致密砂岩微观孔喉结构特征及其对储层含油性的影响——以鄂尔多斯盆地延长组地层为例

Characteristics of micropore-throat structure and its influence on oil-gas charging in tight sandstone——taking Yanchang formation in Ordos basin as an example

微观孔喉结构是影响致密砂岩油气充注与聚集、控制致密油气“甜点”发育的关键。本次研究以鄂尔多斯盆地马岭地区长8致密砂岩为例,利用铸体薄片、扫描电镜、高压压汞及核磁共振等测试手段,定量研究致密砂岩储层孔喉结构特征,并根据压汞及核磁等实验参数,分别探讨孔隙类型、孔喉体积比、孔喉分布大小以及孔喉的连通性对储层含油性的影响。结果表明,致密砂岩储层孔喉具有进汞压力高、中值半径小、束缚水饱和度高等特征,其含油性受物性和孔喉结构共同控制;储层含油性受孔隙类型、孔喉分布及大小、孔喉连通性等因素共同控制。粒间孔发育良好、孔喉体积比中等(Vr为1.7~3)、大于充注下限值(0.077μm)的孔喉含量高且连通性好均为储层含油性有利条件。以马岭地区长8储层为研究对象,深入分析孔喉结构特征对储层含油性影响,明确孔喉结构对原油充注与聚集的机理及致密砂岩油气富集的有利孔喉条件,为致密砂岩油后期增储上产提供依据。

The microscopic pore-throat structure is the key to affecting the charging and accumulation of tight sandstone oil and gas and controlling the development of tight oil and gas“sweet spots”.In this study,the Chang 8 tight sandstone in Maling area of the Ordos basin was taken as an example,and the pore-throat structure characteristics of tight sandstone reservoirs were quantitatively studied by means of casting thin sections,scanning electron microscopy,high pressure mercury intrusion and nuclear magnetic resonance.Nuclear magnetic resonance and other experimental parameters were used to investigate the effects of pore type,pore-throat volume ratio,pore-throat distribution,and pore-throat connectivity on the oil-bearing properties of the reservoir.The results show that tight sandstone reservoirs have the characteristics of high mercury injection pressure,small median radius and high irreducible water saturation,which make their oil content controlled by physical properties and pore-throat structure.Throat distribution and size,pore-throat connectivity,etc.are all important factors affecting the oil content of the reservoir;intergranular pores are well developed,the pore-throat volume ratio is moderate(Vr is 1.7-3),and the distribution is uniform and larger than the lower limit of charging.Higher throat content,higher pore-throat content of free water saturation,and higher ratio of free water to irreducible water saturation are favorable conditions for reservoir oiliness.Taking Chang 8 reservoir in Maling area as the research object,the influence of pore-throat structure characteristics on the oil-bearing property of the reservoir was deeply analyzed,and the mechanism of pore-throat structure on the charging and accumulation of crude oil and the favorable pore-throat conditions for oil and gas enrichment in tight sandstone were clarified.Provide a basis for increasing reserves and production of tight sandstone oil in the later stage.