页岩中黄铁矿类型及其对页岩气富集的影响——以四川盆地及其周缘五峰组—龙马溪组页岩为例

Pyrite type and its effect on shale gas accumulation: a case study of Wufeng-Longmaxi shale in Sichuan Basin and its periphery

张光荣 聂海宽 唐玄 杜伟 孙川翔 陈松

ZHANG Guangrong NIE Haikuan TANG Xuan DU Wei SUN Chuanxiang CHEN Song

中国地质大学(北京)自然资源部页岩气资源战略评价重点实验室, 北京 100083 页岩油气富集机理与有效开发国家重点实验室, 北京 100083 中国石化 石油勘探开发研究院, 北京 100083 中国海洋大学 海洋地球科学学院, 山东 青岛 266100

Key Laboratory of Strategy Evaluation for Shale Gas, Ministry of Natural Resources of the People's Republic of China, China University of Geosciences(Beijing), Beijing 100083, China State Key Laboratory of Shale Oil and Gas Enrichment Mechanism and Effective Development, Beijing 100083, China SINOPEC Petroleum Exploration and Production Research Institute, Beijing 100083, China College of Marine Geosciences, Ocean University of China, Qingdao, Shandong 266100, China

黄铁矿是页岩中普遍存在的矿物之一，对其类型、成因及其对页岩气富集的影响的研究还处在探索阶段。以四川盆地及其周缘上奥陶统五峰组-下志留统龙马溪组页岩为研究对象，通过薄片观察、扫描电镜等手段，识别出草莓状、纹层状、结核状、自形以及他形等黄铁矿类型，五峰组-龙马溪组页岩中的黄铁矿主要形成于同生沉积阶段和早成岩阶段。草莓状黄铁矿主要形成于同生沉积阶段，指示还原环境，有利于有机质富集和保存，其含量与总有机碳呈正相关关系，其发育层段常富含有机质。草莓状黄铁矿与生物成因石英、陆源碎屑石英一起形成刚性颗粒支撑格架，对原始粒间孔隙的保存具有重要作用，有利于油气充注、滞留以及有机质孔的发育。研究区五峰组-龙马溪组底部黑色页岩草莓状黄铁矿非常发育，显示其不仅具有良好的有机质富集的物质基础，也有利于页岩优质储层的形成，草莓状黄铁矿含量可以作为页岩气甜点段判识的依据。

Pyrite is one of the most common minerals in shale, but its type, genesis and effect on shale gas accumulation are still in the initial study stage. The shale in the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in the Sichuan Basin and its periphery was studied. Strawberry-like, stratified, tuberculosis, euhedral and anhedral pyrites were identified through thin section observation, scanning electronic microscopy analyses. The pyrites in the Wufeng-Longmaxi formations are mainly developed during the syngenetic and early diagenetic stages. The strawberry-like pyrites are formed in the syngenetic stage, indicating a reducing environment, which is conducive for organic matter enrichment and preservation. The pyrite content has a positive correlation with the organic carbon content. The layers with a high content of pyrites are usually rich in organic matter. Strawberry-like pyrites, together with biogenic quartz and terrestrial detrital quartz, formed a rigid particle grid supporting the original intergranular pores, which was beneficial to hydrocarbon charging, preservation and organic matter-hosted pore development. The bottom of the Wufeng -Longmaxi shale with well developed strawberry-like pyrite in the Sichuan Basin and its periphery, indicate it not only has a good condition for organic matter enrichment, but also is conducive to the formation of high-quality shale gas reservoirs. The strawberry-like pyrite content can be used as a clue for identifying shale gas "sweet spots".

国家自然科学基金 41872124;国家自然科学基金 41972132;国家自然科学基金 41730421

https://doi.org/10.11781/sysydz202003459