US energy major Chevron said Tuesday it has started drilling itsfirst exploration well for shale gas in Romania despite fierce opposition from localresidents."Chevron can confirm that drilling activities have commenced at its exploration wellsite" near the village of Silistea in eastern Romania, a Chevron spokesman said. "The drilling rig is expected to run until the well reaches a target depth ofapproximately 4000 metres" (13,000 feet), he added.The company expects to search for shale gas for 3 to 5 years.Chevron's attempts to establish its first exploration well in Romania weresuspended twice at the end of 2013 owing to demonstrations by opponents of exploiting shale gas.Many residents from this rural region of Romania fear the use of "fracking", acontroversial extraction technique that consists of injecting water and chemicalsdeep into rock to release gas.Chevron's exploration site is now a "special security zone" that is guarded by policewith people passing nearby required to show identity papers.Chevron says shale gas could prove crucial for Europe's energy security, especiallyas the crisis deepens in Ukraine, a key transit country for Russian natural gassupplies.But environmental rights groups warn against the damaging impact on theenvironment.Romania, unlike many countries in eastern and western Europe, is not heavilydependent on Russian supplies since it produces gas itself. Last year Romaniaimported from Russia only about 10 percent of its supplies, according to financialnewspaper Ziarul Financiar.