Riser technology is one of the critical components in deepwater production. As offset distance and water depth increase, they exponentially compound the severity and complexity of challenges that riser systems have to overcome. Leading offshore producers, service companies, and research consortia have developed a variety of riser systems, including top-tensioned risers, steel catenary risers (SCRs), flexible risers, integrated risers, and hybrid designs, to deal with greater water depths, harsher operating environments, high-pressure/high-temperature (HP/HT) reservoirs, high-volume wells, and more intricate drilling and production strategies.

At the Offshore Technology Conference (OTC) in Houston in early May, leaders in riser design discussed the progress that has been made and some of the challenges that remain.

Riser technology today, tomorrow

Calvin Crossley, manager of the deepwater risers and pipelines group at ExxonMobil Development Co., talked about the challenges risers must address, noting that they are working at 7,000 to 10,000 ft (2,100 to 3,000 m) water depth in harsh environments on large-scale developments where fluid service conditions are a concern. These challenges are compounded in many areas, Crossley said, by the need to meet local content objectives.

All of these issues fall into the category of challenges that require “attention to fundamentals,” Crossley said. “These challenges will arise in every possible combination. The next generation of riser systems will face the challenge of raising the bar considerably.”

In his opinion, finding solutions will require applying sound engineering principles, making continuous advances in analysis techniques, rigorous validation with carefully designed testing programs, appropriate prototyping, careful management of the remaining uncertainty, monitoring performance and tracking lessons learned, and continuing to reassess underlying assumptions.

Dr. Pieter Wybro, deputy chief executive and chief technology officer of INTECSEA, focused his comments on the progress made in the field to date and the expectations for future advances.

Wybro identified a range of challenges, including:
• Drilling issues (such as severe environment and depth, drilling costs, and the need to reduce the platform payload);
• Intervention concerns (including the large number of subsea completions, high rig costs and limited availability, and the need to adapt shallow-water free-standing intervention risers for deepwater applications);
• Production limitations (such as the need for competitive dry-tree risers for water depths greater than 6,000 ft (1,830 m), dry-tree risers for semisubmersibles, HP/HT concerns, fluid properties, and high waves and currents);
• Export issues (including the need to contend with the seabed, flow assurance, water depth, and component feasibility).

All of the technical challenges identified are compounded by low oil and gas prices that lead to the expectation that risers will become less expensive. Researchers are being pressured by customers chanting “deeper and cheaper!” Wybro said.

The problem is that progress is not linear and normally not rapid. “We make changes by nudging the limits, not by leaps and bounds.”

Craig Masson of Petrobras Americas Inc. addressed some of the challenges that ship-shaped vessels pose for riser performance. “Currently, conventional riser solutions are not feasible options combined with a ship-shaped FPSO,” he said, explaining that the motions are too severe for SCRs.

Petrobras’ concern is based somewhat on the company’s deployment of the first floating, production, storage, and offloading (FPSO) vessel on the Cascade Chinook field, at a water depth greater than 8,000 ft (less than 2,400 m) in the Gulf of Mexico (GoM).

“The only option is the free-standing hybrid riser,” Masson said, “because it combines the strong points of a steel riser and a flexible riser for use with an FPSO.”

Because the hybrid riser design necessitates a multidisciplinary approach, it requires a large team of experts in slender construction, hydrodynamics, and vortex induced vibration. In the case of Cascade Chinook, that team was provided by Technip.

Though the solution is a good one for this development, Masson said, there are “significant drawbacks,” including expense, a long lead time for materials, and logistics, all of which impact the project schedule.

Other interesting riser issues addressed at OTC included the changing design criteria standards that will impact flexible riser deployment in the GoM, an aspect of technology in which MCS is investing a great deal of energy. The information presented is the outcome of a four-year joint industry partnership led by MCS and represents the first major revision of the API and ISO standards since the originals were produced in the mid-1990s. The work of the JIP is due to be completed later this year.