CN110187394B - Method and device for acquiring formation resistivity anisotropy by double-field source electromagnetic sounding method - Google Patents
Method and device for acquiring formation resistivity anisotropy by double-field source electromagnetic sounding method Download PDFInfo
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- CN110187394B CN110187394B CN201910536766.4A CN201910536766A CN110187394B CN 110187394 B CN110187394 B CN 110187394B CN 201910536766 A CN201910536766 A CN 201910536766A CN 110187394 B CN110187394 B CN 110187394B
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- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
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Abstract
The invention relates to a method and a device for acquiring stratum resistivity anisotropy by a double-field source electromagnetic sounding method, wherein the method comprises the following steps: two field sources are distributed along two orthogonal directions outside the measuring area; the two field sources alternately transmit two mutually uncorrelated signals step by step; recording the current time sequence emitted by the two field sources; collecting orthogonal horizontal electric field response signals on each measuring point in a measuring area, and/or collecting vertical magnetic field response signals on each measuring point, and recording the signals as a time sequence; acquiring the whole-area apparent resistivity of the stratum below the measuring point of the measuring area according to the current time sequence, the parameters of the working device and the electromagnetic field response signal time sequence; and then, calculating the anisotropy coefficient of the formation resistivity of the measuring area according to the apparent resistivity of the whole area. The method has less observed components and simple and convenient processing process; the method has the advantages of strong anti-interference capability, high measurement precision, rich frequency points of the acquired all-region apparent resistivity, higher resolution ratio to the stratum and capability of improving the working efficiency.
Description
Technical Field
The invention relates to the technical field of geophysical exploration, in particular to a method and a device for acquiring stratum resistivity anisotropy by a double-field-source electromagnetic sounding method.
Background
Due to the fact that components of a medium on the earth shallow earth surface are unevenly distributed and various faults and structures are formed under the geological action, the underground complex geologic body has three-dimensional characteristics and anisotropy. In the field of electromagnetic exploration, the anisotropy characteristics of underground geologic bodies can be obtained through surface detection, and technical parameters can be provided for the fine inversion of electromagnetic sounding data. But the existing observation methods capable of accurately acquiring the anisotropy of the earth resistivity are few. The five-component magnetotelluric sounding method (MT, AMT) estimates two orthogonal electric main axis apparent resistivities by observing orthogonal horizontal electric fields (Ex, Ey), horizontal magnetic fields (Hx, Hy) and vertical magnetic field components (Hz), and can be used for analyzing the characteristics of the resistivity anisotropy. However, the estimation accuracy is not sufficient at some frequency points because the natural field signal is weak.
In addition, the existing artificial source electromagnetic sounding method exploration technology needs to use a plurality of field sources or tensor controllable source electromagnetic sounding method frequency conversion methods to obtain the anisotropy characteristics of the ground resistivity, the processing process is complex, the working efficiency is low, the anti-interference capability is weak, and particularly in mining area operation, high-quality data are difficult to acquire.
Disclosure of Invention
In view of this, the present invention provides a method and an apparatus for obtaining the formation resistivity anisotropy by a dual-field source electromagnetic sounding method to overcome the defects of the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme: a method for acquiring formation resistivity anisotropy by a double-field source electromagnetic sounding method comprises the following steps:
outside the measuring area, two field sources are arranged along two orthogonal directions of an x axis and a y axis: source x and source y;
the two field sources alternately emit two mutually uncorrelated signals step by step;
recording current time sequences Ix (t) emitted by a source x and a source y, Iy (t);
in a measuring area, acquiring orthogonal horizontal electric field response signals Ex and Ey at each measuring point, and/or acquiring vertical magnetic field response signals Hz at each measuring point, and recording the acquired response signals as time sequences Ex (t), Ey (t), and/or Hz (t);
acquiring the whole-region apparent resistivity of the formation of the measured region by a circular cross-correlation method according to the current time sequence, the parameters of the working device and the electromagnetic field response signal time sequence;
and calculating the anisotropic coefficient of the resistivity according to the whole-area apparent resistivity of the formation of the measuring area.
