Abstract

Tandem transfer of crude oil and condensate in dynamic marine conditions has a long history with much accrued experience. Initial systems relied simply on a hawser connection, which was subsequently improved with the advent of Dynamic Positioning Systems.

The new requirement to transfer LNG in true dynamic conditions between two very large floating structures, whilst respecting the stringent rules governing the safety of such operations, has led to the design, testing and qualification of a new heavy duty transfer system, known as the Amplitude-LNG Loading System (ALLS).

The transfer of produced products, mainly LNG but also LPGs and condensate, has to proceed on a regular and repeatable basis, with 2 of the main criteria being:

  • Continuous production and operation of the FLNG over a 20 to 30 year period

  • Project monetization linked to LNG-C rotations

To ensure that these criteria can live in harmony the LNG transfer system must ensure that the correct volumes of LNG can be safely and efficiently offloaded from the FLNG to the LNG-C whilst minimising the turn around time of the carrier.

The ALLS incorporates a custom built Constant Position Monitoring System (CPMS) which can ultimately be integrated into the DP system of the LNG-C and / or the FLNG, and may eventually lead to on-site operations without the need for a hawser link. However full analysis of the project specific conditions will be required prior to taking such an important step.

An offshore LNG project is a multi-billion dollar investment, from subsea drilling and development, through construction of the floating process & liquefaction plant (FSPO-FLNG) to operation of a fleet of LNG carriers, some of which may be dedicated on a project basis. As such the reliability and repeatability of the CPMS /

DP couple is a key element in the overall functioning of the offshore LNG transfer system, as any emergency shut down and prolonged interruption in fluid transfer can have significant consequences on the functioning of the FLNG and its capacity limits for storage.

This paper will investigate the history and evolution of tandem transfer in open sea conditions, elaborate on these issues from the points of view of the Client, the Operator and the transfer system supplier, and detail the importance of a fully integrated and modern LNG transfer system.

Introduction

When developing and proposing new methods and systems to the Oil and Gas Industry, especially when safety of personnel and equipment is paramount, co-operation between the main involved parties at an early stage gives a firm base from which to work. In marine environments involving the transfer of LNG and gas, a concerted approach between the end user, the equipment supplier and experienced marine operators will ensure that practical procedures will result whenever possible in similar methods, based on existing know-how.

This content is only available via PDF.
You can access this article if you purchase or spend a download.