Controllable source electromagnetic apparent parameter extraction method and system based on optimization algorithm

Abstract

The application discloses a controllable source electromagnetic apparent parameter extraction method and system based on an optimization algorithm, and the method comprises the following steps: obtaining the first apparent parameter of the highest frequency of the controllable source electromagnetic; wherein the first apparent parameter is the apparent resistivity or the apparent magnetic conductivity, and the other is the second apparent parameter; fixing the first apparent parameter of the highest frequency, taking each electromagnetic field component measured at the highest frequency as the observation, adopting the uniform half-space formula considering the influence of underground resistivity and magnetic conductivity and the optimization algorithm to calculate the second apparent parameter at the highest frequency; in the order from high to low frequency, taking the two apparent parameters of the previous frequency point as the initial value of the next frequency point in turn, and taking each electromagnetic field component measured at the next frequency point as the observation, adopting the uniform half-space formula considering the influence of underground resistivity and magnetic conductivity and the optimization algorithm to calculate the two apparent parameters at the next frequency point. The application can efficiently and accurately extract the apparent resistivity and apparent magnetic conductivity parameters.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of controllable source electromagnetic, and particularly relates to a controllable source electromagnetic apparent parameter extraction method and system based on an optimization algorithm. BACKGROUND

[0002] The frequency domain controllable source electromagnetic (CSEM) method is one of important means for mineral resource exploration. The method can increase signal strength by increasing transmission power or field source size, can flexibly adjust device form according to the detection target, has the advantages of strong resolution, large exploration depth, wide observation range, high work efficiency, strong adaptability and the like, is widely applied to resource investigation of oil and gas, geothermal, shale gas, metal mine and the like, and plays an important role in deep earth resource exploration. Stable and reliable apparent parameter extraction technology (for example, apparent resistivity) can provide a qualitative description for the geological profile of the work area, and can provide important guidance for field data acquisition and data processing.

[0003] The prior art mainly focuses on the following aspects:

[0004] (1) Extracting apparent resistivity parameters through electric field and magnetic field components. In the early stage of the development of the controllable source electromagnetic method, the Cagniard apparent resistivity was introduced from the magnetotelluric method to obtain the relevant sounding curve, but it is based on the plane wave assumption, and the apparent resistivity results in the “near zone” cannot reflect the true underground structure. With the improvement of electromagnetic method theory, the wide-area apparent resistivity directly extracted from the electric field or magnetic field well avoids this phenomenon, greatly improves the efficiency of CSEM field exploration, and achieves good application effect.

[0005] (2) Extracting apparent resistivity from wave number. In order to further study the sounding performance of the electromagnetic field in the “near zone”, another scheme is to extract the apparent resistivity parameter from the “wave number”, that is, the wave number apparent resistivity. It first calculates the “wave number” through the electromagnetic field, and then extracts the apparent resistivity parameter in the wave number, and the sounding effect is also good.

[0006] Although the existing method technology has made important progress in the extraction of frequency domain CSEM apparent parameters, the current fine geological exploration puts forward higher requirements for the frequency domain controllable source electromagnetic exploration technology, and the complex geological scene puts forward greater challenges to the existing technical means. The current technology still has the following main defects and deficiencies:

[0007] (1) The influence of magnetic permeability parameter on CSEM response is not clarified. At present, it is generally believed in CSEM detection that the earth medium does not contain magnetism, that is, only the apparent resistivity parameter is extracted through the electromagnetic field data. But the magnetic parameters of actual rock and ore also have important influence on the electromagnetic response characteristics.

[0008] (2) cannot simultaneously extract apparent conductivity parameters and apparent magnetic conductivity parameters. At present, the extraction of apparent resistivity parameters is usually based on the uniform half-space formula. Since the formula is relatively simple, the apparent resistivity parameters can be obtained by using the dichotomy method or the iterative solution method. However, when the resistivity and magnetic conductivity parameters are considered simultaneously, the electromagnetic field formula becomes more complex and has multiple solutions, and the existing technical means cannot simultaneously extract the two apparent parameters. SUMMARY

[0009] The application provides a controllable source electromagnetic apparent parameter extraction method and system based on an optimization algorithm, which can efficiently and accurately extract apparent resistivity and apparent magnetic conductivity parameters, and significantly improve the application accuracy and reliability of electromagnetic sounding curves under complex geological conditions.

