哈拉哈塘凹陷新垦区块奥陶系油气成藏的地球化学证据

摘要

根据原油地球化学分析、油气包裹体岩相学及热力学分析和盆地模拟,对哈拉哈塘凹陷新垦区块奥陶系油藏进行充注成藏研究.结果表明:该区奥陶系原油普遍具有C21/C23三环萜烷小于1、规则甾烷内组成呈“V”字型分布、全油及馏分碳同位素均轻于-30‰等特征,属于典型源自上奥陶统源岩的原油；同一原油中同时检测出完整的正构烷烃系列、明显的“UCM”鼓包和完整的25-降藿烷系列,代表原油早期充注后遭严重生物降解,后期又混入了新的正常原油;奥陶系储层具有两个世代的方解石成岩矿物,捕获稠油、中-轻质油、干气等三期油气包裹体,共生的盐水包裹体均一温度呈现与之对应的三峰态分布型式；新垦区块奥陶系油藏具有三次油气充注事件,充注时间分别为402～412 Ma、9～11 Ma和6～8 Ma,其中第三期以干气充注为主,气源可能为寒武系烃源岩,限于具备沟通深部烃源层的深大断裂附近.%Based on the oil geochemistry,petrography and microthermometry of fluid inclusions and basin modeling,the hydrocarbon entrapment and accumulation for Ordovician reservoirs from Xinken block of Halahatang depression was discussed.The results indicate that Ordovician oils are characterized by low C21/C23 tricyclic terpanes (＜ 1),"V" shape of C27-C2s-C29 sterane distribution and light stable carbon isotope (＜-30‰),correlating well with the O3 source rock.The coexisting intact n-alkane series,evident UCM and fully developed 25-norhopanes in the same oil infer the mixture of a severely palaeo biodegraded oil and later fresh oil.Viscous oil,light oil and dry gas were entrapped in two generation of calcite cements with trimodal distribution of homogenization temperatures for aqueous inclusion correspondingly.The Ordovician reservoir has undergone three charges,which occurred in 402-412,9-11 and 6-8 Ma respectively.The third entrapment is mainly dry gas possibly originated from Cambrian source rock and constrains the targets near faults communicating the deep source beds.