鄂尔多斯盆地中西部长8砂岩的流体包裹体特征与油气成藏期次分析

Characteristics of Fluid Inclusions and Its Application in Analysis of Hydrocarbon Accumulation Stages from the Chang 8 Sandstone in the Middle West Area of Ordos Basin

利用流体包裹体的分析测试技术与研究方法，对鄂尔多斯盆地中西部长8油层组的成藏期次进行了研究。烃类包裹体及其伴生的盐水包裹体的岩相学特征、均一温度、盐度、密度及成分分析显示，长8储层主要发育两期烃类包裹体，第一期分布在早期方解石胶结物、石英颗粒表面及其连生的石英加大边中以及未切穿石英颗粒的早期愈合裂缝中，其伴生盐水包裹体的均一温度峰值为80～90℃；第二期烃类包裹体分布在石英颗粒表面和切穿石英颗粒的裂缝中，其伴生盐水包裹体的均一温度峰值为100～120℃。储层成岩作用与油气充注微观分析、成岩一烃类充注演化时间序列研究，结合地层埋藏史和热史分析表明，研究区经历了三期烃类充注事件：第一期（约169～161Ma）充注规模小，砂岩中未捕获到这一期适合进行均一温度与成分测定的烃类包裹体，因此本研究缺乏这期包裹体的温度与成分数据；第二期（约148～135 Ma）烃类充注对应前述获得均一温度与成分数据的第一期烃类包裹体；第三期烃类充注规模最大，发生在早白垩世晚期的125．2～105．7 Ma之间，为主成藏期，对应前述获得均一温度与成分数据的第二期烃类包裹体。

The hydrocarbon accumulation stages of the Chang 8 Group, Yangchang Formation, Upper Triassic in the Middle West area of Ordos Basin were studied by analyzing and testing technology of fluid inclusions. The Chang 8 reservoir shows two periods of hydrocarbon-bearing inclusions according to the analysis of the petrography, homogenization temperature, salinity, density and chemical composition of hydrocarbon-bearing inclusions and the associated brine inclusions. The first stage hydrocarbon-bearing inclusions are mainly hosted in the early calcite cement, quartz grain surfaces and their syntaxial quartz overgrowths, and the cracks healed during the early diagenetic phase that do not cut through the quartz grains. The homogenization temperature peak value of brine inclusions associated with hydrocarbon-bearing inclusions of the first stage is mainly 80-90℃. The second stage hydrocarbon- bearing inclusions are mainly distributed in the quartz grain surfaces and the cracks healed in the late diagenetic phase that cutthrough the quartz grains. The peak value of homogenization temperature dominated the range from 100℃ to 120℃. Evidence from diagenesis and hydrocarbon charging under microscope, diagenesis-hydrocarbon charging evolution sequence study and burial-thermal history analysis show that three periods of hydrocarbon accumulation occurred in the study area. The first hydrocarbon charging stage occurred from 169 Ma to 161 Ma, nearly no hydrocarbon-bearing inclusions suitable for homogenization temperature and chemical component measurement captured in the Chang 8 sandstones due to its limited proportion. Thus inclusions＇ temperature and composition data of this phase are lacking. The second hydrocarbon accumulation stage with larger dimension and broader distribution occurred during 148-135 Ma, which corresponds to the first stage of the hydrocarbon-bearing inclusions with homogenization temperature and composition measurement data. The third hydrocarbon charging stage occurred in the late Early Cretaceous （125.2-105.7 Ma） and is the major hydrocarbon accumulation stage in the study area which corresponds to the second stage hydrocarbon-bearing inclusions with homogenization temperature and composition measurement data in the Chang 8 sandstones.