琼库尔恰克构造带流体包裹体地球化学特征

Geochemical Characteristics of Fluid Inclusions in Qungkurqack Structural Belt, Tarim Basin

位于塔里木盆地西南坳陷麦盖提斜坡上的琼库尔恰克构造带油气显示丰富,多套烃源岩、多期生烃、多次构造活动给油气成藏期的研究带来了很大困难。利用流体包裹体地球化学特征结合沉积埋藏史、古地温史的数值模拟,揭示了油气成藏期次和热流活动的历史。显微镜下观察结果显示,琼库尔恰克构造带群4井油气包裹体丰富的层段与含油层段相对应;伽1井小海子组灰岩和志留系砂岩均发现有油气包裹体,但丰度低,表明曾发生过油气运移,但未形成油气聚集。根据荧光和均一温度特征可将油气包裹体分为两种类型:一种为浅蓝色荧光,均一温度较低;另一种为黄色荧光,均一温度较高。结合一维热模拟计算结果,总结出琼库尔恰克构造带有两期油气成藏作用:第1期发生于晚二叠世,源岩可能为寒武-奥陶系烃源岩,油气成熟度较高;第2期为新近纪,源岩可能为石炭系,油气成熟度较低。水溶液包裹体均一温度显示出,色力布亚断裂带上的伽1井和巴4井均一温度高于该地区同深度的地温值,说明该断裂带存在热流正异常,热流异常由深部高温流体沿断裂向上运移至浅部形成。

Oil and gas shows are enriched in Qungkurqack structural belt on Mageti slope in southwest depression of Tarim basin, but multi-resource rocks, multi-stage hydrocarbon generation and tectonic activities allow its hydrocarbon accumulation period still difficult to study. This paper reveals its hydrocarbon accumulation stages and hydrothermal fluid flowing history based on the geochemical characteristics of fluid inclusions integrated with the numerical simulation of deposit-buried history, paleo-geothermal history. Microscope observation shows that the zone with hydrocarbon fluid inclusion from Well Qun-4 in this structural belt is corresponding to oil-bearing layers; hydrocarbon fluid inclusions are found in limestone of Xiaohaizi formation and sandstone of Silurian formation in Well Jia-1, with relatively low abundance of oil, indicating hydrocarbon migration happened here, but not forming petroleum accumulation. These fluid inclusions can be classified into two types： one is of low homogeneous temperature characterized by light blue fluorescence, the other is of high homogeneous temperature by yellow fluorescence in terms of homogeneous temperature and fluorescence features. It is concluded that two hydrocarbon accumulation stages occurred in this belt, one in Late Permian, with possible Cambrian-Ordovician source rocks and high maturity; the other in Neogene, with possible Carboniferous source rock and low maturity. Also, the homogeneous temperature of aqueous inclusion displays that Well Jia-1 and Well Ba-4 in Selibuya fault belt are higher than the geothermal value at the same depth in this area, showing that normal abnormity of geothermal fluid exists in this fault belt, which could be formed by deep high geothermal fluid migrating to shallow strata along the fault belt.