[0010] To achieve the above technical purposes, the application adopts the following technical solutions:

[0011] A controllable source electromagnetic apparent parameter extraction method based on an optimization algorithm, comprising:

[0012] Step 1: obtaining a first apparent parameter of the highest frequency of the controllable source electromagnetic; wherein the first apparent parameter is the apparent resistivity or the apparent magnetic conductivity, and the other is the second apparent parameter;

[0013] Step 2: fixing the first apparent parameter of the highest frequency, and based on the measured electromagnetic field components of the highest frequency as the observation, using the uniform half-space formula considering the influence of underground resistivity and magnetic conductivity and the optimization algorithm, calculating the second apparent parameter of the highest frequency;

[0014] Step 3: in the order from high to low frequency, sequentially taking the two apparent parameters of the previous frequency point as the initial value of the next frequency point, and based on the measured electromagnetic field components of the next frequency point as the observation, using the uniform half-space formula considering the influence of underground resistivity and magnetic conductivity and the optimization algorithm, calculating the two apparent parameters of the next frequency point.

[0015] Further, if the first apparent parameter is the apparent resistivity, the measured shallow resistivity is regarded as the apparent resistivity of the highest frequency.

[0016] Further, if the first apparent parameter is the apparent resistivity, the magnetic conductivity is constant as the vacuum magnetic conductivity, the measured vertical magnetic field component of the highest frequency is used to calculate the apparent resistivity of the highest frequency by using the uniform half-space formula.

[0017] Further, if the first apparent parameter is the apparent magnetic conductivity, the measured shallow magnetic conductivity is regarded as the apparent magnetic conductivity of the highest frequency.

[0018] Further, the objective function of the optimization algorithm used for calculating the apparent parameter of any frequency point is:

[0019] ;

[0020] wherein, represents the objective function; is the apparent parameter vector, including apparent resistivity and apparent permeability; is the measured electromagnetic field data, is the forward calculated electromagnetic field data; is a diagonal matrix, whose diagonal elements are the inverse of , used to normalize the data fitting difference; is the initial value of the apparent parameter vector; is the weight coefficient; is the Lagrange multiplier.

[0021] Further, the objective function is minimized using the Ocham optimization algorithm, and the iterative update formula of the apparent parameter vector at the k+1th iteration is:

[0022] ;

[0023] ;

[0024] wherein, is the apparent parameter vector obtained at the kth iteration; is the apparent resistivity parameter and apparent permeability parameter at the kth iteration, and I is the unit matrix, is an intermediate temporary vector for easy calculation.

[0025] Further, the uniform half-space formula considering the influence of underground resistivity and permeability is calculated as follows:

[0026] ;

[0027] ;

[0028] ;

[0029] ;

[0030] ;

[0031] ;

[0032] wherein, is the wave number, satisfying , is the dielectric constant, is the circular frequency of the harmonic current; σ is the conductivity, and the resistivity is the reciprocal of each other; is the medium permeability; relative permeability of the subsurface medium, permeability of the subsurface half-space; first kind first order Bessel function; vertical wavenumber, containing attenuation and phase information; 、 、 、 the subscript 1 in the formula represents a subsurface parameter, 、 、 、 the subscript 0 in the formula represents an air parameter; is the included angle of the receiving point relative to the direction of the dipole; is the distance from the receiving point to the center of the dipole source; is the current intensity of the dipole source, is the length of the transmitting dipole; in the formula, z is the vertical distance of the receiving point relative to the transmitting source, that is, the depth coordinate of the receiving point; respectively, are the radial, normal and vertical components of the uniform half-space electric field considering the influence of the subsurface resistivity and permeability, respectively, are the radial, normal and vertical components of the uniform half-space magnetic field considering the influence of the subsurface resistivity and permeability;

[0033] In the cylindrical coordinate system and the rectangular coordinate system, the horizontal electric field and magnetic field component relationship is:

[0034] ;

[0035] In the formula, and respectively, are the electric field components in the x-axis and y-axis directions of the rectangular coordinate system, and respectively, are the magnetic field components in the x-axis and y-axis directions of the rectangular coordinate system.

