Controllable source audio-frequency magnetic field sounding method for geological exploration

Abstract

The invention discloses a controllable source audio-frequency magnetic field sounding method for geological exploration, comprising the following steps: (1) determining a measuring line and distributing an artificial field source; (2) configuring a field source frequency range according to the exploration task; (3) respectively measuring magnetic field vertical amount and magnetic field horizontal amount at a measurement point by utilizing a horizontal magnetic rod and a vertical magnetic rod; (4) calculating a frequency tipper according to the following formula FT=omega<1 / 2> *Hz / H; (5) converting the frequency tipper into apparent resistivity by utilizing the following formula rhos(i)=[FT(i) / FT(i)]<2> (i=1,2?-LN); (6) inverting the resistivity and the depth of an underground medium by utilizing an existing inversion method; and (7) drawing patterns according to the inversion result to deduce and explain geological information such as underground medium construction and the like. The invention can avoid a static effect caused by the measurement of an electric field, can realize the measurement of a tipper on a one-dimensional geologic body, increases the resolution ratio of the frequency tipper on electric longitudinal change of the underground medium by taking the frequency tipper as an conversion parameter, can realize quantitative inversion on the frequency tipper, and realizes high-speed and high-density electromagnetic measurement.

Description

Technical field [0001] The invention relates to a controllable source audio magnetic field sounding method for geological prospecting. Background technique [0002] With the development of the national economy, magnetotelluric sounding (MT), audio-frequency magnetotelluric sounding (AMT) and controllable-source audio-frequency magnetotelluric sounding (CSAMT) are widely used in national life. These methods are mainly based on the Cagniard resistivity to study the underground geology. When the horizontal electrical properties of the surface are uneven or the topography is undulating, static effects will be produced. This effect is always related to the two-dimensional or three-dimensional structure, and the intensity can reach two orders of magnitude, causing errors in the inversion model, causing large deviations in the inferred depth, and complicating the interpretation of the structure. Many scholars have proposed many methods to eliminate static effects. However, static effec...

AI Technical Summary

Problems solved by technology

This effect is always associated with 2D or 3D structure and can be up to two orders of magnitude in magnitude, causing errors in inversion models, causing large shifts in inferred depths, and complicating the interpretation of structures

Many scholars have proposed many methods to eliminate the static effect, but the static effect is inherent in the Cagniard resistivity that must measure the electric field, and it is impossible to eliminate it theoretically. Therefore, so far, there is no method that can eliminate the static effect. effect is completely eliminated

[0003] The audio frequency magnetic field sounding method (AFMAG) only measures the magnetic field, which is minimally affected by static effects, but AFMAG uses natural sources as its field source, which has randomness, weakness, polarization uncertainty, etc., and uses natural field sources Like the MT and AMT methods, the AFMAG method requires a huge effort to record and analyze field data

And because the natural plane wave has no vertical magnetic field in the case of one-dimensional or nearly one-dimensional dielectric medium, AFMAG cannot detect one-dimensional geological bodies

[0004] Tippers used in frequency-domain electromagnetic sounding methods such as MT, AMT, CSAMT, and AFMAG have high sensitivity to lateral changes in underground electrical media, and their dip angles can reflect the dip information of faults and fracture zones. However, Dippers cannot reflect the resistivity change of underground complex electrical media, and the resistivity change of underground media cannot be inferred from the value of dips, and its vertical resolution is low

[0005] For frequency-domain electromagnetic field sounding methods such as MT, AMT, and CSAMT, which are widely used, the electric field must be measured in the field. For areas with complex terrain, it is usually very difficult to arrange electrodes and wires, which greatly reduces the efficiency of field data collection.

And for electric field measurement, it is difficult to achieve high-density electromagnetic sounding, which seriously affects the accuracy of electromagnetic exploration

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