The surging shale energy output in recent years has been centering in North America, but it can also happen in other places like China, a U.S. energy expert said Friday. Shale gas will come to play a more important role in China\'s energy mix in the long term, said IHS Cambridge Energy Research Associates Chairman Daniel Yergin at a seminar on energy boom in North America. \"China has great potential for shale gas but it will take perhaps five to 10 years to develop, due to the lack of infrastructure and logistic capabilities,\" Yergin told Xinhua. He added that Chinese energy companies among others are learning the necessary technologies from their American counterparts to unlock the unconventional energy including shale oil and gas. The energy industry was concerned a decade ago that U.S. energy output had hit the ceiling and started to go down, but now the United States is about to overtake Russia in terms of oil and gas production, said Yergin. The United States produced the equivalent of 22 million barrels a day of oil, natural gas and related fuels in July, according to figures from the Energy Department. The shale energy bonanza reduced U.S. imports of natural gas and crude oil by 32 percent and 15 percent respectively in the past five years. However, the environmental implications of shale gas extraction, a process that includes hydraulic fracturing, remain uncertain. Hydraulic fracturing involves pumping water, sand and chemicals deep underground into horizontal gas wells at high pressure to crack open hydrocarbon-rich shale and extract natural gas. Accelerated shale gas drilling and hydrofracking in recent years has fueled concerns about contamination in nearby drinking water supplies.