摘要
中国四川盆地页岩气开采集中在过成熟海相龙马溪组页岩层段,有机孔作为主要储气空间,其发育具有强烈微观非均质性,控制了页岩气的储集与运移机制。目前对有机孔的非均质性成因尚不明朗,究其原因是对有机质组分及其化学结构复杂性认识不足。本文结合光学显微镜、场发射扫描电镜与激光拉曼光谱技术,对四川盆地典型过成熟龙马溪组页岩的有机岩石学特征、有机质化学结构及其与孔隙发育程度的相关性进行了系统表征和定量分析。结果表明,龙马溪组硅质页岩的显微组分以焦沥青为主,其次为笔石表皮体,在油浸入射白光下颜色呈浅灰色至灰白色,无荧光。基于不同显微组分在电镜下的赋存状态差异,龙马溪组页岩孔隙发育类型可分为生物碎屑孔隙、结构型焦沥青孔隙和无定形焦沥青孔隙。生物碎屑的表观转化率介于0~2%,表面仅见少量孤立状分布的孔隙,其孔径分布范围主要为10~50 nm。结构型焦沥青的表观转化率在8%~11%区间,内部发育相对均匀的海绵状或不规则孔隙,孔径峰值约为60 nm。无定形焦沥青的表观转化率最高,平均约为16%,且孔径峰值向大孔方向偏移。从笔石表皮体到结构型、无定形焦沥青,有机碳的芳构化程度依次降低,对应的孔隙发育程度则依次增高。研究认为有机质的原始组分及生排烃过程中的地层色层效应是导致孔隙发育非均质性的关键。
Shale gas exploitation in the Sichuan Basin of China is concentrated in the overmature marine Longmaxi Formation.As the main gas storage space,the development of organic matter(OM)-hosted pores shows great heterogeneity at micro-scale,which further controls the mechanism of shale gas storage and migration.To date,the origins of OM-hosted pore heterogenerity are still unclear,due to a poor understanding of OM compositional and structural complexity.In this paper,the organic petrology,OM-hosted pore type and its correlation with OM chemical structure of a typical overmature Longmaxi shale in the Sichuan Basin were systematically characterized and quantified,by combining optical microscopy,field emission scanning electron microscopy,and laser Raman spectroscopy.Results show that the OM maceral of examined siliceous Longmaxi shale is dominated by pyrobitumen,followed by graptolites,which display light-gray to grayish color under oil-immersion incident light and have no fluorescence.On the basis of the different OM occurrence under electron microscopy,the pore development types can be divided into bioclastic pores,structural pyrobitumen pores,and amorphous pyrobitumen pores.The apparent transformation rate(ATR)of bioclastics is between 0~2%,with only a small number of isolated pores found on the surface and the pore size distribution mainly of 10~50 nm.The ATR of structural pyrobitumen is in the range of 8%~11%,with relatively uniform sponge-like or irregular pores developed and the peak of pore size about 60 nm.The ATR of amorphous pyrobitumen was the highest,with an average of about 16%,and the peak of pore size is shifted to larger size.In order of graptolites bodies,structural and amorphous pyrobitumen,the OM aromatization decreases and the corresponding pore development increases.The study suggests that the primaty OM composition and chromatographic fractionation during hydrocarbon generation and expulsion are key factors in pore characteristics heterogeneity.
作者
王莹珠
杨继进
Wang Yingzhu;Yang Jijin(Key Laboratory of Shale Gas and Geoengineering,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029;Innovation Academy of Earth Science,Chinese Academy of Sciences,Beijing 100029;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049)
出处
《地质科学》
CAS
CSCD
北大核心
2024年第5期1173-1184,共12页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
国家科技重大专项(编号:2016ZX05034,2017ZX05035)
中国科学院战略性先导科技专项(B类)(编号:XDB10050100)
国家自然科学基金项目(编号:U1562215)资助。
关键词
过成熟海相页岩
龙马溪组
显微组分
有机碳结构
孔隙发育
Overmature marine shale
Longmaxi Formation
Microscopic components
Organic carbon structure
Pore development