Optionally, the two field sources step by step and alternately emit two mutually uncorrelated signals, specifically including:
the source x and the source y need to be excited twice alternately step by step; when source x transmits a first signal, source y transmits a second signal; when source x transmits the second signal, source y transmits the first signal; the source x and the source y alternately emit a first signal and a second signal in steps, and the first signal and the second signal are not correlated with each other.
Optionally, the first signal is a single-frequency square wave signal, the second signal is an inverse repeating M-sequence pseudorandom signal, and the frequency of the single-frequency square wave signal is lower than the lowest frequency of the inverse repeating M-sequence pseudorandom signal.
Optionally, the obtaining the full-area apparent resistivity of the formation of the measurement area by a circular cross-correlation method according to the current time sequence, the working device parameter, and the electromagnetic field response signal time sequence includes:
matching the current time sequence Ix (t) emitted by the source x with an Ex (t) or Hz (t) time sequence, matching the current time sequence Iy (t) emitted by the source y with an Ey (t) or Hz (t) time sequence, and acquiring the frequency response of the formation of the measured area by a circular cross-correlation method;
and obtaining the full-area apparent resistivity of the formation of the measuring area by an iterative method according to the frequency response of the formation of the measuring area, the parameters of the working device, the excitation current and the received electromagnetic field component time sequence.
Optionally, calculating an anisotropy coefficient according to the whole-area apparent resistivity of the stratum to be measured by using a formula (1),
λ＝ρx(wi)/ρy(wi) Formula (1)
Wherein λ is an anisotropy coefficient, ρx(wi) And ρy(wi) Is wiApparent resistivity in both x and y directions at frequency.
Optionally, the distance between the source x and the center of the measurement area is approximately equal to the distance between the source y and the center of the measurement area, and the range of the distance between each field source and the center of the measurement area is 4km to 20 km.
Optionally, the formation comprises: land and sea.
The invention also provides a device for acquiring the anisotropy of the resistivity of the stratum by the double-field source electromagnetic sounding method, which comprises the following steps:
the first field source and the second field source are used for alternately transmitting two mutually uncorrelated signals step by step; the first field source and the second field source are arranged outside the measuring area along two orthogonal directions of an x axis and a y axis;
the current time sequence recording module is used for recording current time sequences Ix (t), Iy (t) emitted by the first field source and the second field source;
the acquisition module is used for acquiring orthogonal horizontal electric field response signals Ex and Ey on each measuring point and/or acquiring vertical magnetic field response signals Hz on each measuring point in the measuring area, and recording the acquired response signals as time sequences Ex (t), Ey (t) and/or Hz (t);
the acquisition module is used for acquiring the whole-area apparent resistivity of the stratum of the measuring area by a circular cross-correlation method according to the current time sequence, the parameters of the working device, the excitation current and the received electromagnetic field component time sequence;
and the calculation module is used for calculating the anisotropy of the formation resistivity of the measurement area according to the full-area apparent resistivity of the formation of the measurement area.
Optionally, the collecting module includes:
the non-polarized electrode and the electric field recorder are used for collecting orthogonal horizontal electric field response signals Ex and Ey on each measuring point; and/or the magnetic field acquisition module is used for acquiring vertical magnetic field response signals Hz on each measuring point;
the magnetic field acquisition module comprises a magnetic field recorder and a broadband induction type magnetic sensor, or a fluxgate sensor, or a high-temperature superconducting magnetometer.
Optionally, the first field source and the second field source are alternately excited twice in steps: when the first field source sends a first signal, the second field source sends a second signal; when the first field source sends a second signal, the second field source sends a first signal;
the first signal is a single-frequency square wave signal, the second signal is an inverse repeating M sequence pseudo-random signal, and the frequency of the single-frequency square wave signal is lower than the lowest frequency of the inverse repeating M sequence pseudo-random signal.
