1. College of Chemistry and Chemical Engineering, Yulin University, Yulin 719000, Shaanxi, P. R. China
2. No. 1 Oil Production Plant, Petrochina Changqing Oilfield Company, Yan’an 716000, Shaanxi, P. R. China
3. Exploration and Development Technology Research Center, Yanchang Oilfield Co. Ltd., Yan’an 716000, Shaanxi, P. R. China