Improved FPSO Offloading Strategy Based on Analysis Including DP System

Direct offloading operations from turret moored FPSOs are traditionally performed with dynamic positioned (DP) shuttle tankers with a bow loading hose and hawser line connected to the stern of the production facility. The hawser line restricts the mobility of the shuttle tanker which is often forced to point towards the FPSO. The inherent increased risk of collision in case of a forward drive-off incident has motivated a study for a hawser-less tandem offloading operation. The structural limits of the flexible loading hose allows for larger operational sector and heading flexibility which enables the shuttle tanker to point away from the FPSO and hence reduces the probability of collision. An analysis model with two representative vessels for offloading operations in the North Sea has been developed in order to investigate the new concept. The model includes a compiled version of the DP system core algorithm, extracted from the real time system of both vessels. The new offloading strategy, with heading offset away from the FPSO, has been implemented in an updated control algorithm for the shuttle tanker. Time-domain analysis of the complete tandem offloading system has been simulated with measured wind, waves and current from a HindCast data base. Heading and relative motion between FPSO and shuttle tanker has been extracted and statistically evaluated in order to determine the time for which the shuttle tanker is directed towards the FPSO. The paper demonstrates how a marine simulation model, including core algorithm of the actual DP system and numerous simulations based on historical measured environment, can be used to document the feasibility of a new offloading operation control strategy.

An Internal Turret Mooring System Design Under Squalls Off The Coast of West Africa

Squalls are intense, low-level winds associated with storms, and they always begin suddenly and last for minutes. They are characterized by large variation of wind speeds. Squalls control the design wind condition for floating production, storage and offloading systems (FPSOs) off the coast of West Africa. In this paper, an internal turret mooring system is designed to study the effects of squalls on the prediction of extreme tensions and offsets, which will be compared with the results from the way of using constant wind speed. Various statistic values of extreme tensions will be calculated and applied in the design. The differences between these values will also be discussed. Finally, the tandem offloading analysis is also performed in order to calculate the extreme hawser loads for the purpose of hawser line design.

Study of Tandem Offloading System for a New Concept Spar FPSO

A new concept Spar FPSO (Floating Production Storage and Offloading) is proposed for South China Sea deepwater oil field development integrating the advantages of the deep-draft Spar concept whose excellent stability and global performance enables dry-tree drilling and production, and the conventional ship-shaped FPSO for oil storage and offloading. This paper presents a study of the tandem offloading system for the new concept Spar FPSO. The paper will first give an overview of various offloading configurations and their characteristics for deepwater development; then a tandem offloading system similar to conventional ship-shaped FPSO is recommended for further investigation considering operational experience, safety and economical benefits. As the offloading operations are generally weather-limited, offloading environmental conditions for the study are selected based on API, ABS and South China Sea offshore operation practices. For a case study, hydrodynamic performance of the Spar FPSO in tandem offloading configuration with a shuttle tanker in 1500m water depth was investigated numerically and experimentally. Numerical simulations were conducted by means of fully coupled nonlinear time-domain analysis. The distance between the shuttle tanker and the Spar FPSO is optimized based on the relative motions of the two floaters and the hawser tension requirement of the shuttle tanker. Experimental results from model test are presented and compared with analytical time-domain simulation results. It is shown that the results of numerical simulations are consistent with the model test. The tandem offloading system demonstrates robust performance and cost-effectiveness for the proposed Spar FPSO concept.

COOL™ Hose Qualification Process of the First EN1474-2 LNG Floating Hose

In 2005, SBM Offshore recognized that in future offshore Floating LNG Production Units, key enabling technologies would be required to ensure the safe and reliable tandem offloading to LNG Carriers. The foundation was thus laid down for the development of the COOL™ Hose: A cryogenic marine floating hose that would enable the tandem offloading between two vessels offshore. This paper presents, after an introduction to the COOL™ Hose design (Hose in Hose concept-HiH), the different steps in the qualification process following the EN1474-2 [1] guidelines and recommendations for design and testing of LNG transfer hoses. This qualification process has been endorsed by two Classification Societies ABS and DNV and has resulted in a Certificate of Fitness for Service from DNV and a Product Design Assessment Certificate from ABS making the SBM COOL™ Hose, the first EN1474-2 qualified LNG floating hose.