Synchronization Signal and Pump Noise Separation Method Based on Fractional Fourier Transform

Abstract

The present invention discloses a method for separating synchronization signals from pump noise based on fractional Fourier transform, and relates to the field of drilling technology. Specifically, the method includes: after a mud pressure wave signal is formed underground, a preliminary noise elimination process is performed on the mud pressure wave signal transmitted by the mud channel on the well, and the signal after preliminary noise elimination is roughly synchronized with the local signal; in combination with the rough synchronization result, only the fractional Fourier transform is used to separate the synchronization signal from the noise signal through the different characteristic performances of different signals in the fractional domain; then, a fine synchronization process is performed, so as to achieve the purpose of improving the signal-to-noise ratio and synchronization accuracy of the synchronization signal at the ground receiving end, and finally the signal after preliminary noise elimination is analyzed. The present invention performs multiple rounds of synchronization and multiple rounds of noise elimination in view of the special noise existing in the measurement while drilling system and its special fractional domain characteristics, thereby effectively improving the accuracy and stability of the synchronization of the measurement while drilling signal, and greatly optimizing the reliability and transmission performance of the entire system.

Description

Technical Field

[0001] The present invention relates to the technical field of drilling, and particularly to a method for separating synchronous signals and pump noise based on fractional Fourier transform. Background Art

[0002] In recent years, in order to further improve the drilling efficiency, the real-time logging information such as orientation, formation characteristics, and drilling parameters required to be transmitted by the measurement while drilling (MWD) system has shown an explosive growth trend.

[0003] The traditional positive / negative pulse MWD data transmission system is limited by a low data transmission rate, which has become a technical bottleneck restricting the further development of the MWD system. To meet the increasing demand for information volume, the industry has proposed a technical solution using a shear valve to realize the mud continuous wave. This continuous wave data transmission technology can significantly improve the data transmission rate of the MWD system and become a promising alternative technology. The MWD mud continuous wave system while drilling achieves the effect of intercepting the mud through the continuous movement of the motor rotor, forming a continuous pressure wave. The swing frequency of the motor rotary valve rotor can reach 40 Hz, and various modulation methods such as OOK, FSK, and PSK are used for carrier modulation, so that a transmission rate of 40 bps can be achieved. Compared with the maximum transmission rate of 5 bps of the positive / negative pulse transmission system, the MWD mud continuous wave system while drilling can better meet the growing demand for downhole data transmission.

[0004] However, the mud pressure wave signal generated in this way is a non-standard sine signal and a non-standard linear frequency modulation (LFM) signal, that is, non-linear distortion occurs at the transmitting end. Especially in practical applications, the peak value of the synchronization curve is affected by noise. Especially as the depth increases, the amplitude of the signal received on the ground gradually decreases, resulting in a gradual deterioration of the synchronization accuracy of the system, further causing an increase in the system bit error rate, and ultimately limiting the effective transmission depth of the MWD system; in addition, there are multiple reflections and refractions in the mud channel, resulting in a multipath effect, and multiple synchronization peaks will be generated at the ground reception, and it is easy to generate false synchronization due to the influence of superimposed noise. Summary of the Invention

[0005] In view of the above, the present invention aims to provide at least a method for separating synchronous signals and pump noise based on fractional Fourier transform, in order to improve the accuracy and stability of synchronization and greatly optimize the reliability and transmission performance of the entire MWD system.

[0006] The technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for separating synchronous signals and pump noise based on fractional Fourier transform, which includes:

[0008] Under the well, a mud pressure wave signal is formed through encoding and modulation;

[0009] Above the well, preliminary noise elimination processing is performed on the mud pressure wave signal transmitted through the mud channel;

[0010] The waveform signal after preliminary noise elimination is preliminarily synchronized with the local waveform signal;

[0011] Above the well, according to the preliminary synchronization result, the waveform signal is subjected to fractional Fourier transform, and separation filtering processing is performed frame by frame in the fractional domain to complete noise elimination;

[0012] The waveform signal after separation and noise elimination is subjected to secondary synchronization;

[0013] Based on the secondary synchronization result, the waveform signal after preliminary noise elimination is demodulated and decoded above the well.

