* Residents oppose shale exploration
* Protesters and riot police turn out in equal numbers
* Romania holds estimated 51 trln cubic feet of shale gas
By Bogdan Cristel
PUNGESTI, Romania, Dec 7 (Reuters) - U.S. oil major Chevron halted exploration works for shale gas in eastern Romania for the second time in two months on Saturday after anti-fracking protesters broke through wire mesh fences around the site.
Thousands of people have rallied across Romania in recent months to protest against government support for shale gas exploration and separate plans to set up Europe's largest open cast gold mine in a small Carpathian town.
The U.S. Energy Information Administration estimates Romania could potentially hold 51 trillion cubic feet of shale gas, which would cover domestic demand for more than a century.
Chevron won approval to drill exploratory wells in the small town of Pungesti in the impoverished county of Vaslui in October but had to halt work soon after when residents blocked access to the site. It resumed work on Dec. 2.
On Saturday, about 300 riot police were deployed in Pungesti, 340 km (210 miles) northeast of capital Bucharest, to try to prevent an equal number of protesters, mostly local residents, from entering the Chevron site. Some broke through into the site, however.
The activists chanted "Stop Chevron" and held banners saying "No drilling allowed here". Dozens were detained by police.
Chevron said some equipment had been damaged on the site. "Chevron can today confirm it has suspended activities ... as a result of unsafe conditions generated by unlawful and violent protester activities," it said in a statement emailed to Reuters.
"Our priority is to conduct our activities in a safe and environmentally responsible manner consistent with the permits under which we operate, however this was not possible today."
Shale gas faces opposition due to concerns around hydraulic fracturing, or fracking, the process of injecting water and chemicals at high pressure into underground rock formations to push out gas.
Critics, including the Pungesti protesters, say it can pollute water supplies and trigger small earthquakes. Advocates say it has a strong safety record and point to countries like the United States, where extensive fracking has driven down energy prices.
Chevron, which also has rights to explore three licence blocks near the Black Sea, does not have plans to use fracking under its five-year exploration programme. It says is abiding by all safety regulations.
It said last month it had filed a civil lawsuit against protesters in Poland who have prevented it from reaching a site where it plans to explore for shale. It said the action was filed on the grounds that protesters were violating its lawful right of access to the site - one of four shale gas exploration concessions the company has in Poland.