Zhu Yan, Yang Yunfei, Zhang Yuheng, Liu Lin, Li Hengquan, Sang Qin
Exploration and Development Research Institute of Sinopec Henan Oilfield Branch, Nanyang, China.
School of Geoscience and Technology, Southwest Petroleum University, Chengdu, China.
PLoS One. 2024 Dec 27;19(12):e0314799. doi: 10.1371/journal.pone.0314799. eCollection 2024.
Clarifying the pore-throat size and pore size distribution of tight sandstone reservoirs, quantitatively characterizing the heterogeneity of pore-throat structures, is crucial for evaluating reservoir effectiveness and predicting productivity. Through a series of rock physics experiments including gas measurement of porosity and permeability, casting thin sections, scanning electron microscopy, and high-pressure mercury injection, the quality of reservoir properties and microscopic pore-throat structure characteristics were systematically studied. Combined with fractal geometry theory, the effects of different pore throat types, geometric shapes and scale sizes on the fractal characteristics and heterogeneity of sandstone pore throat structure are clarified. On this basis, the estimation model of tight sandstone permeability was established. The results indicate that the reservoir physical properties in the study area are poor, the pore types are mainly dissolved pores, and the pore size is mainly distributed in the nano to submicron range. The fractal dimension fitting curve obtained based on the non-wetting phase model has obvious turning points, indicating that the pore-throat structure has multi-scale characteristics. The turning point of fractal dimension divides the pore-throat structure of tight sandstone into large-scale pore-throats with good connectivity (reticular or beaded pore-throats) and small-scale pore-throats with poor connectivity (dendritic or capillary pore-throats), indicating that tight sandstone has binary pore structure characteristics. The geometry of large-scale pore-throat is complex, which is difficult to meet the self-similar characteristics, with the average fractal dimension is 3.72. The small-scale pore-throat morphology is close to the capillary and has obvious fractal characteristics, with the average fractal dimension is 2.22. There are many small pores and micropores in the reservoir, and the pore volume has a significant positive correlation with the total porosity of the rock, but the contribution to the permeability is low. The development degree of large-scale pore throat is an important factor affecting the physical properties of tight sandstone. The turning point radius of fractal curve and the comprehensive fractal dimension can be used as good indicators for permeability estimation.
明确致密砂岩储层的孔喉尺寸和孔径分布，定量表征孔喉结构的非均质性，对于评估储层有效性和预测产能至关重要。通过一系列岩石物理实验，包括孔隙度和渗透率气体测量、铸体薄片、扫描电子显微镜和高压压汞实验，系统研究了储层物性质量和微观孔喉结构特征。结合分形几何理论，阐明了不同孔喉类型、几何形状和尺度大小对砂岩孔喉结构分形特征和非均质性的影响。在此基础上，建立了致密砂岩渗透率估算模型。结果表明，研究区储层物性较差，孔隙类型主要为溶蚀孔，孔径主要分布在纳米至亚微米范围内。基于非润湿相模型得到的分形维数拟合曲线有明显转折点，表明孔喉结构具有多尺度特征。分形维数的转折点将致密砂岩的孔喉结构分为连通性好的大尺度孔喉（网状或串珠状孔喉）和连通性差的小尺度孔喉（树枝状或毛细管状孔喉），表明致密砂岩具有二元孔结构特征。大尺度孔喉的几何形状复杂，难以满足自相似特征，平均分形维数为3.72。小尺度孔喉形态接近毛细管，具有明显的分形特征，平均分形维数为2.22。储层中存在许多小孔和微孔，孔隙体积与岩石总孔隙度呈显著正相关，但对渗透率的贡献较低。大尺度孔喉的发育程度是影响致密砂岩物性的重要因素。分形曲线的转折点半径和综合分形维数可作为渗透率估算的良好指标。
