CN117310824A - Thermocouple source excitation controllable source electromagnetic field time sequence forward modeling method and system - Google Patents
Thermocouple source excitation controllable source electromagnetic field time sequence forward modeling method and system Download PDFInfo
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Abstract
The invention provides a thermocouple source excitation controllable source electromagnetic field time sequence forward modeling method and a system, wherein the method comprises the following steps: establishing a horizontal layered dielectric electric model; equivalent the emission source as a combination of one or more electric dipoles; decomposing the emission current of the electric dipole into a combination of sine and cosine signal components with different frequencies; generating electromagnetic field response of each frequency point of the layered medium model according to forward modeling of the transmitting-receiving position, and obtaining system response of the receiving device through interpolation and polynomial fitting; combining and superposing sine and cosine signal components of the emission current of each frequency point electromagnetic field response of the layered medium model and response of the receiving device system on the electric dipole to obtain a standard electromagnetic field time sequence; the standard electromagnetic field time series excited by a plurality of electric dipoles are overlapped to complete forward modeling of the electromagnetic field time series. By applying the technical scheme of the invention, the technical problem of low modeling accuracy of the controllable source electromagnetic field time sequence signal in the prior art is solved.
Description
Technical Field
The invention relates to the technical fields of geophysics science and underwater target electromagnetic detection, in particular to a thermocouple source excitation controllable source electromagnetic field time sequence forward modeling method and system.
Background
The controllable source electromagnetic method is an artificial source electromagnetic detection method developed on the basis of a natural source magnetotelluric method, can detect in land or ocean areas, continuously transmits periodic alternating current by a transmitting device during specific work, synchronously acquires an induction electromagnetic field time sequence by a receiving device, and further deduces geological features of the area through subsequent data processing. Along with the development of economy and society, various electromagnetic noise interferences become serious, the quality of electromagnetic field signal acquisition of a receiving device is affected, and the electromagnetic noise interferences become important factors for restricting the electromagnetic detection precision and depth of a controllable source. The controllable source electromagnetic method is an artificial source electromagnetic detection method, the emission current and the receiving device are controllable, the standard electromagnetic field time sequence under a typical dielectric medium model is modeled, the high-quality signal without noise interference is obtained at low cost, and further, the noise reduction processing method is developed by analyzing the standard signal and the common noise interference characteristics, so that the quality of follow-up measured data is improved. Therefore, modeling the controllable source electromagnetic field time series signal is a precondition for subsequent quality evaluation and noise reduction processing of the measured data. In recent years, research on forward modeling of a land and marine controllable source electromagnetic method is mainly performed in a frequency domain, and research on forward modeling of a time domain signal of the controllable source electromagnetic method is still immature. The emission current of the controllable source electromagnetic method is not unique, and has various waveforms such as square waves, bipolar waves, pseudo random waves and the like; the electromagnetic field receiving device has system response, and can bring phase shift and amplitude shift to the observed data; different areas such as land, ocean and the like have different electrical characteristics and construction modes, and all factors can influence the modeling accuracy of the controllable source electromagnetic field time sequence signals. Therefore, how to comprehensively consider the above influencing factors to realize high-precision modeling of electromagnetic field time series is one of the problems to be solved urgently.
Disclosure of Invention
The invention provides a galvanic couple source excitation controllable source electromagnetic field time sequence forward modeling method and a system, which can solve the technical problem of low modeling accuracy of controllable source electromagnetic field time sequence signals in the prior art.
According to one aspect of the invention, there is provided a method for modeling a time series forward model of an electromagnetic field of a controllable source excited by a thermocouple source, the method comprising: step one, establishing a horizontal lamellar dielectric electrical model according to priori geological information; step two, the emitting source is equivalent to one or a combination of a plurality of electric dipoles according to the length of the emitting source; step three, aiming at any electric dipole, decomposing the emission current of the electric dipole into the combination of sine and cosine signal components with different frequencies; generating electromagnetic field response of each frequency point of the layered medium model according to forward modeling of the transmitting-receiving position, and obtaining system response of the receiving device through interpolation and polynomial fitting; fifthly, aiming at any electric dipole, combining and superposing all sine and cosine signal components of the electromagnetic field response of each frequency point of the layered medium model and the response of the receiving device system on the transmitting current of any electric dipole, and obtaining a standard electromagnetic field time sequence excited by any electric dipole; step six, if the emission source is equivalent to an electric dipole, completing the forward modeling of the electromagnetic field time sequence of the controllable source excited by the electric dipole according to the standard electromagnetic field time sequence excited by the electric dipole obtained in the step five; and if the emission source is equivalent to a plurality of electric dipoles, repeating the third to fifth steps to sequentially obtain a plurality of standard electromagnetic field time sequences excited by the electric dipoles, and superposing the standard electromagnetic field time sequences excited by the electric dipoles to complete forward modeling of the electromagnetic field time sequences of the controllable source excited by the electric dipole source.
