Identifying deep saturated coal bed zones in China through the use of large loop TEM

Most of the shallow mineral deposits of China have already been mined because of the country's fast-growing social and economic development. Consequently, the exploration and mining of deep-seated coal deposits have become alternative ways to satisfy the energy needs for both domestic and industrial use. To ensure safe mining practices and avoid the intrusion of water from the bases of coal deposits, it has become essential to investigate the distribution of deep-seated coal deposits using appropriate and cost-effective geophysical methods. For example, a coal mine located in the southern part of China's Shanxi Province is characterized by a roof of dry rocks, whereas the coal beds in this area are saturated. A new technique which uses a large loop transient electromagnetic method (hereafter referred to as a modified central loop TEM) to detect geological targets located at deeper levels in the subsurface was successfully developed and applied in this study. The detection abilities of this technique, such as the time-domain responses and depth of investigation, as well as its sensitivity to deep targets, were analyzed. This new method was successfully employed to detect the floor of a 900 m deep coal seam at the location of the saturated coal beds in Shanxi Province. Wells were drilled to confirm the results, showing that the proposed method is both applicable and convenient for future exploration purposes. TEM could potentially be used to detect geological materials located at greater depths with higher detection accuracy.