Experimental study on electrical characteristics of gassy coal during extrusion process in different stage

In this study, a stress-oriented experiment of gas-containing coal extrusion was performed by establishing an experimental system integrating gas injection, loading, and electrical testing. Then, the apparent resistivity images in different stages of gassy coal extrusion evolution were obtained. Finally, multi-parameter electrical characteristic parameters were extracted, and the variation and characterization significance of characteristic parameters were analyzed. The results show that the overall values of apparent resistivity images decrease in the gas adsorption equilibrium and stress loading stages. After the extrusion occurs, the values grow remarkably; in addition, there exist abnormal resistance values in some areas, which is consistent with the distribution of coal fractures. The fundamental reason for this phenomenon lies in the changed conductive channel within gassy coal. Moreover, average and maximum values of apparent resistivity both decrease first before they increase, whereas the current and spontaneous potential both rise first and then fall, of which the current changes more obviously. These changes, which characterize the evolution process of gassy coal extrusion, can provide theoretical guidance and experimental basis for geophysical exploration of gas dynamic disasters in coal and rock.