[0036] A controllable source electromagnetic apparent parameter extraction system based on an optimization algorithm, comprising an initial apparent parameter acquisition module and an apparent parameter iteration acquisition module;

[0037] The initial apparent parameter acquisition module is used to acquire two kinds of apparent parameters of the highest frequency of the controllable source electromagnetic;

[0038] The first kind of apparent parameter is the apparent resistivity or the apparent permeability, and the other kind is the second kind of apparent parameter; the acquisition method of the second kind of apparent parameter is: after the first kind of apparent parameter of the highest frequency is acquired, the first kind of apparent parameter of the highest frequency is fixed, and then based on the measured each electromagnetic field component of the highest frequency as an observation, the uniform half-space formula considering the influence of the subsurface resistivity and permeability is used to calculate the second kind of apparent parameter of the highest frequency;

[0039] The visual parameter iterative acquisition module is used for: in the order from high to low of frequency, taking the two visual parameters of a previous frequency point as initial values of the next frequency point in sequence, and taking the measured electromagnetic field components of the next frequency point as observations, using the uniform half-space formula considering the influence of underground resistivity and magnetic permeability and the optimization algorithm to calculate the two visual parameters of the next frequency point.

[0040] Further, if the first visual parameter is visual magnetic permeability, the magnetic permeability of the shallow ground is measured to be the highest frequency visual magnetic permeability.

[0041] If the first visual parameter is visual resistivity, the following any method is used to obtain:

[0042] (1) The resistivity of the shallow ground is measured to be the highest frequency visual resistivity.

[0043] (2) The magnetic permeability is constant as the vacuum magnetic permeability, the vertical magnetic field component of the highest frequency is measured, and the uniform half-space formula is used to calculate the highest frequency visual resistivity.

[0044] Further, the following objective function is minimized using the Ockham optimization algorithm to calculate the second visual parameter of the highest frequency in step 2, and to calculate the two visual parameters of the next frequency point in step 3:

[0045] ;

[0046] In the formula, The target function is represented by the target function. The visual parameter vector includes visual resistivity and visual magnetic permeability. The measured electromagnetic field data is The forward electromagnetic field data is The diagonal matrix is diagonal, and the diagonal elements are The inverse of the reciprocal is used to normalize the data fitting difference. The initial value of the visual parameter vector is The weight coefficient is The Lagrange multiplier is

[0047] Compared with the prior art, the beneficial effects of the present application are:

[0048] When considering the resistivity and permeability parameters simultaneously, the electromagnetic field formula becomes more complex and has multiple solutions, and the prior art is difficult to extract both of the two apparent parameters simultaneously. The present application obtains the high-frequency apparent resistivity and apparent permeability through the magnetic field vertical component data based on the uniqueness of the influence of permeability on the vertical magnetic field Hz measurement data, or obtains the highest frequency of any apparent parameter based on the relationship between the high-frequency data and the surface geology structure, and then uses the optimization algorithm to extract the two apparent parameters at all frequency points, which significantly improves the application accuracy and reliability of the electromagnetic sounding curve under complex geological conditions. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 is the influence of different relative permeability on the electric field component according to the embodiment of the present application, wherein Figure 1 (a) and Figure 1 (b) are the influences of different relative permeability on the x-axis and y-axis direction components of the electric field respectively.

[0050] Figure 2 is the influence of different relative permeability on the magnetic field component according to the embodiment of the present application, wherein Figure 2 (a), Figure 2 (b), Figure 2 (c) are the influences of different relative permeability on the x-axis, y-axis and z-axis direction components of the magnetic field respectively.

[0051] The above Figure 1 , Figure 2 , wherein the horizontal coordinate represents the frequency, the unit is hertz (Hz), and the logarithmic scale is adopted; the vertical coordinate represents the ratio of each electromagnetic field component under the influence of different permeability to the field value when the relative permeability is 1, and the legend miur represents the relative permeability, that is .

[0052] Figure 3 is the flow chart of the controllable source electromagnetic apparent parameter extraction method based on the optimization algorithm according to the embodiment of the present application.

