BBLT, Block 14 Compliant Piled Tower (CPT), Angola

The Benguela, Belize, Lobito, and Tomboco fields form the BBLT development. It lies in deepwater block 14 off Angola, in the lower Congo basin.

The block lies in 1,280ft of water covering 1,560 square miles. The $2.2bn development centres on the first Compliant Piled Tower (CPT) outside the Gulf of Mexico. The CPT measures approximately 512m (1,680ft) from the seafloor to the top of its derrick. This ranks it as the fifth tallest freestanding structure in the world, standing 212m (694ft) taller than the Eiffel Tower.

Block 14 is operated by Cabinda Gulf Oil Co. Ltd., a subsidiary of Chevron with 31%. The other partners are Agip Angola 20%, Sonangol 20%, Total Angola 20% and Portugal's Petrogal Exploration 9%.

The work is being carried out in a two-phase programme. The first phase consists of the Benguela and Belize developments. It is a compliant piled tower supporting an integrated drilling facility. It includes drilling and completion for more than 30 developments wells from the 40-slots.

The second phase is to develop the Lobito and Tomboco fields, which will produce via subsea wells tied into the central production hub. It will see a combined peak production of 200,000b/d by 2008.

Daewoo was awarded an $820m contract from Mustang, for engineering, procurement, construction and installation of the project's production facilities, CPT, and the oil and gas export pipelines.

The topside modules were built at the yard Daewoo's Okpo in South Korea. The topside section has an operating weight of 43,500t. Delta Engineering fabricated the 157-man accommodation module at its yard in Channelview, Texas.

Meanwhile, Sonamet constructed the drilling template, piles, flare boom, and helideck all weighing over 1,600t, at its yard in Lobito, Angola. Included in the topsides equipment are the facilities to handle 420,000b/d of water re-injection.

JACKET CONSTRUCTION

Fabrication of the tower portion of the production facility was split into two sections.

The tower base section and template, weighing over 26,000t was built by Kiewit Offshore. Technip's Gulf Marine Fabricators constructed the tower's 8,000t top section, The CPT's bottom section consisted of 12 foundation piles, weighing around 11,000t, These were also fabricated in Ingleside, Texas.

SUBSEA CONTRACTS

The subsea part of the project went to Subsea 7 and Vetco Gray.

Subsea 7 won the $270m contract for the 10km tieback of three subsea drill centres to the CPT. The work included fabrication and installation of the steel pipelines, flowline jumpers, connectors and umbilicals, as well as installation of the subsea manifolds.

The steel flowlines were fabricated at the spoolbase in Luanda and the installation work was assigned to the pipelay vessel Skandi Navica.

Vetco Gray carried out the three-year, $125m contract for of 22 horizontal subsea trees, six manifolds, and the fully integrated subsea and surface control systems. The 80t subsea manifolds (three production and three water injection) were built at Lobito, Angola, for Vetco.

THE DRILLING RIG

The $120m engineering, procurement and construction operations and maintenance of the platform drilling rig was won by KCA/Deutag and National Oilwell Varco.

CPT's integrated platform is capable of drilling to 30,000ft. It uses AC variable frequency drives. It is fitted with a mechanical pipehandling system installed in its hook-load derrick. This is equipped with 4,600hp drawworks and a top drive with 60,000lbft torque.

The rig also has three 2,200hp mud pumps rated to 7,500psi with a total mud volume of 4,625bbl.

The CPT's topside modules were lifted by Heerema's semi-submerisble crane vessel Thialf over a five-week period. When the 10,470t north module was installed, it represented Heerema's largest installation using the Thialf's anchorless dynamic positioning system. The vessel's dual crane capacity provides for tandem lifts of up to 14,200t.