Installation date draws near for Mars TLP

Mars Site [25245 bytes]

Shell-BP's Mars TLP takes shape at Aker Gulf Marine's Ingleside, Tex., yard.

Shell Offshore Inc. and BP Exploration Inc. are poised to install their Mars tension leg platform (TLP) in a record water depth in the Gulf of Mexico.

Partners aim to begin towing Mars TLP Apr. 10 from Aker Gulf Marine's fabrication yard at Ingleside, Tex., said Richard A. Pattarozzi, manager of Shell Offshore's deepwater division.

Crews at Ingleside since fourth quarter 1995 have been mating the Mars wellbay, quarters, process, power, and drilling modules, all made in the U.S., to a TLP hull built in Italy.

Shell 71.5% and BP 28.5% will install the 36,500 ton production unit in 2,940 ft of water on Mississippi Canyon Block 807. The block is part of a six tract unit, along with Mississippi Canyon Blocks 762, 763, 806, 850, and 851, about 130 miles southeast of New Orleans.

Upon installation, the Mars TLP will surpass Shell's Auger TLP as the deepest water production facility in the gulf. Shell early in 1994 installed the Auger TLP in 2,860 ft of water on Garden Banks Block 426 (OGJ, Dec. 6, 1993, p. 25).

After installation of the TLP, Mars operator Shell will reenter and drill to TD the first of 14 development wells predrilled to the 20 in. casing point at 5,500 ft by Sonat Offshore's George Richardson semisubmersible rig.

Shell in addition has drilled 10 wells to TD in Mars field and drilled and tested a subsea well in the field.

Partners expect to start Mars production in July, 3-4 months ahead of schedule. The field by second quarter 1997 is to reach production and processing capacity of 100,000 b/d of oil and 110 MMcfd of gas. Topside facilities also are equipped to handle as much as 25,000 b/d of produced water.

Lessons learned

Pattarozzi said the ability to install an offshore oil and gas facility in more than 2,900 ft of water marks another milestone in deepwater development.

Applying lessons learned from developing Auger field, Shell designed and built its Mars TLP more quickly and at less cost but with greater production capacity.

Shell expects Mars Phase 1 recovery to amount to about 500 million bbl of oil equivalent (BOE). Auger is expected to recover about 227 million BOE. Yet both projects carry similar $1.2 billion price tags.

Shell reined Mars fabrication costs by integrating topsides modules with the TLP hull at Aker Gulf's Ingleside yard. By comparison, the company mated Auger topsides and TLP hull on the open sea, a more costly, technically challenging option.

If Mars begins commercial production in July, as expected, elapsed time since Shell executives approved full project funding will be 2 years and 10 months.

Shell also has applied insights gain- ed by developing Auger to that project.

The Auger TLP at first was intended to handle about 46,000 b/d of oil and 126 MMcfd of gas from as many as 32 wells. After starting Auger production in April 1994, Shell found the field's wells capable of much higher production rates than expected.

With two upgrades, the company boosted Auger TLP oil capacity to more than 70,000 b/d from seven wells. Auger oil capacity by early 1997 is to match Mars at about 100,000 b/d.

Such accomplishments support Shell's belief that it is ahead of the rest of the industry in understanding deepwater development.

When well and pipeline costs are taken into account, Pattarozzi said, Shell's cost of developing a deepwater field in the gulf with a TLP based production system won't differ much from the cost of using subsea facilities of comparable capacities.

Similarly, Shell expects the proposed Ram-Powell TLP to cost less than Mars.

Mars overview

Shell acquired the tracts making up the Mars unit at federal lease sales in 1985 and 1988. It drilled the Mars discovery well in 1989 using the Discoverer Seven Seas drillship.

Shell based the decision to develop the field on results of the discovery well, four delineation wells, six sidetracks, and 3D seismic data collected in 1988 and 1993.

Mars field consists of seven or eight reservoirs in five groups at 10,000-20,000 ft below sea level. Geologic ages of Mars formations above 14,000 ft are Pliocene and of deeper intervals Miocene. Crude gravities and sulfur contents increase in the field's shallower reservoirs, while GORs decline.

Shell plans at first to produce several Mars reservoirs at the same time but will complete each well in only one pay zone. Initial primary production will be from lower intervals.

In its reentry drilling program, Shell will drill horizontal sections in some wells and install production tubing in sizes ranging from 31/2 to 41/2 in.

Shell completed the Mars discovery well with a frac pack. For commercial production, the company will complete some wells with frac packs and some with gravel packs.

Each Mars well is expected to produce 10,000-20,000 BOE/day.

Mars oil will flow 116 miles through an 18 in. and 24 in. subsea pipeline to a salt cavern storage site at Clovelly, La. Gas will flow 55 miles through a 14 in. subsea line to a fixed platform on West Delta Block 143. From there, it will move through a 30 in. line to a gas processing plant at Venice, La.

Shell in the next 2-3 years plans to drill another 14 wells to fill Mars TLP's 24 well slots.

Mars TLP specifications

Of Mars' $1.2 billion development cost, Shell and BP will spend about 55% fabricating and installing the deck, hull, related facilities, and pipelines. The remainder will go for well drilling and completion.

Mars TLP's 7,200 ton deck, of open truss framing design, measures 245 ft by 245 ft wide and stands 45 ft high. When fully assembled on site, the TLP will stand 3,250 ft tall from seafloor to the crown block of its drilling rig module.

Helmerich & Payne Inc., Tulsa, is supplying the purpose built drilling unit under a lease agreement. Shell plans to remove the drilling package after drilling the last 14 Mars development wells.

J. Ray McDermott Inc., New Orleans, built the other four Mars TLP modules at its Morgan City, La., yard. McDermott loaded out the first Mars module Sept. 13, 1995. The last module arrived at Ingleside Nov. 13, 1995.

Mars TLP hull consists of four circular steel columns connected at the bottom by pontoons. Each column is 661/2 ft wide and 162 ft high. Each pontoon is 27 ft wide and 24 ft high.

Belleli SpA, Taranto, Italy, built the 15,650 ton TLP hull and delivered it Aug. 31, 1995.

Shell will anchor the Mars TLP with 12 steel tendons, each 28 in. wide with 1.2 in. W.T. Combined weight of the 12 tendons is 6,150 tons.

For installation, crews will connect three tendons to each TLP column on one end and on the other to piles driven into the seabed. Each pile is 84 in. wide and 375 ft long and weighs 260 tons.