[0053] Figure 4 is the apparent parameter extracted according to the x-axis direction component of the electric field according to the embodiment of the present application, wherein Figure 4 (a) is the apparent resistivity extraction result, Figure 4 (b) is the apparent relative permeability extraction result.

[0054] Figure 5 is the apparent parameter extracted according to the y-axis direction component of the magnetic field according to the embodiment of the present application, wherein Figure 5 (a) is the apparent resistivity extraction result, Figure 5 (b) is the apparent relative permeability extraction result.

[0055] The above Figure 4 , Figure 5In the graph, the horizontal axis represents frequency in Hertz (Hz) on a logarithmic scale; the vertical axis represents the extracted apparent parameter values. Detailed Implementation

[0056] The embodiments of the present invention will be described in detail below. These embodiments are based on the technical solutions of the present invention and provide detailed implementation methods and specific operation processes to further explain the technical solutions of the present invention.

[0057] Example 1

[0058] magnetic permeability It can be represented as: , The permeability of free space, The relative permeability is 1. When the underground permeability distribution is not considered, the relative permeability is always 1. Since the CSEM forward modeling formulas that simultaneously consider resistivity and permeability are very complex and it is difficult to obtain asymptotic expressions for the far and near fields, the response characteristics are analyzed directly through numerical calculations. In onshore mineral exploration, the five components of the electromagnetic field, namely the horizontal electric field, are often involved. , and magnetic field , , Since the influence of resistivity on each component has been thoroughly analyzed in scientific research and work in the industry, we will first briefly analyze the influence of permeability on each parameter.

[0059] 1) Permeability versus electric field , The impact.

[0060] Consider an electric dipole source with a measuring point at coordinates (5000, 8000, 0). Assume the first underground layer is 300m thick with a resistivity of 100Ωm. Change the relative permeability to 0.5, 1, 2, 4, 6, 8, and 10. The second layer is also 100Ωm thick with a relative permeability of 1. Obtain the following... Figure 1 The depth sounding curve shown.

[0061] Figure 1 The vertical axis represents the ratio of the calculated electric field amplitude under different relative permeabilities (symbolized as miur in the figure) to the value when the relative permeability is 1. The horizontal axis represents the frequency used in conventional field measurements. When there is a permeability anomaly underground, the electric field will directly increase at high frequencies. The magnetic permeability is increased by a factor of 1 at high frequencies, gradually approaching 1 at low frequencies. This indicates that if an anomaly in magnetic permeability exists underground, neglecting the influence of magnetic permeability in the calculation of apparent resistivity of the electric field will result in a false anomaly. For example, when... When the value is greater than 1, it will lead to an increase in the electric field, resulting in a false anomaly of high resistance.

[0062] 2) The influence of magnetic susceptibility on magnetic field , , .

[0063] Similarly, the magnetic field response characteristics of the above model are analyzed, as shown in FIG. 2. When there is a magnetic susceptibility anomaly in the underground, the horizontal magnetic field component will directly increase by Figure 2 times at high frequencies, and gradually approach 1 at low frequencies. For the vertical magnetic field component, its high frequency is not affected by the magnetic susceptibility. This shows that if there is a magnetic susceptibility anomaly in the underground, and the influence of the magnetic susceptibility is ignored in the magnetic field apparent resistivity calculation, a false anomaly will be presented, but the vertical magnetic field component at high frequencies will be able to reflect the true underground situation. The above-mentioned phenomena are universal, and are summarized as follows: 1) when the relative magnetic susceptibility of the stratum at the measurement point is not 1, the horizontal electromagnetic field from high frequency to low frequency will be seriously affected by the relative magnetic susceptibility, and the high frequency data of the vertical magnetic field component will not be affected by the relative magnetic susceptibility; 2) when the relative magnetic susceptibility of the stratum at the measurement point is 1, and the relative magnetic susceptibilities of the remaining strata are not 1, the high frequency apparent resistivity of all electromagnetic field components can reflect the true underground situation, but the low frequency data will be affected by the magnetic susceptibility. High magnetic susceptibility will cause the electromagnetic field to increase, that is, a high resistance false anomaly is generated. In actual field work, since the relative magnetic susceptibility of the stratum at the measurement point cannot be known, if the influence of the magnetic susceptibility is directly ignored, the obtained apparent resistivity curve can be incorrect.

