By Karlee Weinmann (December 6, 2013, 1:46 PM EST) -- Energy giants Chevron Corp. and PetroChina Co. Ltd. are at odds over how to develop the parts of a $6.4 billion natural gas project in China that are technically difficult, the latest in a series of holdups for the mammoth joint effort, Reuters reported on Friday. The Chuandongbei project, set to produce 7.6 billion cubic meters of gas a year over its 30-year life, was initially expected to deliver first gas in 2010 but since then a series of delays have stymied its owners and provided little insight as to when production will actually begin. California-based Chevron, Chuandongbei's operator, owns a 49 percent stake in the project, with PetroChina holding the remainder....