[0014] In at least one possible implementation manner, the above the well performs fractional Fourier transform on the waveform signal according to the preliminary synchronization result, and performs separation filtering processing frame by frame in the fractional domain to complete noise elimination, including:

[0015] According to the preliminary synchronization result, the synchronization initial position is obtained, and based on the synchronization initial position and the established frame structure of the waveform signal, the synchronization header area of the current frame is obtained;

[0016] Perform fractional Fourier transform on the data segment of the waveform signal corresponding to the synchronization header area, and separate the synchronization signal from the pump noise through different fractional domain angles.

[0017] In at least one possible implementation manner, the obtaining of the synchronization header area of the current frame includes:

[0018] Determine the start position and the end position of the synchronization signal according to the preliminary synchronization result and the frame structure;

[0019] Add a preset redundant interval before and / or after the start position and the end position respectively to obtain the synchronization header area.

[0020] In at least one possible implementation manner, the separation of the synchronization signal from the pump noise includes:

[0021] When performing fractional Fourier transform on the synchronization header area, perform peak search on the waveform signal of each angle;

[0022] Only retain the signal corresponding to the maximum peak angle as the required target signal, and perform inverse fractional Fourier transform to obtain the synchronization signal after noise elimination in the fractional domain.

[0023] In at least one possible implementation manner, the preliminary noise elimination processing includes:

[0024] Learn the pump noise frequency through the pump pulse sensor and generate a simulated pump noise waveform;

[0025] The simulated pump noise waveform is subtracted from the waveform of the received mud pressure wave signal to eliminate the pump noise.

[0026] In a second aspect, the present invention provides a synchronization signal and pump noise separation device based on fractional Fourier transform, comprising:

[0027] A signal generation module, used for encoding and modulating mud pressure wave signals in the well;

[0028] A preliminary noise elimination module is used to perform preliminary noise elimination processing on the mud pressure wave signal transmitted through the mud channel on the well;

[0029] A coarse synchronization module, used for performing preliminary synchronization between the waveform signal after preliminary noise elimination and the local waveform signal;

[0030] The signal-to-noise separation module is used to perform fractional Fourier transform on the waveform signal based on the preliminary synchronization result, and perform separation filtering processing frame by frame in the fractional domain to complete noise elimination;

[0031] A precision synchronization module is used to perform secondary synchronization on the waveform signal after separation and noise elimination;

[0032] The signal analysis module is used to perform uphole demodulation and decoding on the waveform signal after preliminary noise elimination based on the secondary synchronization result.

[0033] In at least one possible implementation, the signal-to-noise separation module includes:

[0034] A data segment determination unit to be processed, used to obtain a synchronization initial position according to a preliminary synchronization result, and obtain a synchronization header area of a current frame based on the synchronization initial position and a predetermined frame structure of a waveform signal;

[0035] The signal-to-noise separation unit is used to perform fractional Fourier transform on the data segment of the waveform signal corresponding to the synchronization header area, and separate the synchronization signal from the pump noise through different fractional domain angles.

[0036] In a third aspect, the present invention provides an electronic device, comprising: one or more processors, a memory and one or more computer programs, wherein the memory may adopt a non-volatile storage medium, wherein the one or more computer programs are stored in the memory, and the one or more computer programs include instructions, and when the instructions are executed by the device, the electronic device performs the method as described in the first aspect or any possible implementation manner of the first aspect.

[0037] Fourthly, the present invention provides a computer-readable storage medium, in which a computer program is stored. When the computer program runs on a computer, it enables the computer to execute the method described in the first aspect or any possible implementation manner of the first aspect.

[0038] Fifthly, the present invention further provides a computer program product. When the computer program product is executed by a computer, it is used to execute the method described in the first aspect or any possible implementation manner of the first aspect. In a possible design of the fifth aspect, the relevant programs involved in this product can be stored in whole or in part on a memory packaged together with the processor, or can be stored in whole or in part on a storage medium not packaged together with the processor.