By adopting the technical scheme, the method for acquiring the anisotropy of the resistivity of the stratum by the double-field source electromagnetic sounding method comprises the following steps: outside the measuring area, two field sources, namely a source x and a source y, are arranged along two orthogonal directions of an x axis and a y axis; the two field sources alternately emit two mutually uncorrelated signals step by step; recording current time sequences Ix (t) emitted by a source x and a source y, Iy (t); in a measuring area, acquiring orthogonal horizontal electric field response signals Ex and Ey at each measuring point, and/or acquiring vertical magnetic field response signals Hz at each measuring point, and recording the acquired response signals as time sequences Ex (t), Ey (t), and/or Hz (t); acquiring the whole-region apparent resistivity of the stratum of the measuring region by a circular cross-correlation method according to the current time sequence, the parameters of the working device and the received electromagnetic field component time sequence; and calculating the anisotropy coefficient of the formation resistivity of the measuring area according to the full-area apparent resistivity of the formation of the measuring area. The method of the invention utilizes the characteristic that a single-frequency square wave signal and an inverse repetitive M sequence pseudo-random signal are not related to each other, and adopts a circular cross-correlation method to carry out electromagnetic prospecting, and the whole area apparent resistivity of the stratum of the measured area can be obtained only by collecting horizontal electric fields (Ex, Ey) in two directions on the measured point or only measuring a vertical magnetic field (Hz), thereby calculating the anisotropic coefficient of the stratum resistivity of the measured area. The method reduces observation components, and has simple and convenient processing process; because the power spectrum of the inverse repeating M sequence pseudorandom signal is a linear spectrum, the frequency band is wide and is irrelevant to power frequency interference, the method has strong anti-interference capability and high measurement precision, the obtained frequency points of the all-region apparent resistivity are rich, the stratum has high resolution and the working efficiency can be improved. In addition, the method simultaneously carries out field source excitation from two orthogonal directions, and is more favorable for obtaining the electromagnetic response of the deep stratum.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic flow chart of a method for obtaining formation resistivity anisotropy by a dual-field electromagnetic sounding method according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a probing layout according to an embodiment of the present invention;
FIG. 3(a) is a waveform diagram of the M-sequence pseudo-random signal with inverse repetition in accordance with one embodiment of the present invention;
FIG. 3(b) is a power spectrum of the M-sequence pseudo-random signal according to the first embodiment of the present invention;
FIG. 3(c) is a diagram illustrating an autocorrelation function of the M-sequence pseudo-random signal in the first embodiment of the present invention;
fig. 4 is a frequency spectrum covered by the single-frequency square wave signal and the inverse-repetitive M-sequence pseudo-random signal according to the first embodiment of the present invention;
FIG. 5 is a schematic structural diagram provided by an embodiment of the apparatus for obtaining formation resistivity anisotropy by dual-field electromagnetic sounding according to the present invention.
In the figure: 1. a first field source; 2. a second field source; 3. a current time sequence recording module; 4. an acquisition module; 5. an acquisition module; 6. and a calculation module.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without any inventive step, are within the scope of the present invention.
FIG. 1 is a schematic flow chart of a method for obtaining formation resistivity anisotropy by a dual-field electromagnetic sounding method according to an embodiment of the present invention.
As shown in fig. 1 and fig. 2, the method of the present embodiment includes:
s11: outside the measuring area, two field sources, namely a source x and a source y, are arranged along two orthogonal directions of an x axis and a y axis;
further, the source x and the source y are two orthogonal electric dipole sources; the distance between the source x and the center of the measuring area is approximately equal to the distance between the source y and the center of the measuring area, and the value range of the distance between each field source and the center of the measuring area is 4 km-20 km.
