Diagenesis and porosity evolution of karst reservoir of the middle Ordovician upper Majiagou formation,Taiyuan area
Li Xue;Ji Hancheng;Wang Simin;Fang Chao;Xiang Pengfei;Li Linzhi;Guo Ruijing;State Key Laboratory of Petroleum Resource and Prospecting,China University of Petroleum(Beijing);School of Geosciences,China University of Petroleum(Beijing);
Based on the observation of the cores outcrops,thin sections and molded thin sections,scanning electron microscope,and other geochemical analysis method,the types of the major storage spaces are identified,the diagenesis types and characteristics and digenetic evolution of karst reservoir within the upper Majiagou formation in middle Ordovician,Taiyuan area and the way they have controlled the development of the reservoir are deeply studied. The result revealed that the gypsum-bearing brecciola,calcarenite,fine crystalline limestone,silty crystalline bioclast-bearing dolomitic limestone,fine crystalline limy dolomite,limy breciated dolostone,calcarenite,medium crystalline dolostone,fine crystalline dolostone are the dominant rock types,and the main reservoir spaces are pores and caves. The reservoir had experienced composite superimposed diagenesis which included compaction,pressure-solution,cementation,metasomatism,tectonic disruption,dissolution,de-gypsum,rejuvenation of crystals in varying ages. The diagenetic evolution can be divided into four stages: Penecontemporaneous pore period( middle Ordovician),weathering leaching period( late Ordovician-Devonian),minerals filling period( Carboniferous-early Cretaceous) and pore dissolution reconstruction period( late Cretaceous-Paleogene).The reservoir is mainly controlled by dolomitization,dissolution,and tectonic fracture. Dolomitization was bene-ficial to the preservation of intergranular pores,and also helped to form cracks by strengthening the compactness and brittleness. The structural fracture provided a fluid channel for the dissolution and expand it along the way.The contribution to the reservoir of penecontemporaneous karstification is limited,while the epigenic karstification was significant to the reservoir and the buried karstification plays a important role in reservoir in late dissolution.
【CateGory Index】： P618.13