含油气盆地砂岩目的层油气富集主控因素与基本模式——以渤海湾盆地南堡凹陷新近系砂岩油气藏为例

随着油气勘探开发难度越来越大，探究油气富集的主控因素并建立地质模式对于提高勘探成效具有重要的现实意义。以渤海湾盆地南堡凹陷为例，采用统计分析法研究了822口探井中8520个砂岩目的层段油气富集程度的影响因素与变化特征。分析表明，含油气目的层的孔渗结构、毛细管压力差以及周边源岩的排烃条件是影响油气富集的关键要素。源岩的排烃提供了物质基础，目的层的孔渗结构决定了容积空间，毛细管压力差是油气运移聚集的关键动力，三者缺一不可。在3种要素联合作用下，油气的富集程度随埋藏深度增大呈现出规律性变化。在初始埋藏阶段，目的层的孔隙空间大，但由于内、外毛细管压力差太小且源岩供烃量不足而不利于油气富集；在中等埋深阶段，源岩供烃充足，目的层的孔隙空间较大，内、外毛细管压力差大而有利于油气富集；在埋深较大阶段，源岩供烃潜力减弱，目的层的孔隙空间小，内、外毛细管压力差低，油气富集程度变差；在埋深非常大的阶段，源岩供烃潜力枯竭，目的层中束缚水的饱和度达100%，内、外毛细管压力差消失，油气不能富集成藏。油气的富集模式从机制上解释了高孔渗目的层不一定富集油气、低孔渗目的层有时能够高度富集油气的地质现象，为复杂条件下评价和优先钻探目标提供了新思路和新方法。

Main controlling factors and basic model for hydrocarbon enrichment in the sandstone target layer of petroliferous basin: a case study of Neogene sandstone reservoirs in Nanpu sag,Bohai Bay Basin

With the increasing difficulty in oil and gas exploration, it is required to explore the main controlling factors of hydrocarbon enrichment and establish the geological model, which is of great practical significance to improve exploration efficiency. Taking the Nanpu sag of Bohai Bay Basin as an example, using the statistical analysis method, this study analyzes the influencing factors and variation characteristics of hydrocarbon enrichment in the 8520 target layers from 822 exploration wells. The results show that the pore-permeability structure of the hydrocarbon-bearing target layer, the capillary pressure difference, and the hydrocarbon expulsion conditions of surrounding source rocks are the key factors affecting oil and gas enrichment. The hydrocarbon expulsion of source rocks provides a material basis; the pore-permeability structure of the target layer determines the volumetric space; the capillary pressure difference is the key driving force for hydrocarbon migration and accumulation; all three are indispensable. Under the combined action of above three factors, the hydrocarbon migration enrichment shows a regular change with the increase of burial depth. In the initial burial stage, the pore space of the target layer is large, but the capillary pressure difference inside and outside target layer is ultra-small, so that the insufficient hydrocarbon supply from source rock is unbeneficial to the oil and gas enrichment. In the medium-deep burial stage, the sufficient hydrocarbon supply from source rock, large pore space in target layer and large capillary pressure difference inside and outside target layer are conducive to oil and gas enrichment. In the deep burial stage, with weakened hydrocarbon supply potential of source rock, decreased pore space of target layer and low capillary pressure difference, the oil and gas enrichment deteriorates. In the ultra-deep burial stage, due to exhausted hydrocarbon supply potential of source rock, saturation of the bound water in the target layer up to 100% and disappearing capillary pressure difference inside and outside target layer, hydrocarbon cannot be accumulated. The hydrocarbon enrichment mode explains the mechanism and phenomena why the target layers with high porosity and permeability may not necessarily enrich oil and gas while those with low porosity and permeability can highly enrich oil and gas, and provides new ideas and methods for evaluating and optimizing drilling targets under complex conditions.