Further, in the second step, when the length of the transmitting source is less than one fifth of the distance between the transmitting device and the receiving device, the transmitting source is equivalent to an electric dipole; when the length of the transmitting source is greater than or equal to one fifth of the distance between the transmitting device and the receiving device, the transmitting source is equivalent to a combination of a plurality of electric dipoles, and the length of any electric dipole is less than one fifth of the distance between the transmitting device and the receiving device.
Further, in the third step, the decomposition formula of the emission current of the electric dipole is as followsWherein I (T) is the emission current, T is the period of the emission current, a 0 As a constant term component, a k For the amplitude of the kth cosine component, b k For the amplitude, ω, of the kth sinusoidal component k The angular frequency of the kth sine component and the cosine component, t is the emission time of the emission current.
Further, constant term component a 0 Amplitude a of the kth cosine component k Amplitude b of the kth sinusoidal component k Can be according toAnd carrying out integral calculation on the emission current to obtain the emission current.
Further, in the fourth step, the electromagnetic field response of each frequency point of the layered medium model is obtained based on the maxwell equation set, and the calculation formula of the electromagnetic field response of each frequency point of the layered medium model is as followsWherein G (r) is the field value of the response of the laminar dielectric electromagnetic field, < >>Is an integral kernel function corresponding to the zero-order Bessel function,>is an integral kernel function corresponding to a first order Bessel function, J 0 (λr) is a zero-order Bessel function, J 1 (λr) is a first order Bessel function, and λ and r are both Bessel function arguments.
Further, maxwell's equations areWherein (1)>E is electric field single frequency response, H is magnetic field single frequency response, omega k The electromagnetic wave frequency is represented by mu, medium magnetic permeability, sigma, conductivity, J, a transmitting current source and i, wherein i is an imaginary unit.
Further, in step four, obtaining the receiving device system response by interpolation and polynomial fitting specifically includes: according to the existing frequency points and the system responses corresponding to the frequency points, when the frequency to be calculated is within the existing frequency point range, obtaining the system responses corresponding to the frequency to be calculated through interpolation, and when the frequency to be calculated is out of the existing frequency point range, performing polynomial fitting on the system responses corresponding to the existing frequency points and the existing frequency points, and fitting out the system responses of the frequency to be calculated according to a polynomial fitting model.
Further, the time sequence of the standard electromagnetic field excited by any electric dipole can be based onCalculation and acquisition, wherein T (T) is a time sequence obtained by forward modeling, T is observation time, and a 0 As a constant term component, a k For the amplitude of the kth cosine component, b k For the amplitude, ω, of the kth sinusoidal component k Angular frequencies for the kth sine and cosine component,/->Phase shift for electromagnetic response of layered dielectric model, < >>Phase shift for receiving device system response, A k Amplitude shift for electromagnetic response of layered medium model, A ks The amplitude shift brought about for the receiving device system response.
Further, in the first step, the first layer of the land horizontal layered medium typical model is an air layer, and the second layer and the layers below are underground rock layers; the first layer of the ocean horizontal layered dielectric electric model is an air layer, the second layer is a sea water layer, and the third layer and below are all rock layers underground.
According to still another aspect of the present invention, there is provided a galvanic source excitation controllable source electromagnetic field time series forward modeling system that performs electromagnetic field time series forward modeling using the galvanic source excitation controllable source electromagnetic field time series forward modeling method as described above.
By applying the technical scheme of the invention, the invention provides a thermocouple source excitation controllable source electromagnetic field time sequence forward modeling method, which comprehensively considers factors such as emission current waveform characteristics, emission-receiving device positions, receiving device system responses, measured area electrical characteristics and the like, forward generates a standard electromagnetic field time sequence signal, and provides support for quality evaluation and noise reduction processing of follow-up measured data. Compared with the prior art, the thermocouple source excitation controllable source electromagnetic field time sequence forward modeling method provided by the invention has the advantages that the electromagnetic field time sequence signal similar to measured data can be modeled by comprehensively considering the factors such as the emission current waveform, the emission-receiving position, the system response of the receiving device, the electrical characteristics of a measuring area and the like in the controllable source electromagnetic exploration, the modeling precision of the controllable source electromagnetic field time sequence signal is high, and the reference can be provided for the quality evaluation and noise reduction treatment of the follow-up measured data.
Drawings
The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. It is evident that the drawings in the following description are only some embodiments of the present invention and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art.
