Electrical Measurements of Coal Measure Rocks for Electromagnetic Applications in Mining Industry

Subsurface imaging technologies are part of the electromagnetic (EM) geophysical methods. EM technologies such as radio imaging method (RIM), ground penetrating radar (GPR), and drill string radar (DSR) have great application potentials in the mining industry. However, the success for applying the EM methods to subsurface observations is largely dependant on the correct evaluation of the electrical properties (i.e., resistivity and dielectric constant) of the rocks in the domain of interest. The depth of penetration of the EM signal in coal, as well as the electrical contrast between coal and subsurface boundary rocks or anomalies, are critical parameters for any successful radar system. Based on the measured electrical properties of the coal seam, the proper operating frequency of the radar system must be chosen in order to successfully detect features such as the coal-roof rock boundary, dykes, and voids ahead of mining. The electrical properties of the rocks in a coal seam are frequency dependent. Even though there has been a great advancement in the hardware and data processing software in the past twenty years, there have not been many examinations of the high-frequency properties of coal measure rocks. In this paper, the laboratory setups, the testing procedure, and case studies will be presented for a wide spectrum of frequencies for coal measure rock samples collected from various US coal fields. Tests have been conducted to study the different conditions, including moisture content, that affect the EM properties.