1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation; Southwest Petroleum University; Chengdu Sichuan 610500 P.R. China
2. College of Chemistry and Chemical Engineering; Southwest Petroleum University; Chengdu Sichuan 610500 P.R. China
3. Oil and Gas Field Applied Chemistry Key Laboratory of Sichuan Province; Southwest Petroleum University; Chengdu Sichuan 610500 P.R. China
4. Radiochemsitry Division; Bhabha Atomic Research Center; Mumbai 400094 India