Conceptual Design and Analyses of Deep-Sea FPSO Converted from VLCC

Abstract

As potential offshore oil fields shift from shallow water to deeper ocean, floating production, storage and offloading (FPSO) systems become more attractive than conventional huge fixed type platforms. Recently we have successfully completed conversion works of two FPSO's from old 280,000 DWT VLCC's and they will be towed and installed at Campos Basin, offshore Brazil. During this project elaborate hydrodynamic and structural analyses were performed to ensure proper function as an FPSO and to convince safety during conversion and towing stage. This paper summarizes general arrangement and typical results of the analyses. Introduction As potential offshore oil fields shift from shallow water to deeper ocean, floating type production platforms such as floating production. storage and offloading (FPSO) systems become more attractive than conventional huge fixed type platforms. The FPSO system is known as economical alternatives to fixed type platforms for deep water applications. Since FPSO has integrated function of production, storage and offloading, its conceptual design is very important to ensure the full performances or these multifunctions. Especially, mooring system has a unique device called turret. Turret enables the FPSO to weathervane with minimum environmental mooring force. A multi-path fluid swivel acts an essential role for oil transfer without leakage during weathervaning. In order to reduce operational cost mooring scheme without thruster-assistance is preferred in spite of quite deep water of around 1,000 meters. Recently Hyundai Heavy Industries has successfully completed conversion works of two FPSO's for Petrobras. Henrique Dias and Jose Bonifacio, from old 280.000 DWT VLCC's and they will be towed and installed at Campos Basin, offshore Brazil. During this project, elaborate Analyses1 were performed to ensure proper function as an FPSO and to convince safety during conversion and towing stage. It covers naval architectural calculations. stability. motion mooring, and fatigue analysis for in-place condition and/or towing condition. Also various global and local structural analyses were performed for floating construction, towing and in-place conditions. During the structural analysis, special attention was paid to consider highly corroded areas arisen from the previous usage as a VLCC. This paper summarizes general arrangement and typical results of the analyses for the Jose Bonifacio. General Arrangement Basically, the hull is converted from 280.000 DWT VLCC that is 17 years old. The general arrangement and principal particulars of FPSO are shown in Figure 1 and Table J respectively. It is claimed that the locations of a flare boom a turret and accommodations are important factors for general arrangement. Generally, the location of accommodation is arranged at stem part as it was for converted hull case. Therefore, the location of the flare boom is at bow which is far from accommodation to prevent the hazardous condition. in spite of forward direction against wind direction. Turret opening may be either at the midship or bow. To ensure the good weathervaning, bow is preferred in our case. However, midship may be chosen in cooperation with thruster-assisted mooring to improve the heave motion characteristics. On the forward part of main deck, a turret and a flare boom are installed.

Ship-Shaped Offshore Installations

“…It is also important to identify and evaluate which trading tanker systems can be reused or renewed, and which systems must be newly installed during conversion. Useful summaries of the information and practices associated with the conversion of trading tankers to ship-shaped offshore installations are given by Johnson (1996), Assayag et al (1997), da Costa Filho (1997, Park et al (1998), Parker (1999aParker ( , 1999b, Neto and de Souza Lima (2001), Terpstra et al (2001), Lane et al (2004), Mones (2004), Terpstra et al (2004) and Biasotto et al (2005).…”

Margins of Safety in FPSO Hull Strength

“…For benign environments, it may be argued that the wave loads acting on the FPSO will be less than that corresponding to a tanker. For example Park et al [10] considered the case of an FPSO moored at Campos Basin, offshore Brazil. It was reported that the total value of the design bending moment is equal to about 60% of the value required by the rule approach.…”