Physical modeling of deepwater projects can be a very useful tool. Despite the advent of computer modeling and immersive computer visualization environments, physical 3D models help vessel operators, riggers, and field engineers find potential problem areas and resolve spatial issues.
Robert (R.J. “Bob”) Brown builds intricate 3D physical models to map the installation of complex subsea systems with many risers and mooring lines. Brown runs R J Brown Deepwater, a subsidiary of Technip that specializes in deepwater energy engineering. His models incorporate subsea system components such as pipelines, manifolds, risers, mooring lines, as well as floating facilities and support vessels.
Brown reviewed the benefits of physical modeling for deepwater pipeline and riser installations in a paper presented at the Offshore Technology Conference in May 2009 (OTC 19962). Brown and Arash Razavinejad, a senior staff member at Genesis Oil and Gas, explained deepwater models and systems in Technip’s Houston model lab in October.
Thunder Horse model
Thunder Horse production-drilling-quarters (PDQ) is the world’s largest production semi-submersible, installed over the deepwater Thunder Horse oil field in the Gulf of Mexico, about 150mi. southeast of New Orleans. It’s moored in 6075ft (1852m) of water in Mississippi Canyon Block 778, was completed in 2005, and delivered first oil in June 2008. Thunder Horse is a joint venture of BP plc (75%) and ExxonMobil (25%).
Technip’s suspended model of the Thunder Horse PDQ includes catenaries and work vessels at a scale of 1:650. A catenary is the curve that an idealized hanging cable assumes under its own weight when supported only at its ends. Bob Brown said the shapes of all the suspended lines in the model are accurate catenaries. Although the mooring lines, umbilicals, production, water, test, and export risers are modeled with different lightweight cords, they respond to gravity in the same way as the actual risers. The only difference is the vertical load in the hanging point of each catenary.
The PDQ can only move within a 350-ft radius due to constraints of the suspended umbilicals. The model is used to measure interferences between rigging, mooring, hull, vessels, flare booms, etc.
The work vessels have 2500hp, 6-wheel drive motors, and the suspended framework allows engineers to simulate yaw (rotation around the vertical axis; side-to-side movement of the ship’s bow), surge (linear longitudinal, front-to-back motion), and sway (linear lateral, side-to-side motion).
Exact coordinates of the PDQ and each vessel is drawn on the seabed (floor of model room) using Autocad. The positions are projected using laser plumb bobs for accurate positioning.
The model was used during the installation of the 21 pipeline end terminations (PLETs) and BP Thunder Horse subsea manager John Bednar congratulated Brown and his colleagues Ken Cross and Kevin Feizkhah, saying the model “provided an unusually effective vehicle for analysis and procedure development, as well as for training and visual demonstrations.”
Frade model
The Frade field is in the northern Campos basin, 122km off the coast of Brazil, in water 3280ft to 4429ft (1000m to 1350m) deep. The area has an irregular sea-bottom and is subject to high and unpredictable bottom currents. Chevron used Acergy’s CSV Polar Queen, a flexible pipelay and subsea construction vessel, to install flexible flowlines, risers, PLETs and umbilicals at Frade.
After field installation, Chevron needed to wet park 18 flexible pipe risers and 4 umbilical risers. Then, after the turret FPSO was in place, the risers and umbilicals needed to be recovered from 3494ft (1065m) water depth and transferred to the Frade FPSO.
In October 2008, Chevron contracted the team from RJ Brown Deepwater to model the wet park, recovery, and installation of the risers, umbilicals, and 9 mooring lines before the work was done in the field. They constructed a 1:290 scale model and held five model simulations of Chevron’s planned procedures (laydown, keel haul, mooring, POQ pull-in, NM pull-in), all videotaped in the Technip model room. The main challenges were examining the wet park curve, anchor clamp chain installation, riser recovery route, transfer depth, and assessing interference risk. The model work highlighted several problem areas with risers and orientation of the installation vessel, and improved the actual field procedures. Acergy authors reviewed the results of the Frade work in a paper presented at the Offshore Technology Conference in May 2010 (OTC 20850).
Chevron’s Frade flexible pipe coordinator, Antonio Critsenelis, said “the model exceeded expectations” and said he would “certainly recommend it for other projects as a high-value design assurance tool…Chevron and the installation contractor [Acergy]…certainly benefited from the insightful learning form the simulations.”
Bob Brown reviewed the benefits of physical modeling for deepwater pipeline and riser installations in a paper presented at the OTC in May 2009 (OTC 19962). Brown’s career was built on his early innovations in marine pipelining, and he was inducted into the Hall of Fame at Galveston’s Offshore Energy Center in January 2009 as an Industry Pioneer, for innovations that made marine pipelining more efficient and much safer. OE
Image Caption (2nd from top): Bob Brown, left, and Arash Razavinejad manipulate the Thunder Horse subsea model at Technip facilities in Houston.
Image Caption (3rd from top): Bob Brown, left, and Arash Razavinejad manipulate the Thunder Horse subsea model at Technip facilities in Houston.
Image Caption (bottom): Bob Brown and assistant Carolina Sones discuss the tabletop model of the north half of the Thunder Horse PDQ.
Photos: Nina Rach
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