A method for simultaneous measurement of polarization field and induction field based on electrical source

Abstract

The present invention discloses a method for simultaneous measurement of polarization field and induction field based on an electrical source, which relates to the field of geophysical exploration technology. The method performs simultaneous measurement of electric field and magnetic field under long pulse width emission conditions, obtains complete underground medium response signals including induction field and polarization field, and helps to obtain accurate electrical parameter information of underground medium, and improves the accuracy of interpreting underground target geological bodies. The main technical scheme of the present invention is: according to the detection requirements, the positions of the electrical excitation source and the measurement area are determined in advance, and the measurement lines and measurement points are arranged in the measurement area according to the specific measurement network layout, and the excitation source is used to emit a long pulse width square wave, and the electric field and magnetic field are measured simultaneously at all measurement points in the measurement area, and then according to the measured electric field and magnetic field data, combined with the primary field emission waveform data, the data containing the underground induction field and polarization field information is inverted and interpreted to obtain the electrical parameter information of the underground medium, and the electrical parameter information is used to interpret the underground target geological body.

Description

Technical Field

[0001] The present invention relates to the field of geophysical prospecting technology, and in particular to a method for simultaneously measuring a polarization field and an induction field based on an electrical source. Background Art

[0002] Transient electromagnetic method is a time domain electromagnetic exploration method. It is a geophysical exploration method that infers the resistivity characteristics of underground media by measuring the secondary induced magnetic field signal of underground media and finds out the underground geological structure. The traditional transient electromagnetic method measures the induction field of underground media, but in fact, the underground media also produces a polarization field under the action of the excitation source, which is particularly obvious in the high polarization geological background (such as underground carbonaceous strata), causing the transient electromagnetic data curve to be distorted.

[0003] At present, this problem is mainly solved by introducing a complex resistivity model that takes into account the polarization characteristics of the medium in data processing. In addition to obtaining resistivity parameters, polarization parameters can also be obtained.

[0004] However, the polarization parameters obtained by this method are not accurate. The reason is that in the traditional transient electromagnetic measurement method, a small pulse width square wave (generally less than 150 milliseconds) is used to stimulate the response of the underground medium, and the polarization response of the underground medium cannot be fully stimulated (polarization measurement requires a pulse width generally greater than 8 seconds, at least 50 times the pulse width of traditional transient measurement). At the same time, the traditional transient electromagnetic measurement collects early delay signals (generally within 50 milliseconds) after shutdown, and the polarization information is not fully collected (polarization measurement collects secondary field late delay signals, generally after 100 milliseconds). As a result, the polarization parameters obtained by the traditional collection method are inaccurate. Ultimately, different underground media cannot be identified by a combination of multiple electrical parameters. Summary of the invention

[0005] In view of this, the present invention provides a method for simultaneous measurement of polarization field and induction field based on an electrical source. The main purpose is to perform simultaneous measurement of electric field and magnetic field under long pulse width emission conditions, obtain a complete underground medium response signal including induction field and polarization field, and obtain accurate electrical parameter information of the underground medium through joint synchronous inversion of electric and magnetic fields, which helps to more accurately interpret the underground target geological body.

[0006] In order to achieve the above object, the present invention mainly provides the following technical solutions:

[0007] The present application provides a method for simultaneously measuring a polarization field and an induction field based on an electrical source, the method comprising:

[0008] Determine the location of the electrical excitation source and the measurement area;

[0009] Lay out the survey lines and points in the survey area according to the specific survey network layout;

[0010] The excitation source emits a long pulse width square wave to complete simultaneous measurement of electric field and magnetic field at all measurement points in the measurement area;

[0011] Based on the measured electric and magnetic field data, combined with the primary field emission waveform data, the data containing the underground induction field and polarization field information are inverted and interpreted to obtain the electrical parameter information of the underground medium, which is used to interpret the underground target geological body.

