Coalbed methane resources and reservoir characteristics of NO. II_1 coal seam in the Jiaozuo coalfield, China

摘要

Jiaozuo coalfield is located in the northwest of Henan province, China, and close to the Southern Qinshui coal basin, the most successfully commercial CBM resource developed area in China. The No. II_1 coal seam is the main economic coal seam in Jiaozuo coalfield and its average thickness exceeds 5.36m. The maximum reflectance of vitrinite (R_(O,max)) of the No. II_1 coal across the Jiaozuo is between 3.16% and 4.78%. The coalbody structure of the No. II_1 coal seam changes greatly in different part and can be generally divided into 1 ~3 sub-layers. The micropores in the No.II_1 coal seam is the major pores, secondly are transitional pores, and then less macropores and mesopores. The No. II_1 coal seam has stronger adsorption, and the reservoir natural permeability has an evident heterogeneity vary from 0.0001 to 83.71mD. High permeability region is often near fault structure or the boundary of fault block. The CBM genetic type is homologous thermal cracking gas of humic coal with high matunity. Gas content with the burial depth of 163～1070m varies very greatly from 4.65 to 45.75m~3/t, with an average value of 18.3m~3/t, and gradually increases from northeast to southwest. According to the latest evaluation for CBM resource in Jiaozuo coalfield, the existing total in-place CBM resources in the No. II_1 coal seam with the depth of shallower than 2000 m are close to 1.2 × 10~(12)m~3, most of them mainly distribute in the depth of 1000 ～ 1500 m. The existing total in-place CBM resources is dominated by the inferred CBM resource reserves (more than 70%), which distribute the undrilled places with few coal geological knowledge and deeper than 1000m. The resource concentration of the No. II_1 coal seam in Jiaozuo coalfield is in the range of (0.513-3.478)×10~8m~3/km~2, with an average value of 1.805×10~8 m~3/km~2. Based on the CBM resource investigation and reservoir evaluation, the most prospective target zones for CBM production in Jiaozuo coalfield include Guhanshan coal mine, Jiulishan coal mine and the west part of Qiangnan coal district.