Surface fractal dimensions as a characterization parameter for methane adsorption–induced coal strains

Abstract

Pore network in coal is important for coal bed methane storage, making it necessary for us to further study coal pore characteristics for better studying and exploiting the coal bed methane resource, also reducing the gas outburst accidents during coal mining process. In this paper, adsorption strain experiments were implemented to distinguish the differences of methane adsorption effects of coal samples directly. A series of pore character experiments of coal samples, mercury intrusion porosimetry, and nitrogen/carbon dioxide adsorption experiments were implemented to obtain the pore distribution. Based on mercury intrusion porosimetry and nitrogen adsorption experiments’ data, surface fractal dimensions were calculated by the fractal method. The relation between surface fractal dimensions and coal volumetric strains due to methane adsorption was analyzed. It turns out that the surface fractal dimension, as a comprehensive parameter describing the pore distribution characteristic, is positively correlated with coal adsorption strain and Langmuir adsorption parameters.