[0064] The above-mentioned phenomena are universal, and are summarized as follows: 1) when the relative magnetic susceptibility of the stratum at the measurement point is not 1, the horizontal electromagnetic field from high frequency to low frequency will be seriously affected by the relative magnetic susceptibility, and the high frequency data of the vertical magnetic field component will not be affected by the relative magnetic susceptibility; 2) when the relative magnetic susceptibility of the stratum at the measurement point is 1, and the relative magnetic susceptibilities of the remaining strata are not 1, the high frequency apparent resistivity of all electromagnetic field components can reflect the true underground situation, but the low frequency data will be affected by the magnetic susceptibility. High magnetic susceptibility will cause the electromagnetic field to increase, that is, a high resistance false anomaly is generated. In actual field work, since the relative magnetic susceptibility of the stratum at the measurement point cannot be known, if the influence of the magnetic susceptibility is directly ignored, the obtained apparent resistivity curve can be incorrect.

[0065] Therefore, the embodiment provides a controllable source electromagnetic apparent parameter extraction method based on an optimization algorithm, which simultaneously considers the influences of underground resistivity and magnetic susceptibility on frequency domain controllable source electromagnetic, as shown in FIG. 3, and includes the following steps: Figure 3

[0066] Step 1: obtaining a first apparent parameter of controllable source electromagnetic at the highest frequency; wherein the first apparent parameter is apparent resistivity or apparent magnetic susceptibility, and the other is a second apparent parameter.

[0067] If the first apparent parameter is apparent magnetic susceptibility, and the second apparent parameter is apparent resistivity: since the high frequency apparent resistivity mainly reflects the shallow resistivity structure, the magnetic susceptibility of the shallow ground can be measured near the measurement point, and the magnetic susceptibility of the shallow ground is regarded as the highest frequency apparent magnetic susceptibility.

[0068] If the first apparent parameter is apparent resistivity, and the second apparent parameter is apparent magnetic susceptibility, then there are two methods for obtaining the apparent resistivity:

[0069] (1) The resistivity of the shallow ground is measured to be the highest frequency apparent resistivity.

[0070] ​​​​Since the high frequency data is mainly affected by the shallow geological structure, the resistivity of the shallow earth can be measured near the measuring point, and the resistivity of the shallow earth is regarded as the highest frequency apparent resistivity.

[0071] (2) The permeability is constant as the vacuum permeability, the highest frequency vertical magnetic field component is measured, and the highest frequency apparent resistivity is calculated by using the uniform half-space formula considering the influence of underground resistivity and permeability.

[0072] In this embodiment, the uniform half-space formula considering the influence of underground resistivity and permeability will be explained in the following step 2. This step (2) is based on the vertical component of the magnetic field at high frequency Not affected by the permeability, the permeability is constant as the vacuum permeability, that is, the relative permeability , so as to calculate the highest frequency apparent resistivity by using the uniform half-space formula considering the influence of underground resistivity and permeability in step 2.

[0073] Step 2, fix the first kind of apparent parameter of the highest frequency, and based on the measured highest frequency electromagnetic field components as observation, use the uniform half-space formula considering the influence of underground resistivity and permeability and the optimization algorithm to calculate the second kind of apparent parameter of the highest frequency. Specifically, it includes:

[0074] Step 2.1, fix the first kind of apparent parameter of the highest frequency obtained by using step 1, and calculate the forward data of each electromagnetic field component under the current two kinds of apparent parameters by using the uniform half-space formula considering the influence of underground resistivity and permeability.

[0075] In the first iteration, an empirical initial value is given for the second kind of apparent parameter.

[0076] Step 2.2, evaluate the fitting degree between the forward data obtained in step 2.1 and the corresponding observation, if the fitting requirement is not met, then proceed to step 2.3, otherwise end the apparent parameter extraction, and take the current value of the second kind of apparent parameter as the final calculated value of the highest frequency second kind of apparent parameter.

[0077] Step 2.3, the sensitivity matrix is solved by using the perturbation method, and the iteration is updated as follows, and returns to step 2.1.

