Shell group outlines Ursa development plan

Shell Offshore Inc. and partners have settled on a $1.45 billion plan of development for Ursa field off Louisiana in the Gulf of Mexico.

The project is expected to set a slew of offshore regional and world records.

When installed in about 4,000 ft of water on Mississippi Canyon Block 810 early in 1999, Ursa tension leg platform (TLP) will claim another gulf water depth record for a drilling-production platform.

Shell and BP Exploration Inc. earlier this year claimed the drilling-production water depth record when they installed Mars TLP in 2,940 ft of water on Mississippi Canyon Block 807. That record will fall in 1997 when another group led by Shell installs Ram-Powell TLP in 3,218 ft of water on Viosca Knoll Block 956, also off Louisiana.

Also upon installation, Ursa TLP will be the largest structure in the gulf, weighing about 63,300 tons.

Ursa operator Shell holds 45% interest in the project, BP 23%, and units of Conoco Inc. and Exxon Corp. 16% each.

High well rates

In addition, Ursa TLP will claim the gulf's deepwater production record soon after it begins to come on line in early to mid-1999.

The 24 slot TLP at peak output is expected to produce about 150,000 b/d of oil and 400 MMcfd of gas. Production from individual wells could reach as much as 30,000 b/d and 80 MMcfd, another gulf record.

Wells at Shell's Auger TLP, in 2,860 ft of water on Garden Banks Block 426, have achieved the gulf's highest individual well production rates to date, reaching as much as 13,000 b/d.

Rich Pattarozzi, general manager of Shell Offshore's deepwater division, said partners expect to achieve higher production rates at Ursa by including horizontal wells and 51/2 in. production tubing in the development plan.

"High individual well ultimate recoveries and production rates reduce the number of wells necessary for field development and are essential in controlling the cost of deepwater projects such as Ursa," Pattarozzi said.

Ursa development plan

Ursa field is about 130 miles southeast of New Orleans on a six tract unit including Mississippi Canyon Blocks 808, 809, 810, 852, 853, and 854.

Shell and BP drilled the field's discovery well in 1991 on Block 854 with Sonat Offshore's Discoverer Seven Seas semisubmersible rig. Partners since have drilled two delineation wells and two sidetracks.

Partners estimate Ursa's reserves at 400 million bbl of oil equivalent in multiple stacked reservoirs. Initial development targets seven pay sands, two of which are thought to contain 80% of the field's reserves.

Ursa's development plan calls for as much as 14 producing wells, including 11 from the TLP and three subsea. Wells on the seafloor are to be arranged in a 100 ft by 60 ft rectangle.

Partners will predrill six of the production wells beginning in mid-1997, with the rest to be drilled by a contract platform rig after the TLP is installed. The TLP will support a single modified platform rig equipped with a surface blowout preventer and high pressure drilling riser. Partners have not yet chosen a drilling contractor.

Ursa TLP production modules will include complete separation, dehydration, and treatment facilities. In addition to 150,000 b/d of oil and 400 MMcfd of gas, the unit will be designed to handle as much as 50,000 b/d of produced water.

Ursa's development plan includes subsea 18 in. pipelines for oil and gas. The lines are to be laid from Mississippi Canyon Block 810 about 47 miles to a shallow water fixed platform on West Delta Block 143 beginning next year. Partners are to select a pipeline contractor later this year.

Shell and BP plan to transport Mars field gas 55 miles through a subsea pipeline to the same platform on West Delta 143 (OGJ, Apr. 8, p. 23).

Ursa TLP described

Ursa TLP will be Shell's fourth in the gulf. Auger TLP came on line in mid-1995, Mars TLP is to begin producing this month, and Ram-Powell TLP is to start producing next year.

When completely assembled on location, Ursa TLP will stretch 4,285 ft from the seafloor to the crown block of the drilling rig.

With total displacement of 97,500 tons, the unit will be designed to withstand simultaneous hurricane force waves and winds.

The TLP topsides will include modules for the well bay, drilling, electric power, and crew quarters, plus two processing modules. The TLP deck will be open frame design, 300 ft by 300 ft and 50 ft high, and weigh about 12,500 tons.

Total topsides weight including all equipment and drilling rig is expected to amount to about 22,000 tons.

J. Ray McDermott International Inc., Morgan City, La., has the contract to build the equipment modules.

Ursa's hull is to consist of four circular steel columns, each 85 ft wide and 177 ft high, and a 35 ft wide-29 ft high ring pontoon with a rectangular cross member. The hull will weigh about 28,800 tons.

Belleli Group, Taranto, Italy, is to fabricate the hull beginning this month.

Ursa TLP will have 16 tendons, including four on each corner, attached to 16 piles by tendon receptacles. Each tendon will be 3,815 ft long, 32 in. diameter, and weigh 1,000 tons. Each pile will be 430 ft long and weigh about 380 tons, with a diameter of 96 in.

HeereMac, Leiden, Netherlands, is to install the TLP.

Ursa partners formed a multicompany team to design the TLP. Waldemar Nelson & Co., New Orleans; W.H. Linder & Associates, Metarie, La.; and Han-Padron Associates, Houston, are developing the vessel's detailed design.

Partners expect to spend about 65% of the development's projected costs fabricating and installing Ursa's hull, deck, production facilities, drilling rig, and pipelines. The remainder is to go for drilling and completing wells.