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非均质多孔介质的地质熵与渗透特性关系研究

STUDY ON THE RELATIONSHIP BETWEEN GEOLOGICAL ENTROPY AND PERMEABILITY CHARACTERISTICS OF HETEROGENEOUS POROUS MEDIA

  • 摘要: 为了分析多孔介质孔隙结构非均质性对其渗透特性的影响, 基于信息熵原理, 提出了多孔介质地质熵理论和非均质性指标-熵尺度, 通过建立球心距不同的球形颗粒填充模型, 将熵尺度与传统几何参数指标对比分析, 验证了熵尺度评价多孔介质孔隙结构非均质性和渗透特性的合理性. 采用改进四参数随机生长法和格子-玻尔兹曼方法, 建立了非均质程度不同的多孔介质并模拟流体渗流, 分析了非均质多孔介质熵尺度与非均质性、渗透特性的相关关系. 结果表明: 当孔隙率一定时, 熵尺度可以考虑孔隙结构的空间排列分布, 更准确地描述孔隙结构非均质性对渗透率的影响; 平均颗粒等效直径与熵尺度呈正相关关系, 非均质性越强, 平均颗粒等效直径与熵尺度的变化范围越广, 多孔介质渗透性增大, 优势流效应更显著, 颗粒尺寸的变化与颗粒的随机分布是孔隙结构非均质性增大的根本原因; 迂曲度、连通孔隙率与比表面积三者的共同作用是孔隙结构非均质性对渗透率的影响机理, 三者的乘积值与熵尺度呈较高的正相关性, 熵尺度越大, 渗透率越大; 熵尺度与渗透率的非线性关系近似满足指数函数.

     

    Abstract: In order to analyze how the heterogeneity of the pore structure of porous media affects its permeability characteristics, the theory of geological entropy for porous media, along with a heterogeneity index called the entropy scale, are introduced based on the principle of information entropy. Utilizing a model consisting of spherical particles with varying distances between their centers, a comparative analysis is carried out between the entropy scale and traditional geometric parameter indicators, which demonstrates the rationality of using the entropy scale for assessing both the heterogeneity of the pore structure and the permeability characteristics of porous media. Using the improved four-parameter random growth method and lattice-Boltzmann method, heterogeneous porous media with different degrees of heterogeneity were established and fluid seepage was simulated. The relationship between the entropy scale of heterogeneous porous media and their heterogeneity and permeability characteristics was analyzed. The results indicate that when porosity is constant, the entropy scale can consider the spatial arrangement and distribution of pore structures, providing a more accurate description of how pore structure heterogeneity affects permeability. The average equivalent particle diameter shows a positive correlation with the entropy scale: stronger heterogeneity leads to a wider range of changes in the average equivalent particle diameter and entropy scale, resulting in increased permeability of porous media and a more pronounced dominance of preferential flow effects. The differences in the size of the particles, along with the irregular and random arrangement of these particles, contribute to the fundamental factors responsible for the increased heterogeneity observed in the pore structure. Tortuosity, connected porosity, and specific surface area collectively play a crucial role in the influencing mechanism through which the heterogeneity of pore structure affects permeability. Their product values exhibit a higher positive correlation with the entropy scale; larger entropy scales correspond to higher permeability. The nonlinear relationship between entropy scale and permeability approximately follows an exponential function.

     

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