湘鄂西地区五峰-龙马溪组泥页岩黄铁矿粒径特征  

The Particle Size Characteristics of Pyrite in Western Hunan and Hubei Areas' Wufeng-Longmaxi Formation Shale

作　　者：刘子驿 张金川[1] 刘飏[1] 余文武[1] 何葳[2] 李波文[1] 

机构地区：[1]中国地质大学(北京)页岩气勘查与评价国土资源部重点实验室,北京100083 [2]西安石油大学地球科学与工程学院,西安710300

出　　处：《科学技术与工程》2016年第26期34-41,共8页Science Technology and Engineering

基　　金：陆域能源矿产地质调查计划(12120115007201)资助

摘　　要：湘鄂西地区位于中扬子板块,该地区五峰-龙马溪组富有机质页岩有机质类型以Ⅱ1型为主,Ⅱ2型次之,具有高TOC含量（0.55%~4.28%）、高成熟度（2.4%~3.2%）的特征;且富有机质页岩中黄铁矿普遍发育。通过岩心样品及扫描电镜观察发现,龙马溪组黑色页岩常发育自形-半自形黄铁矿,扫描电镜下常见草莓状黄铁矿;五峰组黑色页岩岩心观察无明显晶形,扫描电镜下常现呈微晶黄铁矿颗粒,以细小颗粒状分布在有机质中。草莓状黄铁矿通常由微晶颗粒聚集而来,其草莓状直径大小由硫复铁矿的形成和沉积水动力控制。根据草莓状黄铁矿直径D与深度关系分析出湘鄂西地区黑色页岩的沉积环境表现为五峰组闭塞环境、龙马溪组闭塞环境、龙马溪组贫氧-缺氧环境三种。由草莓状黄铁矿直径D与微晶黄铁矿直径d建立D/d的关系表明：从沉积期到成岩期,五峰组闭塞环境的还原性比龙马溪组闭塞环境的还原性强;且五峰组闭塞环境的沉积水动力要比龙马溪组闭塞环境的沉积水动力要弱,水体更稳定。此外,D与d之间的关系能侧面反映该地区五峰-龙马溪组富有机质页岩孔隙度的变化趋势。D/d值与页岩解吸气量也有良好的对应关系,龙马溪组D/d值越大,解吸气量越少。五峰组D/d值较龙马溪组普遍偏小,解吸气量远大于龙马溪组。上述结果表明水体还原环境的强弱是湘鄂西烃源岩有机质形成和保存的重要因素,从而影响页岩气的富集。Wufeng-Longmaxi formation organic-rich shale is featured with high TOC（ 0. 55% 4. 28%） and high thermal maturity（ 2. 4% 3. 2%） in western Hunan and Hubei areas which are located in the middle Yangtze plate. Meanwhile,organic matter of the two set of source rocks in the area are type Ⅱ1 to type Ⅱ2 kerogen and dominated by type Ⅱ1kerogen. In the area,pyrite is abundant in the organic-rich shale. Core sample observations of pyrite indicate that sedimentary pyrite occurs clustered euhedral crystals or semi- euhedral crystals in the Longmaxi formation,but,no obviously crystal morphology is observed in the Wufeng formation. Scanning electron microscope（ SEM） observations of pyrite occurs clustered framboids in the Longmaxi formation and abundance microcrystals within organic matter in the Wufeng formation. The framboids discussed in following sections are related to the initiation and rate of aggregation of microcrystals. Pyrite framboid’ s aggregation and the size is controlled by greigite’s development and hydrodynamic effects. On the basis of the framboidal pyrite diameter（ D） associating with depth has analyzed the performance of depositional environment of black shales in Western Hunan and Hubei area into Wufeng group,Longmaxi group’ s euxinic environment and Longmaxi group’ s dysoxic-anoxic environment. By the framboidal pyrite diameter（ D） and microcrystal pyrite diameter（ d） to establish a relationship between D / d shows that,Wufeng group’ s euxinic environment reduction is stronger than Longmaxi group’ s euxinic environment reduction and Wufeng Formation’s sedimentary hydrodynamic is weaker than Longmaxi formation’s during the depositional stage and diagenetic stage. Therefore,water in Wufeng group is more stable than in Longmaxi group. In addition,the relationship between D and d can reflect the Wufeng-Longmaxi organic-rich shale’ s porosity changing trend,D / d value and shale desorption gas content also has a good corresponding relationship,the greater the

关 键 词：湘鄂西地区 五峰-龙马溪组富有机质页岩 草莓状黄铁矿 微晶黄铁矿 解吸气量 

分 类 号：TE122.112[石油与天然气工程—油气勘探]