宜昌地区寒武系页岩层段吸水特征、孔隙结构差异性及对页岩储层评价的意义  

Significance of water absorption characteristics and difference of pore structures in the Cambrian shale intervals,Yichang area for shale reservoir evaluation

作　　者：张六六 陈更新[1] 乐幸福[1] 张瑜[3] 邵德勇 闫建萍 孟康 张同伟 ZHANG Liuliu;CHEN Gengxin;LE Xingfu;ZHANG Yu;SHAO Deyong;YAN Jianping;MENG Kang;ZHANG Tongwei(Research Institute of Petroleum Exploration and Development-Northwest,Petrochina,Lanzhou 730000,China;School of Earth Sciences,Lanzhou University,Lanzhou 730000,China;State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,China;The Bureau of Economic Geology,Jackson School of Geosciences,The University of Texas,Austin,TX,USA)

机构地区：[1]中国石油勘探开发研究院西北分院,甘肃兰州730000 [2]兰州大学地质科学与矿产资源学院,甘肃兰州730000 [3]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 [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138-150,共13页Earth Science Frontiers

基　　金：国家自然科学基金重点项目(41730421)。

摘　　要：选取宜昌地区ZK003井寒武系页岩样品为研究对象,运用吸水实验、氦孔隙度测试、有机碳含量测定等方法,并结合矿物组成分析对水井沱组不同层段页岩孔隙发育特征及其影响因素进行对比。研究结果表明:宜昌地区寒武系水井沱组自下而上分为4段,不同层段页岩孔隙特征具有显著的差异,总体表现为TOC含量越高,页岩的单位岩石饱和吸水量越高,初始吸水速率越高,孔隙度也越大。其中富有机质一段和二段页岩TOC含量为1.8%~11.5%,平均为4.6%;页岩氦孔隙度为1.6%~5.8%,平均为3.9%;饱和吸水量为6.1~21.4 mg/g,平均为15.3 mg/g。水井沱组富有机质第一段页岩TOC含量比第二段高,而孔隙度、吸水量、吸水速率却明显比二段偏低,分析发现第一段碳酸盐矿物与吸水量呈良好负相关关系,而第二段页岩黏土矿物含量与岩石吸水量呈明显正相关,因此认为第一段中碳酸盐矿物的化学胶结作用阻碍了微、纳米孔隙的发育,而第二段页岩黏土矿物自身发育的微孔隙和较大比表面积,对水分子起到很强的吸附作用。富有机页岩第二段孔隙度高,顶、底板泥灰岩封隔性好,有利于页岩气的富集和保存,是研究区页岩气优质储层。研究结果可为寒武系页岩优质储层筛选及页岩气勘探的“甜点区”预测提供参考。The Cambrian Shuijingtuo shale formation of Well ZK003,Liuxi,Yichang area is selected to study its pore development characteristics,where different formation layers are compared through water absorption experiment,helium porosity test,organic carbon content determination,and mineral composition analysis.The results of the study show that the Cambrian shale formation can be divided into members 14 from bottom to top,and different members have very different pore characteristics.In general,the higher the TOC content,the greater the water saturation limit(per gram of shale weight);and the higher the initial water absorption rate,the greater the porosity of shale.In shales from the organic-rich members 1 and 2,the TOC content ranges from 1.8%to 11.5%,averaging 4.6%;the helium porosity ranges from 1.6%to 5.8%,averaging 3.9%;and the water absorption saturation limit is between 6.121.4 mg/g shale weight,or on average 15.3 mg/g shale weight.Between the two members,shale from member 1 has higher TOC content but significantly lower porosity,water absorption value,and water absorption rate.The carbonate content in member 1 shows a good negative correlation with the water absorption value;whereas a positive correlation is observed for the clay content in member 2.It is believed that in member 1 carbonate cementation hinders the development of micropores and nanopores;while in member 2,development of micropores,which have large specific surface area and autogenic to porous clay,lead to strong water absorption.Overall,member 2 of the organic-rich shale formation has high porosity and good roof/floor isolation by overlaying marl and carbonate,which is conducive to the enrichment and preservation of shale gas,therefore making it a high-quality shale gas reservoir in the study area.The research results can be used for screening high-quality Cambrian shale reservoirs and predicting shale gas exploration“sweet spots”.

关 键 词：宜昌地区 下寒武统 吸水实验 孔隙结构 保存条件 

分 类 号：P618.130.2[天文地球—矿床学]