Study On Detection Methodof Hidden Fire Area In Coalfield Using Transient Electromagnetics

Coal fire refers to a natural disaster which underground coal seams burn spontaneously under natural conditions,resulting in mineral loss and environmental damage.The resistivity of coal seam affected by coal fire will change dramatically [1],which is the basis of coal fire detection through transient electromagnetic method.At present,the transient electromagnetic method used in coal fire detection is generally one-dimensional magnetic source method,while the application of electrical source method is less.The magnetic source method has poor detection effect on the burned out area with low resistivity in the area affected by coal fire.This disadvantage may be improved by selecting an appropriate emission source.Therefore,it is necessary to discuss the effect of magnetic source and electrical source in coal fire detection.The widely used transient electromagnetic method is the one-dimensional magnetic source method.This paper establishes a one-dimensional model with reference to the variation law of resistivity in coalfield fire area,calculates its one-dimensional transient electromagnetic response,and inverts the response into a layered model,so as to compare the detection effects of electrical source transient electromagnetic method and magnetic source transient electromagnetic method in one-dimensional algorithm.Through calculation,it is found that when using one-dimensional transient electromagnetic calculation method,the detection effect of electrical source method and magnetic source method is similar,and they can better identify the burned area,but they also have poor identification effect on the burned out area.The resistivity of coalfield fire area changes dramatically in the horizontal distribution,and the horizontal layered model used in one-dimensional transient electromagnetic method can not show it well.In this paper,the three-dimensional transient electromagnetic response of coalfield fire area resistivity model is calculated based on unstructured vector finite element method,and the response is analyzed and explained.In order to provide guiding suggestions for the actual production work,this paper simulates the magnetic source of ungrounded return line and the electrical source of grounding conductor for three-dimensional forward modeling of transient electromagnetic.Through the numerical simulation analysis,it can be seen that the electrical source transient electromagnetic has an obvious response to the high resistance characteristics of the hidden fire area,which can better reflect the location of the underground hidden fire area.This paper systematically studies the detection theory and application method of hidden fire area in Coalfield Based on transient electromagnetic technology.The research results have a certain guiding role for the actual production.