Cleat structure analysis and permeability simulation of coal samples based on micro-computed tomography (micro-CT) and scan electron microscopy (SEM) technology

Coal has been playing an important role as a valuable source of energy for many years. In turn, gas production from coal reservoirs is a modern development and coal bed methane (CBM), also known as coal seam gas (CSG), is attracting global attention due to its wide occurrence and benefits for the environment as opposed to the conventional energy sources. Developing coal bed methane reservoirs requires better understanding of the flow behaviours of gas and liquids in cleats and analysis of possible contribution of pores to the flow. This paper describes the implementation of micro computed tomography (micro-CT) and scan electron microscopy (SEM) techniques for analysis of coal samples. Intermediate rank coal samples used in this study were collected from Southern Qinshui Basin (China). In the course of the described research, coal samples were scanned, processed and segmented to study the cleat spacing and permeability. Due to the partial volume effect, the resolution of cleats needed improvement which was achieved by subvoxel processing using a novel algorithm as explained in detail in the paper. Permeability was obtained through simulation of one phase flow using Lattice Boltzmann method (LBM). The results show that the simulated permeability is comparable to the analytical approximation. The subvoxel processing has proved an effective method of overcoming the partial volume effect for the low resolution micro-CT images.