1. Key Laboratory of Unconventional Oil & Gas Development, China University of Petroleum (East China), Ministry of Education, Qingdao 266580, P. R. China
2. School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, P. R. China
3. Petroleum Systems Engineering, Faculty of Engineering and Applied Science, University of Regina, Regina, Saskatchewan S4S 0A2, Canada