A worker performs a routine check to the valves at a natural gas appraisal well of Sinopec in Langzhong county, Sichuan province in this March 1, 2011 file photo. China has gone back to the drawing ... more 
A worker performs a routine check to the valves at a natural gas appraisal well of Sinopec in Langzhong county, Sichuan province in this March 1, 2011 file photo. China has gone back to the drawing board on how to develop what could be the world's largest shale gas reserves after an attempt to stimulate competition and engineer an energy revolution brought little progress to the gas fields. To match story CHINA-SHALE/ REUTERS/Stringer/Files (CHINA - Tags: BUSINESS ENERGY) CHINA OUT. NO COMMERCIAL OR EDITORIAL SALES IN CHINA less 
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Reuters | Photo By STRINGER/CHINA / REUTERS
Fri, Sep 6, 2013 12:42 AM EDT