富油凹陷油气分布不均一性及主控因素

Heterogeneity of hydrocarbon distribution and its main controlling factors in oil-rich depression

关键词:  东濮凹陷  油气分布  生烃条件  盐膏岩盖层  主控因素

Key words:  Dongpu depression  hydrocarbon distribution  hydrocarbon generation conditions  gypsum-salt rock  main controlling factors

摘要:

以渤海湾盆地东濮凹陷和东营凹陷为例,对富油凹陷油气分布不均一性及主控因素进行研究。结果表明:富油凹陷油气分布在平面上和纵向上具有较强的不均一性,东濮凹陷具有“北富南贫、纵向分布层系高度集中”的特征,90％以上的已探明油气分布于凹陷北部,纵向上主要富集于古近系沙河街组,以沙三段和沙二段为主力层系,沙一段以上未发现规模储量,而东营凹陷总体上具有“北富南贫、纵向富集层系多”的特征,沙河街组、东营组及新近系均发现了规模储量。多种因素控制了富油凹陷不同地区及层系的油气分布差异:烃源条件的优劣从根本上控制了富油凹陷不同地区的油气富集程度差异,东濮、东营凹陷北部地区的生烃条件远好于南部是造成两个凹陷油气分布总体呈现“北富南贫”的根本原因;源岩与盖层及断层的配置关系控制了纵向油气富集层段,东濮凹陷沙河街组多套盐膏岩盖层有效地限制了油气垂向运移,尤其是沙一段盐膏岩盖层对下伏层系油气的聚集起到了重要的封盖作用,而东营凹陷缺乏沙一段盐膏岩盖层且晚期断层较发育,油气纵向多层系富集;成藏期构造背景和输导体系控制了油气运移主要指向,有利储集砂体与构造脊的叠合控制了油气富集区。

Abstract:

Taking the Dongpu depression and Dongying depression in the Bohai Bay Basin as an example, the heterogeneity in hydrocarbon distribution and its main controlling factors in oil-rich depression were systematically analyzed. The results show that the hydrocarbon distribution of oil-rich depressions is spatially highly heterogeneous. The distribution of hydrocarbon in the Dongpu depression is characterized by rich in the north and poor in the south and enrichment in layered concentration. More than 90% of the proven hydrocarbons are distributed in the northern part of the depression. Hydrocarbons are mainly concentrated vertically in the Shahejie Formation of the Paleogene, especially in the Es₃ and Es₂, and no scale reserves are found above Es₁. Similarly, the distribution of hydrocarbon in the Dongying depression is characterized by rich in the north and poor in the south and multi-layered enrichment. The Shahejie, Dongying Formations and the Neogene all have found large-scale reserves. Multiple factors control the distribution of hydrocarbon in different regions and layers of the depression. The hydrocarbon generation condition in the northern part are much better than that in the southern part of the Dongpu and Dongying depressions, which fundamentally controls the enrichment characteristics of "rich in the north and poor in the south" in those areas. Configuration of source rocks, caprocks and faults controls the vertical hydrocarbon enrichment. Mult-sets of gym-salt of the Dongpu depression effectively control the vertical migration of the fluid and thus result in the vertical enrichment of layered hydrocarbon. Especially the gym-salt cover of Es₁ has an important sealing effect on the accumulation of hydrocarbon in the underlying layers, and the lack of gym-salt caprocks and later faults activity of the Dongying depression controls the hydrocarbon multilayer enrichment. The main direction of hydrocarbon migration is controlled by the tectonic setting and the transport system during the hydrocarbon charging periods, and the combination of favorable reservoir sandbodies and structural ridges control the hydrocarbon enrichment area.