S12: the two field sources alternately emit two mutually uncorrelated signals step by step;
further, the two field sources alternately emit two mutually uncorrelated signals in steps, specifically including:
source x and source y require two excitations in steps alternating: when source x transmits a first signal, source y transmits a second signal; when source x transmits the second signal, source y transmits the first signal; the source x and the source y alternately emit a first signal and a second signal in steps, and the first signal and the second signal are not correlated with each other.
Specifically, as shown in fig. 3 and 4, the first signal is a single-frequency square wave signal, the second signal is an inversely repeated M-sequence pseudorandom signal, and the frequency of the single-frequency square wave signal is lower than the lowest frequency of the inversely repeated M-sequence pseudorandom signal.
S13: recording current time sequences Ix (t) emitted by a source x and a source y, Iy (t);
s14: in a measuring area, acquiring orthogonal horizontal electric field response signals Ex and Ey at each measuring point, and/or acquiring vertical magnetic field response signals Hz at each measuring point, and recording the acquired response signals as time sequences Ex (t), Ey (t), and/or Hz (t);
s15: acquiring the whole-region apparent resistivity of the formation of the measured region by a circular cross-correlation method according to the current time sequence, the parameters of the working device and the electromagnetic field response signal time sequence;
further, the obtaining of the full-area apparent resistivity of the formation of the measurement area by a circular cross-correlation method according to the current time series, the working device parameters and the electromagnetic field response signal time series includes:
matching the current time sequence Ix (t) emitted by the source x with an Ex (t) or Hz (t) time sequence, matching the current time sequence Iy (t) emitted by the source y with an Ey (t) or Hz (t) time sequence, and acquiring the frequency response of the formation of the measured area by a circular cross-correlation method;
according toThe frequency response and the working device parameters of the formation of the measuring area, and the receiving of the electromagnetic field component, and the obtaining of the apparent resistivity rho of the whole area of the formation of the measuring areax(wi) And ρy(wi)。
The specific calculation process of the processing is disclosed in the prior art (patent number: CN201610013962.X) for obtaining the frequency response of the formation of the measurement area through a circular cross-correlation method, and then obtaining the full-area apparent resistivity of the formation of the measurement area according to the frequency response of the formation of the measurement area, the parameters of a working device and the received electromagnetic field component.
Wherein the working device parameters include: parameters such as the distance between two poles of the horizontal galvanic couple source, the electrode distance of the receiving electrode, the distance between the midpoint of the receiving electrode and the midpoint of the two poles of the horizontal galvanic couple source, the included angle between the midpoint of the two poles of the horizontal galvanic couple source and the perpendicular bisector, the frequency of the transmitted signal and the like.
S16: and calculating the anisotropic coefficient of the resistivity according to the whole-area apparent resistivity of the formation of the measuring area.
Further, in step S16, an anisotropy coefficient is calculated according to the formula (1) based on the apparent resistivity of the whole area of the formation to be measured,
λ＝ρx(wi)/ρy(wi) Formula (1)
Wherein λ is an anisotropy coefficient, ρx(wi) And ρy(wi) Is wiApparent resistivity in both x and y directions at frequency.
In practical implementation, two field sources are arranged outside the measurement area along two orthogonal directions, namely an x axis and a y axis: a source x and a source y, the two field sources alternately emitting two mutually uncorrelated signals in steps. Receiving electrodes are distributed at the positions of measuring points in the measuring area along the x direction and the y direction and are used for collecting two orthogonal horizontal electric field components of Ex and Ey, or a broadband induction type magnetic sensor can be used for measuring a vertical magnetic field Hz, or horizontal electric fields Ex, Ey and the vertical magnetic field Hz are measured simultaneously, and electric field or magnetic field signals can be selected and measured in the three modes according to the actual field grounding condition. The same sampling rate is used by the acquisition instrument to record Ex and Ey horizontal electric field or vertical magnetic field Hz component as time series Ex (t) and Ey (t) or Hz (t), and the current signals sent by the source x and the source y are respectively recorded as current time series Ix (t) and Iy (t) by the same acquisition instrument at the same sampling rate.
