塔里木盆地顺北地区中下奥陶统流体改造与油气充注耦合关系

Coupling Relationship between Fluid Transformation and Oil and Gas Filling of Middle Lower Ordovician in Shunbei Area of Tarim Basin

为明确顺北地区中下奥陶统流体改造与油气充注耦合关系,通过对方解石充填物进行阴极发光、流体包裹体显微镜下观察和油包裹体及其伴生盐水包裹体均一温度测试分析,结合方解石微区原位U-Pb同位素定年开展顺北地区中下奥陶统流体改造期次及序列、油气充注期次和时期及流体改造与油气充注耦合关系研究。结果表明:一间房组和鹰山组上段均经历多期流体改造,形成了具有不同阴极发光特征的多期方解石充填物,两者区别在于鹰山组地层未经历大气水改造;油包裹体荧光显示呈现蓝绿色-蓝白色,指示原油成熟度较高,且一间房组与油包裹体共生的盐水包裹体均一温度分布范围为84~98℃,平均均一温度为92.49℃和113~130℃,平均均一温度为119.91℃、鹰山组上段均一温度分布范围91.2~104℃,平均均一温度为96.1℃和112.7~128.1℃,平均均一温度为119.97℃,表明存在加里东晚期和海西晚期-印支期两期油气充注,主成藏期为海西晚期-印支期。烃类包裹体宿主矿物方解石微区原位U-Pb测试表明,其主要形成于加里东中晚期[(466.8±8)~(470.6±4.5)Ma],揭示油气充注发生在加里东晚期混源流体改造形成的具备红色-橙红色阴极发光特征方解石之后。

In order to clarify the coupling relationship between fluid transformation and oil-gas filling in the middle lower Ordovician in Shunbei area,the periods and sequences of fluid transformation in the middle lower Ordovician in Shunbei area were carried out through cathodoluminescence of calcite fillings,microscopic observation of fluid inclusions,and homogenization temperature test and analysis of oil inclusions and their associated brine inclusions,combined with in-situ U-Pb isotope dating of calcite microregions research on oil and gas filling periods and periods and coupling relationship between fluid transformation and oil and gas filling.The results show that both the Yijianfang Formation and the upper Yingshan Formation underwent multi-stage fluid transformation,forming multi-stage calcite fillings with different cathodoluminescence characteristics.The difference between the two is that the Yingshan Formation does not undergo atmospheric water transformation.The fluorescence of oil inclusions shows blue-green-blue-white,indicating high maturity of crude oil,and the homogenization temperature distribution range of brine inclusions symbiotic with oil inclusions in Yijianfang Formation is 84~98℃,the average homogenization temperature is 92.49℃and 113~130℃,the average homogenization temperature is 119.91℃,the homogenization temperature distribution range of upper Yingshan Formation is 91.2~104℃,the average homogenization temperature is 96.1℃and 112.7~128.1℃,and the average homogenization temperature is 119.97℃.It indicates that there are two stages of oil and gas filling in late Caledonian and late Hercynian Indosinian,and the main reservoir forming stage is late Hercynian Indosinian.The in-situ U-Pb testing of calcite micro region,the host mineral of hydrocarbon inclusions,shows that it was mainly formed in the middle and late Caledonian period,which is(466.8±8)~(470.6±4.5)Ma,revealing that oil and gas filling occurred after calcite with red orange red cathodoluminescence characteristics formed by mixed source fluid transformation in the late Caledonian period.