1. Southwest Petroleum University, State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu, Sichuan 610500, China
2. Southwest Petroleum University, The First National Gas Plant of ChangQing Oil Field Constituent Company, Xi'an, Shanxi 750001, China
3. School of Mathematical Sciences, University of Electronic Science and Technology of China, Chengdu, Sichuan 611731, China
4. Department of Mathematics, Sichuan University, Chengdu, Sichuan 610064, China