[0078] The equations for simultaneously extracting apparent resistivity and apparent permeability using a uniform half-space formula that considers both subsurface resistivity and permeability are underdetermined. For example, for Ex data collected in the field, the effects may be caused by resistivity, permeability, or both. Therefore, this leads to highly unstable processes for simultaneously extracting apparent parameters (e.g., using Newton's method). To address this issue, this invention adopts an optimization approach for underdetermined problems, introducing reference value constraints and constructing an objective function for the optimization problem of simultaneously extracting apparent resistivity and apparent permeability, expressed as:

[0079] ;

[0080] In the above formula, the first term on the right is the data fitting term. This is the apparent parameter vector (including apparent resistivity and apparent permeability parameters) for each frequency point. These are electromagnetic field data at various frequencies obtained from field measurements. To obtain the forward modeling data of the electromagnetic field at each frequency, this embodiment uses the forward modeling formula of a uniform half-space. diagonal matrix The diagonal elements are The reciprocal of the vector is used to normalize the data fit difference; the second term is the reference value constraint term. This is an initial or prior value; These are weighting coefficients, used to adjust the weights of the reference value constraint terms; These are Lagrange multipliers, which are obtained using the golden section method in this embodiment.

[0081] The initial value in step 2 of this embodiment It is obtained by taking the first and second visual parameters with fixed highest frequencies and given empirical initial values.

[0082] In addition, this embodiment uses the Occam's algorithm to minimize the objective function, which yields the iterative update formula for the view parameter vector at the (k+1)th iteration:

[0083] ;

[0084] ;

[0085] In the formula, It is the view parameter vector obtained in the k-th iteration; These are the apparent resistivity and apparent permeability parameters from the k-th iteration, where I is the identity matrix. An intermediate temporary vector for ease of calculation.

[0086] Since the apparent parameters are extracted from the uniform half-space formula, each frequency point only contains one apparent resistivity and one apparent permeability, the application adopts the perturbation method to solve the sensitivity matrix The method is simple and fast, and the sensitivity matrix is solved by the perturbation method, that is, a small perturbation is made to the stratum, the partial derivative is approximated by the finite difference method, and then the partial derivative approximation is filled into the corresponding column of the matrix, so that the sensitivity matrix is obtained.

[0087] The uniform half-space formula considering the influence of underground resistivity and permeability is calculated as follows:

[0088] ;

[0089] ;

[0090] ;

[0091] ;

[0092] ;

[0093] ;

[0094] In the formula, k is the wave number, and satisfies , , is the dielectric constant, is the circular frequency of the harmonic current; σ is the conductivity, and is the reciprocal of the resistivity; is the medium permeability; is the relative permeability of the underground medium, is the permeability of the underground half-space; is the first-order Bessel function of the first kind; is the vertical wave number, which contains attenuation and phase information; , , , The subscript 1 in the formula represents the underground parameter, , , , The subscript 0 in the formula represents the air parameter; is the included angle of the receiving point relative to the direction of the dipole; is the distance from the receiving point to the center of the dipole source; is the current intensity of the dipole source, is the length of the transmitting dipole; In the formula, z is the vertical distance of the receiving point relative to the transmitting source, that is, the depth coordinate of the receiving point; respectively, are the radial, normal and vertical components of the electric field of the uniform half-space considering the influence of the underground resistivity and permeability, respectively, are the radial, normal and vertical components of the magnetic field of the uniform half-space considering the influence of the underground resistivity and permeability.

[0095] The above electromagnetic field components in the cylindrical coordinate system are converted to the rectangular coordinate system, and the horizontal electric field and magnetic field components are obtained as follows:

[0096] ;

[0097] In the formula, and respectively, are the electric field components in the x-axis and y-axis directions of the rectangular coordinate system, and respectively, are the magnetic field components in the x-axis and y-axis directions of the rectangular coordinate system.

[0098] Step 3: In the order of frequency from high to low, the two apparent parameters of the previous frequency point are used as the initial values of the next frequency point, and the measured electromagnetic field components of the next frequency point are used as the observations. The uniform half-space formula considering the influence of underground resistivity and permeability and the optimization algorithm are used to calculate the two apparent parameters of the next frequency point, until the apparent resistivity and apparent permeability of all frequency points are obtained, thereby obtaining the complete apparent parameter sounding curve.

