1. Petroleum Engineering School, Southwest Petroleum Univ., No. 8 Xindu Ave., Chengdu, Sichuan 610500, China.
2. Professor, Southwest Petroleum Univ., No. 8 Xindu Ave., Chengdu, Sichuan 610500, China (corresponding author).
3. Senior Lecturer, Dept. of Chemistry and Materials Engineering, Univ. of Auckland, Private Bag 92019, Auckland 1142, New Zealand.