In the production phase gas flows out of the well, through a flowline to the production facility, then down the pipeline to be used by consumers. Gas Mitsui E&P Australia (MEPAU) produces is provided to industrial and retail clients based in the broader Perth metropolitan region.

When preparing for production, the drilling rig is removed from the wellhead and a ‘Christmas Tree’ is positioned over the top.

The Christmas Tree, also known as the Production Tree, controls the well. It’s a collection of barriers, valves and seals, as well as a gas and water separator. The Production Tree controls flow rates, regulates pressure and connects the well to the pipeline heading towards the Production Facility.

The Production Tree also enables MEPAU to test the pressure of the well to make sure it’s safe, both for humans and the subsurface environment.

During the production phase there are typically two staff members working at each gas field, which operates around the clock.

Once the well is exhausted it is decommissioned and rehabilitated before being returned to the landowner.

Production well examples include Senecio-03, Waitsia-01 and Waitsia-02, in the Waitsia Gas Field.

Waitsia Gas Field

In September 2014, Mitsui E&P Australia’s predecessor AWE announced that during drilling of the Senecio-03 well, the underlying Waitsia gas field was discovered below the original target formation.

Flow testing of the Senecio-03 well was completed in March 2015. The testing program was designed to determine gas flow rates from zones of two reservoirs in the Waitsia gas discovery and to collect gas samples for analysis. During the second stage of testing, an average flow rate of 12.3mmscf/d, unstimulated, was measured from the Kingia formation over five hours at the end of the 18 hour “clean up” flow period, a technical term for the initial part of the flow test. This result confirms the Kingia is a conventional reservoir and the Waitsia gas field is capable of producing gas at commercial rates.

The Waitsia gas field, a conventional reservoir, is an exciting new opportunity for the Perth Basin, which potentially rivals WA’s largest onshore gas discovery. This could deliver substantial benefits for WA and the Mid West.

  • MEPAU is continuing to develop the Waitsia gas field in stages, while working to minimise its development footprint.
  • Gas initially produced from Waitsia Stage 1, at the existing Xyris Production Facility (XPF), is being conveyed via a pipeline to the existing Dampier Bunbury Natural Gas Pipeline to customers in WA.
drilling in action

Waitsia Gas Project - Stage 1

Waitsia Stage 1, an extended production test, has been in production since August 2016. Find out more about Waitsia Gas Project Stage 1.

MEPAU stage 1 expansion

Waitsia Gas Project - Stage 1 Expansion

Waitsia Stage 1 Expansion began in January 2020. Find out about Waitsia Stage 1 Expansion.

Care and Maintenance

Care and Maintenance

When a facility is not being used, it’s put into care and maintenance. Read more about Care and Maintenance.

What we do at Mitsui E&P Australia

What we do

We are actively exploring, appraising, developing and producing oil and gas in a number of locations in the northern Perth Basin. Read more about what we do


Before anything can happen we need to plan carefully. Read more about the planning process.


We look for gas, and when we find it we figure out if it’s worth pursuing further. Find out more about our exploration and appraisal process.


Once we’ve confirmed a well is commercially viable we get ready to put it into production. Read more about the development process.

Decommissioning and Rehabilitation

When the exploration or production activity has finished it’s time to clean up. Read more about how we decommission and rehabilitate a well and its surrounding area.

Sustainable energy

Sustainable Energy

MEPAU is actively transitioning to a low-carbon energy future.

The Northern Perth Basin

The northern Perth Basin is a prolific oil and gas producing area covering a large portion of the Mid West region of Western Australia. The town of Dongara, located approximately 360km north of Perth, is the regional economic hub for a number of industries, including oil and gas.