Distribution of coal pore system and its function on coal physical property

Abstract

Coal pore system controls physical properties of coals and influences CO₂ geological sequestration greatly. By using cumulative amplitude ratio method of nuclear magnetic resonance (NMR) measurements, this paper classifies coal pore system of ten samples and analyzes the function of each pore system on coal physical property. Following cognitions are achieved. Ten samples can be divided into four types, and they are all developed type, diffusion pore dominated type, cleat dominated type, and permeation pore dominated type. Both maximum vitrinite reflectance and apparent density have slight positive relationships versus volumetric percentage of diffusion pore, while slight negative relationships with volumetric percentage of cleat. Porosity has a slight negative correlation with volumetric percentage of diffusion pore and a slight positive relationship with volumetric percentage of permeation pore. Irreducible water saturation has a linear relationship versus volumetric percentage of diffusion pore added by 40% of volumetric percentage of permeation pore. Permeability has an exponential relationship versus volumetric percentage of cleat added by 50% of volumetric percentage of permeation pore. It indicates that permeation pore acts as a combination of movable water and irreducible water, and both of them occupy nearly a half the volume of the entire permeation pore. However, as for permeation pore, its function to influence permeability is more emphatic than that to influence irreducible water saturation. It is of great significance to deeply investigate the pore function on gas and water migration and can be useful to guide the engineering processes during coalbed methane drainage and CO₂ geological sequestration.