Abstract:

The exploration and development of coalbed methane（CBM）in the Permian Longtan Formation in south Chongqing is in the initial stage. In order to reveal the general geological conditions of coalbed methane in the coal seam C₂₅, by the experimental and geological data obtained from the coal mines and coalbed methane drilling, the geological characteristics such as coal rock and coal quality, coal pore penetration and gas content have been analyzed. The results show that the C₂₅ coalbed methane of Longtan Formation of Permian in the study area is characterized by “stable development, relatively large thickness, low pore permeability, high metamorphism and high gas content”. The development of the coal seam C₂₅ is stable throughout the whole area, showing the trend of “thick in the north and thin in the south”, and the thickness in the northern part of the coalbed is generally larger than 1.5 m. The coal quality belongs to semi-bright coal. The content of vitrinite in the organic component is 51.7%~72.2%; the vitrinite reflectance ranges from 1.8%~2.2%, and the metamorphism degree is high-over maturity. The porosity and permeability of the coal rock are relatively low, with the porosity ranging from 3.46%~8.46% and the permeability of mostly lower than 0.01×10^-3 μm². The gas content of the coal bed is high, generally more than 10.0 m³/t; meanwhile, the top and bottom plates of the coal bed are good sealing layers. Based on the production of Q1 and Y2, it is believed that the coal seam C₂₅ of Permian Longtan Formation in south Chongqing area has good geological conditions for CBM exploration and development.

Key words: south Chongqing, Longtan Formation, coal seam C₂₅, CBM, geological conditions