低渗致密储层物性对含油性的控制作用浅析——以鄂尔多斯盆地西南缘为例

Discussion on relationship between reservoir oil-bearing and physical properties of Chang 8 section in southwest margin of the Ordos Basin

鄂尔多斯盆地长8段潜力巨大,但含油性差异较大.通过对盆地西南缘环西—彭阳地区长8低渗致密储层含油性与物性关系的研究,并结合烃源岩和充注成藏动力对储层含油性及充注程度影响的分析,探讨了低渗致密油含油饱和度的控制因素.结果表明,西南缘环西—彭阳地区长8段整体上物性较差,但好于盆内主体区块.孔隙结构比较复杂,束缚水饱和度多大于50%.长8储层普遍具有含油性,含油性向下逐渐变差.整体含油显示级别和含油饱和度均显著低于湖盆内部.含油饱和度与储层孔隙度、渗透率之间关系复杂,本区储层物性对含油性没有明显的控制作用.长8储层非均质性较强,一定程度上影响充注均衡度.区内砂体的含油气性与烃源岩品质对应较好,剩余压力高值区含油饱和度较高,同时石油充注动力与初期产油量具有良好的正相关性.

With the deepening of oil and gas exploration,new discoveries have been made in tight reservoirs of Chang 8 reservoir in the lower Yanchang Formation in recent years,but the degree of research on its formation mechanism and reservoir enrichment in southwestern margin of the Ordos Basin is relatively low.Based on the analysis of relationship between reservoir oil-bearing ability and physical properties,combining with research of source rock and charging dynamic influence on oil charge degree,the controlling factors of low-permeability to tight reservoir oil saturation of Chang 8 in Huanxi-Pengyang area were discussed.The results showed that reservoir physical properties is poor but much better than inner basin.The pore structure is complex with high bound water saturation.Chang 8 reservoir is currently oil-saturated and oil-bearing become poor with depth increase.The reservoir oil level or oil-saturation is lower in margin than interior basin.The oil saturation is low and its relationship with reservoir physical properties is complex which means oil saturation has no positive correlations with the porosity and permeability.Reservoir heterogeneity controls the local distribution of the low permeability to tight oil differentiation.The oil-bearing ability is mainly controlled by source rock and reservoir forming power.Although smaller than basin interior,the excess pressure difference still offers the driving force for hydrocarbon migrating and charging from Chang 7 member to Chang 8 member of the study area.Through the above research,it can provide reference for further understanding the enrichment law of Chang 8 oil and guidance for tight oil exploration.