Geochemical characteristics and its origin of CBM in Gujiao blocks

Based on the coal geological exploration data and the data analysis of composition,methane,hydrogen iso- tope mass spectrometry of gas drainage from CBM well,the geochemical characteristics and its origin of CBM in Gujiao blocks could be found out. The results show that the CBM are mainly composed of methane whose concentration ranges from 85. 36% to 99. 23% . It belongs to dry gas-extremely dry gas. The nitrogen gas is less than methane and the heavy hydrocarbon content is the least. The δ13 C of CBM ranges from - 62. 24‰ to - 40. 70‰ and the δD ranges from -244. 3‰ to -229. 3‰. The CBM gives pr1iority to thermogenic gas which has characteristics with proliferation,migra- tion and fractionation. The δ13 C1 of CBM shows a heavier trend with the increase of coal rank. With the increase of bur- ied depth,the change trend of the δ13 C1 is not obvious. The degree of mineralization increases gradually from north to south which shows that the hydrodynamic conditions gradually enhanced from north to south. The methane carbon iso- tope is heavier in southern square,such as Xingjiashe mine,and the north is lighter,such as Zhenchengdi mine,Xiqu mine and some parts of Malan mine. The Ro,max of coal ranges from 1. 14% to 2. 18% . The biogenic and thermogenic mixture gas is formed in the northern study area with the shallow buried depth of coal seam,the outcrop development, and the appropriate hydrogeological condition.