FIG. 1 shows a flow chart of a method for modeling a galvanic source excitation controllable source electromagnetic field time series forward modeling according to a specific embodiment of the invention;
FIG. 2 shows a schematic diagram of a terrestrial controllable source electromagnetic probe layered media model provided in accordance with an embodiment of the present invention;
FIG. 3 shows a schematic diagram of a marine controllable source electromagnetic detection layered media model provided in accordance with an embodiment of the invention;
FIG. 4a shows a schematic diagram of a time domain waveform of a transmit current (square wave) provided in accordance with a specific embodiment of the present invention;
FIG. 4b shows a schematic representation of the amplitude of the various harmonic components of the transmit current (square wave) provided in accordance with a specific embodiment of the present invention;
FIG. 4c shows a schematic error diagram of the reconstruction of the original signal with different number of stages of the emitted current (square wave) provided according to an embodiment of the present invention;
FIG. 5a shows a schematic diagram of a time domain waveform of a transmit current (bipolar wave) provided in accordance with a specific embodiment of the present invention;
FIG. 5b illustrates a schematic diagram of the amplitude of the harmonic components of the emitted current (bipolar wave) provided in accordance with a specific embodiment of the present invention;
FIG. 5c is a schematic diagram showing errors in reconstructing an original signal using different number of stages of a transmitted current (bipolar wave) provided in accordance with an embodiment of the present invention;
fig. 6a shows an emission current (2 n Sequence pseudo-random wave) time domain waveform schematic;
fig. 6b shows an emission current (2 n A sequence pseudo-random wave) amplitude schematic of each harmonic component;
fig. 6c shows an emission current (2 n Sequence pseudo-random wave) to reconstruct an error map of the original signal using different number of stages;
FIG. 7a shows a schematic diagram of a time domain waveform of a transmit current (m-sequence pseudo-random wave) provided in accordance with a specific embodiment of the present invention;
FIG. 7b shows a schematic representation of the amplitude of the various harmonic components of the transmitted current (m-sequence pseudo-random wave) provided in accordance with a specific embodiment of the present invention;
FIG. 7c is a schematic diagram of error of a transmitted current (m-sequence pseudo-random wave) reconstructed original signal using different number of stages according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of a time series of terrestrial controllable source electromagnetic fields modeled by three different sets of periodic square wave currents, according to an embodiment of the present invention;
FIG. 9 shows a schematic diagram of a marine controllable source electromagnetic field time series modeled from a set of continuously emitted square wave currents, provided in accordance with a specific embodiment of the present invention;
FIGS. 10a and 10b are diagrams showing the comparison of measured electromagnetic fields and modeled electromagnetic fields provided in accordance with specific embodiments of the present invention;
FIGS. 10c and 10d are diagrams illustrating the comparison of measured electromagnetic fields with noise-containing interference and modeled electromagnetic fields provided in accordance with specific embodiments of the present invention.
Detailed Description
It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
The relative arrangement of the components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless it is specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective parts shown in the drawings are not drawn in actual scale for convenience of description. Techniques, methods, and apparatus known to one of ordinary skill in the relevant art may not be discussed in detail, but should be considered part of the specification where appropriate. In all examples shown and discussed herein, any specific values should be construed as merely illustrative, and not a limitation. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further discussion thereof is necessary in subsequent figures.
As shown in fig. 1 to 10d, according to an embodiment of the present invention, there is provided a couple source excitation controllable source electromagnetic field time series forward modeling method, including: step one, establishing a horizontal lamellar dielectric electrical model according to priori geological information; step two, the emitting source is equivalent to one or a combination of a plurality of electric dipoles according to the length of the emitting source; step three, aiming at any electric dipole, decomposing the emission current of the electric dipole into the combination of sine and cosine signal components with different frequencies; generating electromagnetic field response of each frequency point of the layered medium model according to forward modeling of the transmitting-receiving position, and obtaining system response of the receiving device through interpolation and polynomial fitting; fifthly, aiming at any electric dipole, combining and superposing all sine and cosine signal components of the electromagnetic field response of each frequency point of the layered medium model and the response of the receiving device system on the transmitting current of any electric dipole, and obtaining a standard electromagnetic field time sequence excited by any electric dipole; step six, if the emission source is equivalent to an electric dipole, completing the forward modeling of the electromagnetic field time sequence of the controllable source excited by the electric dipole according to the standard electromagnetic field time sequence excited by the electric dipole obtained in the step five; and if the emission source is equivalent to a plurality of electric dipoles, repeating the third to fifth steps to sequentially obtain a plurality of standard electromagnetic field time sequences excited by the electric dipoles, and superposing the standard electromagnetic field time sequences excited by the electric dipoles to complete forward modeling of the electromagnetic field time sequences of the controllable source excited by the electric dipole source.
