1. Shijiazhuang University of Economics, Shijiazhuang, Hebei 050031, China.
2. Corresponding author.
3. Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, PO Box 9825, Beijing 100029, China.
4. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China.