ABSTRACT

This paper describes the successful drilling of exploration wells from a dynamically stationed drill ship in water depths ranging between 1, 000 and 2,200 feet. The operating performance of the subsea and stationing equipment is reported. Specifically outlined is the operational experience gained before drilling a full scale exploration well in the record- setting water depth of 2, 150 feet offshore Gabon during 1974.

1. INTRODUCTION

The trend in offshore exploration clearly indicates 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 exist into greater water depths, has encouraged interest in deep water exploration. Figure 1 illustrates the "Shelf" where oil exploration has been conducted to date. The "Slope if and "Riser are potential deep water exploration areas.

In early 1970, SEDCO, in conjunction with Shell Internationale Petroleum began to develop a new generation drilling vessel that could operate without anchors -- The SEDCO 445 (Figure 2). During the ensuing five-year period this concept became a reality and today the technology and equipment are available to conduct exploration drilling operations without anchors and with safe well control at the seabed in water depths beyond 2, 000 feet.

In late 1971, the S-445 went into operation off Borneo. After six months, while moored on anchors to train people and insure the equipment would work satisfactorily, the S-445 moved into 1,350 feet of water to drill the first full scale exploration well ever drilled from a dynamically stationed vessel. Since August, 1972, the S-445 has operated without anchors. During this 2-1/2 year period 9 wells have been drilled in 3 separate areas of the world. Figure 3 is a summary of the S-44-? r s worldwide achievements. In May of 1974, a new water depth record was established when a well was drilled in 2, 150 feet of water off Gabon, West Africa. Figure 4 illustrates the yearly steps into deeper water that the offshore floating drilling industry has achieved -- 635 feet in 1965 to 2 150 feet in Ig74. Today the industry has the capability (equipment and technology) to drill in 4, 000 to 6, 000 feet of water.

The technological advances necessary to permit exploration in deep water are listed below and illustrated in Figure 5.

  • Dynamic Stationing (Stationing without Anchors)

  • Wellhead Sonar Re-Entry (Re-Entry without Guidelines)

  • Electric BOP Controls (Fast BOP Response)

  • Marine Riser Systems (Tension and Buoyancy)

  • Deep Water Drilling Technology (Formation Breakdown, etc.)

The experience gained in these five specific areas is reported in the following section of this paper.

2. OPERATING EXPERIENCE

Through December, 1974 (861 days), the S-445 had been on dynamic stationing (drilling without anchors) and making sonar re-entry into the subsea wellhead.

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