Abstract: The remaining oil resources in the Member 8 of Yangchang Formation (Chang 8) in Ordos Basin account for 21.5×10⁸t. There are less studies of the accumulation controlling factors and distribution rules of shale oil and tight oil, which restricts the exploration and discovery of unconventional reservoirs in the basin. Based on the data of core, logging, source rock evaluation, and experimental simulation in the study area, deep studies have been conducted on source-reservoir-caprock assemblages, pathway system s, and hydrocarbon accumulation mechanisms. The total amount of hydrocarbon expulsion in the west area of Ganquan is 1.41×10⁸t, and the tectonic evolution dominates the interactive distribution of multiple sets of source rocks and multiple types of sandstone reservoirs. Four favorable source-reservoir-caprock assemblages are developed, including the thin intra-source sandstone interlayers of Chang 8 and of both Member 8 and Member 7 of Yanchang Formation, and the neighboring source and reservoir of the single layers Chang 8₂ and Chang 8₁. The shale reservoirs and tight reservoirs are dominated by type Ⅰ and Ⅱ source-reservoir integrated assemblages and type Ⅲ and Ⅳ neighboring source and reservoir assemblages, respectively. The geologic and recoverable reserves are controlled by reservoir quality and crude oil filling degree, which are the keys to form the geological sweet spots of unconventional oil reservoirs. A multi-sources and multi-reservoirs orderly composite accumulation model is established, and characterized with multi-source hydrocarbon-generating pressurization, driven multi-directional hydrocarbon supply, combined transportation via fracture networks, and differential charging among multi-reservoirs. Shale oil is mainly stored in a free state in thin interlayers of beach bar sandstones with excellent reservoir properties in the source rocks, formed by primary migration and accumulation in the hydrocarbon source rocks. In addition, a small quantity of shale oil is adsorbed in the intra-source silty laminae, or occurred in lamellation fractures and pores in a free state, indicating in-situ accumulation. Tight oil is stored in a free state in sand bodies with excellent reservoir-caprock assemblages outside the source rocks, indicating near-source short-distance secondary migration and accumulation. Moreover, shale oil and tight oil are characterized by spatiotemporally orderly migration and accumulation, continuous composite accumulation, locally enriched sweet spots, vertically superimposed development and regional cluster distribution. Under the guide of the orderly composite accumulation model, a hundred-million-ton large oilfield has been discovered in the western Ganquan area, indicating that Chang 8 in Ordos Basin has huge unconventional petroleum resources. Delta front underwater distributary channel sandstones around the continental depression-type lake basin subsidence center and the alternate deposition areas of lacustrine mud shale and beach bar sandstones are the favorable development areas of shale oil and tight oil.

Key words: Ordos Basin, unconventional oil, reservoir genesis, geological sweet spot, accumulation mode

摘要： 鄂尔多斯盆地延长组8段（长8段）剩余油资源量约为21.5×10⁸t，页岩油、致密油复合成藏控因与分布规律等研究较为薄弱，制约着盆地非常规油藏的勘探与发现。通过鄂尔多斯盆地东南部甘泉西区岩心、测井、烃源岩评价、实验模拟等测试资料，深化了生-储-盖组合、输导体系与成藏机理等研究。甘泉西区烃源岩总排烃量为14.1×10⁸t，构造演化控制了多套烃源岩与多类型砂岩储层的交互分布。发育长8段源内砂岩薄夹层型、长8段-长7段源内砂岩薄夹层型、长8₂小层源储近邻型与长8₁小层源储近邻型4种有利生-储-盖组合，其中页岩油藏以"源储一体式"Ⅰ、Ⅱ型配置为主，致密油藏以"源储近邻式"Ⅲ、Ⅳ型配置为主。储层品质与原油充注程度控制着地质储量及可采储量规模，是形成非常规油藏地质"甜点"的关键。建立了非常规油藏多源多储有序复合成藏模式，即"多源生烃增压，驱动多向供烃，裂隙网络联合输导，多储差异充注"。页岩油主要以游离态聚集于烃源岩层系储集性能优良的滩坝砂岩薄夹层，属烃源岩层系内一次运聚成藏；少量页岩油以吸附态滞留于源内粉砂质纹层或以游离态赋存于页理缝孔隙中，属原位成藏。致密油以游离态聚集于烃源岩层系外储-盖配置优越的砂体中，属近源短距离二次运聚成藏。页岩油与致密油时空有序运聚、连续复式成藏，呈局部"甜点"富集、垂向叠置发育、区域集群分布。在有序复合成藏模式的指导下，发现了甘泉西区亿吨级大油田，表明鄂尔多斯盆地长8段非常规石油潜力巨大。陆相坳陷型湖盆沉降中心周缘的三角洲前缘水下分流河道砂岩与湖相泥页岩及滩坝砂岩交互沉积区是页岩油、致密油的有利发育区带。

关键词: 鄂尔多斯盆地, 非常规石油, 油藏成因, 地质“甜点”, 成藏模式