The intrusion of magmatic rocks into coal seams affects the coal quality and leads to unforeseen hazards in safety of the coal mines’ production. This paper summarizes the mechanism of magmatic rocks intruding into coal seams, depicts the electromagnetic characteristics of the coal seams intruded by magmatic rocks, briefly describes the characteristics of transient electromagnetic method (TEM), and introduces the method of detection by TEM and the data processing steps. Then, the effectiveness of TEM in detecting the ranges of the coal seams intruded by magmatic rocks is theoretically analysed. It is observed that after the intrusion of magmatic rocks in the coal seams, the electromagnetic characteristics (secondary field potential and resistivity) will be dramatically affected, namely high secondary field potential and low resistivity. For experimental verification purposes, this study selects the test project of the Tongxin Minefield in the Datong Coalfield in Shanxi, China as an example, and the accuracy for the detection of the ranges of the coal seams intruded by magmatic rock using TEM is successfully verified.

Geothermal resources are a type of important renewable clean energy with high development and usage potential. However, at the same time, geothermal resources are buried deep below the Earth’s surface, they involve significant exploiting hazards. Geophysical methods are frequently required to determine the depth and location of geothermal resources. Among geophysical methods, transient electromagnetic method (TEM) and controlled source audio-frequency magnetotellurics (CSAMT) have comparably high effectiveness and accuracy. This article first introduces the algorithm theory of the finite volume method, then establishes a simplified geothermal system resistivity model. Next, based on this model, simulation analyses of the abilities of CSAMT and TEM were performed to distinguish target faults with different resistivities, dip angles and widths. Finally, combined with theoretical analysis, taking a comprehensive electromagnetic exploration of CSAMT and TEM in Huairen County, Shanxi Province, China as an example, the effectiveness of these two methods in exploring typical geothermal resources is verified. It is shown that both methods can reflect the geoelectric structure from different perspectives, and the efficacy in geothermal exploration using comprehensive electromagnetic method is demonstrated.

The gravity method has been widely used for detecting the subsurface density anomaly and geological structures. The interpretation result based on gravity data can be used for mineral/oil exploration and regional geological study. The effective and successful application of gravity methods depends on the fast forward modeling and stable inversion tools to image the subsurface density structures. In this chapter, we will review the applications and developments of gravity method. We starts form the basic theory for gravity field and the scalar gravity potential and introduce the closed form of the solution for the gravity field caused by a density anomaly. Different gravity data forward modeling and inversion techniques will be introduced in this chapter with their application in petroleum reconnaissance. Several examples will be presented in this chapter to illustrate the application of different gravity modeling and inversion techniques.