Chevron’s subsea development of the Lobito and Tomboco fields offshore Angola met its start-up plan despite a compressed schedule and difficult logistics.
The Benguela, Belize, Lobito, and Tomboco fields are in block 14, about 80 km (50 mi) off the Angolan coast, in up to 396 m (1,300 ft) of water. Together, they make up the BBLT Development, one of Chevron’s major capital projects, operated by its Cabinda Gulf Oil Co. Ltd. subsidiary.
The Lobito/Tomboco project involved the tieback of three subsea drilling and production centers to the Benguela/Belize compliant tower. Each drill center has a production manifold with slots for up to five wells, a water injection manifold with slots for four wells, and a subsea distribution unit. There were 15 pipelines to connect the manifolds and wells back to the platform, comprising 3-in (76 mm) methanol, 6-in (152 mm) gas lift, 8-in (203 mm) test, 10-in (254 mm) production, and 12-in (305 mm) water injection lines. Flexible jumpers connected the pipelines to the manifolds and tree umbilicals at each drill center.
Subsea 7 was awarded the engineering, procurement, installation, and commissioning contract for the subsea installation in September 2004. The project involved the manufacture of 120 km (75 mi) of pipelines as well as 24 associated pipeline end terminations (PLETs), and three umbilicals totaling 29 km (18 mi) in length. There were also 30 flexible jumpers and 22 flying leads, three production manifolds, three water injection manifolds, and three subsea distribution units. These were provided by others, but installed and connected by Subsea 7. All the equipment installed on the seabed was tested and commissioned.
One of the company’s most significant achievements involved building a pipe fabrication facility at the Sonils base in Luanda. At the time of the award, the spoolbase site was under water, and land had to be reclaimed on a tight schedule to allow site construction work. Pipe welding was taking place at the spoolbase within eight months of the start of dredging. Another achievement was the training and employment of Angolans to weld and fabricate the pipe stalks.
Reclaiming land for the spoolbase.
The choice to use Sonils was beneficial because of the company’s location in the shelter of Luanda harbor, the comprehensive and professional services provided by Sonils, and direct access to other local support services the spoolbase required for everyday operations. Also, being close to the city allowed Subsea 7 to access a higher percentage of local personnel for spoolbase operations. One of the company’s main objectives with the Lobito/Tomboco project was to train and employ Angolan nationals. All 24 PLETs were fabricated in the Sonamet yard, with Angoflex manufacturing the three umbilicals. Both of these facilities are in Lobito.
The Lobito/Tomboco project involved building a spoolbase from open water to production within eight months and the technical decision to use coiled tubing for the methanol pipe reduced pipe stalk fabrication time in an already tight schedule at the spoolbase. The coiled tubing pipe was delivered on individual reels, trans-spooled onto two larger offshore reels, and finally installed using the piggy-back method on the 12-in. (305 mm) water injection pipeline. The piggy back approach required the standard PLET to be modified for hot stab connections to the 3-in. (76 mm) methanol jumpers, but also resulted in savings in offshore installation time.
Offshore work began in February 2006 with Subsea 7’s reel lay vesselSkandi Navica starting pipelay operations. It was joined a month later by the construction vessel Toisa Perseus. Each vessel spent about 100 days working offshore Angola in an integrated schedule that saw Chevron achieve first oil ahead of plan. At its peak, Subsea 7 had seven vessels in the field and more than 300 people working in Angola. There were no lost time incidents throughout the installation work.
The biggest challenges lay in achieving the fast-track schedule and difficult logistics, having to engineer, procure, install and commission the pipeline, flexible jumpers, umbilicals, and PLETs in Angola - all within 22 months - all preceded by shipping the parts and equipment into Angola.
Heather Beresford
Subsea 7
