鄂尔多斯盆地中部延长组下组合流体包裹体特征和油气充注期次

通过对储层成岩作用、流体包裹体岩相学和孔隙沥青特征的分析,在烃包裹体期次划分的基础上,结合流体包裹体均一温度特征、烃源岩热演化史、地层埋藏史和储层成岩史,确定了鄂尔多斯盆地中部延长组下组合油气充注期次。结果表明:鄂尔多斯盆地中部延长组长8段和长9段致密储层主要发育压实、胶结、交代和溶解4种成岩作用,自生矿物主要为绿泥石、石英胶结物、长石胶结物和方解石胶结物。根据包裹体宿主矿物形成序列,识别出3期烃包裹体。第一期烃包裹体分布在石英愈合缝、石英次生加大边和充填孔隙的石英胶结物中,少数低成熟的黄色荧光烃包裹体及黑色荧光沥青包裹体代表了烃源岩进入生烃门限后排出的少量烃类充注,多数成熟度较高的蓝色、蓝白色荧光烃包裹体代表了生烃高峰期大量烃类充注; 第二期烃包裹体分布在长石胶结物中,数量较少,显示蓝色和蓝白色荧光,在溶蚀孔隙周围或沿解理分布,呈短柱状,边界平直; 第三期烃包裹体分布在方解石胶结物中,呈孤立或零星分布,形状近六边形; 后两期烃包裹体均是在烃类充注结束后捕获孔隙中烃类形成的。研究区延长组长8段和长9段经历了晚侏罗世末期至早白垩世末期的一期烃类持续充注。

Characteristics of Fluid Inclusions and Hydrocarbon Charging Periods of Lower Yanchang Formation in Central Ordos Basin,China

Based on the analysis of reservoir diagenesis, fluid inclusion petrography and pore bitumen characteristics, and on the basis of the division of hydrocarbon inclusion phases, combined with the homogenization temperature characteristics of fluid inclusions, thermal evolution history of source rocks, stratigraphic burial history and diagenesis history of reservoir, the hydrocarbon charging periods of lower Yanchang Formation in central Ordos Basin were determined. The results show that the minerals of tight reservoirs mainly experience compaction, cementation, metasomatism, dissolution processes in Chang-8 and Chang-9 members of Yanchang Formation in central Ordos Basin; the diagenetic authigenic minerals are dominated by chlorite, quartz cement, feldspar cement and calcite cement. Three different phases of hydrocarbon inclusions were identified according to the formation time series of the host diagenetic minerals. The first phase hydrocarbon inclusions are dispersedly distributed in quartz healing seam, quartz secondary enlarged edge and quartz cement filling the pore, a few low maturity yellow fluorescent hydrocarbon inclusions and black fluorescent bitumen inclusions represent a small amount of hydrocarbon charging when source rocks enter the hydrocarbon generation threshold, while most blue and blue-white fluorescent hydrocarbon inclusions with higher maturity represent a large amount of hydrocarbon charging during the peak period of oil generation; the second phase hydrocarbon inclusions are distributed in feldspar cements with a relatively small number, showing blue and blue-white fluorescence, and are distributed around the dissolution pore and cleavage, showing short columnar shape and flat boundary; the third phase hydrocarbon inclusions are distributed in calcite cements, which are isolated(or sporadic)and nearly hexagonal in shape; the latter two phases of hydrocarbon inclusions are formed by hydrocarbons captured in the pore after hydrocarbon charging. Chang-8 and Chang-9 members of Yanchang Formation experience a period of continuous hydrocarbon charging from the end of Late Jurassic to the end of Early Cretaceous in central Ordos Basin.