COOPER Energy will become the sole operator of the Basker, Manta and Gummy (BMG) gas fields offshore Victoria after Beach Energy announced it would withdraw from a joint venture in October.

Beach will withdraw from the permit under its joint operating agreement with Cooper, assigning its 35 per cent stake to Cooper for nil consideration by the end of the current permit year.

In an announcement, Beach said the decision was consistent with an ongoing focus on portfolio optimisation and prioritising capital allocation in the current lower oil price environment.

The company did not want to participate in the proposed appraisal of the Manta gas field as a result, it said.

Beach will retain liability for its joint venture share of existing abandonment liabilities until October 2021, being five years from the effective date of withdrawal.

The announcement came as the companies accepted an offer from the National Offshore Petroleum Titles Administrator (NOPTA) to convert BMG permits VIC/L 26, 27 and 28 into retention leases.

Located in the offshore Gippsland basin, the permits are also near the Cooper-operated Sole gas field on VIC RL3, which is currently the subject of development plans for production via the Orbost gas plant.

Cooper said its analysis had identified an economic development opportunity for the Manta gas field using the Orbost gas plant, aiming to offer others the opportunity to participate in its plans to develop the fields.