Transient electromagnetic global apparent resistivity definition method based on differential pulse

Abstract

The invention discloses a transient electromagnetic global apparent resistivity definition method based on differential pulses, and relates to the technical field of artificial source electromagnetic detection, and the method comprises a transient electromagnetic field response calculation method based on a step wave emission waveform, and an electromagnetic forward modeling method for obtaining the differential pulses by adopting a time shift method. Based on a differential pulse transient electromagnetic forward modeling method, electromagnetic fields under different pulse widths, different flight heights and different offsets are calculated, and curve characteristics of the electromagnetic fields changing along with resistivity are analyzed; selecting a target electromagnetic field component, and adopting an inverse function theorem to obtain a global apparent resistivity iteration expression based on a differential pulse emission waveform; according to the transient electromagnetic global apparent resistivity defining method, the global apparent resistivity of multiple pulse width differential pulses is calculated through a global apparent resistivity iteration expression, underground comprehensive electrical characteristics are obtained through a correlation superposition algorithm, and the transient electromagnetic data interpretation capacity is improved through the transient electromagnetic global apparent resistivity defining method.

Description

Technical Field

[0001] The invention relates to the technical field of artificial source electromagnetic detection, in particular to a method for defining transient electromagnetic global apparent resistivity based on differential pulses. Background Art

[0002] Transient electromagnetic method is a geophysical exploration method based on the principle of electromagnetic wave propagation. It is widely used in the field of underground detection, including traditional mineral resource exploration, water resource investigation, geological structure and engineering exploration, deep earth detection and energy development, etc. In addition, it has demonstrated its unique advantages in emerging fields such as environmental protection and disaster monitoring. With the continuous development of technology, the application scenarios and accuracy of transient electromagnetic method are constantly expanding, providing strong support for the detection of various underground resources and environments.

[0003] In transient electromagnetic forward modeling and field work, trapezoidal waves or square waves are often used as transmitting waveforms. However, the frequency band of such transmitting waveforms is relatively wide, and the detection effect is greatly affected by low-frequency harmonics. The radiation capability of differential pulses is mainly concentrated near the main frequency, and has a stronger resolution capability.

[0004] Therefore, a method for defining the global apparent resistivity of transient electromagnetic based on differential pulses is urgently needed to improve the electromagnetic data interpretation problem. Summary of the invention

[0005] To solve the above problems, the present application provides a method for defining the global apparent resistivity of transient electromagnetic based on differential pulses, which has a higher resolution than the traditional resistivity imaging of emission waveforms. Under the condition that the emission waveform is a differential pulse, the apparent resistivity of different pulse widths is first calculated, and then the correlation analysis of the apparent resistivity of different pulse widths is performed. Finally, the resistivity of different pulse widths is superimposed using a superposition algorithm, and finally all the electrical information of the underground can be obtained, achieving the purpose of accurate and rapid interpretation of transient electromagnetic data.

[0006] The method for defining the transient electromagnetic global apparent resistivity mentioned in this application includes the following steps:

[0007] S1. A transient electromagnetic field response calculation method based on a step wave emission waveform, and an electromagnetic forward modeling method for differential pulses using a time shift method;

[0008] S2. Based on the differential pulse transient electromagnetic forward modeling method, the electromagnetic field under different pulse widths, different flight altitudes and different offset distances is calculated, and the curve characteristics of the electromagnetic field changing with resistivity are analyzed;

[0009] S3. Select the target electromagnetic field component according to the curve characteristics of the electromagnetic field changing with resistivity, and use the inverse function theorem to obtain the iterative expression of the global apparent resistivity based on the differential pulse emission waveform;

[0010] S4. The global apparent resistivity of multiple pulse width differential pulses is calculated through the iterative expression of the global apparent resistivity, and the correlation superposition algorithm is used to obtain the comprehensive electrical characteristics of the underground.

