1. School of Petroleum Engineering, China University of Petroleum (East China), Qingdao, Shandong 266555, China
2. China United Coalbed Methane Corporation Ltd, Taiyuan, Shanxi 030000, China
3. China Petroloil Production Plant No. 7 Changqing Oilfield Company, Huan County, Gansu 745700, China
4. School of Petroleum Engineering, Yan’an University, Yanan, Shaanxi 716000, China
5. Yanchang Petroleum Group Exploration Company, Yanan, Shaanxi 716000, China