Design One, Build Two - FPSO Experience in Deepwater West Africa
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper IPTC 10956, "FPSO Experience in Deepwater West Africa - The Design One, Build Two Strategy," by L.B. Waters, ExxonMobil, prepared for the 2005 International Petroleum Technology Conference, Doha, Qatar, 21–23 November.

The "design one, build two" strategy was used for recent West Africa deepwater developments including floating production, storage, and offloading vessels (FPSOs) for the large Kizomba A and B developments in Angola and smaller early-production-system projects such as those in Nigeria, Equatorial Guinea, and Angola. When properly managed, this strategy reduces project cycle time and cost.

Introduction

The West Africa experience has identified key project conditions required for successful implementation of the "design one, build two" strategy. These include use of the same engineering design, fabrication contractors and yards, vendors and suppliers, and project-leadership teams and -management systems.

From a project-management point of view, this strategy requires approaches that differ from those of traditional standalone projects. This strategy, if properly planned, managed, and executed, can optimize project economics for plays with multiple large developments that have similar geologic, geographic, economic, and contractual elements. The learnings from the West Africa deepwater applications of this strategy can be applied in other large oil and gas development projects.

Implementation

The "design one, build two" strategy captured cost savings on the order of 10%. Completion of Kizomba B tracked 5 months ahead of Kizomba A. Fabrication on the A project fell as much as 30% behind schedule, resulting in multiple execution plan adjustments and recovery plans. The Kizomba B FPSO consistently tracked the original execution plan; progress never fell behind plan, and no recovery plans were required.

FPSO Design. The FPSO designs were maintained as similar as possible while still meeting the infrastructure needs of different reservoirs. Both FPSOs will develop fields in Angola Block 15 in approximately 100 m water depth. Inlet conditions and production rates for the two FPSOs are essentially equal.

Both vessels are new-build, double-sided hulls with single bottoms. They feature identical dimensions (935 ft long, 206-ft beam, and 105-ft depth) and 2.2×106-bbl crude-oil storage capacity. The topside comprises 10 process/utility modules and nine pipe racks. Each features two oil-separation trains for a 250,000-BOPD total oil capacity, 275-MMscf/D gas-handling capacity, and 340,000-BWPD water-injection capacity.

Living quarters for 100 workers is at one end of each vessel, and a 320-ft flare is at the opposite end. The pipe racks run down the center of the vessel with the process and utility models set on either side. Each FPSO comprises 90,000 metric tons of steel, 40,000 pipe spools, 621 miles of electrical cable, 200 tagged equipment items, 120,000 fittings, and 84,000 supports.

The primary modification for the Kizomba B design was addition of subsea production and related flow-assurance provisions. These changes were managed so they affected only a few modules and required addition of only one new module and one additional upper deck for subsea equipment.