渝南地区二叠系龙潭组C_(25)煤层煤层气基础地质条件分析

Analysis of general geological conditions of coalbed methane in coal seam C_(25) of Permian Longtan Formation,south Chongqing

渝南地区二叠系龙潭组煤层气勘探开发处于起步阶段,为揭示该区主力煤层C_(25)的煤层气基础地质条件,基于区内煤田钻孔、煤层气钻井获取的地质资料和实验测试数据,对煤岩煤质、煤层孔渗、含气性等特征进行了分析。结果表明:研究区二叠系龙潭组C_(25)煤层具有“发育稳定、厚度相对大、孔渗低、变质程度高、含气量高”的特征。C_(25)煤层全区发育稳定,呈“北厚南薄”的趋势,北部一般大于1.5 m;煤岩煤质属于半亮型煤;有机组分中镜质组含量介于51.7%~72.2%;镜质组最大反射率整体介于1.8%~2.2%,变质程度处于高成熟—过成熟阶段;煤岩孔渗较差,孔隙度介于3.46%~8.46%,渗透率大多低于0.01×10^(-3)µm^(2);含气性好,一般大于10.0 m^(3)/t;同时,煤层顶底板均为良好封隔层。结合綦煤1井、Y2井产气效果,认为渝南地区二叠系龙潭组C_(25)煤层具备较好的煤层气勘探开发基础地质条件。

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 C_(25),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 C_(25) 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 C_(25) 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 0.01×10-3μm2. 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 goodsealing layers. Based on the production of Q1 and Y2, it is believed that the coal seam C_(25) of Permian Longtan Formation in southChongqing area has good geological conditions for CBM exploration and development.