Deepwater semi upgrade nearing completion

Ocean Victory drilling rig will go to work for Vastar in Gulf of Mexico's Mississippi Canyon area. Photo courtesy of Diamond Offshore Drilling Inc.

Vastar's Initial Drillsites [110,530 bytes]

Diamond Offshore Drilling Inc., Houston, is nearing completion of a major upgrade of its Ocean Victory drilling rig.

The rig is slated to begin work on Jan. 1 for Vastar Resources Inc., also of Houston.

Vastar is at the front end of a 3-year drilling program in the deepwater Gulf of Mexico. When refurbishing of the fourth-generation semisubmersible is complete, Vastar will put it to work on its King prospect in the Mississippi Canyon area.

Diamond Offshore began the upgrade in June. It will include stability enhancements, a new mooring system for deepwater operation, and a third mud pump.

The rig is in dry dock at Sabine Pass, on the Texas-Louisiana border. Diamond Offshore had expected to complete the $111 million upgrade Nov. 6.

The value of the 3-year lease contract with Vastar is estimated at $141 million. After 3 years, Vastar can extend the contract in three 1-year increments.

Vastar's program

Vastar embarked on a deepwater program in 1995. Since then, the company has leased 86 blocks that include more than 40 prospects.

To date, Vastar has invested more than $130 million in the program. The company has collected about 1,800 blocks of 3D seismic and recently began drilling the Kilmarnock prospect through its partner British-Borneo Petroleum Inc.

Kilmarnock lies in 2,100 ft of water on Garden Banks Block 258. Vastar owns a 30% interest in the block. Partners include Nippon Oil Exploration U.S.A. and Unocal Corp.'s Spirit Energy 76 unit.

Vastar will use Ocean Victory on its King, Mirage, and Sting pros- pects in the Mississippi Canyon and Viosca Knoll areas (see map, this page). King, in 3,300 ft of water on Mississippi Canyon Block 764, will be the first drillsite for the upgraded rig when it begins work next year (OGJ, Apr. 28, 1997, p. 30).

Vastar is a 50% owner of King. Partners are Shell Deepwater Development Inc. and BP Exploration Inc. (OGJ, Sept. 1, 1997, p. 23).

Mirage lies in 3,860 ft of water on Mississippi Canyon Block 941. It is owned 100% by Vastar, as is Sting, which is in 4,000 ft of water on Viosca Knoll Blocks 1000 and 1001. Vastar will drill both prospects next year.

Vastar and Marathon Oil Co. are 50-50 partners in another deepwater Gulf of Mexico prospect-Teton, on Mississippi Canyon Blocks 294, 338, and 339. Water depth in the area is about 4,370 ft. Drilling is scheduled to begin in 1998.

Vastar holds 100% ownership in two additional prospects in the area: Gunnison on Garden Banks Block 303 and Ojai on Mississippi Canyon Blocks 499 and 543. Drilling on these prospects is slated for 1998 and 1999. Water depths are 2,000-2,100 ft.

The rig upgrade

The Ocean Victory is a 12-column semi designed to work in water depths up to 600 ft. Following the upgrade, the Deepwater Victory-class rig will be capable of working in as much as 5,000 ft of water.

The new mooring system will be an Amclyde 8-point combination chain/ wire system with traction winches and Bruce anchors. The system includes 33,600 ft of 31/4-in. chain and 70,400 ft of 31/2-in. wire.

Stability enhancements will provide about 5,000 tons of variable deck load during operations. Variable deck load during transit will be 3,500 tons.

Other upgrades include:

A 15,000 psi blowout prevention and riser system.
Increased riser tensioning (1,280 kips).
A new TDS-4S top drive.
Increased total liquid mud capacity (3,100 bbl).
A new 1,300 kip mast.
A third crane, plus upgrading of existing cranes.

Vastar also has replaced the rig's riser storage and handling system, derrick, and cementing system and added one level of living quarters.

Another upgrade

Last month, Diamond Offshore announced plans to convert the Polyconfidence semisubmersible accommodation vessel to a deepwater-capable drilling rig.

BP Exploration will use that vessel for a 5-year drilling program in the Gulf of Mexico starting in fourth quarter 1999. Contract value is estimated at $320 million.

"The planned conversion will include enhancements that will provide capabilities greater than existing fourth-generation equipment," said Diamond Offshore. These changes include: 6,000 tons of variable deck load, capability to drill in 7,500 ft of water, a 15,000 psi blowout prevention system, and four mud pumps.

Conversion of the Polyconfidence is slated to begin early next year at a Gulf of Mexico shipyard. The vessel is currently working in the U.K. North Sea.