Abstract

Design studies for the offshore pipeline system for the North West Shelf project in Australia commenced in the early 1970's. Flow mode selection project in Australia commenced in the early 1970's. Flow mode selection resulting in a two-phase flow system for gas and condensate was completed in 1978. A diameter of 1016 mm was selected for the 134 km trunkline from the North Rankin platform to shore. During 1978 and 1979 detailed route surveys, oceanographic investigations and cyclone hindcast studies were completed, allowing detailed engineering to commence. Pipe was ordered from Japan in December 1980 and deliveries were made between April and August 1981. Pipe coating was carried out in Western Australia between August 1981 and March 1982. Pretrenching of portions of the pipeline route was completed between December 1981 and September 1982. Pipeline installation commenced in May 1982 and was completed, including post-trenching, by December 1982. Backfilling over the pipe was carried post-trenching, by December 1982. Backfilling over the pipe was carried out between August 1982 and June 1983. The tie-in to the platform and final hydrostatic test on the pipeline were completed by May 1983. Dewatering, drying and inerting is planned for October and November 1983. The slug catcher associated with the two-phase system will be completed by December 1983. The line is expected to be commissioned in June 1984.

Introduction

The trunkline from the North Rankin "A" platform to shore has recently been completed as the first part of the offshore pipeline system for the North West Shelf project. This pipeline originates from the platform in a water depth of 125 m, enters the mouth of Mermaid Sound, and terminates just south of Withnell Bay on the Burrup Peninsula, on the North West coastline of Western Australia (see Figure 1). The pipeline is 1016 mm (40 inches) in diameter and 134.2 km long. It will operate in two phase flow bringing both gas and condensate to the onshore plant near its landfall. A slugcatcher is under construction within the plant to receive liquid hydrocarbon slugs from the pipeline.

The trunkline to shore will initially serve only the one offshore platform and operate at about 25% of its capacity to supply the Western Australian domestic gas market. The domestic gas plant on the Burrup Peninsula is being constructed by Woodside to produce pipeline quality gas for delivery to the State Energy Commission and condensate for shipment by coastal tankers. A 1500 km long onshore pipeline from the Burrup Peninsula to Perth and other localities in the south west of the State of Western Perth and other localities in the south west of the State of Western Australia is being constructed by the State Energy Commission to supply local domestic and industrial users with up to 10.9 million m3/day of gas (385 MMSCFD).

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