Abstract The features of pore and throat structure of an unconventional reservoir are very complex due to multiscale pore-throat size and various pore types and thus hard to characterize. In this study, thin sections, field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), granulometry analysis, physical properties measurements, mercury intrusion capillary pressure (MICP) and nitrogen gas adsorption analysis (N2GA) were combined to investigate the pore-throat structures of the Gaotaizi tight siltstone reservoir in the northern Songliao Basin. The results of observation suggest that the pores are composed of intergranular pores, dissolution pores, intercrystalline pores within clay minerals and micro-fractures. The content of calcite cement has some negative effect on porosity. The content and types of clay minerals have some negative influence on petrophysical properties of reservoir as well. MICP and N2GA are combined to get the full-range of pore-throat size distribution. Based on previous studies and the actual situation of the Gaotaizi reservoir, a new classification for pore-throat size has been proposed, including micropore ( ~ 100 nm), mesopore (100 nm ~ 0.625 μm) and macropore (>0.625 μm). On this basis, the contents of pore-throat in different scales have been calculated. The Gaotaizi tight siltstone reservoir has been divided into three types based on the pore-throat structure. There are big differences among the three types of reservoir with respect to the grain size, the content of matrix, the types of diagenetic minerals, the dominant pore types, the pore-throat size distribution and the percentage of pore-throats in different scales. Accordingly, a pore structure model has been constructed for each type of reservoir. In addtion, it has been found that the pore-throat structure has an important effect on the percolation capacity of the tight siltstone reservoir. Porosity and pore-throat radius have a positive correlation with the permeability. Pore-throats in different scales have different impact on the flow characteristics of tight reservoir. The mesopores and macropores make a great contribution to the flow in the reservoir while the micropores and transition pores do not contribute and even have an inhibitional effect. In general, the permeability or the flow characteristics of the tight siltstone reservoir are mostly controlled by the pore-throats larger than 0.1 μm.

中文翻译：

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松辽盆地北部高台子致密粉砂岩储层孔喉构造特征及其对流动行为的影响

摘要 非常规储集层孔喉尺度多尺度、孔隙类型多样，孔喉结构特征非常复杂，难以表征。在本研究中，结合薄片、场发射扫描电子显微镜（FE-SEM）、X射线衍射（XRD）、粒度分析、物理性质测量、压汞毛细管压力（MICP）和氮气吸附分析（N2GA）松辽盆地北部高台子致密粉砂岩储层孔喉结构研究. 观测结果表明，孔隙由粒间孔、溶蚀孔、粘土矿物晶间孔和微裂缝组成。方解石水泥的含量对孔隙率有一定的负面影响。粘土矿物的含量和类型对储层的岩石物性也有一定的负面影响。MICP 和 N2GA 相结合，可以获得全范围的孔喉尺寸分布。基于前人研究和高台子储层实际情况，提出了一种新的孔喉大小分类，包括微孔（~100 nm）、中孔（100 nm~0.625 μm）和大孔（>0.625 μm）。在此基础上计算了不同尺度的孔喉含量。高台子致密粉砂岩储层根据孔喉结构分为三种类型。三类储层在粒度、基质含量、成岩矿物类型、优势孔隙类型、不同尺度的孔喉尺寸分布和孔喉百分比。相应地，已经为每种类型的储层构建了孔隙结构模型。此外，还发现孔喉结构对致密粉砂岩储层的渗滤能力有重要影响。孔隙度和孔喉半径与渗透率呈正相关。不同尺度的孔喉对致密储层的流动特征影响不同。中孔和大孔对储层内的流动贡献很大，而微孔和过渡孔则没有贡献甚至有抑制作用。一般而言，致密粉砂岩储层的渗透率或流动特性多受大于0.1 μm的孔喉控制。