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鄂西宜昌地区五峰-龙马溪组黑色岩系硅质来源及其油气地质意义
投稿时间:2019-10-11  修订日期:2020-01-03  点此下载全文
引用本文:
DOI:10.19762/j.cnki.dizhixuebao.2020133
摘要点击次数: 21
全文下载次数: 20
作者单位E-mail
蔡全升 中国地质调查局武汉地质调查中心 cqsh0713@163.com 
陈孝红 中国地质调查局武汉地质调查中心  
张保民 中国地质调查局武汉地质调查中心  
刘安 中国地质调查局武汉地质调查中心  
韩京 中国石化勘探分公司 勘探研究院  
张国涛 中国地质调查局武汉地质调查中心  
李炎桂 中国地质大学武汉  
基金项目:本文由中国地质调查局项目“宜昌斜坡页岩气战略调查”(编号: DD20179615)、国家重大科技专项“中扬子高演化海相页岩气赋存机理及富集规律研究”(编号: 2016ZX05034001-002)和湖北省自然科学基金“鄂西地区五峰-龙马溪组富有机质页岩时空分布与古地理研究”(编号:2018CFB330)联合资助。第一
中文摘要:为了查明鄂西五峰-龙马溪组富有机质页岩的硅质来源,明确不同硅质来源的页岩气地质意义,促进页岩气勘探开发,本文通过系统的样品采集与分析测试,对宜昌地区五峰-龙马溪组下部黑色岩系的硅质来源、特征及其对有机质富集和储层特征的影响进行了深入研究。结果表明,鄂西宜昌地区五峰-龙马溪组黑色岩系硅质矿物含量高,过量硅含量在2.59%~88.31%,平均27.91%,且过量硅主要发育于凯迪阶与鲁丹阶的深水陆棚环境;显微镜下可见大量棱角状陆源碎屑石英,硅岩中可见具有溶蚀边的硅质生物化石,如放射虫、海绵骨针等;页岩样品TiO2与Al2O3平均含量只有0.63%和12.41%,且SiO2与TiO2、Al2O3呈现明显的负相关,Si/(Si+AL+Fe)和Al/( Al+Fe+Mn)比值分别为0.81和0.77,Eu/Eu*具有明显的负异常,过量硅与U/Th、Ni含量之间相关性不明显,表明鄂西宜昌地区五峰-龙马溪组黑色岩系硅质来源以陆源硅和生物硅为主,没有受到热液的影响,且五峰组凯迪阶-鲁丹阶以生物硅为主,向上陆源硅影响逐渐增大。深水缺氧还原环境是生物硅发育的有利条件,但生物硅的发育与古生产力、氧化还原条件没有绝对的正相关线性关系,主要表现为不同来源的硅质矿物含量与TOC峰值之间呈正态分布曲线特征,当Al2O3含量达到10%左右,过量硅含量在40%左右所对应的页岩有机碳可出现峰值,而不是硅质矿物含量越高有机质一定越富集。此外,硅质矿物特别是以微晶方式赋存的生物硅的发育不仅可以有效保护页岩储集空间,还能促进裂缝的发育,极大的改善页岩储层的储渗能力,并为后期获得良好的储层压裂改造效果提供有利条件。
中文关键词:五峰-龙马溪组  硅质来源  有机质富集  生物硅  鄂西地区
 
Origins of siliceous minerals in the black shale of the Wufeng and Longmaxi formations in the Yichang area, Western Hubei province: Geological significance for shale gas
Author NameAffiliationE-mail
cai quan sheng Wuhan Institute of Geology and Mineral ResourcesChina Geological Survey cqsh0713@163.com 
chen xiao hong Wuhan Institute of Geology and Mineral ResourcesChina Geological Survey  
zhang bao min Wuhan Institute of Geology and Mineral ResourcesChina Geological Survey  
Liu an Wuhan Institute of Geology and Mineral ResourcesChina Geological Survey  
han jing Research Institute of Exploration CompanySinopec  
zhang guo tao Wuhan Institute of Geology and Mineral ResourcesChina Geological Survey  
li yan gui China University of Geoscience(Wuhan)  
Abstract:The black shale in the lower part of the Wufeng and Longmaxi formations in the Western Hubei Province has become a hot spot for the shale gas exploration in South China. In this paper, in order to determine the different silica sources in the Wufeng and Longmaxi formations and their geological significance for shale gas exploration, we investigate the origins of siliceous minerals in the black shale of the Wufeng and Longmaxi formations in the Yichang area by systematic collection and analytical test of samples, as well as the impact of different original silicon on organic matter accumulation and reservoir characteristics. The results show that the black shale of the Wufeng and Longmaxi formation in the study area has high content of siliceous minerals, the content of excess silicon ranges from 2.59%~88.31%, average of 27.91%, and most excess silicon develops in the deep-shelf environment corresponding to the Katian and Rhuddanian stage. Angular terrigenous quartz and siliceous fossil such as radiolarians and sponge spicules with serrated edges can be observed by microscopic examination. Element geochemistry analysis indicates the average content of TiO2 and Al2O3 in samples is only 0.63% and 12.41% respectively, and the relationship between SiO2 and TiO2, Al2O3 are negative. The ratio of Si/(Si+AL+Fe) and Al/( Al+Fe+Mn) is 0.81 and 0.77, and Eu/Eu* has clear negative anomaly. Excess silicon has not linear relationship with U/Th and the content of Ni. These data above demonstrate that terrigenous silicon and biosilicon are the main sources of siliceous minerals in the black shale of the Wufeng and Longmaxi formations, and hydrothermal silicon has little impaction on the origins of siliceous minerals. Deep-water anoxic and reducing environment should be favorable conditions for the development of biosilicon, but the biosilicon has not evident linear relationship with paleoproductivity and redox conditions, which can be demonstrated by the normal distribution curve relation between the high value of TOC and the contents of different original silicon. According to the normal distribution curves, it can be found that when the contents of Al2O3 and excess silicon are around 10% and 40% respectively, the TOC of shale will have highest value, which indicates the complicated relation between organic matter accumulation and siliceous mineral content. Furthermore, the development of siliceous mineral, especially the biosilicon with microcrystal occurrence can not only provide effective protection for reservoir space, but also promote the development of microfractures, which can greatly improve the reservoir capacity and flowing ability, as well as the reservoir fracturing reformation effect.
keywords:Wufeng and Longmaxi formations  siliceous sources  organic matter accumulation  biosilicon  Western Hubei Province
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