[0012] In some modified implementations of the present application, the arranging of the measuring lines and measuring points in the measuring area according to the specific measuring network arrangement includes:

[0013] A Cartesian plane rectangular coordinate system is established in the survey area, and the direction along the survey line is set as the x-axis direction, and the direction perpendicular to the survey line is set as the y-axis direction;

[0014] The measurement network is arranged according to a preset layout rule, which at least includes: the distance between measurement points on the same measurement line is a first threshold, the distance between adjacent measurement lines is a second threshold, and the measurement network layout size is the product of the first threshold and the second threshold.

[0015] In some modified implementations of the present application, the collection of the electric field and the magnetic field are synchronized with the excitation source, wherein the electric field adopts a full waveform measurement method, and the magnetic field measures the early delay signal after shutdown.

[0016] In some modified implementations of the present application, the electric field measurement is measured along two directions, namely, an Ex component along the direction of the measurement line and an Ey component perpendicular to the direction of the measurement line.

[0017] In some modified implementations of the present application, the magnetic field measurement is carried out at multiple times within 56 microseconds to 1000 microseconds after the square wave is linearly turned off, and the magnetic field measurement at least includes measuring the magnetic field value of Hz in the vertical direction.

[0018] In some modified implementations of the present application, the emission waveform is recorded separately each time the excitation source emits.

[0019] In some modified implementations of the present application, the long pulse width square wave is a set of signals with adjustable pulse width between 4 seconds and 256 seconds, and the pulse width is selected after conducting experiments based on the actual geological conditions in the survey area.

[0020] In some modified implementations of the present application, the data containing underground induction field and polarization field information are inverted and interpreted based on the measured electric field and magnetic field data in combination with the primary field emission waveform data to obtain the electrical parameter information of the underground medium, including:

[0021] Preprocessing of full waveform electric field data;

[0022] By introducing the Cole-Cole complex resistivity model, the polarization parameters other than resistivity are fully considered in the forward and inversion models, an objective function including both electric field and magnetic field terms is constructed, and inversion is carried out to obtain the electrical parameter information of the underground medium.

[0023] In some modified implementations of the present application, the preprocessing of the full-waveform electric field data includes: eliminating the influence of the excitation waveform change on the measurement through full-waveform sampling comparison.

[0024] In some modified implementations of the present application, the electrical parameter information includes at least: resistivity, polarizability, time constant and frequency correlation coefficient.

[0025] By means of the above technical solution, the technical solution provided by the present invention has at least the following advantages:

[0026] The present invention provides a method for simultaneous measurement of polarization field and induction field based on an electrical source. According to the detection requirements, the present invention predetermines the position of the electrical excitation source and the measurement area, and arranges the measurement lines and measurement points in the measurement area according to the specific measurement network layout. The excitation source is used to emit a long pulse width square wave to complete the simultaneous measurement of the electric field and magnetic field of all measurement points in the measurement area. Then, according to the measured electric field and magnetic field data, combined with the primary field emission waveform data, the data containing the underground induction field and polarization field information is inverted and interpreted to obtain the electrical parameter information of the underground medium, and the electrical parameter information is used to interpret the underground target geological body. Compared with the prior art, the problem that the traditional transient electromagnetic method is incomplete in obtaining polarization information and cannot accurately invert the polarization parameters of the underground medium is solved. The present invention performs simultaneous measurement of the electric field and magnetic field under the condition of long pulse width emission, obtains a complete underground medium response signal containing the induction field and polarization field, and obtains accurate electrical parameter information of the underground medium through the joint synchronous inversion of the electric and magnetic fields, thereby facilitating a more accurate interpretation of the underground target geological body.

[0027] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0029] Figure 1A flow chart of a method for simultaneously measuring a polarization field and an induction field based on an electrical source provided in an embodiment of the present invention;

[0030] Figure 2 A flow chart of another method for simultaneously measuring polarization field and induction field based on an electrical source provided in an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of an observation system according to an embodiment of the present invention;

[0032] Figure 4 This is a measurement point measurement layout diagram exemplified in an embodiment of the present invention;

[0033] Figure 5 This is a schematic diagram of the electric field and magnetic field component measurement period exemplified in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to enable the scope of the present invention to be fully communicated to those skilled in the art.

[0035] The embodiment of the present invention provides a method for simultaneously measuring the polarization field and the induction field based on an electrical source, such as Figure 1 As shown, the method provides the following specific steps:

[0036] 101. Determine the location of the electrical excitation source and the measurement area.

