Jan 11 PetroChina and Chevron began production at an onshore natural gas field in China's southwest at the end of 2015, PetroChina's parent said on Monday, after years of delays. The Luojiazhai field, whose 'A' well began operating on Dec. 30, has an annual production capacity of 3 billion cubic metres of gas, the state-controlled China National Petroleum Corporation said in a statement on its website.