Workers carry out a practice drill in case of a hydrogen sulfide leak at a natural gas appraisal well of Sinopec in Langzhong county, Sichuan province in this March 1, 2011 file photo. Picture taken ... more 
Workers carry out a practice drill in case of a hydrogen sulfide leak at a natural gas appraisal well of Sinopec in Langzhong county, Sichuan province in this March 1, 2011 file photo. Picture taken March 1, 2011. To match Special Report CNOOC-NEXEN/ 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 / REUTERS
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