The Longtom gas field, located in production licence VIC/L29, lies approximately 30km south west of Marlo in East Gippsland, Victoria. Longtom was discovered in 1995, Longtom-3 was drilled in 2006, Longtom-4 in 2008 and gas production commenced in October 2009. The subsea facilities consist of the following:
• Two existing subsea wells Longtom-3 and Longtom-4, each located within a Petroleum Safety Zone (PSZ).
• A 17 km 300mm nominal diameter Longtom pipeline originating at the Longtom-3 well and connecting into the offshore end of the Patricia Baleen (PB) pipeline. The Longtom pipeline is covered by licence VIC/PL38.
• A subsea umbilical extension connected to the existing Patricia Baleen umbilical line that provides electrical, hydraulic and chemical services to the Longtom facilities.
• A third subsea well, Longtom-5, is proposed to be drilled within the Longtom-3 PSZ (subject to a separate drilling EP) and will tie-in to the existing offshore facilities. The tie-in activity will also be covered by a separate EP.
From the commencement of production in 2009 the Longtom gas flowed to shore via the Patricia Baleen offshore gas pipeline, and then to the Orbost gas plant. In May 2015 an electrical fault in the offshore umbilical resulted in the loss of communications with the offshore facilities and led to an unplanned shutdown and the cessation of production. The Longtom-3 and, Longtom-4 tree valves are the pipeline valves are all closed. An offshore inspection and maintenance campaign was undertaken in early 2017 to confirm the status of the subsea facilities and to rectify the electrical connection to the Longtom-3 well.
Periodic inspection, maintenance and repair (IMR) activities will require offshore vessel operations and this may include survey activities, ROV operations, diving, lifting and the installation of items such as concrete mattresses. Vessel operations for IMR activities are expected to be required for 1 week every 3 years.
The facilities are currently in a preservation phase for resolution of technical issues and until commercial agreements
