1. 1State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Engineering, Southwest Petroleum University, Chengdu, Sichuan, China
2. 2School of Material Science and Engineering, Southwest Petroleum University, Chengdu, Sichuan, China
3. 3State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Engineering, Southwest Petroleum University, Chengdu, Sichuan, China 610500; fax: +86-28-8303-2901