By applying the configuration mode, the method for modeling the forward modeling of the electromagnetic field time sequence of the controllable source excited by the thermocouple source is provided, and comprehensively considers factors such as the waveform characteristics of the emission current, the positions of the emission-receiving devices, the system response of the receiving devices, the electrical characteristics of a measuring area and the like, and forward modeling generates a standard electromagnetic field time sequence signal, so that support is provided for quality evaluation and noise reduction processing of follow-up measured data. Compared with the prior art, the thermocouple source excitation controllable source electromagnetic field time sequence forward modeling method provided by the invention has the advantages that the electromagnetic field time sequence signal similar to measured data can be modeled by comprehensively considering the factors such as the emission current waveform, the emission-receiving position, the system response of the receiving device, the electrical characteristics of a measuring area and the like in the controllable source electromagnetic exploration, the modeling precision of the controllable source electromagnetic field time sequence signal is high, and the reference can be provided for the quality evaluation and noise reduction treatment of the follow-up measured data.
Specifically, in order to realize the time series forward modeling of the electromagnetic field of the controllable source excited by the couple source, the invention firstly needs to establish a land or ocean horizontal lamellar medium electrical model according to priori geological information. According to priori geological feature information such as drilling, petrophysics and the like, the area where the measuring point is located in the controllable source electromagnetic exploration is equivalent to a horizontal lamellar medium model, and model parameters comprise total layers, thicknesses of all layers and electrical parameters of all layers. In the land area, the first layer is an air layer, the second layer and the layers below are underground rock layers, and in the ocean area, the first layer is an air layer, the second layer is a sea water layer, and the third layer and the layers below are underground rock layers. The electrical parameters of each layer comprise resistivity, magnetic permeability, dielectric constant and the like, and the resistivity of each layer is generally changed greatly, the change of the magnetic permeability is smaller, the change of the dielectric constant is larger, but the influence on electromagnetic response is smaller in the controllable source electromagnetic detection frequency band, so that the magnetic permeability and the dielectric constant of each layer can be the same as the air layer, and only the resistivity parameters of each layer need to be set. When the drilling, rock physical property measurement and other works are carried out in the early stage of the measuring area, the layer number, the layer thickness and the layer resistivity parameters of the electrical model are set according to the rock stratum distribution, rock conductivity characteristics and other prior geological information. When the drilling and rock physical property measurement work is not performed in the measuring area, the initial value of the layered model parameter can be approximately generated according to the data of other measuring areas, then the forward time series is obtained by respectively executing the first step to the sixth step, and then the forward time series is compared with the measured data to further modify the model parameter. For terrestrial electromagnetic exploration, the transmitting and receiving positions are generally on the ground, for marine electromagnetic exploration, the transmitting source is generally towed by a marine cable, the transmitting electrode is located about 50 meters from the sea floor, and the measuring electrode is generally all positioned on the sea floor. Fig. 2 and 3 show schematic diagrams of a model of a certain land and ocean controllable source electromagnetic detection layered medium respectively.
Further, after the terrestrial or marine level layered dielectric electrical model is established, the emission source can be equivalent to a combination of one or more electric dipoles according to the length of the emission source. In the second step of the invention, in the controllable source electromagnetic exploration, the transmitting device is usually a power supply line with a certain length, and when the length of the transmitting source is less than one fifth of the distance between the transmitting device and the receiving device, the transmitting source is equivalent to an electric dipole; when the length of the transmitting source is greater than or equal to one fifth of the distance between the transmitting device and the receiving device, the transmitting source is equivalent to a combination of a plurality of electric dipoles, and the length of any electric dipole is less than one fifth of the distance between the transmitting device and the receiving device.
Then, after the emission source is equivalent to the combination of one or more electric dipoles, the emission current of each electric dipole can be decomposed into the combination of sine and cosine signal components with different frequencies for any electric dipole. The current signals commonly used in the electromagnetic detection of the controllable source comprise square waves, bipolar waves, 2n sequence pseudo-random waves, m sequence pseudo-random waves and the like, and are periodic signals which are continuously transmitted. According to the Fourier series decomposition theory, the periodic signal can be decomposed into a series of sine and cosine stagesAnd (3) stacking numbers, wherein each sine-cosine series represents a signal component under one frequency point. In the third step, the decomposition formula of the emission current of the electric dipole is as followsWherein I (T) is the emission current, T is the period of the emission current, a 0 As a constant term component, a k For the amplitude of the kth cosine component, b k For the amplitude, ω, of the kth sinusoidal component k The angular frequency of the kth sine component and the cosine component, t is the emission time of the emission current.
