Challenges posed by the hostile environmental characteristics of Brazilian presalt oil and gas fields have prompted Petrobras to weigh use of rigid risers instead of flexible risers, which are mostly used by the company offshore Brazil.

Such characteristics include polluting gases, specifically CO2. Challenges have resulted in what experts call stress corrosion cracking (SCC). SCC causes riser structures to fail, suspending production of fields and threatening the environment with possible oil and gas leaks. Petrobras is evaluating how flexible risers can be improved to avoid corrosion during E&P presalt activities.

The company’s eyes were opened to the problem after there were two failures regarding TechnipFMC-supplied risers in 2017 in the Lula and Sapinhoá presalt fields, two of the company’s top-producing fields. The incidents prompted Petrobras to think about changing its pipeline connections in presalt fields, using rigid risers.

“Petrobras’ goals are always to seek the best technical solution for each project,” Felipe Matoso, subsea engineering general manager for Petrobras, said in October 2017. “We have a greater tradition of using flexible risers mainly because we have a local industry more focused on flexible risers. But today our goal is to seek competitiveness in that segment, according to project characteristics.”

Matoso said Petrobras is planning to promote a competition between rigid and flexible risers to evaluate which solution is best for each presalt project.

Petrobras has not set a timeline for its riser model evaluation process for presalt fields.

But “choosing the best strategy will address technical and economic issues, promoting competition between different solutions, according to project characteristics,” the company said in a statement. “Petrobras has in its register the main suppliers of this equipment worldwide. Other companies will also be in the process of technical qualification.”

Flexible Risers

For more than two decades, flexible risers have been successfully adopted in Brazil’s deep and ultradeep waters, and Petrobras decided to bring this equipment to its presalt fields.

Comprising various layers of different materials such as an inner flexible metal carcass, leak-proof thermoplastic barriers and spiral wound, corrosion-resistant steel, use of flexible risers dates back to the early 1970s when they were used in relatively benign and shallow water areas such as offshore West Africa, the Far East and the Mediterranean.

Today the equipment can reach up to nearly 2,250 m (7,382 ft) water depth in configurations that include the “steep S” and “lazy S,” using anchored buoyancy modules, as well as the “steep wave” and “lazy wave,” incorporating buoyancy modules. Flexible risers are able to withstand severe vertical and horizontal motions in adverse weather conditions.

TechnipFMC is Petrobras’ main supplier for flexible risers, although NOV and GE also have contracts for flexible risers supply services. It is estimated that Petrobras can spend up to $300 million for each contract.

Rigid Risers

The possibility of contracting rigid risers for Petrobras can mean business for more supply companies, such as Vallourec and Tenaris, which work in this segment.

There are some benefits for rigid risers, some say.

“Rigid risers can be very competitive in the presalt E&P activities. They are cheaper and have more resistance against corrosion,” Ilson Paranhos of Rio de Janeiro Federal University said.

He added that rigid risers typically have a service life of between 25 to 30 years, and they can handle the HP/HT conditions typically found in Brazil’s ultradeep water.

However, “other aspects must be evaluated such as logistics and the presalt characteristics,” Paranhos added.

He explained that the corrosion resistance of rigid risers is guaranteed by the high properties of the carbon steel used, which is coated internally with a layer of corrosion-resistant alloy (Inconel) through a clipping process, a technology known for decades and widely used in the global offshore sector.

“The advantage of using the rigid riser is the possibility of manufacturing lines lighter and [in] larger diameters, which offer greater oil flow and, consequently, greater capacity of production,” explained Vallourec Superintendent of Quality Júlio Márcio Silva. “Rigid pipes have an internal diameter of 14 inches. They can produce more with less cost [for] infrastructure, installation and maintenance.

Over the past 10 years, Petrobras’ presalt activities have been successful. Currently, presalt activities accounts for roughly 50% of Brazil’s total oil output of 2.6 MMbbl/d. Production is expected to grow further as new auctions set for this year and 2019 work to lure potential investment.

Comments