[0099] In this step, the optimization algorithm is used to minimize the objective function to obtain the two apparent parameters of the next frequency point. In step 2, the same method is used to minimize the objective function using the Ockham optimization algorithm to obtain the apparent parameter vector in the k+1 iteration:

[0100] ;

[0101] .

[0102] The difference between step 3 and step 2 of this embodiment is that the initial values are composed of the two apparent parameters of the previous frequency point, and the difference in the number of apparent parameters solved.

[0103] Since the apparent parameter curve is smooth and continuous, the apparent permeability and apparent resistivity parameters of the previous high frequency point can be used as the initial values of the next low frequency point. The value of the initial value can be set according to the reliability (generally set to 0.1-1, and the smaller the value, the more reliable the initial value) to solve the apparent parameters of the next frequency point.

[0104] A three-layer ground model shown in Table 1 is set, the measurement point is located at (5000, 8000, 0) m, and the field source is an electric dipole in the x-direction of the coordinate origin. The middle layer has high resistivity and high permeability.

[0105]

[0106] set up =0.1, the effect of extracting the horizontal component of the electric field Ex data as a parameter is as follows: Figure 4 As shown, the apparent parameter extraction effect of the horizontal component Hy data of the magnetic field is as follows: Figure 5 As shown. Scheme 1 assumes a known relative magnetic permeability of 1; Scheme 2 assumes a known surface resistivity of 100 Ωm; Scheme 3 assumes the existence of Hz measurement data. The extraction results of all three schemes are consistent with... Figure 4 , Figure 5 The results are consistent and will not be repeated. The extracted results show that the apparent parameters in the mid-frequency band can effectively reflect the high resistivity and high magnetism of the actual intermediate anomalous strata.

[0107] The above embodiments are preferred embodiments of this application. Those skilled in the art can make various changes or improvements based on them. Without departing from the overall concept of this application, these changes or improvements should fall within the scope of protection claimed in this application.

Claims

1. A method for extracting the apparent electromagnetic parameters of a controllable source based on an optimization algorithm, characterized in that, include: Step 1: Obtain the first apparent parameter of the highest frequency electromagnetic frequency of the controllable source; wherein, the first apparent parameter is apparent resistivity or apparent permeability, and the other is the second apparent parameter; Step 2: Fix the first apparent parameter of the highest frequency, and use the electromagnetic field components of the highest frequency as observations, and use the uniform half-space formula that considers the influence of underground resistivity and magnetic permeability and the optimization algorithm to calculate the second apparent parameter of the highest frequency. Step 3: In descending order of frequency, take the two apparent parameters of the previous frequency point as the initial values ​​of the next frequency point, and use the electromagnetic field components measured at the next frequency point as observations. Using the uniform half-space formula that considers the influence of underground resistivity and permeability and the optimization algorithm, calculate the two apparent parameters of the next frequency point. The formula for a uniform half-space considering the effects of underground resistivity and magnetic permeability is as follows: ； ； ； ； ； ； In the formula, For wave number, satisfying , Where is the dielectric constant. σ is the angular frequency of the harmonic current; σ is the conductivity, which is the reciprocal of the resistivity. The dielectric permeability; The relative magnetic permeability of the underground medium. The magnetic permeability of the underground semi-space; It is a first-order Bessel function of the first kind; The vertical wavenumber contains attenuation and phase information. , , , The subscript 1 in the text represents underground parameters. , , , The subscript 0 in the text represents air parameters; The angle between the receiving point and the direction of the dipole; The distance from the receiving point to the center of the dipole source; The intensity of the dipole source current. The length of the emitted dipole; In this context, z represents the vertical distance between the receiving point and the transmitting source, i.e., the depth coordinate of the receiving point. These represent the radial, normal, and perpendicular components of the electric field in a uniform half-space, taking into account the effects of underground resistivity and permeability. These are the radial, normal, and vertical components of a uniform half-space magnetic field considering the effects of underground resistivity and permeability. The relationships between the horizontal electric and magnetic field components in cylindrical and rectangular coordinate systems are as follows: ； In the formula, and These represent the electric field components along the x-axis and y-axis in a Cartesian coordinate system. and These are the magnetic field components along the x-axis and y-axis in a rectangular coordinate system, respectively.

