1. School of Resources and Geosciences China University of Mining and Technology Xuzhou 221116 China
2. Key Laboratory of Coalbed Methane Resources & Reservoir Formation Process Ministry of Education Xuzhou 221008 China
3. Research Institute of Petroleum Exploration & Development of Changqing Oilfield Company, PetroChina Xi’an 710021 China
4. School of Energy and Materials Engineering Taiyuan University of Science and Technology Taiyuan 030024 China