山西煤层瓦斯分布规律研究

山西晚古生代含煤岩系是华北大型聚煤盆地的一部分,晚石炭世至中生代三叠纪为连续沉积,煤层埋藏深度、深成变质作用由北往南逐渐加深,生烃量也相应增多;燕山期是构造变形最为强烈的时期,也是侏罗纪聚煤盆地的形成期,大同、河东、宁武、沁水等4个聚煤(气)盆地构造格局基本形成,煤变质仍然是随埋深的加大而增高,属再次深成变质作用,煤化程度进一步加深,生烃作用持续发生;喜马拉雅期为强烈拉伸的构造环境,造就了山体整体抬升和雁行排列的新裂陷盆地的沉降。就山西煤层瓦斯而言,上覆基岩厚度是煤层瓦斯保存的主控因素,其次为岩浆活动、不同构造类型及水文地质条件等。区域岩浆热变质作用表现为在深变质作用背景上的叠加效应,山西境内的两个东西向高变质带与岩浆岩体的分布吻合,使阳泉矿区和晋城矿区成为煤层瓦斯(煤层气)开发利用基地;从聚气构造背景来说,封闭型构造使煤储层中瓦斯含量较高,如沁水盆地的沁南区、古交、邢家社、东社区以及河东盆地的石楼、大宁—吉县区、三交—柳林区,瓦斯含量在10～15m3/t或更高;开放型构造具有逸散煤层瓦斯的便利通道,瓦斯含量较低,如河东盆地的离石矿区、沁水盆地霍西构造区以及浑源、五台煤产地等。

A Study on Coal Seam Gas Distribution Pattern in Shanxi

The Late Paleozoic coal-bearing rock series is a part of North China mega coal-accumulation basin.Sedimentation from Late Carboniferous to Mesozoic Triassic Period is continuous.Coal seam buried depth and hypozonal metamorphism is deepening from north to south,hydrocarbon generation correspondingly increasing.The Yanshanian stage is a strongest tectonic deformation period,also the Jurassic coal-accumulation basin forming period;the structural pattern of four coal（gas） accumulation basins of Datong,Hedong,Ningwu and Qinshui were basically formed;coal metamorphism was enhanced along with the depth increasing and still once more hypozonal metamorphism;degree of coalification deepening,hydrocarbon generation still went on.The Himalayan stage is a strong extensional tectonic setting and formed mountain massif integer uplift and new rift basins subsidence en echelon.As for Shanxi coal seam gas,overburden thickness is main control factor of preservation,then magmatic activities,different structural types and hydrogeological conditions.Regional magmatic thermometamorphism appeared as a kind of superimposed effect.Two EW metamorphic belts in Shanxi tallied with magmatic rock masses have brought up Yangquan and Jincheng mining areas as coal seam gas（CBM） exploitation and utilization bases.From gas-accumulation structural setting,closed type structures make high gas content in coal reservoir,such as Qinnan,Gujiao,Xingjiase,and Dongse areas in the Qinshui Basin,Shilou,Daning-Jixian and Sanjiao-Liulin areas in the Hedong Basin,gas content is 10~15m3/t or even higher.The open structures have convenient channels for coal seam gas effusion;make lower gas content,such as Lishi mining area in Hedong Basin,Huoxi structural area in Qinshui Basin and Hunyuan,Wutai coal districts.