The find comes after North Sea-focused Ithaca agreed to acquire a 10% working interest in the licence from operator Total in December.
Ithaca was encouraged by the find, although it is understood the interest is not a key element of its portfolio.
The commercial value of the discovery, made in a mature area within 10km of the Heimdal production hub, has still be assessed.
The Trell interest is part of Ithaca's strategy to develop its portfolio of low-risk exploration assets in the Norwegian North Sea.
Ithaca's operations are largely focused on production in the central North Sea's Greater Stella Area.
It recently said its focus this year will be on drilling the third and fourth Stella field development wells, and completing sub-sea infrastructure installation work.
Westhouse Securities Analyst said: "The discovery is within approximately 10km of the Heimdal production hub and this fits well with Ithaca's strategy in Norway of gaining access to lower risk exploration opportunities capable of monetisation prior to development.
"We think this discovery is not priced in by the market and although small in terms of valuation, it is a welcome addition."
It added: "The core of Ithaca's story remains to be in production and development and we continue to look to timely progress on the GSA development and progress on existing producing assets as [the] potential driver for the stock."
Shares in Ithaca Energy closed up 4.75p at 136.5p.