OTC 2015: Doris updates subsea projects offshore Angola

HOUSTONDoris Engineeringhas been involved in one major expansion/upgrade program and studies for three new field developments offshore Angola. Company officials, exhibiting at this year’s Offshore Technology Conference in Houston, providedOffshorewith an update on these projects.

Presently, the company is working for operator Total on the Dalia debottlenecking project in block 17 offshore Angola. Dalia was the company’s second deepwater hub development on the block, producing first oil at the end of 2006 through a 264,000-b/d capacity FPSO. In addition, the facility is designed to handle 405,000 b/d of liquids from low-gravity Upper Miocene turbidite reservoirs, and to supply a similar volume of injection water, along with 240,000 b/d of seawater.

Dalia’s subsea production system currently comprises 37 oil producer wells on four loops; three gas injectors on two gas injection lines; and 31 water injectors on four injection lines. Total plans a series of new developments including further infill/stepout wells (Phase 1a); tie-ins of additional reservoirs and extension of water injection (Phase 1b); debottlenecking of the liquid process chain and improvements to water injection (Doris’ responsibility); and a notional drilling phase to saturate the available well slots (Phase 2).

The main aim of the debottlenecking is to restore the liquid treatment and water injection capacities to the initial design parameters. A secondary aim is to extend the oil production plateau and to compensate for the lack of reservoir pressure support provided by water injection previously.

“The program involves numerous modifications to existing equipment on the FPSO,” Doris chairman Loïc des Déserts said, “and adding new equipment to maintain the plateau. There is much more work to do compared with Total’s previous upgrades to theGirassolFPSO in the same block.”

Last December, Eni produced first oil from the West Hub development in block 15/06, 130 km (81 mi) west of Soyo, via the 100,000-b/d capacityN’GomaFPSO. The development calls for progressive tie-ins of at least six fields in water depths of 1,000-1,500 m (3,281-4,921 ft), with 21 wells initially over three of the discoveries. Doris provided support for and an independent review of various subsea components of SURF contractor Technip’s EPCI detailed design for the Mpungi tieback (flowlines, pipeline end terminations and spools).

Additionally, the company undertook front-end engineering design for a subsea multi-phase boosting station and for a tie-in of the Vandumbu field; conceptual studies for a future tie-in of the recent 300-MMbbl Ochigufu discovery; and a gas export system connecting to the Angola LNG network.

Eni’s East Hub project, another FPSO-based development in the same block, is due to come onstream in 2017. Here, Doris has provided support for and an independent review of Saipem’s EPCI detailed design, including the flexible risers and umbilicals, flowlines, PLETS, and spools. Additionally, it has performed engineering for future tie-ins focused on the risers (interfacing with the ongoing FPSO detailed engineering) and the field layout.

In Angola’s offshore block 14, Doris’ Houston and Luanda branches have completed the scope for the FEED for tying back the 2006 Malange discovery to Cabinda Gulf Oil Co.’s Tombua Landana compliant tower, 14 km (8.7 mi) to the southwest. Water depths range from 244 to 366 m (800 to 1,200 ft). The current plan is to install two subsea production centers and a single well mid tie-in, with equipment including riser base gas lift and chemical injection systems. However, the project is currently on hold due to the lower oil price.

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