1. Postdoctoral Researcher, Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process of the Ministry of Education, China Univ. of Mining and Technology, Xuzhou, Jiangsu Province 221116, PR China (corresponding author).
2. Doctoral Student, School of Resources and Geosciences, China Univ. of Mining and Technology, Xuzhou, Jiangsu Province 221116, PR China.