Abstract
The rational characterization and quantitative analysis of the complex internal pore structure of rock is the foundation to solve many underground engineering problems. In this paper, CT imaging technology is used to directly characterize the three-dimensional pore network topology of sandstone with different porosity. Then, in view of the problem, which is difficult to quantify the detailed topological structure of the sandstone pore networks in the previous study, the new complex network theory is used to characterize the pore structure. PageRank algorithm is based on the number of connections between targets as a measure index to rank the targets, so the network degree distribution, average path length, clustering coefficient, and robustness based on PageRank algorithm and permeability-related topological parameters are studied. The research shows that the degree distribution of sandstone pore network satisfies power law distribution, and it can be characterized by scale-free network model. The permeability of rock is inversely proportional to the average path length of sandstone network. The sandstone pore network has strong robustness to random disturbance, while a small number of pores with special topological properties play a key role in the macroscopic permeability of sandstone. This study attempts to provide a new perspective of quantifying the microstructure of the pore network of sandstone and revealing the microscopic structure mechanism of macroscopic permeability of pore rocks.
Highlights
Reservoir rocks contain huge numbers of pores with different sizes and complex shapes, and most part of the pores are connected with each other under the natural or artificial intervention, which is the main space for the migration of underground oil and gas
In order to study the microseepage mechanism of porous rock, scholars put forward the research methods based on continuum mechanics and pore network structure, respectively
Pan et al [10] studied the influence mechanism of effective stress on the permeability of coal samples, and the results show that the permeability of coal samples changed exponentially with gas pressure
Summary
Reservoir rocks contain huge numbers of pores with different sizes and complex shapes, and most part of the pores are connected with each other under the natural or artificial intervention, which is the main space for the migration of underground oil and gas. Lin and Zhou [13] found that the permeability of coal samples with parallel bedding is most closely related to the confining pressure effect and studied the variation law of coal seam permeability with stress evolution under the action of in situ stress. Gao et al [15] used the hybrid network theory to analyze the network parameters, modularization, and pore aggregation degree of sandstone with different porosity This method can quantitatively analyze the structural parameters that cannot be quantified by traditional connectivity analysis and fractal dimension analysis. In order to analyze the influence mechanism of micropore structure on the permeability of porous rocks, Darabi et al [18] studied the gas seepage process in dense porous media. Liu et al [26,27,28] characterized pores and fractures by fractal dimension of pore, fractal dimension of curved capillary, and fractal
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