Three drillships ordered for deep water

Drilling contractors have let construction contracts for three drillships following receipt of long-term charters for deepwater exploration.

Transocean Offshore Inc., Houston, let two contracts to Astilleros Espa?oles SA, Madrid, for construction of sister drillships to operate in the Gulf of Mexico under charter to Unocal Corp. and Chevron Corp.

Meanwhile, BHP Petroleum Pty. Ltd. issued a letter of intent to Global Marine Inc., Houston, for a deepwater drillship. The contractor then let a $300 million construction contract to Harland & Wolff Holdings plc, Belfast.

The contracts are the latest in a spate of deepwater drillship projects that began in late 1996 when Conoco Inc. and contractor Reading & Bates Corp. embarked on a deepwater drilling joint venture (OGJ, Nov. 11, 1996 p. 34).

Transocean vessels

Astilleros will build the two drillships at its Astano yard in Spain, where it is currently nearing completion of a similar ship, also destined for the Gulf of Mexico, for Amoco Corp. This drillship is due for delivery soon and is slated to drill its first well in July 1998 (OGJ, May 26, 1997, p. 69).

Navion AS, Stavanger, also is building two drillships, one for use by Stat- oil off Norway and one by Shell Offshore Inc. in the Gulf of Mexico (OGJ, Mar. 9, 1998, p. 37).

Amoco's ship is called Discover Enterprise.

The ships to be taken by Unocal and Chevron will be called Discover Spirit and Discover Enterprise II, respectively.

The three ships will be built to the same design. They will be 255 m long and 38 m broad, with crude oil storage capacity of 40,000 tons and total variable deck load of 20,000 tons for drilling equipment and topsides.

The three ships each will be dynamically positioned, with twin derricks to enable deployment of two complete drillstrings at once. They will be able to operate in water as deep as 10,000 ft and carry a crew of as many as 200.

Astilleros said the most striking feature of the Discoverer class drillships will be their twin drilling areas set 40 ft apart on an 80x80 ft drill floor. The rigs will incorporate Transocean's patented Expedrill technology.

This allows different drilling tasks associated with a single well to be performed simultaneously, rather than in sequence.

"While one area is drilling ahead, the other can be used for tasks such as changing BOPs, cementing, or logging runs," said Astilleros.

The firm said Conoco's newbuild will be equipped with one drillstring, while Navion's will have two drillstrings, one of which will be used only as an auxiliary hook to speed drilling of one well. "Unlike Discover Enterprise and its sisters, they will not be able to drill two wells at once with two risers."

Global Marine vessels

BHP's agreement with Global is for charter of a newbuild dynamically positioned drillship for 3 years following delivery in fourth quarter 1999. The operator has two 1-year options to extend the contract.

BHP claims to be the third largest leaseholder in water depths of more than 1,500 ft in the central Gulf of Mexico. It has specified the new drillship should be capable of operating in water depths of 10,000 ft and outfitted to perform extended well tests.

The ship earmarked for BHP will be built to the Glomar 456 design.

Harland & Wolff said the drilling contractor has an option to order a second drillship to the same design, to be exercised by the end of March. If ordered, this second rig could be completed in first quarter 2000.