A MULTI-FIELD COUPLED SEEPAGE MODEL FOR COAL SEAM WITH FRACTURES OF POWER LAW LENGTH DISTRIBUTIONS

Abstract

In the process of gas mining, the fracture distribution with power law length and the pore structure with adsorption effect have an important influence on the coal seam permeability. In recent years, the research on the internal structure of coal seam and the fluid flow mechanism has attracted a large number of researchers. In this paper, by considering the coal matrix deformation caused by adsorption, a pore-fracture model coupled with the multi-field effects and with power law length distribution of fractures in coal seam is established based on the fractal theory for porous media. In this work, we study the influences of the power law exponent [Formula: see text] of fracture length and the ratio [Formula: see text] of the minimum to maximum fracture lengths on the permeability of coal seam and the evolution mechanism of permeability with the structural and mechanical parameters of coal seam. It is found that the permeability of coal seam is inversely proportional to [Formula: see text], directly proportional to [Formula: see text], and to Langmuir volume constant and Langmuir volume strain constant. Compared with other factors, the power law component [Formula: see text] of fractures has the most significant effect on the coal seam permeability.