The source x and the source y work simultaneously and respectively send a single-frequency square wave signal and an inverse-repetition M sequence pseudo-random signal, and the two field sources need to alternately excite the signals twice step by step: the first step is that a source x sends a single-frequency square wave, and a source y sends an inverse repetitive M sequence pseudo-random signal; and then, performing a second step, wherein when the source x sends the inverse repeating M pseudo-random signal, the source y sends a single-frequency square wave. The two field sources alternately emit two types of signals step by step, and the field source emission signal and the acquisition instrument acquisition signal are synchronously sampled at two ends through a satellite.
The horizontal electric and magnetic fields at the survey point are superimposed responses to the formation under excitation by source x and source y. Respectively matching the current time sequence Ix (t) emitted by the source x with an Ex (t) or Hz (t) time sequence, matching the current time sequence Iy (t) emitted by the source y with an Ey (t) or Hz (t) time sequence, and calculating the apparent resistivity rho of the whole area in two directions of the measuring point by using a calculation method disclosed in the prior document (patent number: CN201610013962.X) through a circular cross-correlation methodx(wi) And ρy(wi) Reuse the same frequency wiApparent resistivity rho in lower x and y directionsx(wi) And ρy(wi) And calculating the anisotropy coefficient.
The method of the embodiment has the following working bases: when Ix is a single-frequency square wave signal current, Iy is an inverse repeating M sequence pseudo-random signal current; ix is the current of the inverse repeating M sequence pseudo-random signal, Iy is the current of the single-frequency square wave signal; as shown in fig. 3, the power spectrum of the inverted repeat M sequence is a line spectrum, and the single-frequency square wave signal and the inverted repeat M sequence pseudo-random signal are uncorrelated, that is, when the Ix inverted repeat M sequence pseudo-random signal current is cyclically correlated with the electric field Ex or the vertical magnetic field Hz, the response of the Iy single-frequency square wave current is suppressed; similarly, when the Ix single-frequency square wave current and the electric field Ex or the vertical magnetic field Hz are used for circular cross correlation, the response of Iy inverse repetition M sequence pseudo-random signal current is suppressed; by two fieldsThe two times of excitation of the source and the corresponding response signals received by the acquisition module at the measuring point can obtain the apparent resistivity rho of the whole area calculated by the horizontal electric field in the x and y directionsx(wi) And ρy(wi) Or the apparent resistivity p of the whole region calculated from the measured vertical magnetic fieldx(wi) And ρy(wi) Wherein the frequency range comprises a single frequency square wave frequency and a frequency covered by the inverse repeating M-sequence pseudo-random signal.
In actual operation, an engineer sets the sequence order and the corresponding frequency of the M sequence pseudo-random signals according to different site grounding conditions and media, and after the sequence order and the frequency of the M sequence pseudo-random signals are determined, the frequency of the single-frequency square wave signals is set, wherein the frequency of the single-frequency square wave signals is lower than the lowest frequency of the M sequence pseudo-random signals and is adjustable.
It should be noted that the strata described in this embodiment include both terrestrial and marine strata; the measurement of the vertical magnetic field disclosed in the present embodiment is not limited to ground observation, and the vertical magnetic field may be measured by using an aircraft in the air, or by using an underwater vehicle in a marine environment, or by projecting a magnetic field receiver at the sea bottom. Similarly, field source excitation can be arranged in the ocean for ocean electromagnetic detection.
In addition, in the technical solution disclosed in this embodiment, the signal selection is not limited to the single-frequency square wave signal unrelated to the M sequence pseudo-random signal, and other signals unrelated to the M sequence pseudo-random signal may also be used.
