Abstract:

Based on the data of core, thin section, scanning electron microscopy, well logging and the physical property of reservoir, we understand the following points according to the research about characteristics of the Carboniferous volcanic reservoirs in Santanghu basin. ①The lithology is mainly composed of basalt, andesite and transitional lithology； ②The lithofacies are based on overflow facies, with pyroclastic flow subfacies and inner loose layer of explosive facies; ③Secondary storage space is often superimposed on the original storage space, and the pore, hole, slit together form the effective storage space；④The overall performance of the reservoir property shows that the andesite is the best, followed by the basalt；⑤The phenomena such as laumontitization, albitization，arfvedsonization，sideritation and SiO₂ dissolving prove that the hydrocarbon alkali fluid is obtained in the Carboniferous volcanic rocks, and the mineral composition in the rocks migrate because of the alkali metasomatism, which offer the mineralogy basis for the formation of reservoir；⑥Alkaline diagenesis in the Carboniferous volcanic rocks is common,the vertical zoning laws of “alkali under the silicium” formed and preserved a large number of secondary porosity, which built up the foundation for the development of secondary pore zone；⑦Fluid plays an important role in the formation of reservoir. The formation of Carboniferous volcanic reservoirs in the study area shows the formation mechanism in volcanic reservoir is “acidity and alkali” superposition of dissolution.

Key words: Santanghu basin, volcanic reservoir, alkaline diagenesis, alkali metasomatism, secondary pore zone, petroleum oil