US 12,092,784 B2
Multi-line source ground-borehole transient electromagnetic detection method and multi-line source ground-borehole transient electromagnetic detection
Nannan Zhou, Beijing (CN); Guoqiang Xue, Beijing (CN); Weiying Chen, Beijing (CN); and Shun Zhang, Beijing (CN)
Assigned to Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing (CN)
Filed by Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing (CN)
Filed on Aug. 15, 2022, as Appl. No. 17/887,572.
Application 17/887,572 is a continuation of application No. PCT/CN2021/089125, filed on Apr. 23, 2021.
Claims priority of application No. 202110274854.9 (CN), filed on Mar. 15, 2021.
Prior Publication US 2022/0390640 A1, Dec. 8, 2022
Int. Cl. G01V 3/08 (2006.01); G01V 3/38 (2006.01)
CPC G01V 3/081 (2013.01) [G01V 3/38 (2013.01)] 4 Claims
OG exemplary drawing
 
1. A multi-line source ground-borehole transient electromagnetic detection method for detecting metal mineral resources and geothermal resources, comprising:
S1, constructing a multi-line source ground-borehole transient electromagnetic forward model using a multi-line source emitting device arranged on the ground, consisting of four pairs of grounding conductor sources with opposite current directions, and through transmission lines, a grounding electrode and a magnetic sensor are inserted into the borehole to observe vertical electric and magnetic field multi-components;
S2, obtaining multi-line source ground-borehole transient electromagnetic responses of an underground target layer using one or more receiving magnetic probes and electrode pairs arranged downward along the borehole, with the receiving magnetic probes and electrode pairs connected to a ground receiver controlling them and collecting received signals; and
S3, recognizing the underground target layer according to electromagnetic diffusion characteristics of the multi-line source ground-borehole transient electromagnetic responses;
wherein the S1 is specifically as follows:
when an electromagnetic field is excited in a layered earth surface and received in a borehole, an electromagnetic field component excited by a single grounding conductor source in an x-direction is expressed as follows:

OG Complex Work Unit Math
wherein I represents an emission current, R1 and R2 represent distances between two grounding electrodes and a receiving point, J1(λr) and J0(λr) are first-order and zero-order Bessel functions, respectively, λ represents a horizontal wave number, ri represents receiving and sending distances of measuring points in coordinate systems to which different line sources belong; zj represents an impedance of the j-th layer, ŷj represents an admittance of the j-th layer, and z represents a height of the receiving point;

OG Complex Work Unit Math
indicates a reflection coefficient of an electromagnetic wave when an electric field component is incident on a plane,

OG Complex Work Unit Math
indicates the reflection coefficient of the electromagnetic wave when a vertical magnetic field is incident on the plane,

OG Complex Work Unit Math
indicates an intrinsic admittance of a free space, Ŷ1 indicates a surface admittance,

OG Complex Work Unit Math
indicates an intrinsic impedance of the free space, and Z1 indicates a surface impedance, where z0=iωμ0 and ŷ0=iωε0; ω represents an angular frequency, i represents a complex number, ε0 represents a dielectric coefficient of an underground uniform half space, and μ0 represents a magnetic permeability of the underground uniform half space;
for a multi-line source ground-borehole transient electromagnetic field, z is positive; z is equal to 0 when observed on the ground, but negative when observed in the air; a solution of the responses is obtained by a superposition calculation of the responses of various line sources; EX, EY, EZ, HX, HY, and HZ represent electric field components and magnetic field components in an x direction, a y direction, and a z direction respectively.