Accumulation Model of Petroleum in the Tertiary System of the Northwestern Qaidam Basin
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摘要: 柴达木盆地北缘西段是一个以中下侏罗统煤系地层为烃源岩的含油气系统, 产油气层位主要是第三系.逆断层及相关褶皱组合构成柴北缘油气藏的主要圈闭类型.渐新世晚期(E32) 与上新世末到第四纪(N23—Q) 是柴北缘构造变形和圈闭形成的重要时期, 第三系油气成藏也主要发生在这2个关键时期.油藏原油组成和石油包裹体成分分析结果证明第三系油气藏存在不同期次的油气充注历史.下第三系的油气藏存在2期油气充注, 渐新世断层活动破坏侏罗系古油藏并连通侏罗系烃源岩, 导致古油藏中的低成熟石油和侏罗系烃源岩新生的成熟油气沿断层运移到下第三系圈闭中, 构成第1期油气充注; 上新世末到第四纪(N23—Q) 期间, 继续活动的断层导致侏罗系烃源岩高成熟油气沿断层运移到下第三系圈闭中, 形成第2期油气充注.上第三系油气藏主要为一期充注, 即在上新世末到第四纪(N23—Q) 新生断层破坏下第三系油气藏, 部分油气沿断层充注到上第三系合适的圈闭中形成次生油气藏.在柴北缘第三系油气藏形成过程中, 断层起到了重要的控制作用.Abstract: The northwestern Qaidam basin is a Jurassic-Tertiary petroleum system. Thrust faults and anticlines are related with faults form main types of traps of the area. The E32 and N23-Q are the two key elements for the formation of the traps and for the migration and accumulation of petroleum. The composition of petroleum in the reservoirs and in the inclusions indicates that the reservoirs of the Eocene and Neocene underwent different times and stages of petroleum filling. The reservoir of Eocene underwent two stages of petroleum filling: in the end of Eocene, the low-mature petroleum was formed at the end of Jurassic period and entrapped in the Jurassic reservoirs and the mature petroleum formed at the end of Eocene epoch migrated up through the faults and was mixed in the Eocene reservoirs. During N23-Q, newly formed high-mature petroleum migrated up once more through the reliving faults and was mixed with the petroleum in the Eocene reservoirs. While the reservoirs of the Neocene mainly underwent one stage of petroleum filling. During N23-Q, petroleum in the Eocene reservoirs was pumped up through faults, with some petroleum entrapped secondly in the Neocene reservoirs and some petroleum escaped to the surface. It is concluded that the faults played a very important role in the migration and accumulation of petroleum in the Tertiary system of the northwestern Qaidam basin.
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