Brutus, Gulf of Mexico, USA

Brutus is located 165 miles south-west of New Orleans. Target reserves are in the Plio-Pleistocene sands, at a depth of 12,500 to 17,500ft, subsea.

In December 1988, the Brutus discovery well was drilled on Green Canyon Block 158. In 1994, an appraisal well was then drilled on the same block. In April 1999, Shell (100% owners) announced plans to develop Brutus, using a tension leg platform (TLP) for installation on the same block, in 2,985ft of water. The tension leg platform consists of five modules weighing 11,500t.

The estimated ultimate gross recovery from the development is greater than 200 million barrels of oil equivalent (boe), with a 70:30 oil to gas ratio. Average API gravity for the oil is low-mid 30 degrees. Sulphur is at 1.5%.

The batch setting of the eight wells was completed on 3 January 2000, using Diamond's Ocean Worker semi-submersible drilling rig. Six of the planned development wells for the eight-slot TLP were subsequently predrilled, with the well layout on the seafloor arranged in a rectangular pattern.

In February 2002, the Brutus tension leg platform was closed due to valve failures in the production processing system.

Shell utilised this downtime to increase the production capacity to 130,000 barrels of oil per day. At that juncture Brutus was producing 60,000 barrels and 90 million cubic feet of natural gas per day from four wells.

Design

The TLP facilities are designed to accommodate a peak gross production of approximately 110,000 barrels of oil per day and 150MMcf/d of gas. The TLP will be used as a hub for surrounding developments and thus, it is designed to handle an amount of gas greater than that required for the Brutus development (which is about 150MMcf/d of gas). Completely assembled, the TLP will be 3,250ft high, from the seafloor to the crown block of the drilling rig.

The hull is comprised of four circular steel columns, 66.5ft in diameter and 166ft high. Pontoons connect the columns, which will be 35.5ft wide and 23ft high, with a rectangular cross section. The hull will weigh approximately 13,500t, with a total displacement of 54,700t. Daewoo Heavy Industries had delivered the hull in January 2001.

The installed deck is 245ft² and approximately 40ft high. It is composed of five modules: processing, drilling, power, living quarters and a wellbay.

The deck modules are set in an open-truss frame design with a total structural steel weight of approximately 7,650t. The total topside weight will be approximately 22,000t, including all process equipment and the drilling rig.

Development

J Ray McDermott is building the modules at its Amelia fabrication yard in Los Angeles. In 2001, the modules were delivered at CSO Gulf Maritime's integration yard.

The hull and deck were integrated at Aker Gulf Marine's Ingleside fabrication yard, near Corpus Christi, Texas. The five-deck modules were lifted into position on the hull, using the specialised lifting device originally developed for the Mars TLP integration.

The TLP supports a contract-drilling rig, equipped with a surface BOP and a high-pressure drilling riser. The quarters module will be able to house up to 94 people.

The TLP is secured by 12 tendons, three per corner, each with a diameter of 32in and a wall thickness of 1.25in. Each tendon is approximately 2,900ft long. The total weight for the 12 tendons is approximately 7,500t.

The TLP foundation system is comprised of 12 piles, to which the tendons will be attached. The piles will be 82in in diameter and 340ft long, weighing approximately 245t each. Aker Gulf Marine will fabricate the piles and tendons at their Ingleside fabrication yard.

Production

Oil production is piped approximately 26 miles via a 20in-diameter pipeline to the South Timbalier 301 B platform, where it is then connected to the existing Amberjack System.

Gas will be piped 24 miles via a 20in gas pipeline and is connected to the existing Manta Ray Offshore Gathering System in Ship Shoal Block 332.

Installation of the TLP took place in mid-2001. Heerema is the contractor for the installation, using the derrick barge Hermod.

The production was on track from August 2001.