Constant term component a 0 Amplitude a of the kth cosine component k Amplitude b of the kth sinusoidal component k Can be according toAnd carrying out integral calculation on the emission current to obtain the emission current. In controllable source electromagnetic detection, an infinite number of sine and cosine components are needed in principle to be equivalent to the original emission current, the emission current bandwidth is limited in actual work, and the emission current can be approximated by series combination of hundreds to thousands according to the precision requirement. FIGS. 4a to 7c show square waves, bipolar waves, 2 n The schematic diagrams of four waveforms of the sequence pseudo-random wave and the m sequence pseudo-random wave show the amplitude variation of each harmonic component after the sine and cosine components are decomposed, and finally the error of reconstructing the original signal by adopting different numbers of series items is compared. The harmonic amplitude of square wave and bipolar wave is rapidly attenuated with the increase of frequency, when the number of sine and cosine series terms exceeds 5000, the reconstruction error is lower than 0.1%, and the m-sequence pseudo-random wave and 2 n The harmonic energy of the sequence pseudo-random wave is relatively uniform, and when the sine and cosine series term number exceeds 5000, the reconstruction error is lower than 1%.
Further, after the transmitting current of the electric dipole is decomposed into the combination of sine and cosine signal components with different frequencies, the electromagnetic field response of each frequency point of the layered medium model can be generated forward according to the transmitting-receiving position, and the system response of the receiving device can be obtained through interpolation and polynomial fitting. In the invention, in the electromagnetic detection of the controllable source, the waveform of the emitted current andthe transmitting-receiving and other acquisition devices are determined, and the electromagnetic field response of the layer-shaped medium model in the step one under single frequency can be obtained through forward calculation. The forward modeling formula is derived from maxwell's equations satisfied by the electromagnetic field in the horizontal layered medium, which are in the form of:wherein (1)>E is electric field single frequency response, H is magnetic field single frequency response, omega k The electromagnetic wave frequency is represented by mu, medium magnetic permeability, sigma, conductivity, J, a transmitting current source and i, wherein i is an imaginary unit.
Deducing the electromagnetic field response of each frequency point of the layered medium model based on Maxwell equation set, wherein the calculation general formula of the electromagnetic field response of each frequency point of the layered medium model is as followsWherein G (r) is the field value of the response of the laminar dielectric electromagnetic field, < >>Is an integral kernel function corresponding to the zero-order Bessel function,>is an integral kernel function corresponding to a first order Bessel function, J 0 (λr) is a zero-order Bessel function, J 1 And (lambda r) is a first-order Bessel function, lambda and r are Bessel function independent variables, and the lambda and the r are calculated according to the layered medium model parameters and the transmitting-receiving device parameters. The integral of the Bessel function is calculated through fast Hank transformation, so that the electromagnetic field response of each frequency point is obtained. The electromagnetic response of single frequency is calculated in the process, the calculation of the electromagnetic responses of different frequencies has natural parallelism, and the electromagnetic field frequency domain response corresponding to the sine and cosine components of all frequencies in the third step can be rapidly forward calculated by means of parallel calculation.
Meanwhile, in order to enable the modeling result to be sufficiently close to the measured data, the system response of each measuring point receiving device needs to be considered. In controllable source electromagnetic exploration, the receiving device comprises an electric field sensor, a magnetic field sensor and a multichannel receiver. Each receiver manufacturer will provide a system response (including amplitude and phase shift) at some of the sub-points of the device that is insufficient to cover the frequencies of all signal components in step two. When the frequency to be calculated is within the frequency point range provided by the manufacturer, the system response corresponding to the frequency point is obtained through interpolation, and when the frequency to be calculated is outside the frequency point range provided by the manufacturer, polynomial fitting is firstly carried out on the system response provided by the manufacturer and the frequency point, and then the system response of the calculated frequency is fitted by utilizing the polynomial model.
Further, after generating the electromagnetic field response of each frequency point of the layered medium model according to forward modeling of the transmitting-receiving position, obtaining the response of the receiving device system through interpolation and polynomial fitting, aiming at any electric dipole, combining and superposing sine and cosine signal components of the transmitting current acted on any electric dipole, to which the electromagnetic field response of each frequency point of the layered medium model and the response of the receiving device system are applied, so as to obtain the standard electromagnetic field time sequence excited by any electric dipole.
In the invention, the layered medium electromagnetic response of each frequency point obtained in the step four and the corresponding receiving device system response are acted on the formulaAnd a sine and cosine signal component after the current decomposition is transmitted. The amplitude of the electromagnetic response and the system response changes the amplitude of the sine and cosine signal component, and the phase changes the time delay of the sine and cosine signal. And finally, combining and superposing all sine and cosine components applied with the electromagnetic response of the layered medium and the system response of the receiving device to obtain a standard electromagnetic field time sequence excited by an electric dipole source under the layered medium, wherein the formula is as follows:
wherein T (T) is positiveThe time sequence obtained is, t is the observation time, a 0 As a constant term component, a k For the amplitude of the kth cosine component, b k For the amplitude, ω, of the kth sinusoidal component k For the angular frequencies of the kth sine and cosine components,phase shift for electromagnetic response of layered dielectric model, < >>Phase shift for receiving device system response, A k Amplitude shift for electromagnetic response of layered medium model, A ks The amplitude shift brought about for the receiving device system response.
