In the Lewino-1G2 vertical test well near Gdansk in northern Poland, gas exploration company San Leon Energy said it had found shale gas deposits that would yield up to 400,000 cubic feet per day (about 11,300 cubic metres) of gas, adding that the total could rise to millions of cubic feet per day after further exploration.

The Ireland-based firm, which plans to make an announcement on flow rates within 60 days, said the project was the most commercially advanced in Poland. "We've basically cracked the nut in terms of the recipe, in terms of how to frack," executive chairman Oisin Fanning told the news agency Reuters.

The find brightens the prospects for shale gas in Poland after recent setbacks. Chevron and ConocoPhillips are the only global players still active in the country. According to still unconfirmed reports, Italian energy giant Eni is pulling out.

Fanning said San Leon, which began fracking in Poland in July 2013, had succeeded where others had failed through the use of a ceramic of proppant to keep hydraulic fractures open.