SS - Safe Transfer of Liquefied Gas in the Offshore Environment
Authors: Newby Mark Andrew , Pauw Willemijn 
Published: July 2010

In order to capture value from stranded gas reserves, operators are looking to offshore gas production from FPSOs and also from platforms stripping liquids and exporting through FSOs. This is a relatively new area for F(P)SO operations. In order for this to be carried out safely, there was a need to capture important lessons learned from the successful operations and ensure other operators apply the lessons at the feed engineering stage. The value of modeling in order to establish important parameters must also be considered.

This paper outlines the development of the new OCIMF guideline on the " Safe Transfer of Liquefied Gas in the Offshore Environment?? (STOLGOE) primarily for Side by Side transfer of LPG. The industry experience was used to develop the guideline. Important safety factors that need to be taken into account when doing side-by-side (SBS) transfer operations for LPG include:Mooring layout and release capabilityHeading ControlUse of hoses / hard armsEmergency release capability of hoses / hard armsFendering systemsCrane operations

ConocoPhillips is leading the way with 2 LPG FSOs conducting SBS operations. " Liberdade?? is the 3 product LPG FSO operating in the Timor Sea on the Bayu Undan Field and has achieved more than 130 SBS offloading operations. This facility has become industry benchmark for safe transfer operations of LPG in the offshore environment. In order to achieve such a safe and successful operation, modeling of parameters was vital to being able to determine mooring layout, tug assistance, heading control and operational limits

Modeling for design purposes and check with reality is necessary in order to improve the quality of models. It is important to get feedback from experienced personnel and to conduct full scale measurements to help ensure the success of future designs.

The operating experience of Liberdade is being used to help act as a reality check of the software and model tests. This real life experience with design and operation is being used to give feedback on design tool developed through the Offloading Operability JIP and will be able to be applied to any transfer of LPG from an F(P)SO to a conventional LPG Gas Carrier using SBS method and can be used as the basis for transfer of LNG from an F(P)SO to a conventional LNG Gas Carrier.

Introduction

The future of the hydrocarbon industry will be determined on our ability to capture maximum value from the resources and to be able to capitalize and produce resources that are further offshore or away from shore based infrastructure. It is no longer acceptable to flare vast quantities of gas in the pursuit of the more valuable heavier products. Operators need to be able to either store the gas back in the reservoir, export to a shore facility for processing or process the gas offshore into a transportable liquid product for export.

To date, the offshore processing has been limited to Liquid Petroleum Gas production often in the form of Butane and Propane as separate products rather than a combined LPG blend. At the time of writing this paper, there are no LNG offshore floating production facilities in operation, however there are numerous designs under development within the industry.