Stronger, lighter buoyancy systems improve safety levels
Jennifer Pallanich Hull
Gulf of Mexico Editor
Balmoral Group took its observations about buoyancy needs, added what it found lacking in broken modules that entered its repair yard, and molded these findings into the UltraFloat and, later, RetroFloat buoyancy systems.
Buoyancy providers found various issues cropped up as fields went deeper. The increasing operating depth is what led Balmoral to create the UltraFloat drilling riser buoyancy system. Balmoral worked up the concept for UltraFloat to strengthen buoyancy units while reducing the weight associated with longer riser strings in response to drilling contractor requests to improve buoyancy module safety levels.
"Traditional buoyancy has been made the same way for probably 20 years," said Gary Brown, president of Balmoral Group in Houston. The traditional style of buoyancy is well suited to calm, shallow conditions, not for places like the Gulf of Mexico or off Brazil, where units have not only deeper water but also loop and eddy currents to contend with. "We saw a large proportion of buoyancy units being damaged," he said.
How it works
Brown calls UltraFloat the next generation of buoyancy and says it is tougher than previous systems and stands up better to harsh operating conditions.
UltraFloat's buoyancy comes from a mix of syntactic foam, epoxy resin, hollow glass microspheres, and fiber-reinforced plastic minispheres.
Harsh operating conditions call for abrasion protection to reduce the effect of contact between the dressed riser string and the rig steelwork, Balmoral says. UltraFloat's layer of epoxy composite protects the syntactic foam from this damage. The units must also provide stiffness and flexural performance. The system's composite reinforcement system was designed to enhance module stiffness while increasing flexure tolerance, according to the company. In some cases, extreme impacts or riser flexures will crack or fracture a buoyancy module. These breaks pose a safety hazard to personnel and could damage equipment if module sections become detached during running or pulling of the string. Balmoral said it added UltraFloat's internal reinforcement system to increase the cracking and fracture resistance of the piece in addition to providing residual structural integrity of the piece should it break.
Balmoral unveiled UltraFloat last year, and the buoyancy product has drawn support from Transocean and GlobalSantaFe. GSF already has strings for its Development Driller I and Development Driller II and recently ordered a third string as a backup for these two semis, formerly Rig 184 and Rig 185. When complete, the modules will head to Kværner's yard in Louisiana for dressing before meeting the rig for sea trials.
Because of the amount of time associated with the steel phase of constructing the buoyancy and riser string, it takes 30 to 40 weeks to create a full string.
Once the buoyancy units are complete, 5-10% of the pieces take a 24-hour quality assurance dunking in the Hydrospace Test Center at Balmoral's Houston facility. The facility, which conduced its first trial in November 1999, can test three modules at a time and can accommodate a 21-ft piece. The test simulates the target water depth at a designated pressure for 24 hours. Balmoral then checks the buoyancy lost, seeking less than a 3% loss per unit.
Assessing breaking points
Balmoral recently identified an upturn in the drilling riser module repair business. Modules that had been subjected to the deepwater rigors of GoM and South Atlantic currents were coming onshore in increasing numbers for repair. So, the company established dedicated repair facilities in Houston and Macaé, Brazil. The repair business, originally not expected to be a focus for the company, has developed over the last couple of years, Brown said.
While examining cracked or fractured modules, Balmoral was able to ascertain the weaker spots of buoyancy modules and find ways to offset the weakness in those spots, such as integrating notched clamping areas.
The data gleaned from the repair shop gets fed into the company's in-house development and testing cycle. The information also found itself incorporated into the development of RetroFloat, Balmoral's retrofit system.
RetroFloat
If an UltraFloat module breaks, the unit contains a retention system that holds it together so pieces of the buoyancy system do not fall off. Balmoral devised and patented a way to retrofit UltraFloat's integral retention features to existing modules, Brown said, after Transocean approached the company seeking to add safety retention to existing buoyancy modules.
Transocean was not open to replacing all the units on all of the company's drillships, so the company asked Balmoral to come up with a way to upgrade Transocean's existing buoyancy pieces. Balmoral answered with RetroFloat.
"You can't tell it from a new one," Brown said about the effectiveness of the approach. "It took a lot of development to get there."
In RetroFloat, the retention system is fitted to contain the frequent types of breaks. Developing RetroFloat required finding the balance between retaining buoyancy performance while adding the safety factor. Developing RetroFloat required finding the balance between still providing buoyancy and adding the safety factor. Balmoral opted not to add steel to the units because "it's pretty tough but it doesn't float and it doesn't like salt water," Brown said. Instead, Balmoral uses polymers to accomplish the task.
Balmoral sees its future paralleling the industry's descent into deepwater. The company is studying ongoing seismic programs to evaluate whether it needs to work up buoyancy solutions for 10,000-12,000-ft water depth, Brown said.