[0011] Preferably, in S1, based on the transient electromagnetic field response of the step wave emission waveform, the specific content of the electromagnetic field response of the differential pulse obtained by the time shift method is:

[0012] Based on the transient electromagnetic forward modeling method of step wave, according to the composition relationship between step wave and differential pulse, the transient electromagnetic field response of differential pulse emission waveform is obtained by using the time shift addition and subtraction strategy;

[0013] Among them, the expression of transient electromagnetic field response of differential pulse emission waveform is obtained by using time shift phase addition and subtraction strategy:

[0014] B(t)=[B2(t)-B1(t)]+[B4(t)-B3(t)]

[0015] =[B0(t-t1)-B0(t)]+[-B0(t-t2)-(-B0(t-t1))]

[0016] =2B0(t-t1)-B0(t)-B0(t-t2);

[0017] Among them, B0(t) represents the magnetic induction intensity corresponding to the step wave, B(t) represents the magnetic induction intensity corresponding to the differential pulse, B1(t), B2(t), and B3(t) represent the electromagnetic field responses of the step wave at three different moments respectively; t represents time, and t1 and t2 represent two different moments respectively.

[0018] Preferably, the specific content of S2 is:

[0019] Set up a uniform half-space model and set uniform half-space model parameters;

[0020] Select three different measuring points and calculate the three components of magnetic induction intensity, namely the horizontal component B, according to the uniform half-space model x , horizontal component B y , vertical component B z ;

[0021] The parameters of the uniform half-space model include: source length, coordinates of two end points, emission current, and pulse width of the differential pulse.

[0022] Preferably, in S3, the target electromagnetic field component is selected according to the curve characteristics of the electromagnetic field changing with resistivity, and the inverse function theorem is used to obtain the specific content of the iterative expression of the global apparent resistivity based on the differential pulse emission waveform:

[0023] Among them, the vertical component of magnetic induction intensity is expressed as Bz (ρ, C, t), where ρ represents the apparent resistivity parameter, C represents the coordinates of the measuring point, and t represents the time;

[0024] Use a value in the middle of the resistivity range as the initial value, and The neighborhood of B z By performing Taylor expansion on (ρ, C, t), we can get the first Taylor expansion;

[0025] The linear main part of the first Taylor expansion is retained and rewritten to obtain the iterative definition of the global apparent resistivity.

[0026] Preferably, the expression of the first Taylor expansion is:

[0027]

[0028] Preferably, the iterative expression for defining the global apparent resistivity is:

[0029]

[0030] in,

[0031] Preferably, the iteration termination condition of the global apparent resistivity definition iteration is:

[0032]

[0033] Among them, ε represents the pre-given termination error limit, B z (ρ,C,t) represents the vertical component of magnetic induction intensity obtained by transient electromagnetic forward modeling or field acquisition, The resistivity at time t is The vertical component of the magnetic induction intensity calculated under uniform half-space conditions.

[0034] Preferably, in S4, according to the characteristic that a differential pulse with a specific pulse width can reflect geological information at a specific depth, a scanning detection is performed by emitting a series of differential pulses with different pulse widths, and the global apparent resistivity is defined respectively, so that resistivity imaging results of geological bodies at different depths underground can be obtained;

[0035] The correlation analysis of apparent resistivity results of different pulse widths is carried out, and the superposition algorithm is used to achieve multi-resolution imaging of the electrical characteristics of transient electromagnetic data.

[0036] In summary, compared with the traditional technology, the method for defining the global apparent resistivity of transient electromagnetic based on differential pulse of the present invention first calculates the apparent resistivity of different pulse widths under the condition that the transmitting waveform is a differential pulse, then performs correlation analysis on the apparent resistivity of different pulse widths, and finally uses the superposition algorithm to superimpose the resistivity of different pulse widths, and finally obtains all the electrical information of the underground, realizes the purpose of accurate and rapid interpretation of transient electromagnetic data, and achieves the effect of high resolution of transmitting waveform resistivity imaging.

[0037] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The present invention contains a three-dimensional model of three low-resistance blocks underground;

[0039] Figure 2 The apparent resistivity results of the multi-pulse width differential pulse and the related superposition of the model containing three low-resistance blocks of the present invention;

[0040] Figure 3 A flow chart of a method for defining global apparent resistivity of transient electromagnetic based on differential pulses of the present invention;

[0041] Figure 4 Schematic diagram of the differential pulse composed of step waves of the present invention;

[0042] Figure 5 Curves of the three components of magnetic induction intensity at different positions changing with resistivity when the pulse width of the present invention is 1 ms: (a)-(c) The receiving point coordinates are (30m, 40m, 10m); (d)-(f) The receiving point coordinates are (300m, 400m, 10m); (g)-(i) The receiving point coordinates are (30m, 40m, 60m);

