陇东地区延长组构造裂缝方解石脉特征及其与烃类流体活动的关系  

Geochemical characteristics of tectonic fracture-filling calcite in Yanchang formation of Longdong area and its relationship with hydrocarbon fluid flow

作　　者：郭凯[1,2] 曾溅辉[1,2] 李元昊[3] 刘涛涛[1,2] 

机构地区：[1]中国石油大学油气资源与探测国家重点实验室,北京102249 [2]中国石油大学地球科学学院,北京102249 [3]中国石油长庆油田勘探开发研究院,陕西西安710021

出　　处：《中国石油大学学报（自然科学版）》2013年第2期36-42,49,共8页Journal of China University of Petroleum(Edition of Natural Science)

基　　金：国家自然科学基金项目(40772088;41172128)

摘　　要：通过微量元素与稳定同位素分析对鄂尔多斯盆地陇东地区延长组广泛发育的构造裂缝方解石充填物的成因及其与烃类流体活动的关系进行研究。结果表明:该区砂泥岩裂缝中充填的方解石为相对富集Fe和Mn而贫Mg的(含)铁方解石,其δ13CPDB为-6.6‰～2.7‰,δ18OPDB为-23.0‰～-14.9‰;方解石脉中富集的Mn元素主要源于酸性烃类流体对长7段源岩内部凝灰岩的溶蚀,其成因主要与有机质演化过程中甲烷生成作用产生的相对富13C二氧化碳和脱羧作用产生的贫13C二氧化碳有关;方解石脉主要形成于早白垩世长7段烃源岩生排烃期间,稍早于或同步于烃类流体的大规模活动,侏罗纪末期形成的裂缝构成了延长组烃类流体活动的重要通道,有利于烃源岩排烃及低渗透砂岩储层的油气运移。The origin of calcite veins and their relationship with hydrocarbon fluid flow were studied by analyzing trace element and stable isotope, which occurred extensively in the widely distributed tectonic fractures of Yanchang formation in Longdong area of Ordos Basin. The results show that calcite veins in sandstones and mudstones are all ferrocalcite with relatively high Fe and Mn content and low Mg content, and their δ^13 ranges from -6.6‰ to 2.7‰ （PDB） and δ^18 ranges from -23.0%‰ to -14. 9‰ （PDB）. Combining these data with geological features, it is indicated that the enrichment of Mn in calcite veins is attributed to corrosion of volcanic tuff in Chang 7 member by hydrocarbon fluid, and the formation of these calcite veins is associated with carbon dioxide of rich ^13 C generated by microbial methanogenesis and that of poor ^13 C generated by thermal decarboxylation. The calcite veins mainly formed in the Early Cretaceous during oil generation and expulsion of source rocks in Chang 7 member, and their formation was prior to or coeval with extensive hydrocarbon fluid flow. The tectonic fractures formed in the Late Jurassic are significant fluid flow pathway and play an important role for oil expulsion from source rocks and migration through low permeability sandstones.

关 键 词：裂缝充填方解石 微量元素 稳定同位素 烃类流体 鄂尔多斯盆地 

分 类 号：TE122[石油与天然气工程—油气勘探]