Horizontal electric dipole source full offset transient sounding method

Abstract

According to the horizontal electric dipole source full-offset transient sounding method disclosed by the invention, a secondary field is observed in a turn-off gap of a bipolar transmitted pulse, and transient sounding can be realized in other offsets which do not include 0 offset in an area which has stable signals, does not exceed the range of a receiver and meets the signal-to-noise ratio. The horizontal positions of the recording points in the early stage, the middle stage and the late stage are all located at the observation points, and the vertical positions of the recording points are all located at the exploration depth below the observation points.

Description

Technical Field

[0001] The invention belongs to the field of electromagnetic exploration, and in particular relates to a horizontal electric dipole source full-offset transient sounding method. Background Art

[0002] In horizontal electric dipole transient electromagnetic (TEM) exploration, when the offset is greater than the exploration depth (Strack, 2017, p. 5, 13), it is called long-offset TEM. In practice, if observations are made during the intervals between the bipolar pulse current cutoffs and the apparent resistivity defined by the full-period formula (Spies and Frischknecht, 1991, p. 294) is calculated using the binary search method (Yang, 1986; Yan Liangjun et al., 1999; Chen Qingli et al., 2009), then time-domain horizontal electric dipole sources can achieve transient depth measurements within any offset, excluding the dipole source and its immediate vicinity, within the receiver range and signal-to-noise ratio. Unlike frequency-domain horizontal electric dipole source frequency sounding (Cao et al., 2024; Cao Qinghua and Yan Shu, 2023), where the recording point changes with the induction number, the recording point of horizontal electric dipole source full-offset moment transient sounding is always at the exploration depth below the observation point. Therefore, the existing technical solution is not applicable to horizontal electric dipole source full-offset moment transient sounding. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this paper proposes a horizontal electric dipole source full-offset transient sounding method. This method uses observations made during the off-time intervals of bipolar transmit pulses. Within a region with satisfactory signal-to-noise ratio, transient sounding can be achieved at offsets other than zero offset. The exploration depth is determined solely by the observation window and is independent of offset. Apparent resistivity is obtained using a full-period formula through a binary search method, with the recording point for each period located below the observation point.

[0004] The technical solution adopted in the present invention is:

[0005] The horizontal electric dipole source full-offset transient sounding method has the following scheme:

[0006] Observe the secondary field during the interval between bipolar emission pulses, and observe the horizontal positions of the early, middle, and late recording points. All are at the observation point, recording the vertical position of the point All are located in the exploration area below the observation point;

[0007] The apparent resistivity is calculated using the universal expression of each field quantity, and the diffusion depth is obtained based on the apparent resistivity, so that transient depth measurement can be achieved at all offsets in an area that does not include the electric dipole source and its vicinity, where the signal is stable, the receiver range allows, and the signal-to-noise ratio is satisfied.

[0008] Furthermore, the apparent resistivity is defined by the following universal expressions for all field quantities:

[0009]

[0010] Where, yes The electric field strength component, yes The electric field strength component, yes Magnetic field strength component, yes Magnetic field strength component, yes directional magnetic field intensity component, i=1,2,…,m is the observation point number, j=1,2,…,n is the time window number; r i is the offset, is the apparent resistivity, t i,j is the observation time window, μ0 is the magnetic permeability of the non-magnetic earth, p is the electric dipole moment, is the offset distance r i The angle between the electric dipole moment and the θ is 0; erf is the error function, I0 and I1 are the 0th and 1st order modified Bessel functions of the first kind, respectively.

[0011] Furthermore, the apparent resistivity is calculated by the full-period definition formulas (1a), (1b) and (2a), (2b), (2c) through an iterative algorithm.

[0012] Furthermore, the iterative algorithm includes but is not limited to a binary search method.

[0013] Furthermore, the apparent resistivity is substituted into the diffusion depth formula to calculate the exploration depth.

[0014] Furthermore, the apparent resistivity-depth profile, one of the basic maps for data interpretation, was generated according to conventional methods.

