First gulf subsalt field poised to start up

Installation by a group led by Phillips Petroleum Co. of Mahogany platform in the oil and gas field of the same name-the first commercial subsalt development in the Gulf of Mexico-occurred in late August. Photo at upper left shows the platform jacket being launched. At upper right, Heeremac vof's construction barge prepares to mate Mahogany topsides with the platform jacket. At lower left, mating of jacket legs with topsides is closely monitored. At lower right, the nighttime mating of jacket and topsides is almost complete. Photos courtesy of Phillips.

Phillips Petroleum Co. and partners Aug. 26 installed the three-deck, 20 slot topsides on Mahogany platform jacket on Ship Shoal-South Addition Block 349. The field also covers part of Ship Shoal-South Addition Block 359, about 80 miles off Louisiana.

Mahogany operator Phillips, Anadarko Petroleum Corp., Houston, and Amoco Corp. launched Mahog-any's eight-pile, 387 ft jacket in 370 ft of water about 3 weeks earlier.

Phillips and partners opened an era of subsalt development in the gulf in late September 1993 when they announced discovery of Mahogany field (OGJ, Oct. 4, 1993, Newsletter).

The group's 1 Mahogany wildcat flowed 3,700 b/d of oil and 559 Mcfd of gas from an undisclosed depth through a 14/64 in. choke with 6,800 psi flowing tubing pressure. In further tests of a longer perforated interval, the 16,500 ft wildcat flowed 7,256 b/d of oil and 7.3 MMcfd of gas through a 1/2 in. choke with 7,063 psi flowing tubing pressure (OGJ, Oct. 11, 1993, p. 30).

Partners in April 1995 disclosed plans to develop Mahogany with a $200 million project expected at peak to produce 45,000 b/d of oil and 100 MMcfd of gas (OGJ, Apr. 24, 1995, p. 36). Mahogany production in December is expected to come on line at 22,000 b/d of oil and 30 MMcfd of gas.

Interests are Phillips and Anadarko each 37.5% and Amoco 25%.

Mahogany progress reviewed

Phillips acquired Ship Shoal Blocks 349 and 359 for bonuses totaling $1.1 million at Minerals Management Service lease Sale 123 for acreage on the central Gulf of Mexico's Outer Continental Shelf. Anadarko bought into the acreage in 1992 and Amoco in 1993.

After the discovery by 1 Mahogany wildcat, partners installed a six-slot subsea template at the discovery well site and continued drilling from a semisubmersible rig. The group's 2 Mahogany appraisal well-also from a bottomhole location on Block 349-in August 1994 flowed 4,366 b/d of oil and 5.32 MMcfd of gas through a 20/64 in. choke with 6,287 psi flowing tubing pressure. Partners drilled the well to a measured depth of 19,100 ft.

Immediately after declaring the field a commercial discovery, fabrication began of Mahogany's platform jacket and topsides at Aker Gulf Marine's (AGM) Ingleside, Tex., fabrication yard near Corpus Christi. AGM is a partnership of Aker Oil & Gas Contractors Inc., Houston, and units of Kiewit Construction Group Inc., Omaha.

In late April 1995, the Phillips group disclosed results of the 3 Mahogany well. Drilled to 17,400 ft TD at a bottomhole location on Block 359, 3 Mahogany encountered the same zone that flowed 7,200 b/d of oil in the discovery well on Ship Shoal 349, but not the deeper productive interval encountered by the field's first appraisal well (OGJ, May 1, 1995, p. 50).

Still, Phillips said the failure to find the deeper zone didn't change the group's development plans.

The group in May 1996 said 4 Mahogany well had cut more than 180 ft of gross pay at 14,976-15,158 ft, increasing the field's estimated reserves. Partners completed both 3 and 4 Mahogany wells and suspended them as producers, pending installation of the platform jacket and topsides over the field's drilling template.

sss After hooking up and commissioning platform facilities, partners installed a platform rig on Mahogany on the structure to connect the four predrilled wells back to the platform, install production equipment on each, and treat Mahogany's producing formation.

Partners plan to drill more wells from Mahogany platform after placing the first four wells on production.

Production transportation plans

Mahogany production is to flow by way of subsea pipelines to gathering systems in the gulf.

Partners agreed in March 1996 to transport oil to shore through Poseidon pipeline system, a 20 in. segment of which passes less than 1.5 miles from Mahogany platform (OGJ, Mar. 4, p. 46). A unit of Texaco Inc. operates Poseidon through Poseidon Oil Pipeline Co. LLC, a 50-50 venture of Texaco and Leviathan Gas Pipeline Partners LP, Houston.

Leviathan in January agreed to transport Mahogany gas to shore through Louisiana Offshore Gathering System (LOGS) (OGJ, Jan. 29, p. 49). Mahogany gas will reach LOGS through a 9 mile, 16 in., Leviathan-operated pipeline.

Brown & Root Energy Services provided design, engineering, and procurement services for Mahogany's offshore facilities, including the platform's drilling, production, and cellar decks and steel jacket.

The Phillips group in May 1995 awarded AGM a contract to fabricate and install Mahogany's 5,000 ton integrated topsides, 4,200 ton jacket, and 3,400 tons of piles.

AGM, in turn, awarded a subcontract to Heeremac vof-a partnership of Heerema Nederland BV, Leiden, Netherlands, and McDermott (Holland) BV unit of J. Ray McDermott SA, New Orleans-to launch Mahogany jacket and piles, transport the jacket and topsides, and lift the deck for installation.

Copyright 1996 Oil & Gas Journal. All Rights Reserved.