[0043] Figure 6 Curves of the three components of magnetic induction intensity at different positions changing with resistivity when the pulse width of the present invention is 5 ms: (a)-(c) The receiving point coordinates are (30 m, 40 m, 10 m); (d)-(f) The receiving point coordinates are (300 m, 400 m, 10 m); (g)-(i) The receiving point coordinates are (30 m, 40 m, 60 m);

[0044] Figure 7 Curves of the three components of magnetic induction intensity at different positions changing with resistivity when the pulse width of the present invention is 10 ms: (a)-(c) The receiving point coordinates are (30 m, 40 m, 10 m); (d)-(f) The receiving point coordinates are (300 m, 400 m, 10 m); (g)-(i) The receiving point coordinates are (30 m, 40 m, 60 m);

[0045] Figure 8The present invention discloses a flow chart of a transient electromagnetic full-domain apparent resistivity multi-resolution imaging process based on differential pulses. DETAILED DESCRIPTION

[0046] The technical solution of the present invention is further described below by means of the accompanying drawings and embodiments. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​described in these embodiments do not limit the scope of the present application.

[0047] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or uses.

[0048] Technologies, systems, and devices known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, systems, and devices should be considered part of the specification.

[0049] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0050] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0051] like Figure 1 As shown, this embodiment adopts a three-dimensional model containing three low-resistance blocks underground. The model parameters are as follows: the resistivity of the uniform half space is 100Ω·m; the burial depths of the three abnormal bodies underground are 30m, 100m and 180m, the resistivities are 3Ω·m, 2Ω·m and 1Ω·m, and the geometric dimensions are 40m×40m×10m, 80m×80m×10m and 120m×120m×10m, respectively. The transmitting source is an electrical source with a length of 1000m, and the coordinates of the two end points are (-500m, -100m, 0m) and (500m, -100m, 0m); the transmitting current waveform is a differential pulse, and the pulse width is set to 100μs, 600μs, 1ms, 2.5ms and 4ms respectively; the receiving point is located in the air, and the coordinates of the two end points of the measuring point are (-200m, 0m, -30m) and (200m, 0m, -30m), and the point distance is 10m.

[0052] Figure 2The global apparent resistivity imaging diagrams of three low-resistance block models after differential pulses with different pulse widths and related superposition are shown, where Figures ae and f show the global apparent resistivity definition results with pulse widths of 100μs, 600μs, 1ms, 2.5ms and 4ms, respectively, and Figure f shows the imaging results after superposition of the apparent resistivities of the five pulse widths. It can be seen from the figure that the narrow pulse width reflects the electrical characteristics of the shallow low-resistance block, while the wide pulse width reflects the electrical characteristics of the deep low-resistance block; the resistivity information of the three underground blocks can be obtained by superimposing the apparent resistivity results of the five different pulse widths. Therefore, the differential pulse emission waveform has a strong differentiation ability, and the global apparent resistivity definition with multiple pulse widths can realize multi-resolution imaging of underground resistivity.

[0053] like Figure 3 As shown, the method for defining the transient electromagnetic global apparent resistivity mentioned in this application includes the following steps:

[0054] S1. A transient electromagnetic field response calculation method based on a step wave emission waveform, and an electromagnetic forward modeling method for differential pulses using a time shift method;

[0055] Furthermore, the transient electromagnetic forward modeling method based on the step wave emission waveform in S1 uses the time shift method to obtain the specific content of the electromagnetic field response of the differential pulse:

[0056] like Figure 4 As shown, the transient electromagnetic forward modeling method based on the step wave, according to the composition relationship between the step wave and the differential pulse, uses the time shift addition and subtraction strategy to obtain the transient electromagnetic field response of the differential pulse emission waveform;

[0057] Among them, the expression of transient electromagnetic field response of differential pulse emission waveform is obtained by using time shift phase addition and subtraction strategy:

[0058] B(t)=[B2(t)-B1(t)]+[B4(t)-B3(t)]

[0059] =[B0(t-t1)-B0(t)]+[-B0(t-t2)-(-B0(t-t1))]

[0060] =2B0(t-t1)-B0(t)-B0(t-t2);

[0061] Among them, B0(t) represents the magnetic induction intensity corresponding to the step wave, B(t) represents the magnetic induction intensity corresponding to the differential pulse, B1(t), B2(t), and B3(t) represent the electromagnetic field responses of the step wave at three different moments respectively; t represents time, and t1 and t2 represent two different moments respectively.