[0015] Furthermore, the data obtained from exploration is a reflection of the geological structure below the observation point and is not affected by the field source copy effect and shadow effect.

[0016] Beneficial effects

[0017] 1) The horizontal electric dipole source full-offset transient sounding method described in the method of the present invention provides construction convenience for determining signal strength and avoiding ground obstacles.

[0018] 2) Between the two horizontal electric dipole source sounding methods in the time domain and frequency domain, it provides more choices and flexibility for using transient or frequency sounding according to needs.

[0019] 3) The horizontal electric dipole source full-offset transient sounding method described in the present invention is not affected by the field source copy effect and shadow effect, which facilitates data interpretation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Bipolar pulse emission waveform and observation time window.

[0021] Figure 2 The observation area of ​​horizontal electric dipole source full-offset transient sounding is as follows: Figure 2 a is and Observation area, Figure 2 b is Observation area, Figure 2 c is Observation area.

[0022] Figure 3 Observation and Installation diagram.

[0023] In the figure: 1 emission current of bipolar waveform; 2 observation time window of emission current off gap; 3 electric dipole source; 4 and Observation area; 5 Observation area; 6 Observation area; 7 Serving size: 8 Component; 9 offset; 10 observation point No.i. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] The horizontal electric dipole source full-offset transient electromagnetic sounding method proposed in the present invention specifically includes the following steps:

[0026] The secondary field is observed in the interval between the bipolar emission pulses being turned off ( Figure 1 ), horizontal positions of early, middle, and late recording sites All are at the observation point, recording the vertical position of the point All are at the diffusion depth below the observation point.

[0027] The apparent resistivity is calculated using the universal expression of each field quantity, and the diffusion depth is obtained based on the apparent resistivity, so that transient sounding can be achieved at all offsets in an area that does not include the electric dipole source and its neighborhood, where the signal is stable, the receiver range allows, and the signal-to-noise ratio meets the requirements.

[0028] The apparent resistivity is defined by the following universal expressions for all field quantities:

[0029]

[0030]

[0031] Where, yes The electric field strength component, yes The electric field strength component, yes Magnetic field strength component, yes Magnetic field strength component, yes directional magnetic field intensity component, i=1,2,…,m is the observation point number, j=1,2,…,n is the time window number; r i is the offset, is the apparent resistivity, t i,j is the observation time window, μ0=4π×10 -7 H / m is the magnetic permeability of the non-magnetic earth, the electric dipole moment p=idl, where i is the source current, dl is the length of the magnetic pole, is the offset distance r i The angle between the electric dipole moment and the θ is 0; erf is the error function, I0 and I1 are the 0th and 1st order modified Bessel functions of the first kind, respectively.

[0032] The apparent resistivity is calculated from the full-period definition equations (1) and (2) by an iterative algorithm, such as the binary search method.

[0033] The apparent resistivity-depth profile, one of the basic maps for data interpretation, can be generated using conventional methods.

[0034] During exploration, there is no need to consider the influence of field source copy effect and shadow effect.

[0035] The following is further explained with reference to specific examples:

[0036] In actual exploration, rectangular coordinates are often used. According to the relationship between cylindrical coordinates and rectangular coordinates, equations (1) and (2) can be rewritten as follows:

[0037]

[0038]

[0039] The observation area of ​​each field component in equations (3) and (4) is as follows: Figure 2 As shown in (a), (b) and (c) in Figure 1, all offsets are available within the observation area as long as the receiver range allows and the signal-to-noise ratio is met.

[0040] Assume that on a uniform ground with a resistivity of 100Ω·m, at an offset distance of r i Observation point No.i and Quantity, such as Figure 3 As shown, the device shown in the figure Substituting equations (3a) and (4c) into the equations, we have

[0041]

[0042] In the formula and The values ​​are in column 3 of Table 1 and column 3 of Table 2.

