Research On The Electromagnetic Response Characteristics Of The Borehole-surface Vertical Long Wire Source In Layered Earth

Borehole-surface Electromagnetic Method is a electromagnetic exploration method, which is AC power supply in well finite wire and receiving electromagnetic response in the ground. Compared with airborne electromagnetic method and ground electromagnetic method, borehole -surface electromagnetic method which probing depth is greater, the ability to probe more deeply target body is more powerful. It has the advantage of fast speed, low cost, good generality, do not destroy the environment, can be used for marine etc. It has the good effects that other exploration methods can not achieve. Borehole-surface electromagnetic method can be better adapted to Chinese large-scale survey of mine, large-scale to find water in arid regions, and the increasingly serious problem of resources. Therefore, it is necessary to study of vertical long wire source in layered earth.Based on existing ground electromagnetic method, the main research work and achievements are as follows:(1) Study the basic theory of electromagnetic fields and combined with the characteristics of borehole-surface electromagnetic method, according to Misac Nabighian's method of deriving formula of electric dipole, I derive the formula of S.A.Schelkunnoff's vector potential of vertical electric dipole which is below the well of the height h, then integral it along the vertical long wire to derive the formula of well vertical long wire source.(2)In this paper, the electromagnetic response of the vertical long wire in layered earth was calculated. By D. Guptasarma and Singh proposed a digital filtering method to solve the integral of Bessel function, the results and accuracy meet the requirements. Then, the correctness of the program was verified. The borehole-surface electromagnetic response of several typical earth models were forward calculation.(3)Study the characteristics of the response of the borehole-surface vertical long wire. Use several typical earth models to analyze the borehole-surface electromagnetic response curve of the different transmitting current, the different transmitting frequency, the different length of vertical long wire source, the vertical long wire source in different layers and the length of vertical long wire less than the depth of abnormal body.(4) In this paper, the phase of borehole-surface electromagnetic date was studied and the application effect was analyzed. In the three and five layered earth models, the combined interpretation of the phase and amplitude curves has achieved significant results. In the borehole-surface electromagnetic method, the utilization of the phase and the amplitude parameter can improve the interpretation accuracy of the measurement of borehole-surface electromagnetic date in the frequency domain, and increase the accuracy of judging layer.This paper achieved the theoretical calculation of the electromagnetic response of the well vertical long wire source in layered earth, and do research on the electromagnetic response characteristics of the well vertical long wire source. It has laid the theoretical foundation for the inversion and interpretation of field data, and provided the basis for the application of the frequency domain borehole-surface electromagnetic survey system.