The pore-throat size determines the oil and gas occurrence and storage properties of sandstones and is a vital parameter to evaluate reservoir quality. Casting thin sections, field emission scanning electron microscopy, high-pressure mercury injection and rate-controlled mercury injection are used to qualitatively and quantitatively investigate the pore-throat structure characteristics of tight sandstone reservoirs of Xiaoheba Formation in the southeastern Sichuan Basin. The results show that the pore types include intergranular pores, intragranular dissolved pores, matrix pores, intercrystalline pores in clay minerals, and microfractures, and the pore-throat sizes range from the nanoscale to the microscale. The high-pressure mercury injection testing indicates that the pore-throat radius is in range of 0.004–11.017 µm, and the pore-throats with a radius >1 µm account for less than 15%. The rate-controlled mercury injection technique reveals that the tight sandstones with different physical properties have a similar pore size distribution (80–220 µm), but the throat radius and pore throat radius ratio distribution curves exhibit remarkable differences separately. The combination of the high-pressure mercury injection and rate-controlled mercury injection testing used in this work effectively reveals the total pore-throat size distribution in the Xiaoheba sandstones (0.004–260 µm). Moreover, the radius of the pore and the throat is respectively in range of 50–260 µm and 0.004–50 µm. The permeability of the tight sandstones is mostly affected by the small fraction (<40%) of relatively wide pore-throats. For the tight sandstones with good permeability (>0.1 mD), the larger micropores and mesopores exert a great influence on the permeability. In contrast, the permeability is mainly influenced by the larger nanopores. Furthermore, the proportion of narrow pore-throats in tight sandstones increases with reducing permeability. Although the large number of narrow pore-throat (<100 nm) makes a certain contribution to both reservoir porosity and permeability, they have contribution to the former is far more than to the latter.

中文翻译：

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一种表征致密砂岩储层孔喉结构的改进方法：组合高压和控速压汞技术

孔喉大小决定了砂岩的油气赋存特性，是评价储层质量的重要参数。采用铸造薄片、场发射扫描电镜、高压压汞和控速压汞等方法对川东南小河坝组致密砂岩储层孔喉结构特征进行定性和定量研究。结果表明，孔隙类型包括粒间孔、粒内溶孔、基质孔、粘土矿物晶间孔和微裂缝，孔喉尺寸范围从纳米级到微米级。高压压汞试验表明，孔喉半径在 0.004-11.017 µm 范围内，半径>1 µm的孔喉占比不到15%。控速压汞技术表明，不同物性的致密砂岩具有相似的孔径分布（80-220 μm），但喉道半径和孔喉半径比分布曲线分别表现出显着差异。这项工作中使用的高压压汞和速率控制压汞测试相结合，有效地揭示了小河坝砂岩中的总孔喉尺寸分布（0.004-260 µm）。此外，孔和喉道的半径分别在 50-260 µm 和 0.004-50 µm 的范围内。致密砂岩的渗透率主要受较小比例（<40%）相对较宽的孔喉影响。对于渗透性好的致密砂岩（>0. 1 mD)，较大的微孔和中孔对渗透率有很大影响。相比之下，渗透率主要受较大纳米孔的影响。此外，致密砂岩中狭窄孔喉的比例随着渗透率的降低而增加。大量窄孔喉（<100 nm）虽然对储层孔隙度和渗透率都有一定的贡献，但对前者的贡献远大于对后者的贡献。