[0037] In the embodiment of the present invention, the positions of the electrical excitation source and the measuring area are determined according to the detection target and task of the working area.

[0038] 102. Survey lines and points shall be laid out in the survey area according to the specific survey network layout.

[0039] 103. The excitation source emits a long pulse width square wave to complete the simultaneous measurement of the electric field and magnetic field at all measuring points in the measuring area.

[0040] In the embodiment of the present invention, the purpose of using a long pulse width square wave is to fully excite the polarization response of the underground medium, thereby achieving full excitation and measurement of the complete polarization field and induction field information of the underground medium based on the electrical source transient electromagnetic measurement.

[0041] 104. Based on the measured electric field and magnetic field data, combined with the primary field emission waveform data, the data containing the underground induction field and polarization field information are inverted and interpreted to obtain the electrical parameter information of the underground medium. The electrical parameter information is used to interpret the underground target geological body.

[0042] In an embodiment of the present invention, the electrical parameter information includes at least resistivity, polarizability, time constant and frequency correlation coefficient. The embodiment of the present invention can obtain more accurate electrical parameter information of the underground medium, thereby utilizing the difference in electrical parameters of the underground medium to eliminate geological background interference and enhance the recognition capability of the target geological body under a high polarization background.

[0043] As described above, the method for simultaneous measurement of polarization field and induction field based on electrical source provided by the embodiment of the present invention solves the problem that the traditional transient electromagnetic method is incomplete in obtaining polarization information and cannot accurately invert the polarization parameters of the underground medium. The present invention performs simultaneous measurement of electric field and magnetic field under long pulse width emission conditions to obtain a complete underground medium response signal including induction field and polarization field, and obtains accurate electrical parameter information of the underground medium through joint synchronous inversion of electric and magnetic fields, thereby helping to more accurately interpret the underground target geological body.

[0044] In order to explain the above embodiment in more detail, the embodiment of the present invention also provides another method for simultaneously measuring the polarization field and the induction field based on an electrical source, such as Figure 2 As shown, the method is a further detailed explanation of the above embodiment, and the embodiment of the present invention provides the following specific steps:

[0045] 201. Determine the location of the electrical excitation source and the measurement area.

[0046] 202. Establish a Cartesian plane rectangular coordinate system in the survey area, set the direction along the survey line as the x-axis direction, and the direction perpendicular to the survey line as the y-axis direction.

[0047] 203. The measurement network is arranged according to a preset arrangement rule, wherein the preset arrangement rule at least includes: the distance between measurement points on the same measurement line is a first threshold, the distance between adjacent measurement lines is a second threshold, and the measurement network arrangement size is the product of the first threshold and the second threshold.

[0048] In the embodiment of the present invention, steps 202-203 are specific implementation methods for laying out the measurement network. For example, the measurement network is generally laid out as 50m×200m, the distance between measurement points on the same measurement line is 50m, and the distance between adjacent measurement lines is 200m.

[0049] For example, Figure 3 The schematic diagram of the observation system shown in the figure shows the measurement area and measurement network. The measurement network is laid out in the measurement area according to the grid size of 50m×200m. The number of measurement lines is n and they are numbered L. i (i=0,1,2…n), each measuring line has m measuring points, numbered S j (j=0, 1, 2, ...m), measure the full waveform electric field in the x and y directions and the magnetic field in the z direction after shutdown.

[0050] 204. The excitation source emits a long pulse width square wave to complete simultaneous measurement of the electric field and magnetic field at all measuring points in the measuring area to obtain measured electric field and magnetic field data.

[0051] Among them, the long pulse width square wave can be a group of signals with adjustable pulse width between 4 seconds and 256 seconds, and the pulse width is selected after conducting experiments based on the actual geological conditions in the survey area.

[0052] In an embodiment of the present invention, the excitation source emits a long pulse width square wave, and the measurement of all measuring points in the measurement area is completed through the measurement unit. The collection of electric field and magnetic field is synchronized with the excitation source, wherein the electric field adopts a full waveform measurement method, and the magnetic field measures the early delay signal after shutdown.

