Submerged Turret Loading Buoy based Offshore Gas Receiving Terminals for LNG and CNG
Authors: Kaalstad J.P. , Hovde G.O. 
Published: October 2008

The Submerged Turret Loading Buoy System (STLTM), which is well proven in the North Sea for Offshore Loading of Crude Oil, is now developed for Discharge of Gas and will be used as an Offshore LNG receiving Terminal. Presently two 138,000 m3 LNG Carriers are being constructed at Daewoo Shipyard with onboard re-gasification and shipboard system for connection to the STL Buoy. The first Submerged Loading Buoy based Offshore LNG Receiving Terminal installation will be in Gulf of Mexico - West Cameron Block 603. The paper presents the technology and how the same loading technology system can be used for CNG Vessels; both for loading and offloading of Natural Gas.

Introduction

Energy Bridge is an innovative technology in which a standard LNG vessel is customized to convert liquefied natural gas cargo to vapor on board the ship; later referred to as the LNG Regas Vessel (LNGRV). Then, utilizing the proven Submerged Turret Loading (STL?) technology that has been deployed for more than a decade in the harsh North Sea environment, gas flows through lines connected to the ship and linked to an existing network of underwater, high-pressure offshore natural gas pipelines or a new pipeline direct to shore. Because of its inherent mobility, the Energy Bridge System can be deployed virtually anywhere to meet incremental demand for natural gas.

The proposed Gulf of Mexico Deepwater Port, which will be located 116 miles offshore Louisiana, will be capable of delivering baseload gas volumes in excess of 500 million cubic feet per day. The Energy Bridge port will be the first offshore LNG re-gasification terminal in the world and is scheduled to be capable of supplying natural gas to the U.S. market by late 2004 or early 2005.

Deepwater Port / Offshore Terminal Description

The Energy Bridge Gulf of Mexico Deepwater Port is located in West Cameron Block 603 in approximately 90 m water depth. The complete Deepwater Port consists of the following main components:STL Subsea SystemOffloading Pipeline from STL to Metering Platform20" diameter ~1.9 milesMetering PlatformExport Pipeline to the Sea Robin Pipeline20" diameter ~3.9 milesExport Pipeline to the Blue Water Pipeline20" diameter ~1.4 miles

The LNGRV connects to the STL Buoy and sends vaporized/re-gasified LNG through the flexible riser, via the subsea PLEM and offloading pipeline to the metering platform. The gas is regulated to export gas pipeline pressure, metered and distributed to the Sea Robin and/or the Blue Water Pipeline System. Gas pressure can be regulated on the LNGRV or on the metering platform. The metering platform is designed for unmanned, remote operation, but will be equipped with quarters for temporary personnel onboard.

The STL System and Offloading Pipeline System are designed for 690 MMSCFD and 130 bar pressure.

Field layout of STL, Pipelines and Metering Platform is illustrated in Figure 6, while the location of West Cameron Block 603 is shown in Figure 7.

STL System Description

The STL System is divided into two separate systems, i.e. the STL Subsea System, which is the field related equipment, and the STL Shipboard System, which is the STL related structure and equipment on the LNGRV vessel.