Characterizing coal pore space by gas adsorption, mercury intrusion, FIB–SEM and µ-CT

Understanding multiphase flow properties is essential for assessing and exploiting coals. These properties depend on the 3D pore space information, i.e. geometry and topology. However, determining the geometric and topological properties in coals are still challenging due to the complicated pore structures comprising several length scales. Studying pore scale structures in coals in a continuous range across over several length scales and integrating these information are necessary to increase the understanding of the role of pore structure on transport properties. Most of the current modeling methods are usually based on one or two experimental methods with limited and insufficient information. In this work, CO2 adsorption, N2 adsorption, MIP, X-ray µ-CT and FIB–SEM are used to study the pore structure characteristics of coal samples cored from the No. 9 coal seam of upper Permian Longtan formation at the Longfeng mine, China. The porosity, pore surface area, pore size distribution, connectivity and pore shapes measured by different methods are analyzed. We show that a combination of these techniques provides a richer picture of pore structure in coals. The obtained 3D pore structure can be applied to predict transport properties which are important to capture coal mine methane (CMM) and optimize field development. The results will also be helpful for the gas control in coal mines.