[0053] Further, the embodiments of the present invention provide Figure 4 The measurement point layout diagram shown in the figure, Figure 4 The measuring instruments and accessories involved and their functions are as follows: ① Electromagnetic field collector, used for collecting and storing electric field and magnetic field signals; ② Non-polarized electrode, used for collecting electric field signals; ③ Cable, used to connect non-polarized electrode and electromagnetic field collector; ④ Magnetic sensor, used for collecting magnetic field signals; ⑤ Magnetic sensor connecting line, used to connect magnetic sensor and electromagnetic field collector.

[0054] Figure 4 It shows that the electric field measurement is measured in two directions, namely the electric field along the measuring line (Ex component) and the electric field perpendicular to the measuring line (Ey component). Four lead chloride non-polarized electrodes are used as grounded measuring electrodes. When arranged, shielded electrode lines are used to connect to the measuring host from the east, west, south and north directions. The magnetic field measurement is carried out with early delay after the square wave linear shutdown (for example, multiple moments within 56 microseconds-1000 microseconds), mainly measuring the vertical magnetic field (Hz component), and using a fluxgate sensor to obtain low-frequency magnetic field signals. During the measurement, the excitation source and the receiving unit are strictly synchronized with GPS or a constant temperature crystal oscillator. In order to eliminate the influence of the change in the intensity of the excitation source emission signal during the acquisition process, the excitation source records the emission waveform separately each time it is emitted, so that the acquired signal can be corrected once in the inversion interpretation.

[0055] Explanation of the relationship between the transmitted square wave waveform and the collected signal, such as Figure 5The diagram of the measurement period of the electric field and magnetic field components is shown. (a) in the figure is the square wave waveform emitted by the excitation source, which is used to stimulate the induction field and polarization field response of the underground medium. It is plotted in a rectangular coordinate system, with the horizontal axis being the power supply time in seconds (s) and the vertical axis being the power supply voltage in volts (V). (b) in the figure is a measurement schematic diagram corresponding to the emission waveform. A quarter of the emission waveform is extracted from (a) and plotted in a rectangular coordinate system, with the horizontal axis being the power supply time in seconds (s) and the vertical axis being the power supply voltage in volts (V). The electric field component adopts a full waveform acquisition method, that is, it is acquired during the power supply period in addition to the power off period. The magnetic field component adopts a post-shutdown acquisition method, and the magnetic field response within 56-1000 milliseconds is acquired after the power supply is completely shut down.

[0056] For the embodiments of the present invention, by measuring the electric field and magnetic field under the long pulse width transmission signal, the underground medium response including the complete polarization field and the induction field is obtained, which can effectively solve the problem that the traditional transient electromagnetic method is incomplete in obtaining polarization information and cannot accurately invert the polarization parameters of the underground medium.

[0057] Furthermore, the embodiments of the present invention obtain complete polarization field and induction field information of underground media through full-waveform electric field measurement under long pulse width emission of the electrical source and magnetic field measurement after shutdown, thereby obtaining richer electromagnetic response information of underground media without significantly increasing the workload, that is, obtaining multiple electrical parameters, which helps to improve the interpretation accuracy of underground target bodies and thus enhance the ability to identify underground media.

[0058] 205. Preprocessing of full waveform electric field data.

[0059] According to the embodiment of the present invention, the influence of the excitation waveform change on the measurement is eliminated through full waveform sampling comparison.

[0060] By introducing the complex resistivity model of Cole-Cole, the polarization parameters other than resistivity are fully considered in the forward and inverse models, and an objective function including both electric field terms and magnetic field terms is constructed to carry out inversion and obtain the electrical parameter information of the underground medium.

[0061] Among them, the objective function is constructed based on relative error, and the singularity of the inversion process is reduced and overfitting is avoided by introducing a regularization term based on roughness. Its formula is as follows (1):

[0062]

[0063] in, is the objective function, e T C m e is the electric field term, h T C m h is the magnetic field term,

[0064] E obs To measure the electric field value, E pre To predict the electric field value, H obs To measure the magnetic field value, H pre To predict the magnetic field value, e T is the transpose of e, h T is the transpose of h, m represents the number of model parameters, C m is the data fitting error matrix, m T is the transpose of m, D is the roughness matrix, and this item can be used to impose smooth constraints on the model parameters.