[0062] S2. Based on the differential pulse transient electromagnetic forward modeling method, the electromagnetic field under different pulse widths, different flight altitudes and different offset distances is calculated, and the curve characteristics of the electromagnetic field changing with resistivity are analyzed;

[0063] Furthermore, the specific content of S2 is:

[0064] Set up a uniform half-space model and set uniform half-space model parameters;

[0065] Select three different measuring points and calculate the three components of magnetic induction intensity, namely the horizontal component B, according to the uniform half-space model x , horizontal component B y , vertical component B z ;

[0066] The parameters of the uniform half-space model include: source length, coordinates of two end points, emission current, and pulse width of the differential pulse.

[0067] Set up a uniform half-space model with the following parameters: source length 1000m, coordinates of the two end points are (0m,-500m,0m) and (0m,500m,0m), emission current is 10A, pulse width of differential pulse is set to 1ms, 5ms and 10ms, three different measuring points are selected with coordinates of (30m,40m,10m), (300m,400m,10m) and (30m,40m,60m), and calculate the three components of magnetic induction intensity B x , B y , B z The calculation results are as follows Figure 5-Figure 7 shown.

[0068] By Figure 5-Figure 7 It can be seen that when the flight altitude remains unchanged and the horizontal offset increases, the extreme point moves toward the high resistivity direction; when the horizontal offset remains unchanged and the flight altitude increases, B x and B z The curve shape of B has almost no obvious change, while y The curve shape changes greatly; in general, the curve shape of the three components of magnetic induction intensity changing with formation resistivity is relatively simple and suitable for calculating the global apparent resistivity.

[0069] S3. Select the target electromagnetic field component according to the curve characteristics of the electromagnetic field changing with resistivity, and use the inverse function theorem to obtain the iterative expression of the global apparent resistivity based on the differential pulse emission waveform;

[0070] Furthermore, in S3, the target electromagnetic field component is selected according to the curve characteristics of the electromagnetic field changing with resistivity, and the inverse function theorem is used to obtain the specific content of the iterative expression of the global apparent resistivity based on the differential pulse emission waveform:

[0071] Among them, the vertical component of magnetic induction intensity is expressed as B z (ρ, C, t), where ρ represents the apparent resistivity parameter, C represents the coordinates of the measuring point, and t represents the time;

[0072] Use a value in the middle of the resistivity range as the initial value, and The neighborhood of B z By performing Taylor expansion on (ρ, C, t), we can get the first Taylor expansion;

[0073] Furthermore, the expression of the first Taylor expansion is:

[0074]

[0075] The linear main part of the first Taylor expansion is retained and rewritten to obtain the iterative definition of the global apparent resistivity.

[0076] Keeping the linear principal part of the first Taylor expansion, we get:

[0077]

[0078] Furthermore, the iterative expression of the global apparent resistivity definition is:

[0079]

[0080] in,

[0081] The iterative form of the global apparent resistivity definition is expressed as:

[0082]

[0083] Furthermore, the iterative termination condition of the global apparent resistivity definition is:

[0084]

[0085] Among them, ε represents the pre-given termination error limit, B z (ρ,C,t) represents the vertical component of the magnetic induction intensity obtained by transient electromagnetic field forward modeling or field collection. The resistivity at time t is The vertical component of the magnetic induction intensity calculated under uniform half-space conditions.

[0086] S4. The global apparent resistivity of multiple pulse width differential pulses is calculated through the iterative expression of the global apparent resistivity, and the correlation superposition algorithm is used to obtain the comprehensive electrical characteristics of the underground.

[0087] like Figure 8As shown, in S4, according to the characteristic that a differential pulse with a specific pulse width can reflect geological information at a specific depth, a series of differential pulses with different pulse widths are emitted for scanning detection, and the global apparent resistivity is defined respectively, so that resistivity imaging results of geological bodies at different depths underground can be obtained;

[0088] The correlation analysis of apparent resistivity results of different pulse widths is carried out, and the superposition algorithm is used to achieve multi-resolution imaging of the electrical characteristics of transient electromagnetic data.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for defining global apparent resistivity of transient electromagnetic based on differential pulse, characterized in that: The following steps are involved: S1. A transient electromagnetic field response calculation method based on a step wave emission waveform, and an electromagnetic forward modeling method for differential pulses using a time shift method; S2. Based on the differential pulse transient electromagnetic forward modeling method, the electromagnetic field under different pulse widths, different flight altitudes and different offset distances is calculated, and the curve characteristics of the electromagnetic field changing with resistivity are analyzed; S3. Select the target electromagnetic field component according to the curve characteristics of the electromagnetic field changing with resistivity, and use the inverse function theorem to obtain the iterative expression of the global apparent resistivity based on the differential pulse emission waveform; S4. The global apparent resistivity of multiple pulse width differential pulses is calculated through the iterative expression of the global apparent resistivity, and the correlation superposition algorithm is used to obtain the comprehensive electrical characteristics of the underground.

