1. Hebei Natural Gas Company Limited, Shijiazhuang, P. R. China
2. No.2 Exploration Team, Hebei Bureau of Coal Geological Exploration (Hebei Province Hot Dry Rock Research Center), Xingtai, Hebei, P. R. China
3. State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, China
4. University of Chinese Academy of Sciences, Beijing, China