In 2011, Commonwealth approval (EPBC 2008/4208) was obtained to develop the Ichthys Field in the Browse Basin. This included, but was not limited to, the installation and operation of the offshore infrastructure for the 40-year field life. The Ichthys Field is in petroleum production licence WA-50-L in the Browse Basin about 220 kilometres off the north west coast of Western Australia and 820 kilometres south west of Darwin. Water depths range from 235 to 275 m in WA-50-L and along the gas export pipeline (GEP) range from 250 m at the gas export riser base (GERB) in WA-50-L, to 30 m at the boundary of Commonwealth waters and the NT three nautical mile (nm) limit.
Hydrocarbon production involves gas from the Ichthys Field undergoing preliminary processing at the offshore central processing facility (CPF) to remove water and raw liquids, including the greater part of the condensate. This condensate is pumped to the interlinked floating production, storage, and offtake facility (FPSO) with hydrocarbon processing and monoethylene glycol (MEG) regeneration capabilities. The gas and some condensate are transported from the CPF along an 890 kilometre long subsea GEP for further processing at Bladin Point in Darwin. Liquefied petroleum gases (LPG) and liquefied natural gas (LNG) and condensate are produced onshore from the export gas on behalf of the Ichthys Downstream Incorporated Joint Venture.
This EP is the first 5-year EP revision for the operation of the GEP and covers the next 5 years of the expected 40-year Ichthys field life. Operations are ongoing on a continuous 24/7 basis. During the life of this EP, inspection, maintenance repair activities may be required to ensure the safe and efficient operation of the GEP and associated infrastructure.
Inspection of the GEP will be conducted in accordance with a risk-based inspection schedule. Inspections of the pipeline will generally involve a vessel travelling along the route of the pipeline using towed acoustic instruments, a remotely operated vehicle connected to the vessel via an umbilical, or an autonomous underwater vehicle which is launched and recovered from the vessel. In addition, marine acoustic surveys (e.g. side scan sonar and multibeam echo sounders) may also be undertaken. These inspections are typically conducted from a vessel or autonomous underwater vehicle fitted with acoustic instruments. Typically vessels will be on site for approximately 5 to 60 days per year depending on the type of inspection. Events such as cyclones, known dropped/ dragged objects or seismic activity that could affect the GEP may also trigger inspections.
Maintenance and repair activities (such as a minor repair involving installation of a clamp) will be conducted based on the results of inspection and monitoring of the GEP. Should a major repair (spool replacement) be required, the activity of de-pressuring the GEP, including pigging/dewatering/isolation and discharges of GEP contents into the marine environment is within the scope of this EP. If maintenance or repairs are required, a vessel may remain on site for approximately 15 to 60 days at a time, depending on the nature of the work required.