金湖凹陷闵桥玄武岩中微量元素向烃源岩的 迁移及其地质意义

Migration of trace elements from basalts to oil source rocks and its geological significance in Minqiao area of Jinhu depression

关键词:  金湖凹陷  闵桥地区  玄武岩  烃源岩  有机酸  微量金属元素  蚀变作用

Key words:  Jinhu depression  Minqiao area  basalt  source rock  organic acid  trace metal element  corrosion

摘要:

金湖凹陷闵桥构造阜宁组烃源岩中发育玄武岩,并且形成了玄武岩-烃源岩组合体。对阜宁组烃源岩中的微量 元素系统分析发现,在生油门限深度附近，玄武岩被周围烃源岩有机质形成的有机酸蚀变改造，其中的微量金属元 素被活化、溶蚀和迁移,然后沉淀于烃源岩中。其结果造成玄武岩原生气孔和收缩裂缝进一步扩大和连通，形成了 良好的储集空间；同时周围烃源岩中微量金属元素含量显著增加。这种元素迁移是导致玄武岩蚀变、储集性能改善 的重要原因,这也使有机质热演化得到某些过渡金属的催化作用成为可能。

Abstract:

A large volume of basalts was distributed in oil source rocks of Funing formation in Minqiao area of Jinhu depression. ^he basalts and source rocks are interbedded together forming a kind of assemblage of basalt and source rock. A series of measurements were conducted on trace elements for both the basalts and the source rocks. The results show that the basalts were altered by organic acids and carbonic acid generated from its surround source rocks during their burial history and the trace elements were migrated from the basalts to the source rocks. In fact, the basalt alteration is process of element activation, mineral corrosion and material transportation in the basalts by the acids from source rocks. Then the trace elements are migrated and deposited in the source rocks. At the early alteration, original gas pores and shrink fractures of the basalts were enlarged, and late, the pores arid fractures were further enlarged and connected to each other to produce good reservoir spaces for oil and gas accumulation. Meanwhile, the source rocks around the basalts were abnormally rich in the trace metal elements. The interaction between basalt and source rocks is an important mechanism for the basalt corrosion and the reservoir space formation, and for catalysis of organic matter into hydrocarbons by the trace elements in the source rocks.