Further, after obtaining the standard electromagnetic field time sequence excited by any electric dipole, if the emission source is equivalent to an electric dipole, completing forward modeling of the electromagnetic field time sequence of the controllable source excited by the electric dipole source according to the standard electromagnetic field time sequence excited by the electric dipole obtained in the step five; and if the emission source is equivalent to a plurality of electric dipoles, repeating the third to fifth steps to sequentially obtain a plurality of standard electromagnetic field time sequences excited by the electric dipoles, and superposing the standard electromagnetic field time sequences excited by the electric dipoles to complete forward modeling of the electromagnetic field time sequences of the controllable source excited by the electric dipole source.
According to another aspect of the invention, there is provided a galvanic source excitation controllable source electromagnetic field time series forward modeling system, which performs electromagnetic field time series forward modeling using the galvanic source excitation controllable source electromagnetic field time series forward modeling method as described above.
By applying the configuration mode, the system comprehensively considers the factors such as the waveform characteristics of the emission current, the positions of the emission-receiving devices, the system response of the receiving devices, the electrical characteristics of the measuring area and the like, and forward generates a standard electromagnetic field time sequence signal, thereby providing support for the quality evaluation and noise reduction processing of follow-up measured data. Therefore, compared with the prior art, the thermocouple source excitation controllable source electromagnetic field time sequence forward modeling system provided by the invention can model electromagnetic field time sequence signals similar to measured data by comprehensively considering factors such as emission current waveforms, emission-receiving positions, system response of a receiving device, electric characteristics of a measuring area and the like in controllable source electromagnetic exploration, has high modeling precision of the controllable source electromagnetic field time sequence signals, and can provide references for quality evaluation and noise reduction processing of follow-up measured data.
For further understanding of the present invention, the method for modeling the time series forward modeling of the electromagnetic field of the controllable source excited by the thermocouple source provided by the present invention is described in detail below with reference to fig. 1 to 10 d.
As shown in fig. 1 to 10d, according to an embodiment of the present invention, there is provided a method for modeling a galvanic couple source excitation controllable source electromagnetic field time series forward modeling, which specifically includes the following steps.
Step one, establishing a land or ocean layered medium electrical model according to prior geological feature information such as drilling in a measuring area, petrophysics and the like. In a land area, the first layer is an air layer, the second layer and layers below the first layer are earth mediums, and the transmitting device and the receiving device are generally positioned on the ground; in the ocean area, the first layer is an air layer, the second layer is a sea water layer, the third layer and below are earth mediums, the transmitting device is generally dragged by a ship cable to be located at a position 50 m away from the ocean floor, and the receiving device is generally all arranged on the ocean floor.
And step two, when the distance between the transmitting device and the receiving device is more than five times of the length of the transmitting source, the transmitting source is equivalent to an electric dipole, otherwise, the transmitting source is equivalent to a combination of a plurality of electric dipoles.
Step three, according to the Fourier series decomposition theory, decomposing the periodic emission current into a series of superimposed sine and cosine series, wherein each sine and cosine series represents a signal component at one frequency point, and in actual operation, the emission current signal is usually a square wave, bipolar wave or 2 with limited bandwidth n Periodic signals such as sequence pseudo-random waves, m-sequence pseudo-random waves and the like can be approximated by series combinations of hundreds to thousands of items according to the precision requirement.
Step four, carrying out single-frequency point electromagnetic response calculation through fast Hank transformation according to the layered medium model in the step one and the specific position of the transmitting-receiving device, and then sequentially obtaining electromagnetic field frequency domain responses corresponding to sine and cosine components of all frequency points in the step three through parallel calculation; and meanwhile, according to system response data provided by a receiving device manufacturer, obtaining the system response of the receiving device corresponding to all the frequency points in the third step through interpolation and polynomial fitting.
And fifthly, acting the layered medium electromagnetic field response corresponding to each frequency point obtained in the fourth step and the receiving device system response on each component of the emission current together, and finally combining and superposing all sine and cosine components to obtain a standard electromagnetic field time sequence excited by the galvanic couple source.
