The company said the completion of post-drilling studies on the Merakes-1 well in the East Sepinggan Block off East Kalimantan in Borneo had led them to upgrade the forecast of its reserves from 36 bcm to 56 bcm (1.3 trillion cubic feet to 2.0 tcf).
The well was drilled in October 2014 at a depth of 1,372 metres.
ENI said it was looking to fast track development of the find so it can be exploited at the same time as the nearby Jangkrik field, which it also owns.
The Italian company has 85 percent of the East Sepinggan block. It has been active in Indonesia since 2001.