Abstract
The pore geometry and topology properties of pore space in rocks are significant for a better understanding of the complex hydrologic and elastic properties. However, geometry and topology information about the sandstone pore structures is not fully available. In this study, we obtained the topological and geometrical pore parameters from a representative elementary volume (REV) for fluid flow in sandstone samples. For comparison, eight types of sandstones with various porosities were studied based on the X-ray micro-computed tomography technique. In this study, the REV size was selected based on the parameters from the respective pore network models (PNM), not just the porosity. Our analysis indicates that despite different porosity, all the sandstone samples have highly triangular-shaped pores and a high degree of pore structural isotropy. The high porosity group sandstones exhibit wider ranges of pore sizes than the low porosity group sandstones. Compared to the high porosity group sandstones, the low porosity group sandstones samples showing a higher global aspect ratio, indicating some pores exist in the form of bottlenecks. The pore topological properties of different sandstones show a high dependence of the porosity. The high porosity group sandstones obtain large coordination numbers, large connectivity densities and low tortuosities. The results from this study will help better understand the complex pore structure and the fluid flow in sandstone.
Highlights
As natural geological materials, rocks usually have discontinuous, non-homogeneous, multi-phase composite structures
The above eight parameters were extracted from the pore network model for quantitative parameter analysis
We presented geometric properties and topological properties obtained from representative elementary volume (REV) of each sandstone sample
Summary
Rocks usually have discontinuous, non-homogeneous, multi-phase composite structures. Geometric and topological properties of pore space in rocks play significant roles in mechanical and transport properties [1]. Further quantifying the complex pore space (both geometry and topology) of rocks has become a goal of scientists and engineers in numerous engineering fields. X-ray micro-computed tomography (micro-CT) technology enables quantitative measurements of the internal structure of rock material in a precise and nondestructive manner. Most of the geometric and topological properties of the pore structure can be quantitatively assessed using micro-CT technique. Digital image analysis with micro-CT method has been widely used for analyzing actual 3D pore spaces in sandstones [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16], carbonates [17,18,19,20,21,22,23], coals [24,25] and shales [26]
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