2. The method for defining global apparent resistivity of transient electromagnetic based on differential pulse according to claim 1 is characterized in that: In S1, based on the transient electromagnetic field response of the step wave emission waveform, the specific content of the electromagnetic field response of the differential pulse obtained by the time shift method is: Based on the transient electromagnetic forward modeling method of step wave, according to the composition relationship between step wave and differential pulse, the transient electromagnetic field response of differential pulse emission waveform is obtained by using the time shift addition and subtraction strategy; Among them, the expression of transient electromagnetic field response of differential pulse emission waveform is obtained by using time shift phase addition and subtraction strategy: B(t)=[B2(t)-B1(t)]+[B4(t)-B3(t)] =[B0(t-t1)-B0(t)]+[-B0(t-t2)-(-B0(t-t1))] =2B0(t-t1)-B0(t)-B0(t-t2); Among them, B0(t) represents the magnetic induction intensity corresponding to the step wave, B(t) represents the magnetic induction intensity corresponding to the differential pulse, B1(t), B2(t), and B3(t) represent the electromagnetic field responses of the step wave at three different moments respectively; t represents time, and t1 and t2 represent two different moments respectively.

3. The method for defining global apparent resistivity of transient electromagnetic based on differential pulse according to claim 2 is characterized in that: The specific contents of S2 are: Set up a uniform half-space model and set uniform half-space model parameters; Select three different measuring points and calculate the three components of magnetic induction intensity, namely the horizontal component B, according to the uniform half-space model x , horizontal component B y , vertical component B z ; in The parameters of the uniform half-space model include: source length, coordinates of two end points, emission current, and pulse width of the differential pulse.

4. The method for defining global apparent resistivity of transient electromagnetic based on differential pulse according to claim 3 is characterized in that: In S3, the target electromagnetic field component is selected according to the curve characteristics of the electromagnetic field changing with resistivity, and the inverse function theorem is used to obtain the specific content of the iterative expression of the global apparent resistivity based on the differential pulse emission waveform: Among them, the vertical component of magnetic induction intensity is expressed as B z (ρ, C, t), where ρ represents the apparent resistivity parameter, C represents the coordinates of the measuring point, and t represents the time; Use a value in the middle of the resistivity range as the initial value, and The neighborhood of B z By performing Taylor expansion on (ρ, C, t), we can get the first Taylor expansion; The linear main part of the first Taylor expansion is retained and rewritten to obtain the iterative definition of the global apparent resistivity.

5. The method for defining global apparent resistivity of transient electromagnetic based on differential pulse according to claim 4 is characterized in that: The expression of the first Taylor expansion is:

6. The method for defining global apparent resistivity of transient electromagnetic based on differential pulse according to claim 5 is characterized in that: The iterative expression for the global apparent resistivity definition is: in, 7. The method for defining global apparent resistivity of transient electromagnetic based on differential pulse according to claim 6 is characterized in that: The iterative termination condition of the global apparent resistivity definition is: Among them, ε represents the pre-given termination error limit, B z (ρ,C,t) represents the vertical component of the magnetic induction intensity obtained by transient electromagnetic field forward modeling or field collection. The resistivity at time t is The vertical component of the magnetic induction intensity calculated under uniform half-space conditions.

8. The method for defining global apparent resistivity of transient electromagnetic based on differential pulse according to claim 7 is characterized in that: In S4, according to the characteristic that differential pulses with specific pulse widths can reflect geological information at a specific depth, a series of differential pulses with different pulse widths are emitted for scanning detection, and the global apparent resistivity is defined respectively, so that resistivity imaging results of geological bodies at different depths underground can be obtained; The correlation analysis of apparent resistivity results of different pulse widths is carried out, and the superposition algorithm is used to achieve multi-resolution imaging of the electrical characteristics of transient electromagnetic data.

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