The main diagenetic types of sandstone reservoirs in the Yanchang Formation of Zichang area, the Ordos Basin, include compaction, cementation, disolution and fracturing. The diagenetic authigenic minerals are dominated by chlorite, authigenetic quartz and calcite. Two different phases of hydrocarbon inclusions have been identified according to the formation time series of the host diagenetic minerals. The hydrocarbon inclusions formed in the first phase mainly occur in the dissolution pores of quartz and feldspar or along early-healed fractures, and are coated by quartz or feldspar overgrowth. The hydrocarbon inclusions formed in the second phase are distributed along the late-formed fractures or in sparry calcite cement. The late fractures cut the early fractures or the quartz overgrowth, and go beyond the grain contact. The homogenization temperature of the pa-ragenetic brine inclusions of hydrocarbons has two peaks at 90 - 105℃ and 105 - 120℃ respectively. Analysis of salinity and density of the two generations of fluid inclusions reveal that the oil/gas reservoirs in the Yanchang Formation were formed continuously in one stage. The test data of fluid inclusions and illitic K-Ar isotope dating and the thermal history show that late Early Cretaceous (100-120Ma) is the main hydrocarbon accumulationperiod in Zichang area, the Ordos Basin.%鄂尔多斯盆地子长地区延长组砂岩储层主要成岩作用有压实作用、胶结作用、溶蚀作用和裂隙作用等,成岩自生矿物以绿泥石、自生石英、方解石为主.根据油气包裹体寄主成岩矿物的形成时间序列,识别出两期油气包裹体.第一期油气包裹体主要分布在石英和长石等矿物溶蚀孔隙、早期裂隙中,被石英和长石后期次生加大边包裹起来.第二期油气包裹体分布在石英晚期裂隙和亮晶方解石胶结物中,晚期裂隙切割了早期裂隙或石英加大边,并切穿了颗粒边界.通过对与烃类共生的盐水包裹体进行均一化温度测试,得到两期流体包裹体的均一温度:早期主要在90～105℃,晚期主要在105～120℃.两期均一温度分布连续,主要集中在90～120℃范围内.结合流体包裹体含盐量、密度分析,认为研究区延长组油气主要为连续一期成藏.对比研究区埋藏史、地热史分析及延长组储层伊利石K-Ar同位素定年结果得出,研究区主要的油气成藏期发生在距今100 ～ 120 Ma,即早白垩世晚期.
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