[0065] The electrical parameter information includes at least resistivity, polarizability, time constant and frequency correlation coefficient. Furthermore, the underground target geological body is interpreted by combining multiple electrical parameters with geological data.

[0066] In summary, the method for simultaneous measurement of polarization field and induction field based on an electrical source provided by an embodiment of the present invention can utilize a long pulse width square wave signal to fully stimulate the induction field and polarization field response of the underground medium, and obtain the complete induction field and polarization field response of the underground medium by jointly acquiring the electric field and magnetic field, thereby reducing the singularity of the inversion, and obtaining reliable polarization parameters while obtaining the resistivity parameters, thereby providing a guarantee for the identification of multiple electrical parameters of the underground medium. This method is based on the transient electromagnetic principle of an electrical source, does not require additional improvements to the instrument and equipment, is convenient for field data collection, and is easy to implement.

[0067] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent insertion, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

[0068] It should be understood by those skilled in the art that it is also necessary to explain that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity or device including the element.

Claims

1. A method for simultaneously measuring polarization field and induction field based on an electrical source, characterized in that: The method comprises: Determine the location of the electrical excitation source and the measurement area; Lay out the survey lines and points in the survey area according to the specific survey network layout; The excitation source emits a long pulse width square wave to complete simultaneous measurement of the electric field and magnetic field at all measuring points in the measuring area; the long pulse width square wave is a set of signals with adjustable pulse width between 4 seconds and 256 seconds, and the pulse width is selected after conducting experiments based on the actual geological conditions of the measuring area; the acquisition of the electric field and the magnetic field are synchronized with the excitation source, wherein the electric field adopts a full waveform measurement method, and the magnetic field measures the early delay signal after shutdown; Based on the measured electric and magnetic field data, combined with the primary field emission waveform data, the data containing the underground induction field and polarization field information are inverted and interpreted to obtain the electrical parameter information of the underground medium, which is used to interpret the underground target geological body.

2. The method according to claim 1, characterized in that The method of laying out the measuring lines and measuring points in the measuring area according to the specific measuring network arrangement includes: A Cartesian plane rectangular coordinate system is established in the survey area, and the direction along the survey line is set as the x-axis direction, and the direction perpendicular to the survey line is set as the y-axis direction; The measurement network is arranged according to a preset layout rule, which at least includes: the distance between measurement points on the same measurement line is a first threshold, the distance between adjacent measurement lines is a second threshold, and the measurement network layout size is the product of the first threshold and the second threshold.

3. The method according to claim 1, characterized in that The electric field measurement is measured in two directions, namely, the Ex component along the direction of the measuring line and the Ey component perpendicular to the direction of the measuring line.

4. The method according to claim 1, characterized in that: The magnetic field measurement is carried out at multiple times within 56 microseconds to 1000 microseconds after the square wave is linearly turned off, and the magnetic field measurement at least includes measuring the magnetic field value of Hz in the vertical direction.

5. The method according to claim 1, characterized in that The emission waveform is recorded separately for each emission of the excitation source.

6. The method according to claim 1, characterized in that According to the measured electric field and magnetic field data, combined with the primary field emission waveform data, the data containing the underground induction field and polarization field information is inverted and interpreted to obtain the electrical parameter information of the underground medium, including: Preprocessing of full waveform electric field data; By introducing the Cole-Cole complex resistivity model, the polarization parameters other than resistivity are fully considered in the forward and inversion models, an objective function including both electric field and magnetic field terms is constructed, and inversion is carried out to obtain the electrical parameter information of the underground medium.

7. The method according to claim 6, characterized in that The preprocessing of the full waveform electric field data includes: eliminating the influence of the excitation waveform change on the measurement through full waveform sampling comparison.

8. The method according to claim 1, characterized in that: The electrical parameter information includes at least: resistivity, polarizability, time constant and frequency correlation coefficient.

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