Effect on permeability of anthracite subjected to cyclical microwave modification

ZHANG Liankun; WANG Yuefang; ZHANG Xiaoyu; LI Geng; ZHOU Tianbai; YIN Bo; MI Wentian

doi:10.13347/j.cnki.mkaq.20231225

Abstract：Increasing the permeability via microwaves is one of the potential feasible reservoir modification technologies to improve the efficiency of coalbed methane extraction.The microwave oven is used to conduct 3 cycles of microwave modification experi-ments on No.15 anthracite in Jincheng area of Qinshui Basin.The gas permeability of anthracite samples before and after each modi-fication is tested using a self-built solid-gas coupling seepage platform.The pore properties are tested by micro CT scanning com-bined with image processing technology.In addition,the complexity index of pore-fracture network of coal samples before and after modification is discussed based on fractal theory.The results show that the gas permeability of anthracite sample increases with the increase of cycle times,and increases by 8.8 times after 3 cycles.The expansion and connection of pores/fractures in anthracite caused by microwave radiation is the fundamental reason for the increase of gas permeability.After three cycles,the total porosity of anthracite samples increases from 3.48%to 6.19%,in which the proportion of connected pores and fractures increases from 27.0%to 77.4%,and the proportion of isolated pores decreases from 73.0%to 22.6%.The pore number,pore volume,pore surface area and throat number,throat surface area and pore-throat coordination number of connected pores/fractures increase with the increase of cycle times,while the maximum throat length decreases,which confirms the"expansion and connection"effect of microwave modi-fication on pores/fractures in anthracite.The two-dimensional fractal dimensions of pores/fractures of three typical sections in anthra-cite samples increase with the increase of cycle times,and increase from 1.25,1.16,and 1.09 to 1.46,1.54,and 1.37 respectively after three cycles,which clarifies that the cyclical microwave modification will make the pore-fracture network(gas seepage channel)in coal samples more complex.