[0043] The apparent resistivity of the entire area is calculated by the above formula (5) and formula (6) using the dichotomy method. The interval value, if electrical logging or other data are available, is given by the maximum and minimum values ​​of the formation resistivity in the work area; if it cannot be determined, a larger range can be given, such as 0.1Ω·m to 10000Ω·m. In this embodiment, the earth resistivity is known (100Ω·m), and the value range is 50Ω·m to 150Ω·m. After successful calculation, the obtained value is the apparent resistivity of the entire period. As shown in column 4 of Table 1 and column 4 of Table 2.

[0044] The exploration depth can be used to determine the apparent resistivity of the entire period Substitute the diffusion depth formula to calculate

[0045]

[0046] As shown in column 5 of Table 1 and Table 2.

[0047] Horizontal positions of early, middle, and late recording sites They are all at the observation point, so there is no need to divide them into stages. The vertical position of the recording point All are at the exploration depth below the observation point (see columns 5, 6, and 7 of Tables 1 and 2):

[0048]

[0049] As such, the apparent resistivity-depth profile, one of the fundamental data interpretation maps, can be generated using conventional methods. The data obtained from exploration reflects the geological structure beneath the observation point and is unaffected by source copying and shadowing effects.

[0050] Table 1 Transient sounding of horizontal electric dipole source Component and total apparent resistivity (observation point No.i, offset distance r i = 1000m, earth resistivity 100Ω.m, electric dipole moment p = 1.)

[0051]

[0052] Table 2 Transient sounding of horizontal electric dipole source Component and total period apparent resistivity|(Observation point No.i, offset distance r i = 1000m, earth resistivity 100Ω.m, electric dipole moment p = 1.)

[0053]

[0054] The above embodiments are intended only to illustrate the design concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. The scope of protection of the present invention is not limited to the above embodiments. Therefore, any equivalent changes or modifications made based on the principles and design concepts disclosed in the present invention are within the scope of protection of the present invention.

Claims

1. The horizontal electric dipole source full-offset transient sounding method is characterized by: Observe the secondary field during the interval between bipolar emission pulses, and observe the horizontal positions of the early, middle, and late recording points. All are at the observation point, recording the vertical position of the point All are located in the exploration area below the observation point; The apparent resistivity is calculated using the universal expression of each field quantity throughout the entire period, and the diffusion depth is obtained based on the apparent resistivity. This allows transient sounding to be achieved at all offsets in an area that does not include the electric dipole source and its vicinity, where the signal is stable, the receiver range allows, and the signal-to-noise ratio meets the requirements.

2. The horizontal electric dipole source full-offset transient sounding method according to claim 1, characterized in that: The apparent resistivity is defined by the following universal expressions for all field quantities: Where, yes The electric field strength component, yes The electric field strength component, yes Magnetic field strength component, yes Magnetic field strength component, yes directional magnetic field intensity component, i=1,2,…,m is the observation point number, j=1,2,…,n is the time window number; r i is the offset, is the apparent resistivity, t i,j is the observation time window, μ0 is the magnetic permeability of the non-magnetic earth, p is the electric dipole moment, is the offset distance r i The angle between the electric dipole moment and the θ is 0; erf is the error function, I0 and I1 are the 0th and 1st order modified Bessel functions of the first kind, respectively.

3. The horizontal electric dipole source full-offset transient sounding method according to claim 2, characterized in that: The apparent resistivity is calculated by the full-period definition formulas (1a), (1b) and (2a), (2b), (2c) through an iterative algorithm.

4. The horizontal electric dipole source full-offset transient sounding method according to claim 1, characterized in that: The iterative algorithm includes but is not limited to a binary search method.

5. The horizontal electric dipole source full-offset transient sounding method according to claim 1, characterized in that: Substitute the apparent resistivity into the diffusion depth formula to calculate the exploration depth.

6. The horizontal electric dipole source full-offset transient sounding method according to claim 1, characterized in that: The apparent resistivity-depth profile, one of the basic maps for data interpretation, is generated using conventional methods.

7. The horizontal electric dipole source full-offset transient sounding method according to claim 1, characterized in that: The data obtained from exploration is a reflection of the geological structure below the observation point and is not affected by the source copy effect and shadow effect.

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