Experimental study of the self-potential anomaly caused by coal fires

Self-potential method has been used to detect coal fires for decades. However, the origin of self-potential anomaly relating to coal fires is still unclear. In this paper, we first analyze three possible sources of self-potential anomaly that relating to coal fires, i.e., the thermoelectric potential, the redox potential and the streaming potential, among which the streaming potential is negligible. Then, an experimental system is designed to research the above-mentioned three possible sources, in which six experiments are conducted finally. The results verify the existence of the thermoelectric potential and the redox potential. The self-potential that measured on the surface increases with the increase of temperature of the heat source, but decreases dramatically with the increase of its buried depth. Furthermore, the redox potential reduces the total self-potential values on the surface.