BP's tight exploration program, timely delivery of services and equipment was crucial.

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