Subsea Challenges in Australia
Authors: Lawlor Chris , Morgan Julie Elizabeth P. 
Published: October 2008

Offshore gas production, supplying LNG trains, has been carried out in the Indian Ocean off the North West coast of Western Australia since 1989. The producing fields are in water depths of approximately 130m with ambient seawater temperatures and operating conditions that result in only occasional concerns about potential hydrate formation in the production systems. The latest tranche of gas fields under exploration and development offshore WA, which will also supply LNG or GTL facilities, has much more onerous hydrate management challenges, which result in significant facilities demands. Why? This paper discusses the contributory factors, as well as mentioning other challenges to the development of these deepwater gas fields offshore WA.

Introduction

LNG is considered the fuel of choice for the 21st century as it is the cleanest of the fossil fuels, with one third to one half of the greenhouse gas emissions of oil and coal; which is important in maintaining air quality in some of the highly populated countries of the Asia-Pacific region. Australia, through the exploitation of reserves in the Carnarvon Basin under the Indian Ocean, which has 80% of Australia's discovered hydrocarbon resources, seeks to be the world's most reliable and secure supplier of LNG.

LNG is an important contributor to Western Australia's economy with LNG exports from the NWS Venture commencing in 1989 from the North Rankin field. The NWS Venture accounts for 44% of Australia's oil and gas production; it is WA's largest producer of natural gas, supplying about 65% of WA's gas demand. The North Rankin reserves have been supplemented over time by those from the Goodwyn, Echo-Yodel, Cossack, Wanaea, Lambert and Hermes fields. These fields are approximately 135 km offshore in water depths of 125 to 130m. The gas produced offshore is dehydrated and exported via multiphase trunklines to the NWS Venture gas processing plant at Karratha which has receiving facilities complete with slugcatcher. Thus there is a long history of successful gas production offshore WA (Woodside, 2008).

The gas fields offshore WA which are under exploration and development, such as Pluto, Gorgon / Janz, Ichthys, Browse, Wheatstone and Scarborough, are giants and will be supplying gas to LNG (or possibly GTL) plants for well in excess of 20 years. These fields are further offshore than those currently supplying the NWS Venture and on the whole are in deeper waters, with depths ranging from 200 m to 1,400 m, i.e. venturing into depths that are considered deepwater. With the ever increasing demand for energy there is increasing pressure to " fast-track?? these giant deepwater gas developments.

For LNG related field developments the schedule is typically driven by components in the LNG plant, i.e. the main compressors and their drivers, the cryogenic exchangers and the LNG storage tanks, however, with the large number of hydrocarbon deposits under development currently worldwide, other items, such as construction yard capacity, availability of steel for flowlines and export pipelines, equipment production schedules and installation vessel capacities, are also impacting the project schedules once the design of the facilities required to exploit the fields has been set.

Not only does the execution phase impact the schedule, but the design and operability of the production facilities associated with the exploitation of these more remote, deeper water gas reserves has also become more complex. Why? What are the challenges associated with deepwater gas production? What makes it more onerous than shallow water gas production?