2. The method for extracting controllable source electromagnetic apparent parameters according to claim 1, characterized in that, If the first apparent parameter is apparent resistivity, then the apparent resistivity of the shallow surface is considered to be the highest frequency apparent resistivity.

3. The method for extracting controllable source electromagnetic apparent parameters according to claim 1, characterized in that, If the first apparent parameter is apparent resistivity, and the permeability is kept constant at the vacuum permeability, the apparent resistivity at the highest frequency is calculated using the uniform half-space formula by measuring the highest frequency vertical magnetic field component.

4. The method for extracting controllable source electromagnetic apparent parameters according to claim 1, characterized in that, If the first apparent parameter is apparent permeability, then the permeability measured at the shallow surface is considered as the highest frequency apparent permeability.

5. The method for extracting controllable source electromagnetic apparent parameters according to claim 1, characterized in that, The objective function of the optimization algorithm used to calculate the apparent parameters at any frequency point is: ； In the formula, Represents the objective function; This is the apparent parameter vector, including apparent resistivity and apparent permeability; For the electromagnetic field data obtained by measurement, The electromagnetic field data obtained from forward modeling; It is a diagonal matrix with diagonal elements as follows: The reciprocal of is used to normalize the data fit difference; These are the initial values ​​for the view parameter vector; These are weighting coefficients; It is a Lagrange multiplier.

6. The method for extracting controllable source electromagnetic apparent parameters according to claim 5, characterized in that, Using Occam's algorithm to minimize the objective function, the iterative update formula for the apparent parameter vector in the (k+1)th iteration is obtained as follows: ； ； In the formula, It is the view parameter vector obtained in the k-th iteration; These are the apparent resistivity and apparent permeability parameters from the k-th iteration, where I is the identity matrix. An intermediate temporary vector for ease of calculation.

7. A controllable source electromagnetic apparent parameter extraction system based on an optimization algorithm, used to implement the controllable source electromagnetic apparent parameter extraction method of claim 1, characterized in that, It includes an initial view parameter acquisition module and a view parameter iterative acquisition module; The initial apparent parameter acquisition module is used to: acquire two apparent parameters of the highest frequency electromagnetic frequency of the controllable source; Among them, the first apparent parameter is apparent resistivity or apparent permeability, and the other is the second apparent parameter; the method for obtaining the second apparent parameter is as follows: after obtaining the first apparent parameter of the highest frequency, the first apparent parameter of the highest frequency is fixed, and then based on the electromagnetic field components of the highest frequency as observations, the second apparent parameter of the highest frequency is calculated using a uniform half-space formula that considers the influence of underground resistivity and permeability. The apparent parameter iteration acquisition module is used to: sequentially take the two apparent parameters of the previous frequency point as the initial values ​​of the next frequency point in order from high to low frequency, and calculate the two apparent parameters of the next frequency point based on the electromagnetic field components measured at the next frequency point as observations, using a uniform half-space formula that considers the influence of underground resistivity and magnetic permeability and an optimization algorithm.

8. The controllable source electromagnetic apparent parameter extraction system according to claim 7, characterized in that, If the first apparent parameter is apparent permeability, the apparent permeability measured at the shallow surface is considered to be the highest frequency apparent permeability; If the first apparent parameter is apparent resistivity, it can be obtained by any of the following methods: (1) The resistivity of shallow ground surface is considered as the highest frequency apparent resistivity; (2) Keep the permeability constant at the vacuum permeability, and calculate the apparent resistivity of the highest frequency by measuring the vertical magnetic field component of the highest frequency using the uniform half-space formula.

9. The controllable source electromagnetic apparent parameter extraction system according to claim 7, characterized in that, The Occam's algorithm is used to minimize the following objective function to compute the second apparent parameter at the highest frequency in step 2, and to compute the two apparent parameters at the next frequency in step 3: ； In the formula, Represents the objective function; This is the apparent parameter vector, including apparent resistivity and apparent permeability; For the electromagnetic field data obtained by measurement, The electromagnetic field data obtained from forward modeling; It is a diagonal matrix with diagonal elements as follows: The reciprocal of is used to normalize the data fit difference; These are the initial values ​​for the view parameter vector; These are weighting coefficients; It is a Lagrange multiplier.

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