Ultra-Deepwater Production System: Model Test Study of Cylindrical FPSO in GoM Hurricane Conditions

Abstract

Abstract To address the challenges of Gulf of Mexico (GoM) Lower Tertiary exploitation, alternative FPSO concepts are studied by the industry. This paper documents Phase 2 of a UDW RPSEA study which had as its main objective the validation of a production concept based on a permanently moored cylindrical FPSO designed by Sevan Marine with steel catenary risers (SCR). The present work focuses on model testing of the cylindrical FPSO hull design, performed at the Offshore Technology Research Center (OTRC) at Texas A&M University in College Station, in May 2016. The experiments were performed at a scale of 1:64. The model was subjected to the Central GoM Hurricane environmental conditions. The process of analysis includes extreme hurricane waves, wind, and currents, combined with ultra deep water, to demonstrate the feasibility of the concept in the GoM. This combination implicates complex hydrodynamic behavior of the hull, mooring and riser system. Thus, the model test provides better understanding of the new concept performance. Model test results, including motions and mooring loads, are compared with numerical predictions for a series of test cases. The importance of viscous effects on motions of the cylindrical unit and of the green water effect is discussed. Finally, to assess the feasibility of the hull and riser system, the numerical results of a hybrid approach, full scale, coupled riser analysis are presented, as based on measured hull motions and environmental conditions. This is finally followed by a discussion of the implications of technical and regulatory aspects of the FPSO concept. Following the project criteria, the present system based on SCR configuration seems feasible; however optimization of hull and mooring system is necessary to improve green water and viscous effects on hull motions in extreme current. The paper represents one sub-scope of the RPSEA study "Low Cost Flexible Production System for Remote Ultra-Deepwater Gulf of Mexico Field Development.", Project No. 10121-4404-03.