Work on a $55 million investment in the project is under way which includes an upgrade of the plant.

Head of External Affairs Bindi Gove said about 20 to 30 workers had spent the past three or four months carrying out maintenance on the plant in anticipation that gas would start to flow in the September quarter of 2021.

The company took over the Minerva gas plant from BHP in December, and last year discovered gas off the Peterborough coast - the first in 11 years.

The gas was discovered in the Annie gas field which is about nine kilometres offshore.

It was part of a shared $80 million exploration with Mitsui in mid-July which was in search of gas at the Annie and Elanora gas fields which were named after nearby historic shipwrecks.

A depletion of gas from existing nearby Bass Strait fields and an increase in gas prices has driven the search off the south-west coast by a number of companies for new gas to supply south-east Australia.

Ms Gove said the plant, which has been renamed Athena, was currently dormant but it hoped to start producing gas back through the plant by September prompting the need for the upgrade and maintenance of the site.

"That additional work has 20 to 30 locally-based people working on that maintenance work at the plant," she said.

"We're hoping we have first gas by the September quarter in 2021.

"The gas plant has been dormant, and not operable, but by September 2021 we're hoping to have the maintenance and upgrade work completed so that we can bring the gas plant back on line and be producing gas."

She said that once the plant comes back online it would employ about 16 permanent staff.

The company announced to the stock exchange in mid-December that its sole gas agreements would kick in on January 1.

That means gas would now be sold at agree term contract prices rather than at the lower spot prices it had been.

Cooper Energy Managing Director David Maxwell said the commencement of the agreement was a significant milestone which would deliver a material step-change in production, revenue, cash flow and earnings.

"We are pleased to be increasing gas supply to our utility and industrial customers and providing a competitive new source of natural gas to the domestic market," Mr Maxwell said.

Last year, he said the company was spending about $25 million connecting the Minerva plant to existing Henry and Casino gas fields, which had been in use since 2007, and estimated it could now spend $120 million connecting the plant to Annie.

In November, nearby Beach Energy also made a new gas discovery about three kilometres from Port Campbell as part of its $1 billion investment in offshore gas exploration.

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