HOUSTON -- ABS has provided basic design approval for Petrobras' Mono-Column Floater, Production, Storage and Offloading Unit (MPSO) intended for ultra deepwater operation in the Gulf of Mexico. ABS says the approval is significant as it consolidates the MPSO design concept as one viable option for the next phase of the Cascade Chinook development in the GoM. The concept is also being considered for offshore Brazil.
ABS provided an early conceptual stage review of the design and issued its approval in principle in 2005.
"A round FPSO design was unheard of ten years ago," says Luiz Feijo, ABS project manager for the MPSO. "Today we are not surprised by the designs being put forward for classification review. If we are not able to review a design to prescriptive rules then we take a risk-based approach for determining criteria," he says.
For example, the MPSO has some characteristics of a spar but a much shallower draft. The design is such that it minimizes heave and pitch making it more suitable for the application of steel catenary risers. Also, this new Petrobras hull design is intended to reduce heave thus lessening the fatigue on SCRs, Feijo says.
The MPSO was designed to be permanently moored to the seabed, remaining on station for its operational life. This presents a major advantage over the traditional ship-shaped FPSO which would require a disconnectable turret due to the environmental characteristics of the Gulf of Mexico, according to ABS.
The MPSO was assessed by ABS for its hull strength by evaluating load components, conducting fatigue assessments and reviewing the Global Motions and Stability reports. ABS also conducted a Hazards Identification Study (HAZID) to identify possible safety issues associated with the offloading system. Feijo says the intent is for offloading to be carried out using DP-2 shuttle tankers. ABS provided its approval of the DP system on the shuttle tanker design as well.
Since the unit is slated for the GoM, ABS has provided regulatory compliance assistance to Petrobras. "Our extensive experience in the GoM and our ability to work closely with the US Coast Guard as well as the Minerals Management Service has been a valuable contribution to the project," says Feijo.
Petrobras and Japan Oil, Gas and Metals National Corp. (JOGMEC) have been jointly working toward the practical application of the MPSO concept together with partners National Maritime Research Institute (NMRI) and IHI Group in Japan. The unit calls for storage capacity of 800,000 barrels.