The method of the embodiment utilizes the characteristic that a single-frequency square wave signal and an inverse repetitive M sequence pseudo-random signal are irrelevant to each other, and adopts a circular cross-correlation method to perform electromagnetic prospecting, so that the whole-area apparent resistivity of the stratum of the survey area can be obtained only by collecting horizontal electric fields (Ex, Ey) in two directions on a survey point or only measuring a vertical magnetic field (Hz), and the anisotropic coefficient of the stratum resistivity of the survey area is calculated. The method reduces observation components, and the processing process is simple and convenient; because the power spectrum of the inverse repeating M sequence pseudorandom signal is a linear spectrum, the frequency band is wide and is irrelevant to power frequency interference, the method has strong anti-interference capability and high measurement precision, the obtained frequency points of the all-region apparent resistivity are rich, the stratum has high resolution and the working efficiency can be improved. In addition, the method simultaneously carries out field source excitation from two orthogonal directions, and is more favorable for obtaining the electromagnetic response of the deep stratum.
FIG. 5 is a schematic structural diagram provided by an embodiment of the apparatus for obtaining formation resistivity anisotropy by dual-field electromagnetic sounding according to the present invention.
As shown in fig. 5, the apparatus according to this embodiment includes:
the device comprises a first field source 1 and a second field source 2, which are used for alternately transmitting two mutually uncorrelated signals step by step; the first field source and the second field source are arranged outside the measuring area along two orthogonal directions of an x axis and a y axis;
the current time sequence recording module 3 is used for recording current time sequences Ix (t), Iy (t) emitted by the first field source and the second field source;
the acquisition module 4 is used for acquiring orthogonal horizontal electric field response signals Ex and Ey on each measuring point and/or acquiring vertical magnetic field response signals Hz on each measuring point in the measuring area, and recording the acquired response signals as time sequences Ex (t), Ey (t) and/or Hz (t);
the acquisition module 5 is used for acquiring the whole-area apparent resistivity of the stratum of the measured area by a circular cross-correlation method according to the current time sequence, the working device parameters and the electromagnetic field response signal time sequence;
and the calculation module 6 is used for calculating the resistivity anisotropy according to the whole-region apparent resistivity of the formation of the measuring region.
Further, the acquisition module 4 includes:
the non-polarized electrode and the electric field recorder are used for collecting orthogonal horizontal electric field response signals Ex and Ey on each measuring point; and/or the magnetic field acquisition module is used for acquiring vertical magnetic field response signals Hz on each measuring point;
the magnetic field acquisition module comprises a magnetic field recorder and a broadband induction type magnetic sensor, or a fluxgate sensor, or a high-temperature superconducting magnetometer.
Further, the first field source and the second field source are alternately excited twice in steps: when the first field source sends a first signal, the second field source sends a second signal; when the first field source sends a second signal, the second field source sends a first signal;
the first signal is a single-frequency square wave signal, the second signal is an inverse repeating M sequence pseudo-random signal, and the frequency of the single-frequency square wave signal is lower than the lowest frequency of the inverse repeating M sequence pseudo-random signal.
In practical use of the device described in this embodiment, as shown in fig. 2, first, outside the measurement area, the first field source (source x) is arranged along the x-axis direction, the second field source (source y) is arranged along the y-axis direction, the source x and the source y work simultaneously to respectively send a single-frequency square wave signal and an inverse-repetitive M-sequence pseudorandom signal, and the two field sources need to alternately excite the signal twice step by step: the first step is that a source x sends a single-frequency square wave, and a source y sends an inverse repetitive M sequence pseudo-random signal; and then, performing a second step, wherein when the source x sends the inverse repeating M pseudo-random signal, the source y sends a single-frequency square wave. The two field sources alternately transmit two types of signals step by step, and the current time sequence recording module 3 and the acquisition module 4 perform synchronous sampling at the transmitting end and the receiving end through satellite time signals.
