鄂尔多斯盆地三叠系长7段致密油成藏机理

Tight oil accumulation mechanisms of Triassic Yanchang Formation Chang 7 Member, Ordos Basin, China

为研究鄂尔多斯盆地三叠系延长组7段致密油成藏机理和分布特征，对长7段致密储集层沉积环境、岩石学特征、孔喉结构特征、运聚动力和成藏过程等进行系统分析。长7段致密油储集层主要为半深湖一深湖相砂质碎屑流沉积和三角洲前缘水下分流河道沉积。场发射扫描电镜、CT扫描等高分辨率显微技术研究表明，致密油储集层物性差，发育微一纳米级孔喉，以粒间孔和长石溶孔为主，管束状和条带状孔隙是有利的储集空间。致密油储集层生烃和成藏模拟实验结果表明，长7段优质烃源岩生烃增压动力强，成藏阶段储集层含油饱和度逾50％，随着动力的持续增加油气开始富集，含油饱和度可超70％。长7段致密油源储共生，烃类在高压驱动下，沿着相互叠置的相对高渗砂体、网状裂缝等输导体系运移，形成大面积连续或准连续分布的油气聚集。

The sedimentary environment, petrology, pore throat structure, migration and accumulation power, and accumulation process are analyzed to study the oil accumulation mechanism and distribution of Triassic Chang 7 Member tight oil in Ordos Basin. Chang 7 tight oil reservoirs are mainly semi-deep lake - deep lake sandy debris flow deposits and delta front underwater distributary channel deposits. The results of field emission scanning electron microscopy, CT scans and other high-resolution microscopy techniques show the physical properties of Chang 7 oil reservoirs are poor, micro- and nano-meter pore throats are developed, inter-granular pores and feldspar dissolved pores are the main pores, and tube- and strip-shaped pores are favorable reservoir space. The hydrocarbon generation and accumulation simulation of tight oil reservoirs shows that the hydrocarbon charging power of Chang 7 high-quality source rocks is strong. The oil saturation of the Chang 7 were more than 50% in the accumulation phase and even reached 70~/0 or more with the continued power increase and oil enrichment. The source and reservoir rocks of Chang 7 tight oil coexist, so the hydrocarbons migrated under high pressure to migrate along relatively high permeable superimposed sands, reticular fractures and other pathways, and formed large-area continuous or quasi-continuous lithologic oil reservoirs.