Three-dimensional numerical simulation of short-offset transient electromagnetic responses to water-rich bodies in coal mines
This study performed forward modeling for the short-offset transient electromagnetic(SOTEM)responses of a three-dimen-sional geoelectric model using the three-dimensional finite-difference time-domain method.The results reveal that:(1)The attenuation curves of the Ex responses from the electric field above the goaf or collapse column were above the background response curve at early times but below it at later times;(2)A shorter offset corresponded to a higher relative anomaly of ∂Bz/∂t response signals.Increasing the length of the transmitting source could enhance the signal intensity while slightly decreasing the relative anomaly;(3)In the case of survey lines close to the transmitting source,the overall ∂Bz/∂t responses of the goaf or collapse column were weaker than the back-ground responses.For survey lines away from the transmitting source,the overall ∂Bz/∂t responses of the goaf or collapse column were stronger than the background responses.In summary,the calculation results demonstrate significant implications for understanding the ability of the SOTEM method to detect typical water-rich bodies in coal mines,laying a theoretical foundation for the parameter selection of SOTEM devices and their generalized application in the coal sector.
waterlogged goaf in a coal minewater-bearing collapse columnSOTEM responsethree-dimensional numerical simula-tion
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