Integrated fractal description of nanopore structure and its effect on CH4 adsorption on Jharia coals, India

Internal pore surface heterogeneity and pore matrix irregularities have a decisive influence on the gas adsorption capacity and transportation in the coalbed methane (CBM) reservoir. This study integrates novel idea of relating the multiple approaches to customize the obtained results from analytical techniques to attain efficient elucidation and quantification of pore features and its influence on gas storage and transport in CBM reservoirs. Fractal profiles are analyzed to evolve fractal dimensions from LPA-N-2 and imaging techniques for surface fractals and matrix fractals. Measured results of fractal dimension depict surface texture, complexity and heterogeneity of pore structure, thereby its relationship with CH4 adsorption are investigated. A 3D model of pore structure and connectivity are reconstructed to quantify the porous regions using 2D FE-SEM data and 3D tomographic interface-Amira software. In contrast to the conventional surface fractal approaches, this technique helps to illustrate pore structure and provides realistic pore connectivity. Study analysis reveals that the pores with higher surface fractal dimension, i.e. (D-S > 2.65) have possibly large amount of adsorption sites, where adsorption of gases becomes easier than desorption due to surface roughness. However, the higher matrix fractal dimension results in a more complex pore microstructure in contrary to that of surface fractal dimension, which directly effects the adsorption mechanism causing pore filling adsorption and the adsorption capacity decreases because of relatively higher liquid/gas surface tension.