The acquisition module respectively matches a current time sequence Ix (t) emitted by a source x with an Ex (t) or Hz (t) time sequence, matches a current time sequence Iy (t) emitted by a source y with an Ey (t) or Hz (t) time sequence, and then calculates the apparent resistivity rho of the whole region of the measuring point by a circular cross-correlation method by using a calculation method disclosed in the prior document (patent number: CN10013962. X)x(wi) And ρy(wi) (ii) a Finally, the same frequency w is utilized by the calculation moduleiApparent resistivity rho in lower x and y directionsx(wi) And ρy(wi) And calculating the anisotropy coefficient.
The working principle of the device of the embodiment is the same as that of the method described above, and the detailed description is omitted here.
It should be noted that the strata described in this embodiment include, but are not limited to, land and marine strata; the device described in this embodiment can be deployed in the ocean for marine electromagnetic detection, in addition to detecting land.
In addition, in the technical solution disclosed in this embodiment, the signal selection is not limited to the single-frequency square wave signal unrelated to the M sequence pseudo-random signal, and other signals unrelated to the M sequence pseudo-random signal may also be used.
The device reduces observation components, and is more portable; because the power spectrum of the inverse repeating M sequence pseudorandom signal is a linear spectrum, the frequency band is wide and is irrelevant to power frequency interference, the response signal acquired by the device has strong anti-interference capability and high measurement precision, the acquired frequency points of the all-region apparent resistivity are rich, the resolution ratio of the stratum is high, and the working efficiency can be improved. In addition, the device simultaneously carries out field source excitation from two orthogonal directions through the first field source and the second field source, and is more favorable for obtaining the electromagnetic response of the deep stratum.
It is understood that the same or similar parts in the above embodiments may be mutually referred to, and the same or similar parts in other embodiments may be referred to for the content which is not described in detail in some embodiments.
It should be noted that the terms "first," "second," and the like in the description of the present invention are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. Further, in the description of the present invention, the meaning of "a plurality" means at least two unless otherwise specified.
Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps of the process, and alternate implementations are included within the scope of the preferred embodiment of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present invention.
It should be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the various steps or methods may be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a Programmable Gate Array (PGA), a Field Programmable Gate Array (FPGA), or the like.
It will be understood by those skilled in the art that all or part of the steps carried by the method for implementing the above embodiments may be implemented by hardware related to instructions of a program, which may be stored in a computer readable storage medium, and when the program is executed, the program includes one or a combination of the steps of the method embodiments.
In addition, functional units in the embodiments of the present invention may be integrated into one processing module, or each unit may exist alone physically, or two or more units are integrated into one module. The integrated module can be realized in a hardware mode, and can also be realized in a software functional module mode. The integrated module, if implemented in the form of a software functional module and sold or used as a stand-alone product, may also be stored in a computer readable storage medium.
The storage medium mentioned above may be a read-only memory, a magnetic or optical disk, etc.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (7)
1. A method for acquiring formation resistivity anisotropy by a double-field source electromagnetic sounding method is characterized by comprising the following steps:
outside the measuring area, two field sources are arranged along two orthogonal directions of an x axis and a y axis: source x and source y;
the two field sources alternately emit two mutually uncorrelated signals step by step;
recording current time sequences Ix (t) emitted by a source x and a source y, Iy (t);
in a measuring area, acquiring orthogonal horizontal electric field response signals Ex and Ey at each measuring point, and/or acquiring vertical magnetic field response signals Hz at each measuring point, and recording the acquired response signals as time sequences Ex (t), Ey (t), and/or Hz (t);
acquiring the full-area apparent resistivity of the stratum of the measuring area in the x direction and the y direction by a circular cross-correlation method according to the current time sequence, the working device parameters and the electromagnetic field response signal time sequence;
calculating the anisotropy coefficient of the formation resistivity of the measuring area according to the full-area apparent resistivity of the formation of the measuring area in the x direction and the y direction;
wherein the content of the first and second substances,
the two field sources alternately emit two mutually uncorrelated signals in steps, and the method specifically comprises the following steps:
the source x and the source y need to be excited twice alternately step by step; when source x transmits a first signal, source y transmits a second signal; when source x transmits the second signal, source y transmits the first signal; alternately transmitting a first signal and a second signal by a source x and a source y in steps, wherein the first signal and the second signal are not related to each other;
the first signal is a single-frequency square wave signal, the second signal is an inverse repeating M sequence pseudo-random signal, and the frequency of the single-frequency square wave signal is lower than the lowest frequency of the inverse repeating M sequence pseudo-random signal.
