黔北龙潭组菱铁质泥岩解吸气来源及元素背景  

Source and element background of desorbed gas from the siderite-bearing mudstone in northern Guizhou Province

作　　者：徐宏杰[1] 桑树勋[2] 杨景芬[1] 金军 周效志[2] 高为 刘会虎[1] XU Hongjie;SANG Shuxun;YANG Jingfen;JIN Jun;ZHOU Xiaozhi;GAO Wei;LIU Huihu(School of Earth Science and Environment,Anhui University of Science and Technology,Huainan 232001,China;School of Resources and Geoscience,China University of Mining and Technology,Xuzhou 221008,China;Guizhou Engineering Research Center for Coalbed Methane (CBM) and Shale Gas,Guiyang 550008,China)

机构地区：[1]安徽理工大学地球与环境学院,安徽淮南232001 [2]中国矿业大学资源与地球科学学院,江苏徐州221008 [3]贵州省煤层气页岩气工程技术研究中心,贵州贵阳550008

出　　处：《煤炭学报》2019年第6期1817-1826,共10页Journal of China Coal Society

基　　金：国家自然科学基金资助项目(41727801);安徽省2018年度重点研究与开发计划资助项目(1804a0802203);安徽省高校优秀拔尖人才培育基金资助项目(gxgwfx2019012)

摘　　要：贵州省含煤区龙潭组泥岩广泛发育,是煤系非常规天然气开发层位的重要组成部分。部分泥岩因含较多菱铁矿物致含气来源具有特殊性。基于贵州省北部LC-1井上二叠统煤系地层钻孔样品气测录井和实验测试结果,研究了龙潭组菱铁质泥岩的含气性及其元素地球化学背景。开展了现场解吸、气测录井、孔隙结构电镜观测、结构物性测试分析(汞注入法、液氮与CO2注入法)、矿物成分测试、岩石热解和有机碳测定、显微组分与同位素测定等系列实验。结果表明:有机质类型主要为Ⅲ型并处于过成熟阶段,TOC含量变化较大,在0.90%~2.71%,碳同位素指示了陆相有机质来源。岩芯样品解吸气组分以CH4为主,解吸气含量介于0.08~7.79m3/t,平均1.60m3/t;样品黏土矿物和石英含量分别为35.0%和15.7%;多数样品含有较多的菱铁矿(38.1%)和白云石(9.5%)。研究发现:样品解吸气量与气体注入法测试BET比表面积和BJH总孔体积、石英和黏土矿物含量均呈显著负相关关系,揭示了有机质是解吸气的主要物质来源,但存储空间并非由矿物质内部的介孔和微孔提供。菱铁矿含量与比表面积、孔体积负相关,暗示菱铁矿自身发育的晶间孔也不足以提供解吸气赋存的容储空间。菱铁矿以似层状、葡萄状、透镜状或结核状分布在有机质周围且层理连续性保持完好,形成对有机质的包围从而形成泥岩内部“微圈闭”环境,形成对有机质内烃类气体的封堵,可能是解吸气与菱铁矿含量正相关的主要原因。有机质生烃后就地吸附存储并被“微圈闭”局限,随有机质和“微圈闭”增多,封闭气体量增大,具有进一步形成超压的可能性。菱铁质泥岩与临近煤层缺乏气体运移和交换,可以具有独立的“微含气系统”。元素地球化学指标反应的氧化还原条件与区域海平面升降一致。随海平面由底至顶先降后升,解吸气量、Longtan shale is widely developed in Guizhou Province and is an important part of the unconventional natural gas for the development in coal-bearing formations.Some mudstones have special characteristics due to some siderite minerals contained.This paper takes the Upper Permian Longtan shale in the northern Guizhou as an example to examine the coal-bearing mudstone reservoir.Based on the canister desorption,well logs and test results of sideritebearing mudstones(core samples from LC-1 well),the authors present systematic pore structure,inorganic and Rock-Eval analyses of the mudstones to examine their gas content,reservoir properties,depositional environ-ment and origin.The results show that the Longtan shale contains typeⅢgas-prone organic matter with an over-mature stage and has total organic carbon values ranging between 0.90%and 2.71%.Carbon isotope data clearly indicate the terrestrial organic matter source dominating the Upper Longtan formation.Desorbed gas content(obtained by canister desorption,dominated by methane)of core samples ranges from 0.08 to 7.79 m3/t with an average of 1.60 m3/t.The mudstones are mainly composed of clays(35%)and quartz(15.7%),and most of them contained high siderite and dolomite with an average of 38.1%and 9.5%,respectively.Desorbed gas content of core samples are positively correlated with TOC but negatively correlated with quartz and clay mineral contents,BET specific surface areas and BJH total pore volumes measured by gas injection method,which suggests that the organic matter is the main material source for desorbed gas,but the storage space is not provided by mesopores or micropores.However,the negative correlation between siderite content and specific area with pore volume(obtained by gas injection method),suggesting that the intercrystalline pore of siderite is insufficient to provide the storage space for the occurrence of the desorbed gas.The distribution of siderite around the organic matter is stratified,botryoidal,lenticular or tuberculous,and the stratigraphic co

关 键 词：菱铁质泥岩 解吸气 气体来源 元素背景 龙潭组 

分 类 号：P618.11[天文地球—矿床学]