The cylindrical FPSO is now in operation at three offshore oilfields, on in Brazil and two in the UK Central North Sea. It is furthermore selected for a field development in the harsh and sub-arctic Norwegian Barents Sea. Full scale monitoring of motions on units in operation has verified predictions, confirming very favorable motions when compared to shipshape FPSOs and even semi submersibles. In 2009, a study was awarded by a major oil company to investigate the feasibility of applying Steel Catenary Risers (SCR) with a cylindrical FPSO at a location with deep water and very harsh environment. Results from the initial analysis proved feasibility and associated model testing has allowed calibration of first order and second order analysis methods and particularily have lead to a better understanding of second order and heave coupled pitch motion effects. Adaptation of the cyclindrical hull to improve its characteristics as a host platform for steel catenary risers has been the incentive for the case study outlined in this paper. Platform and riser optimisation should be field specific, but the results presented for a very harsh environment, demonstrate the feasibility of steel catenary risers with a cylindrical FPSO at any location, worldwide. In this paper, the focus is on demonstrating how a cylindrical FPSO/SCR design spiral can progress towards meeting the challenges of a harsh environment with competitive hull/riser combinations. Introduction The cyclindrical FPSO/SCR challenge is to provide an SCR hang-off location with motions, as follows, even in very harsh environments.The maximum downwards vertical velocity in 100-year design conditions should be less than 2,4 m/s (1,9m/s in 100 year conditions is achieved)The long term distribution of all motions at the riser hang-off shall provide a robust SCR fatigue life (achieved with low amplitude heave RAO within Tp range with high % occurrence)Angular motion should stay within a range of +/- 25 degrees at hang-off (achieved 18,1 degres)Horizontal offsets envelope within 2,5% of waterdepth in 100 year conditions with intact mooring (achieved 2,3%) A cylindrical FPSO with SCR hang-off in a moonpool is demonstrated to meet the above criteria with margins, even for very harsh environments. The Cylindrical FPSO is arranged so that the SCR hang-off is located very close to the centre of the FPSO, within a moonpool, and thus the predominantly heave induced vertical motion at the riser hang-off meets SCR hang-off motion targets. Mooring systems are developed to meet the offset criteria. The case study responses are reported for a 16" gas export riser, based on API standard seamless pipe dimensions with 5 mm corrosion protection coating, resulting in an "OD/weight submerged" ratio with 148 kg/m3 contents of 3,0 m2/tonne. Equivalent 123/4" and 103/4" production SCRs with contents 800 kg/m3 and high insulation are outlined for benchmarking.
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