2. The method of claim 1, wherein the obtaining the full zone apparent resistivity of the survey zone formation in both x and y directions by cyclic cross-correlation based on the current time series and working device parameters, and electromagnetic field response signal time series comprises:
matching the current time sequence Ix (t) emitted by the source x with an Ex (t) or Hz (t) time sequence, matching the current time sequence Iy (t) emitted by the source y with an Ey (t) or Hz (t) time sequence, and acquiring the frequency response of the formation of the measured area by a circular cross-correlation method;
and acquiring the full-area apparent resistivity of the formation of the measuring area in the x direction and the y direction by an iterative method according to the frequency response of the formation of the measuring area, the parameters of a working device, the excitation current and the received electromagnetic field component.
3. The method of claim 1, wherein the anisotropy coefficient is calculated from the full apparent resistivity of the formation in both x and y directions by equation (1),
λ＝ρx(wi)/ρy(wi) Formula (1)
Wherein λ is an anisotropy coefficient, ρx(wi) And ρy(wi) Is wiApparent resistivity in both x and y directions at frequency.
4. A method according to any one of claims 1 to 3, wherein the distance from the source x to the centre of the survey area is equal to the distance from the source y to the centre of the survey area, and the distance from each field source to the centre of the survey area ranges from 4km to 20 km.
5. The method of any one of claims 1 to 3, wherein the formation comprises: land and sea.
6. A device for acquiring formation resistivity anisotropy by a double-field source electromagnetic sounding method is characterized by comprising the following steps:
the first field source and the second field source are used for alternately transmitting two mutually uncorrelated signals step by step; the first field source and the second field source are arranged outside the measuring area along two orthogonal directions of an x axis and a y axis;
the current time sequence recording module is used for recording current time sequences Ix (t), Iy (t) emitted by the first field source and the second field source;
the acquisition module is used for acquiring orthogonal horizontal electric field response signals Ex and Ey on each measuring point and/or acquiring vertical magnetic field response signals Hz on each measuring point in the measuring area, and recording the acquired response signals as time sequences Ex (t), Ey (t) and/or Hz (t);
the acquisition module is used for acquiring the full-area apparent resistivity of the stratum of the measuring area in the x direction and the y direction through a circular cross-correlation method according to the current time sequence, the parameters of the working device and the received electromagnetic field component time sequence;
the calculation module is used for calculating the anisotropy of the resistivity according to the full-area apparent resistivity of the formation of the measuring area in the x direction and the y direction;
wherein the content of the first and second substances,
the first field source and the second field source are alternately excited twice in steps: when the first field source sends a first signal, the second field source sends a second signal; when the first field source sends a second signal, the second field source sends a first signal;
the first signal is a single-frequency square wave signal, the second signal is an inverse repeating M sequence pseudo-random signal, and the frequency of the single-frequency square wave signal is lower than the lowest frequency of the inverse repeating M sequence pseudo-random signal.
7. The apparatus of claim 6, wherein the acquisition module comprises:
the non-polarized electrode and the electric field recorder are used for collecting orthogonal horizontal electric field response signals Ex and Ey on each measuring point; and/or the magnetic field acquisition module is used for acquiring vertical magnetic field response signals Hz on each measuring point;
the magnetic field acquisition module comprises a magnetic field recorder and a broadband induction type magnetic sensor, or a fluxgate sensor, or a high-temperature superconducting magnetometer.
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