BBLT brings firsts to Angola, industry

Dec. 1, 2006
Chevron completed the $2.3-billion Benguela/Belize/Lobito/Tombocco (BBLT) compliant tower offshore Angola ahead of schedule and within budget on Jan. 24, 2006.

Chevron completed the $2.3-billion Benguela/Belize/Lobito/Tombocco (BBLT) compliant tower offshore Angola ahead of schedule and within budget on Jan. 24, 2006. The BBLT structure, a compliant piled tower (CPT) with topsides weighing over 40,000 tons, is situated in 396 m (1,300 ft) of water in block 14. The 512-m (1,680-ft) tower is the first CPT installed outside the Gulf of Mexico and is one of the largest structures in the world. Chevron, with a 31% interest in BBLT, operates the project on behalf of the other Angola block 14 partners: Sonangol, Total and ENI - each with 20% interest - and GALP with 9%.

The BBLT development, located 80 km (50 mi) offshore, is being developed in two phases. Installing the CPT was the first phase. Phase 2 - Lobito/Tomboco - involves the construction and installation of three subsea centers, each able to handle nine subsea wells, tied back to the CPT. When BBLT is fully onstream, maximum total production is expected to be 200,000 b/d of oil.

When planning development of the block 14 fields, Chevron originally called for a conventional floating production storage vessel with subsea completions. Following a design competition, Chevron selected Mustang Engineering’s “bottom-founded” CPT solution for the BBLT project. The term “compliant” in CPT refers to the inherent flexibility of the tower that allows it to mitigate the forces of wind, wave, and currents. The result was cost savings of $230 million.

According to Mustang, which performed front-end engineering design and pre-FEED services for the development, compliant towers provide bottom-founded developments with surface trees in these water depths (396 m or 1,300 ft) at costs appreciably less than conventional structures due to reduced steel requirements. Other advantages of compliant towers include good constructability characteristics and the use of conventional, inexpensive drilling and production risers with dry trees.

Daewoo Shipbuilding & Marine Engineering Co. Ltd. (DSME), the prime $700-million engineering, procurement, construction, and installation contractor, awarded Mustang the engineering contract. Daewoo selected Alliance Engineering, another Wood Group company, to provide project management personnel in support of several phases of the development, leading to first production.

Chevron awarded DSME an $820-million contract for engineering, procurement, construction, and installation of the project’s production facilities, CPT, and the oil and gas export pipelines. KCA/Deutag with partner National Oilwell Varco picked up the $120-million contact for engineering, procurement and construction of the platform drilling rig, and the contract for the future operations and maintenance of the rig.

The KCA/Deutag team started fabrication on the CPT’s integrated 4,600 hp platform drilling rig in September 2003. The primary steelwork fabrication was carried out by Omega Natchiq in New Iberia, Louisiana. National Oilwell Varco supplied the complete package of drilling equipment from its product divisions in Stavanger, Edmonton, and Houston. The completed rig components were then transferred to the Galena Park yard on the Houston ship channel for assembly and commissioning.

The platform rig is capable of drilling to 9,144 m (30,000 ft) and uses AC variable frequency drives. The completed product is fitted with a mechanical pipe-handling system installed in its 1.3-MMlb hook-load derrick, which is equipped with 4,600-hp drawworks and a top drive with 60,000-ft lb torque. The rig also has three 2,200 hp mud pumps rated to 7,500 psi with a total mud volume of 4,625 bbl.

The fully integrated platform rig departed on March 11, 2005, and arrived in Angola on April 19. KCA/Deutag performed hookup and commissioning of the drilling package in Angola, and Heerema handled transportation and installation of the rig on the CPT.

DSME’s offshore division was responsible for fabricating of the production facility’s topside modules. The work was performed at the company’s yard in Okpo, South Korea. The overall topside section has a designed operating weight of 39,463 metric tons (43,500 short tons), and is fitted with capacity to handle 220,000 b/d of oil and 420,000 b/d of water re-injection. The topside production modules were loaded out in early March 2005 and arrived in Angola in early April.

The other two major components of the topside, living quarters and flare boom, were loaded out and arrived in Angola in April 2005 as well. Delta Engineering fabricated the 157-man accommodation module at its yard in Channelview, Texas, and Sonamet constructed the CPT’s drilling template with piles, leveling pile template with piles, flare boom, helideck, and related facilities, weighing over 1,451 metric tons (1,600 short tons), at its yard in Lobito, Angola.

Fabrication of the tower portion of the production facility was split into two sections; Kiewit Offshore Services Ltd. built the tower base section and template, weighing over 23,587 metric tons (26,000 short tons), and Technip’s Gulf Marine Fabricators (now owned by Gulf Island) constructed the tower’s top section, weighing in at almost 7,257 metric tons (8,000 short tons). Both sections were fabricated in Ingleside, Texas.

The CPT’s bottom section consisting of 12 foundation piles, weighing close to 9,979 metric tons (11,000 short tons), was fabricated in Ingleside, Texas, as well.

Chevron issued contract awards for the subsea portion of the project to Subsea 7 and Vetco Gray. Subsea 7 secured the $270-million contract for the 10-km (6.2-mi) tieback of three subsea drill centers to the CPT.

Vetco Gray picked up the three-year, $125-million contract to supply 22 horizontal subsea trees, six manifolds, and the fully integrated subsea and surface control systems. Sonamet is fabricating the subsea manifolds (three production and three water injection) at its yard in Lobito, Angola, for Vetco. The manifolds each weigh around 73 metric tons (80 short tons).

Heerema Marine Contractors, the topsides installation contractor, used its semisubmersibleThialf crane vessel to set the CPT’s topside modules in place over a five-week period. The heavy-lift vessel, equipped with dual 7,100-metric ton (7,826-short ton) cranes, performed 11 lifts ranging from 170 to 10,470 metric tons (187 to 11,541 short tons).

Eldon Ball, Editor-in-Chief

BBLT features

The BBLT platform 80 km (50 mi) offshore Angola in the block 14 concession includes a number of unique features:

  • Is the first compliant piled tower in Africa
  • Has the world’s largest single-piece piles ever installed
  • Has a production rate of 220,000 b/d of oil from BBLT
  • Has the largest Chevron-operated topsides with design operating weight of 39,463 metric tons (43,500 short tons) and an area of approximately 2.5 football fields
  • Provides living quarters for 157 people
  • Has the first fully automated drilling rig in CABGOC - integrated with topsides
  • Is the first offshore production facility in Chevron to enable produced water re-injection up to 420,000 b/d of water.