Abstract Pore–throat structure is a key factor that influences the storage and fluid flow capacity of tight sandstone reservoirs. By performing petro-physical characteristic tests, scanning electron microscopy, and casting thin sections, the main pore types of tight sandstone reservoir samples collected from the Upper Triassic Yanchang Formation in the Baibao area of the Southwest Ordos Basin in China were identified to be dissolved pores, intergranular pores, intercrystalline pores, and micro-cracks. Meanwhile, the size of the pore–throat was widely distributed, whereas its shape varied. Given the advantages and disadvantages of various technical methods, high-pressure mercury injection (HPMI) and nuclear magnetic resonance (NMR) technology were used to study the distribution characteristics of a full-size pore–throat. All 10 samples showed bimodal and unimodal distribution characteristics, and their distribution characteristics were consistent with the results of the petro-physical characteristics, high-pressure mercury injection, and movable fluid saturation tests. The throat distribution characteristics of the reservoir were studied by applying constant-rate mercury injection (CRMI), and the throat radius ranged from 0.43 μm to 9.76 μm with an average of 3.34 μm. The fractal features of the pore–throat and throat were quantitatively characterized by CRMI. The fractal curves of the pore–throat showed self-similarities, and the fractal dimension D ranged between 2.6297 and 2.9529 with an average of 2.7865. The fractal curves of the throats were broken down into two segments, and the fractal dimensions corresponded to two ranges, namely, the small (Dt1) and large throats (Dt2) fractal dimensions. The average of fractal dimension Dt1 was 2.9170, and the average of fractal dimension Dt2 was higher than that of Dt1 with an average of 2.9828, thereby indicating the complex structure and strong heterogeneity of the former. The fractal dimensions D, Dt1, and Dt2 were negatively correlated with permeability, movable fluid saturation, average throat radius, clay mineral content, and laumontite content, positively correlated with quartz content, and showed poor correlation with feldspar. Compared with Dt2, the fractal dimension Dt1 had a higher correlation with pore–throat parameters and mineral content. Given the higher self-similarity of small throats, their distribution is considered highly homogeneous.

中文翻译：

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鄂尔多斯盆地延长组致密砂岩孔喉结构及分形特征

摘要 孔喉结构是影响致密砂岩储层储量和流体流动能力的关键因素。通过岩石物性测试、扫描电镜、铸件薄片等分析，确定了鄂尔多斯盆地西南百宝地区上三叠统延长组致密砂岩储集层样品的主要孔隙类型为溶蚀孔隙。 、粒间孔、晶间孔和微裂纹。同时，孔喉大小分布广泛，形态各异。鉴于各种技术方法的优缺点，采用高压压汞（HPMI）和核磁共振（NMR）技术研究了全尺寸孔喉的分布特征。10个样品均表现出双峰和单峰分布特征，其分布特征与岩石物理特征、高压压汞、可动流体饱和度试验结果一致。采用恒速压汞（CRMI）方法研究储层喉道分布特征，喉道半径范围为0.43～9.76 μm，平均为3.34 μm。CRMI定量表征了孔喉和喉道的分形特征。孔喉分形曲线表现出自相似性，分形维数D介于2.6297～2.9529之间，平均为2.7865。喉道的分形曲线被分解为两段，分形维数对应两个范围，即，小 (Dt1) 和大喉道 (Dt2) 分形维数。平均分维Dt1为2.9170，平均分维Dt2高于Dt1，平均为2.9828，说明前者结构复杂，异质性强。分形维数D、Dt1、Dt2与渗透率、可动流体饱和度、平均喉道半径、粘土矿物含量、海蒙石含量呈负相关，与石英含量呈正相关，与长石相关性较差。与 Dt2 相比，分形维数 Dt1 与孔喉参数和矿物含量的相关性更高。鉴于小喉道的自相似性较高，它们的分布被认为是高度均匀的。分形维数Dt2的平均值高于Dt1，平均值为2.9828，说明前者结构复杂，异质性强。分形维数D、Dt1、Dt2与渗透率、可动流体饱和度、平均喉道半径、粘土矿物含量、海蒙石含量呈负相关，与石英含量呈正相关，与长石相关性较差。与 Dt2 相比，分形维数 Dt1 与孔喉参数和矿物含量的相关性更高。鉴于小喉道的自相似性较高，它们的分布被认为是高度均匀的。分形维数Dt2的平均值高于Dt1，平均值为2.9828，说明前者结构复杂，异质性强。分形维数D、Dt1、Dt2与渗透率、可动流体饱和度、平均喉道半径、粘土矿物含量、海蒙石含量呈负相关，与石英含量呈正相关，与长石相关性较差。与 Dt2 相比，分形维数 Dt1 与孔喉参数和矿物含量的相关性更高。鉴于小喉道的自相似性较高，它们的分布被认为是高度均匀的。分形维数D、Dt1、Dt2与渗透率、可动流体饱和度、平均喉道半径、粘土矿物含量、海蒙石含量呈负相关，与石英含量呈正相关，与长石相关性较差。与 Dt2 相比，分形维数 Dt1 与孔喉参数和矿物含量的相关性更高。鉴于小喉道的自相似性较高，它们的分布被认为是高度均匀的。分形维数D、Dt1、Dt2与渗透率、可动流体饱和度、平均喉道半径、粘土矿物含量、海蒙石含量呈负相关，与石英含量呈正相关，与长石相关性较差。与 Dt2 相比，分形维数 Dt1 与孔喉参数和矿物含量的相关性更高。鉴于小喉道的自相似性较高，它们的分布被认为是高度均匀的。