Research And Application Of Advanced Detection Technology Based On Borehole Transient Electromagnetic Method

With the advancement of coal mining towards deeper levels,the geological environment underground becomes increasingly complex,posing new challenges to the accurate detection of sources of water hazards in mines.To ensure safe coal mine production,the research and application of geophysical exploration technology are of great significance.This thesis conducts research and application analysis of the drilling transient electromagnetic(TEM)leading detection technology from three aspects:numerical simulation,physical simulation,and field measurements.By establishing a three-dimensional numerical model of the underground and conducting relevant experiments,the thesis investigates the distribution of magnetic fields and the characteristics and differences of response signals under changes in azimuth,volume,radial distance,and apparent resistivity of strata,providing theoretical support for experimental applications.The main research results are as follows:(1)In the azimuthal experimental study,the equal magnetic field intensity in different azimuths was demonstrated by analyzing the characteristics of the anomalous body magnetic field intensity and coil signals when the radial distance was the same.It was also proven that the closer an anomalous body is to the normal direction of a certain component,the higher the induced voltage of that component.The experimental results showed that the three-component coil divides the tested space into eight regions,and the positive and negative polarity of the induced voltage can reflect the region in which the anomalous body is located,with an azimuthal accuracy of up to 87.5%.When combined with the trend of induced voltage changes,the accuracy will be slightly improved.(2)In the volumetric experimental study,it was demonstrated by studying the distribution of the anomalous body magnetic field and the induced voltage curve that the larger the volume of the anomalous body,the longer the duration of the secondary field,the slower the magnetic field decay,and the greater the induced voltage.As the volume increased,the induced voltage of the small volume anomalous body increased more significantly,while the induced voltage of the large volume anomalous body increased less.The amplitude of the induced voltage gradually decreased as the volume increased.(3)In the distance experimental study,it was demonstrated by analyzing the magnetic field intensity and induced signal characteristics of the numerical model that as the radial distance increased,the duration of the secondary field became shorter,the magnetic field decay rate became faster,the magnetic field intensity became smaller,and the induced voltage decreased.Numerical simulation results showed that when the radial distance was less than 5m,the induced voltage decreased rapidly,with a decrease of more than 50%.When the radial distance was greater than 5m,the induced voltage decreased slowly,and the voltage curve gradually approached horizontal.Through field testing,it was proven that the effective radial radius of the borehole transient electromagnetic instrument developed jointly by the research team was greater than12.5m for underground detection.(4)In the experiment on layer identification,it was demonstrated by analyzing the variations of magnetic field intensity and induced voltage in the rock and soil layers that the impact of the apparent resistivity factor on the magnetic field distribution was greater than that of the distance factor.The lower the apparent resistivity,the higher the induced voltage.The greater the difference in the apparent resistivity of the rock and soil layers,the more obvious the changes in magnetic field and induced voltage values.Low-resistivity rock and soil layers can increase the induced voltage values of the surrounding rock and soil layers.The higher the apparent resistivity and the farther the distance,the lower the degree of increase.The quality of the Y-component coil induction signal is better than that of the X-and Z-component coils,providing guidance for data interpretation.This article confirms through the study of the magnetic field distribution and induction signals under the influence of factors such as azimuth,volume,radial distance,and apparent resistivity that in underground advanced exploration,borehole transient electromagnetic is more precise and sensitive than mine transient electromagnetic and tunnel transient electromagnetic.This provides guidance for future inversion algorithm research and data interpretation.Through the application of underground advanced exploration,the apparent resistivity anomaly area can be delineated horizontally and vertically,the low-resistivity anomaly area can be identified,and the evaluation of water-richness can be conducted.The thesis includes 74 figures,14 tables,and 84 references.