Jansz-Io Gas Field

Jansz-Io Field is located within production licences WA-36-L, WA-39-L and WA-40-L, approximately 70km north-west of the Gorgon gas field and 220km off the north-west coast of Western Australia.

Project Type
Gas field development
Start of Drilling
Production Expected
Development Partners
Chevron (47.3%, operator), ExxonMobil (25%), Shell (25%), Osaka Gas (1.25%), Tokyo Gas (1.0%) and Chubu Electric Power (0.417%)
Number of Development Wells (Phase I)
Major Contractors
J P Kenny and Technip Oceania JV, GE, Aker Solutions, Subsea 7


Jansz-Io Field is located within production licences WA-36-L, WA-39-L and WA-40-L, approximately 70km north-west of the Gorgon gas field and 220km off the north-west coast of Western Australia. Water depths at the field range from 1,200m to 1,400m.

The gas field is being developed as part of the larger Gorgon Project, which also involves the development of the Gorgon fields offshore, as well as onshore elements including a three-train LNG plant for producing 15.6 million tonnes of LNG a year, a domestic gas plant for supplying 300TJ of gas a day to Western Australia, CO2 removal and compression facilities, a 4km-long loading jetty and export pipelines.

Drilling activities at the field started in March 2012 and as of January 2015, the drilling of the wells and installation of subsea facilities for the Jansz-Io field were completed, while pre-commissioning activities are in progress. Jansz-Io will be the first gas field to be commissioned, when it comes online in mid-2015, as part of the Gorgon project.

The overall investment for the Gorgon Project is estimated to be A$43bn (approximately $36.5bn). The joint venture (JV) partners in the Gorgon Project include Chevron (47.3%, Operator), ExxonMobil (25%), Shell (25%), as well as gas buyers Osaka Gas (1.25%), Tokyo Gas (1.0%) and Chubu Electric Power (0.417%).

Discovery and drilling at Jansz-Io offshore field

The Jansz field was discovered in April 2000 by drilling the Jansz-1 discovery well in the WA-18-R permit area. The Io field was discovered in January 2001 by drilling the Io-1 discovery well in the adjacent permit area WA-25-R.

“Jansz-Io will be the first gas field to be commissioned, when it comes online in mid-2015, as part of the Gorgon project.”

The Jansz field was further appraised by drilling the Jansz-2, Jansz-3 and Jansz-4 wells in 2002, 2003 and 2009 respectively, while the Io discovery was appraised in 2006 by drilling the Io-2 well.

The two gas fields were agreed to be unitised by the Gorgon Project JV in May 2009.


The Gorgon and Jansz-Io gas fields are estimated to together hold more than 40 trillion cubic feet (tcf) of gas and are expected to have a production life of at least 40 years. The total production capacity of the fields is estimated to be approximately 2.6 billion cubic feet (bcf) of natural gas and 20,000 barrels of condensate a day.

Jansz-Io field development details

The gas field is being developed in two phases. The first phase, currently in progress, involves the development of ten production wells, the conversion of the existing Jansz-4 appraisal well to a pressure monitoring well and a subsea tieback to the onshore LNG plant.

Major offshore facilities include subsea trees, two manifolds, offshore feed gas pipeline system, a monoethylene glycol (MEG) injection pipeline, and an electro-hydraulic control umbilical.

The wells were drilled from two drill centres, drill centre 1 (DC-1) and DC-2, with five wells located at each site. Transocean Deepwater Frontier (DWF), a dynamically positioned (DP) drillship, was employed to execute the drilling activities.

A fast-supply and intervention vessel (FSIV) named FOS Polaris, two other supply vessels and a remote-operated vehicle (ROV) provided offshore support during the drilling phase.

Phase II will involve the drilling of five additional wells from the DC-3 drill centre and is expected to be completed in five years following the start of production from the Gorgon fields.

Contractors involved

The front-end engineering and design studies for the project were performed by the JV of J P Kenny and Technip Oceania. The JV is also the engineering, procurement, construction and management (EPCM) contractor for the project.

The Persephone gas field is located within Permit Area WA-1-L (Program Area) offshore north-west coast of Australia.

GE supplied the subsea trees, subsea wellhead systems, pipeline end terminations (PLETs), manifolds, pig launchers / receivers and umbilical distribution assemblies, spools and multi-bore well jumpers, and production control systems for the field.

Steel tube umbilicals and monoethylene glycol (MEG) system were supplied by Aker Solutions. Subsea control fluids for the project were supplied by MacDermid Offshore Solutions.

Heavy lifts and tie-ins were performed by Subsea 7 employing its heavy lift vessel Sapura 3000. Subsea 7 subcontracted Matrix Composites & Engineering (Matrix) to supply subsea installation buoyancy to facilitate the tie-in operations.

Maersk and Farstad are the suppliers of the support vessels. Miclyn Express Offshore (MEO) was subcontracted by Mermaid Marine Australia to supply two anchor handling tugs and nine barges to support Subsea 7 with the installation works.

Certain subsea installation works for the project, primarily comprised of the installation of six trunklines and 15 infield pipelines, covering a length of more than 660km, 36 PLETs, 800 mattresses and 12 pipe supports, the trenching of more than 120km of pipeline, flooding, gauging and hydro testing of pipelines and fabrication and installation of buckle initiators were performed by Allseas using the Solitaire, Lorelay and Calamity Jane vessels.

NRI Energy Technology

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