[0039] It should be understood that the technical solutions of the second to fifth aspects of the embodiments of the present application are consistent with those of the first aspect of the embodiments of the present application, and the beneficial effects obtained by each aspect and the corresponding feasible implementation manners are similar, so they will not be elaborated here.

[0040] The main design concept of the present invention is to form a mud pressure wave signal through encoding and modulation underground, perform preliminary noise cancellation processing on the mud pressure wave signal transmitted through the mud continuous wave channel on the ground, and perform coarse synchronization between the preliminarily noise-cancelled signal and the local signal; then, in combination with the coarse synchronization result, only use the fractional Fourier transform to separate the synchronization signal and the noise signal through the different characteristic performances of different signals in the fractional domain, and then perform fine synchronization processing after converting to the time domain, so as to achieve the purpose of improving the signal-to-noise ratio and synchronization accuracy of the synchronization signal at the ground receiving end. Finally, based on the fine synchronization result, the preliminarily noise-cancelled pressure wave signal is demodulated and decoded on the ground. Compared with the traditional scheme, the present invention performs at least two rounds of synchronization and two rounds of noise cancellation processing for the special noise and the special fractional domain characteristics existing in the MWD system while drilling, so as to effectively improve the accuracy and stability of the synchronization of the measurement signal while drilling, and greatly optimize the reliability and transmission performance of the entire MWD system. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described below in conjunction with the drawings, where:

[0042] Figure 1 FIG. is a schematic diagram of the rotor of a pulser for an MWD mud continuous wave system;

[0043] Figure 2 FIG. is a schematic diagram of the waveform of the LFM signal emitted by the pulser;

[0044] Figure 3 FIG. is a schematic flowchart of a method for separating a synchronization signal and pump noise based on the fractional Fourier transform provided by an embodiment of the present invention;

[0045] Figure 4 Schematic diagram of the representation of time-domain signals and frequency-domain signals in a three-dimensional rectangular coordinate system;

[0046] Figure 5 Schematic diagram of the Fourier transform in the time-frequency plane;

[0047] Figure 6 Schematic diagram of the FRFT in the time-frequency plane;

[0048] Figure 7 Schematic diagram of two signals in the time-frequency plane;

[0049] Figure 8 Schematic diagram of two signals in the fractional domain with a rotation angle of ;

[0050] Figure 9 Schematic diagram of two signals in the fractional domain with a rotation angle of ;

[0051] Figure 10 Time-domain waveform diagram of the simulated pump noise provided by the embodiment of the present invention;

[0052] Figure 11 Spectrum diagram of the simulated pump noise provided by the embodiment of the present invention;

[0053] Figure 12 Schematic diagram of the fractional domain of the LFM signal and the sine signal provided by the embodiment of the present invention;

[0054] Figure 13 Schematic diagram of the synchronization signal and pump noise separation device based on the fractional Fourier transform provided by the embodiment of the present invention;

[0055] Figure 14 Schematic diagram of the electronic device provided by the embodiment of the present invention. Detailed implementation manners

[0056] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

[0057] In the MWD (Measuring While Drilling) mud continuous wave system while drilling, the ground pump noise is dozens of times the amplitude of the useful signal. Therefore, how to eliminate the ground pump noise is one of the important technologies to ensure the high-speed transmission of this system.

[0058] As mentioned above, the MWD mud continuous wave system while drilling achieves the interception effect on the mud by continuously moving the rotor of the motor-controlled pulser, forming a continuous pressure wave. The mud pressure wave signal generated in this way is a non-standard sine signal and a non-standard linear frequency modulation (LFM) signal, that is, nonlinear distortion occurs at the transmitting end. To elaborate, the fluid flow rate through the gap between the rotor and the stator can be expressed as:

[0059] (1)

[0060] Among them, is the flow coefficient, is the pore area, is the flow rate through the void, is the density of the liquid, is the pressure difference across the void. From the above equation, we can obtain:

[0061] (2)

[0062] According to Figure 1 the schematic diagram of the pulser rotor, the maximum area through which the fluid can flow is:

[0063] (3)

[0064] Among them, , and are the characteristic radii of the stator, with the unit of ; is the clearance width between the outer ring of the rotor and the inner wall of the drill pipe, with the unit of .

