FPSOs in Storm-Prone Areas to Benefit from New Mooring System

Using SCRs in disconnectable mooring system will aid companies' cost-cutting efforts.

Atlantia SBM announced new technology for a lower-cost disconnectable mooring system for deepwater FPSOs Wednesday at the Offshore Technology Conference (OTC).

Called the MoorSpar ™ system, the technology uses lower-cost steel catenary risers (SCRs) as part of the mooring design instead of flexible risers and jumpers or a single line offset riser. Previously, the use of SCRs was limited by fatigue issues since they are sensitive to floater heave. "This technology will be especially usable in areas such as the Gulf of Mexico, Eastern India, Western Australia and China," said Philippe Lavagna, SBM Atlantia engineering project manager for the MoorSpar system. "Through this system, we are able to discouple the heave motion from the spar."

The MoorSpar unit consists of a truss structure set atop a long, slender buoy and moored to the seafloor by a combination of lateral polyester lines and vertical tethers. The FPSO is connected to the facility through an articulated yoke system linked to a main roller bearing situated below a gimbal table at the top of the MoorSpar unit. This arrangement accommodates the vessel's roll and pitch motions, while allowing the FPSO to weathervane. SCRs are, in turn, connected to the MoorSpar unit at riser porches located along the keel of the buoy. The risers are then linked to internal piping which is routed up through the central column and then across hard piping and swivels to the FPSO. The MoorSpar system also can be used in reservoirs with high pressure and high temperature issues.

Model tests were conducted with a considered water depth of 8,000 ft. and an Aframax-size FPSO with 80,000 bopd production facilities. Disconnect time for the MoorSpar is approximately eight hours with reconnection assisted by a standby vessel at approximately four to six hours.

"The MoorSpar system fills a technology gap," said Lavagna, "yet it uses proven technology in a new combination." For a specific project, Lavagna estimates there will be approximately six months of FEED design with detailed design, fabrication and installation lasting another 24 months for a total delivery time of 30 months.

"Typically, up to now, deep and ultra-deepwater FPSOs had no choice but to use expensive riser towers or hybrid riser systems as the vessel's heave motions prohibit the use of SCRs," said Lavagna. "The MoorSpar system basically eliminates fatigue issues while at the same time allowing for disconnection in the event of a storm."

Share this article with friends and coworkers.

Visit Rigzone, the leading source for news in the oil and gas industry.