川东南綦江地区深层煤层气储层特征及勘探方向OA

Against the backdrop of global energy transition,deep coalbed methane(CBM)at burial depths greater than 1 500 m has emerged as a highly promising unconventional natural gas resource.Multiple coal seams are developed in the Permian Longtan Formation in the Qijiang area,southeastern Sichuan.However,their reservoir characteristics remain poorly understood,and future exploration targets have yet to be clearly defined.To address these issues,reservoir characteristics,gas enrichment conditions and exploration targets of deep coal seams in the Longtan Formation were systemically investigated based on core observations,laboratory analyses and experi-mental data from multiple wells.As indicated by the research results,the Longtan Formation contains coal seams with large cumulative thickness and wide lateral distribution in research area.The coal rank is high-rank anthra-cite,with an average vitrinite reflectance of 2.93％.Measured gas contents range from 4 to 46.7 m3/t,with free gas accounting for approximately 18％-36％,indicating high gas contents and a relatively high proportion of free gas.The reservoirs are characterized by a dual pore-cleat system comprising micron-to nano-scale pores and cleats.Macropores account for 64.1％of the pore system,and pore-fracture connectivity is favorable.Clay minerals are dominated by illite/smectite mixed-layer minerals(averaging 68％).The reservoir exhibits low Young's modulus and high Poisson's ratio,indicating that stress-related risks should be carefully considered during hydraulic fracturing.Based on lithological assemblages,coal quality and preservation conditions,a three-category,twelve-parameter evaluation system was established,within which three favorable coal assemblage types were identified:thick coal seams,medium-thick coal seams interbedded with mudstone,and medium-thick coal seams interbedded with mudstone and sandstone.Accordingly,favorable areas covering approximately 5 243 km2 were delineated,with estimated geological resources of 1.38 × 1 012m3.The C4-C5-C6 coal-bearing assemblages in the 2nd member of the Longtan Formation(Longtan 2 Member)within the Guanshengchang Synclinorium,the plunging end of the Dingshan-Dongxi Structure,and the Lizi Gentle Fold Belt exhibit the most favorable geological conditions.These areas cover approximately 1 204.6 km2 and contain estimated geological resources of 316.2×108 m3,making them priority targets for future exploration.