FPSO Nexan Buffalo External Turret
Scope of Work
SOFEC designed, constructed and supplied an external turret mooring system for a MODEC-converted 103,000 dwt FPSO in BHP Petroleum’s Buffalo oil field, located in Western Australia’s sector of the Timor Sea. The selected option to develop the Buffalo field consisted of a wellhead platform producing to the nearby leased FPSO vessel. The Buffalo reservoir lies below the shallow portion of the Big Bank, which is surrounded by deeper water ranging from 255 to 350 meters.
Although the number of risers (6) were small, and the waves moderate (4.6 meters significant), the severely sloped seabed (up to 75 degrees) and high currents (5 knots) presented a unique challenge to both mooring and riser designers. The two anchor legs on the bank have an all-chain double catenary configuration, and terminate in a depth of 28 meters. The four deep water anchor legs are of the single catenary type utilizing both chain and wire rope, and terminate in depths ranging from 280 to 330 meters.
General Description
| Client Name: | *Nexen Petroleum Pty. Ltd. |
| Contract Award: | October 1998 |
| Installation Date: | December 1999 |
| First Oil: | December 1999 |
| Decommissioned: | December 2004 |
| Vessel Size: | 106,000 dwt |
| Storage Capacity: | 800,000 bbls |
| Water Depth: | 255m (837ft) @ FPSO |
| Anchors @ | 30 - 350m (98 - 1,148 ft) |
| Fabrication: | Turret - Malaysia Vessel - Singapore Topsides - Singapore |
Design Environmental Criteria
(50-year storm)
| Maximum Wave Conditions Significant Wave Height: | 4.6m (15ft) |
| Wind Velocity: | 21.3m/s (41.4 knots) |
| Current: | 2.1m/s (4.1 knots) |
| Maximum Wave Current Significant Wave Height: | 4.1m (13.6ft) |
| Wind Velocity: | 21.3m/s (41.4 knots) |
| Current: | 2.6m/s (5 knots) |
Mooring System
Turrets
6-leg Symmetric catenary:
4-in. ORQ chain
3.75-in. 6-strand wire
20mt & 40mt drag anchors
External Cantilevered Bow
Fluid Swivel Assembly
| Product Fluid Swivel: | Single path toroid with dual 8-in. outlets |
| Gas Lift Swivel: | 1 x 6-in. toroid (2,220 psi design) |
| Hydraulic Swivel: | 15 paths |
| Electrical Swivel: | 16 paths |
| Optical Swivel: | 10 paths |
Riser System
1 x 10-in. Flexible riser (production)
1 x 4-in. Flexible riser (gas lift)
1 Umbilical (hydraulic / electrical)
3 planned for future
Comments
This SOFEC external turret mooring system is ABS classed.
*Transferred ownership from BHP Petroleum Pty. Ltd.