扬子准地台南缘志留系碎屑岩的几种成岩作用与储集层特征

本文对扬子准地台南缘一些地区和层段的含沥青砂岩的成岩作用进行了论述。指出麻江背斜中带的成岩作用以早期白云石胶结作用和白云石溶蚀交代石英碎屑为主,晚期广西运动使该区形成背斜并继续抬升,背斜轴部遭到剥蚀和大气淡水淋溶,致使白云石被溶蚀形成大量次生孔隙,利于石油储集;麻江背斜东翼和无锡、常熟、黄桥地区的砂岩矿物成熟度高,成岩作用以石英次生加大和高岭石充填原生孔隙为主,沥青充填在石英次生加大残留的原生孔隙中,储集条件略差;安吉康山及下扬子广大地区中上志留统的砂岩,由于浅变质泥岩屑含量高,它们在上覆巨厚地层压力下,表现为强烈的机械压实作用所引起的碎屑彼此镶嵌以及粘土杂基的充填,致使砂岩储集性能最差,仅能形成以构造断裂为主的脉状沥青。 

THE DIAGENESIS AND RESERVOIR PROPERTIES OF SILURIAN CLASTIC ROCKS IN THE SOUTHERN MARGIN OF YANGTZE PARA-PLATFORM

The diagenesis on the sandstones bitumen bearing in certain regions and sections of the southern margin,Yangtze Para-platform is discussed in this paper. It is suggested that the diagenesis in Majiang Anticline Belt is dominated dy early stage dolomite cementation and by the corrosion and replacement of dolomite in clasts. The late Guangxi movement caused the formation and then the successively upliftings of the anticline in the area. The axis of the anticline was eroded and eluviated by atmosphere fresh water, resulted the development of secondary pores in dolomites, which would be favourable for oil/gas accumulations. The maturities of sandstone minerals in the eastern flank of Majiang Anticline, Wuxi, Changshu and Huangqiao areas are rather high and the diagenesis are mainly quartz overgrowth and kaolinites filling the primary pores. The bitumen was filled into the residual primary pores of quartz overgrowth,so that the accumulation of oil/gas is unfavourable and poor. The Middle-Lower Silurian sandstones in a large area of Anjikang Mountains and lower section area of Yangtze River are observed as mosaicism of clasts and clay matrix fillings which are resulted by severe mechanical compaction, since the content of metamorphic debris is quite high and the heavy load-press of overlain strata. That is why the oil/gas accumulation in such a sandstone area is poor and only vein bitumen controlled by fractures can be formed.