Step six, if the emission source is equivalent to an electric dipole, completing the forward modeling of the electromagnetic field time sequence of the controllable source excited by the electric dipole according to the standard electromagnetic field time sequence excited by the electric dipole obtained in the step five; and if the emission source is equivalent to a plurality of electric dipoles, repeating the steps three to five to sequentially obtain a plurality of standard electromagnetic field time sequences excited by the electric dipoles, and combining and superposing the standard electromagnetic field time sequences excited by the electric dipoles to obtain an electromagnetic field signal of the current total emission source so as to complete forward modeling of the electromagnetic field time sequences of the controllable source excited by the electric dipoles. In the invention, fig. 1 shows a forward modeling flow of a couple source excitation land and ocean controllable source electromagnetic field time sequence, wherein the prior geological feature of a measurement area, the position of a transmitting-receiving device, the waveform feature of a transmitting current and the partial frequency division point system response of the receiving device are known information determined before modeling, the modeling calculation process comprises the steps one to six, and finally, the modeled standard electromagnetic field time sequence is obtained.
Based on the first step to the sixth step, forward modeling is performed on the layered medium model shown in fig. 2 and fig. 3, and a time sequence forward modeling result of the land and ocean controllable source electromagnetic field is obtained. FIG. 8 shows a land controlled source electromagnetic survey, wherein three groups of square waves are emitted, the periods are respectively 10s, 0.15s and 0.004s, the waveforms of the electromagnetic fields which are being performed at the three frequencies are different, the waveforms are respectively similar to sharp pulse waves, sine waves, triangular waves and the like, and only one period of waveform is shown in the figure. FIG. 9 is a schematic illustration of a marine controlled source electromagnetic survey continuously emitting a 1s periodic square wave signal over a number of periods, modeled to yield induced electric and magnetic field signals. A further comparison was made with a set of measured electric and magnetic field data and modeling data. Fig. 10 (a) and 10 (b) show the comparison result of the measured electromagnetic field and the modeling electromagnetic field, fig. 10 (c) and 10 (d) show the comparison result of the measured electromagnetic field and the modeling electromagnetic field containing noise interference, and the modeling data substantially coincide with the measured data, indicating that the modeling method is effective.
In summary, the invention provides a method for modeling a forward modeling of a galvanic couple source excitation controllable source electromagnetic field time sequence, which comprehensively considers factors such as emission current waveform characteristics, emission-receiving device positions, receiving device system responses, measured area electrical characteristics and the like, generates a standard electromagnetic field time sequence signal in forward modeling, and provides support for quality evaluation and noise reduction processing of follow-up measured data. Compared with the prior art, the thermocouple source excitation controllable source electromagnetic field time sequence forward modeling method provided by the invention has the advantages that the electromagnetic field time sequence signal similar to measured data can be modeled by comprehensively considering the factors such as the emission current waveform, the emission-receiving position, the system response of the receiving device, the electrical characteristics of a measuring area and the like in the controllable source electromagnetic exploration, the modeling precision of the controllable source electromagnetic field time sequence signal is high, and the reference can be provided for the quality evaluation and noise reduction treatment of the follow-up measured data.
Spatially relative terms, such as "above … …," "above … …," "upper surface at … …," "above," and the like, may be used herein for ease of description to describe one device or feature's spatial location relative to another device or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "above" or "over" other devices or structures would then be oriented "below" or "beneath" the other devices or structures. Thus, the exemplary term "above … …" may include both orientations of "above … …" and "below … …". The device may also be positioned in other different ways (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
In addition, the terms "first", "second", etc. are used to define the components, and are only for convenience of distinguishing the corresponding components, and the terms have no special meaning unless otherwise stated, and therefore should not be construed as limiting the scope of the present invention.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The utility model provides a galvanic source excitation controllable source electromagnetic field time sequence forward modeling method which is characterized in that the galvanic source excitation controllable source electromagnetic field time sequence forward modeling method comprises the following steps:
step one, establishing a horizontal lamellar dielectric electrical model according to priori geological information;
step two, the emitting source is equivalent to one or a combination of a plurality of electric dipoles according to the length of the emitting source;
step three, aiming at any electric dipole, decomposing the emission current of the electric dipole into the combination of sine and cosine signal components with different frequencies;
generating electromagnetic field response of each frequency point of the layered medium model according to forward modeling of the transmitting-receiving position, and obtaining system response of the receiving device through interpolation and polynomial fitting;
fifthly, aiming at any one of the electric dipoles, combining and superposing sine and cosine signal components of the electromagnetic field response of each frequency point of the layered medium model and the response of the receiving device system on the emission current of any one of the electric dipoles, and obtaining a standard electromagnetic field time sequence excited by any one of the electric dipoles;
step six, if the emission source is equivalent to an electric dipole, completing the forward modeling of the electromagnetic field time sequence of the controllable source excited by the electric dipole source according to the standard electromagnetic field time sequence excited by the electric dipole obtained in the step five; and if the emission source is equivalent to a plurality of electric dipoles, repeating the third step to the fifth step, sequentially obtaining a plurality of standard electromagnetic field time sequences excited by the electric dipoles, and superposing the standard electromagnetic field time sequences excited by the electric dipoles to complete forward modeling of the electromagnetic field time sequences of the controllable source excited by the electric dipole source.
