Poland's dream of becoming a shale gas "El Dorado", bringing untold riches and assuring energy independence, is turning into a mirage as Western firms abandon prospecting efforts, citing poor results.

"We can no longer talk of a new El Dorado," said Grazyna Piotrowska-Oliwa, a former president of Poland's PGNiG gas utility.

"The hopes and promises were excessive," she said, even though the official results of the explorations have yet to be published.

Optimistic estimates suggested Poland could have up to 1.92 trillion cubic metres (67.8 trillion cubic feet) of exploitable shale gas deposits, fuelling interest from top energy giants around the world.

But those forecasts were "exaggerated", and now "there's disappointment" in Poland, according to analyst Grzegorz Kus of the consultancy PwC.

Leading Polish geology scholars also say that the country's shale deposits are structured so differently from those found in the United States that extraction technologies developed there cannot be applied in Poland.

US energy major Chevron was the latest to pull the plug on shale gas prospecting in Poland.

ExxonMobil, Marathon Oil and Talisman Energy had led the exodus, followed by French oil giant Total and Italy's Eni last year.

"It's not a surprise and it's not the last withdrawal," Kus said of Chevron. "It turns out that this market is not as interesting as it was thought to be."

He attributed the retreat of global oil giants to the disappointing results of exploration, the drop in global fuel prices, more interesting extraction opportunities elsewhere in the world, Polish bureaucracy and planned tax hikes in Poland's energy sector.

Fifteen firms are still in the game, including US major ConocoPhillips, PGNiG and Polish oil group PKN Orlen.

- Pipe dream -

Chevron said plunging oil prices had prompted severe spending cuts in worldwide exploration.

But energy sector expert Andrzej Szczesniak says "it was the geological conditions that were decisive".

"Of the 68 exploratory drillings carried out to date across Poland, not a single one brought positive results in terms of profitability," he said.

However, Szczesniak said: "It's not yet officially over," adding that "any discovery of profitable deposits will revive hopes."

The spokeswoman for Poland's environment ministry, Katarzyna Pliszczynska, also remained hopeful, telling AFP: "At this stage, it is premature to speak of the results of the drilling."

New official assessments of exploration are expected this year.

"The drilling will continue. We're going ahead with explorations, even if the last ones weren't successful," Polish Prime Minister Ewa Kopacz said last week.

The EU member state of 38 million people, central Europe's largest economy, is highly dependent on Russian gas. Of the 16 billion cubic metres it consumes annually, more than 60 percent is imported, mainly from Russia.

In a bid to curb energy dependence on Russia, the Polish government laid out plans to invest 12.5 billion euros ($14.2 billion) with a view to tapping its shale gas deposits by 2020.

Banking on studies suggesting that Polish reserves are the third largest in Europe after those of Norway and The Netherlands, it had initially hoped to begin commercial production of shale gas in 2014.

But that turned out to be a pipe dream.