Indonesia has identified 54 oil and gas blocks that have the potential to be offered to investors up to 2028, an energy ministry director said on Thursday, as the Southeast Asian nation races to replenish oil and gas reserves.

The government is keen to reverse the declining trend of Indonesia's oil production and aims to achieve an output of one million barrels of oil per day and 12 billion standard cubic feet per day of gas by 2030.

Half of the 54 blocks are expected to be offered until 2028 in regular auctions, while the other half will be awarded through direct offer following a joint study of the blocks, Ariana Soemanto, a director at the energy ministry, told participants of the Indonesia Petroleum Association conference.

The energy minister said the government is focusing its efforts on boosting the exploration of its many untapped hydrocarbon basins as Indonesia launched offerings for five oil gas blocks this week.

Meanwhile, the upstream regulator SKK Migas is keen to promote exploration into the often-considered mature area of western Indonesia. The North Sumatra and Northeast Java basins there have remained under-explored, according to SKK Migas.

The North Sumatra and Northeast Java basins were each estimated to have over 9 billion barrels of oil equivalent yet to be discovered, Nanang Abdul Manaf, advisor to the SKK Migas chief, said at the same conference.

"Mubadala has just announced a second big discovery through the Tangkulo-1 exploration well, which proves the big hydrocarbon potential in this area," he said.

Mubadala Energy said on Monday its Tangkulo-1 exploration well had found gas in the South Andaman Block, located around 100 km (62 miles) off northern Sumatra, where it said there was potential of more than 2 trillion cubic feet (tcf) of gas-in-place.

It followed the discovery in the Layaran-1 well with the potential for more than 6 tcf of gas-in-place, which analysts said was the world's second-largest deep water discovery last year. (Reporting by Fransiska Nangoy; Editing by Sohini Goswami)