Poland's supply of shale natural gas reserves may be much smaller than early estimates but still enough to cover its needs for decades, a government report says.

Poland's Geological Institute published a report Wednesday concluding that while the country's recoverable reserves may be as high as 1.9 trillion cubic meters, they are more likely in the range of 346 billion-768 billion cubic meters -- much less than the 5.3 trillion cubic meters estimated earlier by the U.S. Energy Information Administration.

Though disappointing in that respect, Piotr Wozniak, Poland's chief geologist, said the shale gas analysis carried out in conjunction with the U.S. Geological Survey confirmed the country remains in position to become a major energy producer and that more drilling will likely reveal greater reserves.

"This research shows that natural gas in Poland is worth investing in," he said in a statement issued by the geological institute PGI. "The estimated resources of conventional gas from unconventional deposits such as shale put us in third place in terms of recoverable natural gas in Europe" -- behind Norway and the Netherlands.

Poland is pinning its hopes on developing its shale gas reserves as a way to break its dependence on Russian supplies. The country imports 14 billion cubic meters of gas annually and, even with the lower estimates, unconventional gas could satisfy domestic demand for 35-65 years, the PGI report said.

The new estimates were based on archival data collected at 39 key wells from 1950-90, the institute said, and will be revisited every two years as new data from shale gas and oil exploration wells drilled since 2010 come in.

"The report gives a more precise estimate than before but is still based on data from a few dozen exploration wells," Polish Treasury Minister Mikolaj Budzanowski told The Wall Street Journal. "The last one was made 20 years ago, so more intensive drilling is needed to accurately determine resources of both crude and gas."

Major oil multinationals such as ConocoPhillips, Exxon and Chevron Corp., and others have been attracted by Poland's shale gas potential, obtaining 109 licenses to drill in its Baltic Sea basin so far.

Three more domestic Polish companies -- PGE, Tauron and KGHM -- signed letters of intent with Polish National Oil and Gas Company to set up shale gas projects in January.

Despite the sobering PGI estimate, the potential still remains for shale gas to change Poland's energy future, the London ratings agency Fitch said Wednesday.

"It is still too early to make any meaningful assumptions about the future of shale gas in Poland, believed to have one of the highest development potentials in Europe," it wrote in a report. "Less than 20 exploration wells have been drilled by domestic and foreign companies, in many cases with disappointing results."

But, it added, the PGI estimate is still "substantial" -- enough to "shape Poland's future power generation mix as the country aims to diversify from the dominance of coal in power generation by investing in renewables, nuclear energy and gas-fired power plants."