Synchrotron radiation facility-based quantitative evaluation of pore structure heterogeneity and anisotropy in coal

Abstract

Abstract In order to quantify coal pore structure heterogeneity and anisotropy, synchrotron radiation SAXS (Small Angle X-ray Scattering) was applied to obtain the SAXS images of two different rank coal samples. The surface fractal dimension (D1) and pore fractal dimension (D2) were obtained by processing the image data. The pore structure heterogeneity of two coal samples was quantified by pore fractal dimension (D2). Pore fractal dimension of Xinzhouyao coal is 2.74 and pore fractal dimension of Tangshan coal is 1.69. As a result, the pore structure heterogeneity of Xinzhouyao coal is stronger than that of Tangshan coal. 3D pore structure imaging was achieved by synchrotron radiation nano-CT. The selected Region of Interest (ROI) of coal sample was divided into a certain number of subvolumes. Pore structure heterogeneity was quantified by calculating the limit of the relative standard deviation of each subvolume's porosity. The heterogeneity value of Xinzhouyao coal pore structure is 3.21 and the heterogeneity value of Tangshan coal pore structure is 2.71. As a result, the pore structure heterogeneity of Xinzhouyao coal is also stronger than that of Tangshan coal, namely, pore structure heterogeneity from synchrotron radiation SAXS and synchrotron radiation nano-CT is consistent. Considering the corresponding relationship between the pore structure anisotropy and the permeability anisotropy, the quantification of pore structure anisotropy was realized by computing the permeability tensor of pore structure using the Lattice Boltzmann method (LBM), and the pore structure anisotropy was characterized by the eigenvalues and eigenvectors of the permeability tensor. The pore structure anisotropy obtained by the method proposed in this paper was validated by the pore structure geometrical morphology.