2. The method of modeling a time series forward model of an electromagnetic field of a controllable source excited by a galvanic source according to claim 1, wherein in the second step, when the length of the transmitting source is less than one fifth of the distance between the transmitting device and the receiving device, the transmitting source is equivalent to an electric dipole; when the length of the transmitting source is greater than or equal to one fifth of the distance between the transmitting device and the receiving device, the transmitting source is equivalent to a combination of a plurality of electric dipoles, and the length of any one electric dipole is smaller than one fifth of the distance between the transmitting device and the receiving device.
3. The method of modeling a time series forward model of an electromagnetic field of a controllable source excited by a galvanic source according to claim 2, wherein in the third step, the decomposition formula of the emission current of the electric dipole is as followsWherein I (T) is the emission current, T is the period of the emission current, a 0 As a constant term component, a k For the amplitude of the kth cosine component, b k For the amplitude, ω, of the kth sinusoidal component k The angular frequency of the kth sine component and the cosine component, t is the emission time of the emission current.
4. A method of modeling a time series forward model of a source electromagnetic field of controllable source excited by a galvanic source according to claim 3, wherein the constant term component a 0 Amplitude a of the kth cosine component k Amplitude b of the kth sinusoidal component k Can be according toAnd carrying out integral calculation on the emission current to obtain the emission current.
5. The method according to any one of claims 1 to 4, wherein in the fourth step, the electromagnetic field response of each frequency point of the layered medium model is derived based on maxwell's equations, and the calculated general formula of the electromagnetic field response of each frequency point of the layered medium model is as followsWherein G (r) is the field value of the response of the laminar dielectric electromagnetic field, < >>Is an integral kernel function corresponding to the zero-order Bessel function,>is an integral kernel function corresponding to a first order Bessel function, J 0 (λr) is a zero-order Bessel function, J 1 (λr) is a first order Bessel function, and λ and r are both Bessel function arguments.
6. The method for modeling a time series forward model of an electromagnetic field of a controllable source excited by a thermocouple of claim 5, wherein said maxwell's equations areWherein (1)>E is electric field single frequency response, H is magnetic field single frequency response, omega k The electromagnetic wave frequency is represented by mu, medium magnetic permeability, sigma, conductivity, J, a transmitting current source and i, wherein i is an imaginary unit.
7. The method of modeling a time series forward model of an electromagnetic field of a controllable source excited by a galvanic source according to claim 6, wherein in the fourth step, obtaining a system response of a receiving device by interpolation and polynomial fitting specifically comprises: according to the existing frequency points and the system responses corresponding to the frequency points, when the frequency to be calculated is within the existing frequency point range, obtaining the system responses corresponding to the frequency to be calculated through interpolation, and when the frequency to be calculated is out of the existing frequency point range, performing polynomial fitting on the system responses corresponding to the existing frequency points and the existing frequency points, and fitting out the system responses of the frequency to be calculated according to a polynomial fitting model.
8. The method for forward modeling of electromagnetic field time series of controllable source excited by electric dipole as defined in claim 7, wherein said standard electromagnetic field time series of electric dipole excitation is based onCalculation and acquisition, wherein T (T) is a time sequence obtained by forward modeling, T is observation time, and a 0 As a constant term component, a k For the amplitude of the kth cosine component, b k For the amplitude, ω, of the kth sinusoidal component k Angular frequencies for the kth sine and cosine component,/->Phase shift for electromagnetic response of layered dielectric model, < >>Phase shift for receiving device system response, A k Amplitude shift for electromagnetic response of layered medium model, A ks The amplitude shift brought about for the receiving device system response.
9. The method of modeling a time series forward model of a source electromagnetic field of a galvanic source excitation controlled source according to claim 1, wherein in the first step, a first layer of a typical model of a terrestrial horizontal layered medium is an air layer, and a second layer and layers below are layers of underground strata; the first layer of the ocean horizontal layered dielectric electric model is an air layer, the second layer is a sea water layer, and the third layer and below are all rock layers underground.
10. A couple source excitation controllable source electromagnetic field time series forward modeling system, characterized in that the couple source excitation controllable source electromagnetic field time series forward modeling system uses the couple source excitation controllable source electromagnetic field time series forward modeling method as claimed in claims 1 to 9 to perform electromagnetic field time series forward modeling.
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