TotalFinaElf's Girassol project uses innovative riser towers to bring production up from the deep, but before it could do so, it needed a buoyancy system to take the weight off the production risers.

Thermal insulation and buoyancy-to-mooring specialist Balmoral Group has carved a name for itself by bringing several drilling-related product lines to the drilling market.
These include a family of thermal insulation and buoyancy, advanced drilling riser buoyancy and ancillary engineered elastomer products.
Jim Milne, chairman and managing director of Balmoral, said: "We began our deepwater R&D program back in the early '80s, and it has taken almost 20 years to see our products being used in the way we predicted."
TotalFinaElf's Girassol project is 93 miles (150 km) off Angola in 4,429-ft (1,350-m) waters. The US $2.7 billion project is unique in many aspects, not least because of its requirement for thermal insulation and buoyancy on the three riser towers and sea-line bundles.
Balmoral secured the industry's highest-ever value insulation contract for Girassol and developed a completely new syntactic foam system. It had to be manufactured to very tight tolerances, able to withstand temperatures of 193°F (90°C) and pressures to 2,320 psi, and provide a 20-year service life.
Balmoral's solution was Ultratherm, a pure syntactic system offering ultimate insulation performance, temperature tolerance, collapse resistance and hydrothermal stability. Ultratherm can work to depths of 9,843 ft (3,000 m), the company said.
Girassol's riser towers required cladding in nearly 4,000 modules using two designs, while the sea-line bundles required a further 6,500 modules. End-to-end, these modules would stretch 150 miles (241 km).
The Girassol towers and bundles were installed earlier this year, and first oil is due to flow before the end of 2001.
For a different deepwater solution - this time an advanced drilling riser buoyancy system - Balmoral introduced UltraFloat, which Santa Fe chose for its new-build semisubmersibles 184 and 185.
Low density, minimum cost
Deepwater drilling has necessitated the use of ultraheavy-construction drilling risers. And to address the potentially massive increase in drillship tensioner loads, drilling contractors have asked buoyancy module manufacturers to produce syntactic foam of the lowest possible density at a minimum cost.
While considerable density improvements have been achieved with advanced materials, much of the requested density reduction can only be achieved by eroding safety factors in critical performance characteristics such as water ingress, creep and hydrostatic collapse resistance.
Standard "improved" syntactic foams have failed to address structural performance, impact resistance and flexure damage from vessel motions and high ocean currents operating on the drillstring.
Module integrity and safety
Cracking and full fracture of buoyancy modules is a regular feature of deepwater drilling. While module repair and replacement have major cost and operational impacts, of far greater importance to drillship operators are the hazards of injury to personnel and damage to equipment associated with the breakup of cracked modules while running drillstrings and riser joint handling. The UltraFloat system was designed specifically to address impact and flexure damage, as well as a lack of residual structural integrity in damaged traditional modules (Table 1).
To find out how the UltraFloat system performed following extensive development, Balmoral subjected it to a rigorous bend and impact-testing program at its Aberdeen, Scotland, technical department, where full-sized modules can be subjected to three-point bend and swing-hammer impact testing.
The bend test involves loading by a hydraulic cylinder on the top of the module. Load and deflection can be recorded for each test to produce a graphical result.
Initial module-bending trials demonstrated the massive enhancement in permissible module and riser deflection and outstanding residual structural integrity of the UltraFloat module. During the initial stages of the bend test, the UltraFloat module demonstrated a 25% stiffness enhancement over the standard module.
Thereafter, the flexure tolerance of the UltraFloat system became manifest. Whereas a standard module suffers sudden and complete fracture at a deflection of 20 mm to 30 mm, UltraFloat resisted major cracking up to about 70 mm. Beyond this, the module suffers internal cracking but retains its full structural integrity until final fracture at about 90 mm. Even after final fracture, internal reinforcement ensures the UltraFloat module still may be handled safely as a single unit, without pieces breaking off.
"UltraFloat is a huge step forward for the drilling sector," Milne said. "Most importantly for me, though, is the improved safety performance of the modules. It is recognized that fatalities have occurred in the industry due to the failure and breakup of riser buoyancy modules. This is the something the industry had to address. As far as I know, Balmoral is the only company to have researched, developed and brought such a product to market."

Comments