Numerical investigation on seepage characteristics of anthracite multi-scale pore-fracture structureOA

The key to evaluate the effectiveness of coalbed methane(CBM)extraction is to establish an appropriate permeability model,however,the existing permeability models barely distinguish the influence of pores and fractures on the seepage of coal body,which leads to the inability to clarify the contribution of each parameter,and thus the inability to realize the effective adjustment of parameters in order to improve the total flow of coal seam.To address issue,we developed a three-dimensional fracture network model and further derive a three-dimensional pore-fracture dual medium permeability model,and found that in the millimeter scale,the permeability of the coal is dominated by the fracture permeability,which is approximately four orders of magnitude larger than that of the matrix permeability.On this basis,the effects of fracture network parameters such as initial fracture porosity,ratio of fracture length to fracture width,ratio of fracture opening to width,fracture azimuth,fracture inclination,and maximum fracture volume on the permeability of the fracture network were investigated.The results show that the ratio of fracture length to width and fracture inclination are negatively correlated with the permeability of fracture network,while the rest of the parameters are positively correlated with the permeability of fracture network,among which the permeability is more sensitive to the changes of the initial fracture porosity,the ratio of the fracture length to the width,and the fracture azimuth.The results have important implications for optimizing the strategy of coal seam permeability enhancement.