1. State Key Laboratory of Coal Resources and Safe Mining, College of Geosciences and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
2. PetroChina Research Institute of Petroleum Exploration and Exploitation, Beijing 100083, China
3. China United Coalbed Methane Co., Ltd., Beijing 100011, China
4. CNOOC EnerTech−Drilling & Production Co., Tianjin 300457, China