鄂西宜昌地区寒武系水井沱组页岩破碎气地球化学特征及其对页岩含气性的指示意义  

Geochemical characteristics of residual gas released from crushed shale from the Shuijingtuo Formation in Yichang,western Hubei-indication for gas-bearing capacity of shale

作　　者：孟康 邵德勇 张六六 李立武 张瑜[1] 罗欢 宋辉 张同伟 MENG Kang;SHAO Deyong;ZHANG Liuliu;LI Liwu;ZHANG Yu;LUO Huan;SONG Hui;ZHANG Tongwei(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,China;School of Earth Sciences,Lanzhou University,Lanzhou 730000,China;Northwest Institute of Eco-Environment and Resources,Chinese Academy of Sciences,Lanzhou 730000,China;Bureau of Economic Geology,Jackson School of Geosciences,The University of Texas at Austin,Austin,TX 78713,USA)

机构地区：[1]西北大学地质学系,大陆动力学国家重点实验室,陕西西安710069 [2]兰州大学地质科学与矿产资源学院,甘肃兰州730000 [3]中国科学院西北生态环境资源研究院,甘肃兰州730000 [4]Bureau of Economic Geology,Jackson School of Geosciences,The University of Texas at Austin,Austin,TX 78713,USA

出　　处：《地学前缘》2023年第3期14-27,共14页Earth Science Frontiers

基　　金：国家自然科学基金重点项目“中国南方寒武系页岩有机质、流体和孔隙演化耦合机制研究(41730421)”。

摘　　要：本文选取鄂西宜昌地区流溪ZK003井水井沱组页岩岩心样品13块,开展破碎气测试分析,并结合TOC含量、矿物组成含量以及邻近地区高氮气井—秭地1井的解吸气特征,综合探讨鄂西宜昌地区寒武系页岩气中氮气成因和富集机理。结果表明,研究区水井沱组页岩样品破碎气含量为1.45~14.75μL.STP/g,变化大,主要受控于页岩中碳酸盐矿物丰度;破碎气以氮气和甲烷为主,相对含量分别为7.92%~86.27%和10.10%~90.88%,且氮气含量明显受控于页岩中TOC含量和黏土矿物含量,并与页岩破碎气含量呈良好的负相关关系。破碎气主要保存在方解石、白云石、黏土矿物及有机质封闭孔隙中,高—过成熟阶段有机质中氮和铵基黏土矿物中氮的释放是水井沱组富有机质页岩中氮气的主要来源。此外,持续性构造抬升剥蚀等地质过程不仅可能造成页岩气散失,还会导致氮气的相对富集。结合我国南方不同地区古生界海相页岩气中氮气含量和氮同位素组成特征的对比分析发现,寒武系页岩气中氮气含量(2.69%~98.92%)远高于下志留统龙马溪组页岩气(0.01%~9.30%)。鄂西宜昌地区水井沱组页岩气中氮气δ^(15)N_(N_(2))相较于其他地区明显偏重(Δ^(15)N_(N_(2))=1.5‰~12.7‰),可能与铵基黏土矿物高温热裂解成因氮气有关。In this paper,13 shale samples from the Lower Cambrian Shuijingtuo Formation of well Liuxi ZK003,Yichang area,western Hubei Province were collected for the degassing experiment where residual shale gas released from the crushed shale samples were analyzed.Combined with results on TOC content and mineral composition in shale samples as well as characteristics of desorbed nitrogen-rich shale gas from adjacent area(well ZD1),the origin and source of nitrogen in the Cambrian shale gas were discussed.The total residual gas content in shale samples ranged between 1.4514.75μL.STP/g,varying greatly according to the abundance of carbonate minerals.The residual gas was dominated by nitrogen and methane with relative respective abundances of 7.92%86.27%and 10.10%90.88%,where the nitrogen abundance was obviously controlled by TOC and clay mineral contents in shale and negatively correlated with residual gas content.The residual gas was mainly hosted in the closed pores of calcite,dolomite,clay minerals and organic matter;whilst nitrogen released from organic matter and amino-clay minerals,under increasing thermal maturation,was the main source of nitrogen in the organic-rich shale formation.In addition,geological processes such as continuous tectonic uplift and denudation might not only cause shale gas leakage,but also lead to nitrogen enrichment in shale.The comparison of nitrogen contents and nitrogen isotopic compositions in Lower Paleozoic marine shale gas from different regions of southern China revealed that the nitrogen content in Cambrian shale gas(2.69%98.92%)was much higher compared to the Lower Silurian Longmaxi Formation(0.01%9.30%),and theδ^(15)N_(N_(2)) value in the Shuijingtuo shale gas was obviously higher compared to other areas(Δ^(15)N_(N_(2))=1.5‰12.7‰).This enrichment of nitrogen might be related to nitrogen released from high temperature pyrolysis of amino-clay minerals.

关 键 词：页岩气 氮气 地球化学特征 破碎气 宜昌地区 水井沱组 

分 类 号：P593[天文地球—地球化学]