Research On Abnormal Range Of Central Loop By Transient Electromagnetic Method

In the actual detection of transient electromagnetic method,there is a great difference between the abnormal range and the actual range of the object with low resistance,which not only affects the interpretation of the anomaly,but also causes the reduction of the accuracy of the detection.Therefore,it is of practical value to explore the relationship between the abnormal range of the low resistivity body and its actual range by transient electromagnetic method.In this paper,the relationship between the change of the working parameters of transient electromagnetic and the abnormal range of the low resistance target body and the actual range is studied by a geological model built and a positive and negative simulation worked.In this thesis,based on the basic theories of transient electromagnetic method,using EMIT Maxwell transient electromagnetic data processing software,a geological model is established.Through the discussion of the different transmission line frame,power supply current and frequency parameters of the center loop,the forward simulation is carried out,and the relationship between the abnormal range of transient electromagnetic method and the low resistivity body by the transmission line frame,the power supply current and frequency are obtained by the inversion and analysis: When the ratio of the half width and the buried depth of the low resistance body is 100:20,the abnormal range of low resistivity body apparent resistivity of the border length(40-100m)of the wire frame increases with the increase of the line frame.When the border length of the frame is larger than 100 m,the abnormal range of the apparent resistivity of the low resistance body is not related to the increase of the wire frame.The abnormal range of the apparent resistivity of the low resistance body with the emission current of 9-15 A increases with the increase of the current;when the emission current is greater than 15 A,The range of the apparent resistivity of the low resistivity body will remain unchanged.If the frequency of the transmitting signal is within the range of 4-32 Hz,the range of the apparent resistivity of the low resistivity body will remain unchang ed.Through the discussion of the different resistivity of surrounding rock,the thickness and buried depth of low resistance body,the relationship between the resistivity of the surrounding rock,thickness and depth of the low resistance body and the abnormal range of the transient electromagnetic the low resistancebody is obtained by inversion and analysis,that is,the abnormal range of apparent resistivity of low resistivity body of 100-2000??m increases with the reduce of the resistivity of surrounding rock.The thickness of low resistance body is 1-10 m and the apparent resistivity of low resistivity body increases with the increase of thickness.When the thickness of the low resistance body is greater than that of 10 m,the abnormal range is basically unchanged.The apparent resistivity anomaly range of 80-130 m with low resistivity increases with the increase of buried depth.When the buried depth of the low resistance body is greater than 130 m,the anomaly range is basically unchanged.Then,in the plane rectangular coordinate system,the scatter plots of the resistivity of the surrounding rock,thickness,the buried depth the abnormal range of the low resistance body is obtained.The fitting polynomial is used to get the fitting relation curve and relation of the abnormal range of the low resistance body and the resistivity of the surrounding rock,thickness,buried depth.Using the conclusions obtained in this paper,the measured data of transient electromagnetic method in a mining area in Linfen,Shanxi,are inverted and analyzed.It is found that the abnormal range of the goaf is about 92 m,and the abnormal boundary is redefined.In order to verify the correctness of this conclusion,the data of the mining area have been found.The results show that the simulation analysis results are basically consistent with the actual situation,which proves that the simulation is correct and effectively improves the accuracy of exploration.