[0065] When the pulser is operating, the flow area is:

[0066] (4)

[0067] Among them, is the angular velocity of the rotation of the pulser rotor, with the unit of , and can be expressed as:

[0068] (5)

[0069] Among them, is the rotation frequency of the rotor, with the unit of ; is the included angle of the rotor blades, with the unit of °; is the speed controlling the rotation of the rotor, that is, the given control signal.

[0070] Therefore, the flow area when the pulser is operating is:

[0071] (6)

[0072] In summary, the pressure signal of the pulsator .

[0073] From the above formula, it can be obtained that the pressure signal and the given signal have the following relationship.

[0074] (7)

[0075]

[0076] From the above formula, it can be seen that the pressure signal and the given signal show a non-linear relationship. When the given waveform is an LFM signal, the waveform diagram of the pressure wave signal generated by the pulsator is as Figure 2 shown. This non-linear relationship causes the peak value of the synchronization curve to decrease when using the correlation algorithm, affecting the accuracy and reliability of the synchronization of the measurement-while-drilling system. At the same time, in the actual application process, the traditional correlation synchronization method is greatly affected by noise. When there is too much residual noise, the synchronization peak will not be obvious, resulting in system missed synchronization or false synchronization. In addition, there are multiple reflections and refractions in the mud channel, resulting in the multipath effect, and multiple synchronization peaks will be generated at the ground reception, and it is easy to generate false synchronization due to the superposition of noise effects.

[0077] From the above analysis of the current situation, the present invention believes that this non-linear distortion can be separated and filtered in the fractional domain, so as to achieve the effect of denoising the received mud pressure wave signal. In addition, for the multipath effect caused by multiple reflections and refractions in the mud channel, multiple synchronization peaks will be generated at the ground reception. When there is too much residual noise, the synchronization peak will not be obvious and it is easy to generate false synchronization. Similarly, this multipath effect changes to multiple signal peaks in the fractional domain. Since the parameters of the transmitted LFM signal are known, the multipath components can be filtered out in the fractional domain, so as to achieve the effect of denoising the received mud pressure wave signal.

[0078] And it needs to be mentioned here first that the measurement-while-drilling mud continuous wave system is mainly divided into two parts: downhole and uphole. Downhole, the system mainly consists of modules such as a continuous wave generator, a motor drive circuit, a downhole central control unit, and a power supply; uphole, the system mainly consists of modules such as a ground sensor, a ground data processing unit, a decoding unit, and a control unit.

[0079] Different from the past, the downhole part can control the mud (drilling fluid) pressure to generate the expected waveform, and this waveform signal is transmitted to the uphole through the mud. The process of the uphole part performing data processing and decoding and restoring the data on the waveform received from the downhole via the ground sensor can be refined into Figure 3The shown process solution, one of the main concepts of which is the separation of the synchronization signal and pump noise based on the fractional Fourier transform, specifically including:

[0080] Step S1: The downhole encodes and modulates to form a mud pressure wave signal;

[0081] The downhole transmitter of the MWD mud continuous wave system while drilling will control the motor according to the agreements such as the encoding method, frame structure, modulation method, data rate, etc. of the protocol to make the rotor rotate, so that the mud flow rate between the rotor and the stator changes regularly, and finally it is reflected in the change of the mud pressure wave. This has been described above and will not be elaborated here.

[0082] Step S2: The wellhead conducts preliminary noise elimination processing on the mud pressure wave signal transmitted through the mud channel;

[0083] What can be elaborated here is that the influence of the mud continuous wave channel on the useful signal is mainly divided into two parts: interference and attenuation. Specifically for the treatment of interference, the MWD system while drilling is mainly affected by pump noise, bit reflection, motor noise, etc. Therefore, the present invention proposes that before implementing subsequent synchronization, digital signal processing can be first performed at the wellhead to reduce the influence of interference on the decoding of the useful signal, so as to obtain relatively more useful downhole data as much as possible.

[0084] Therefore, it can be considered to adopt the technology of data signal processing at the wellhead to perform preliminary filtering processing on the mud pressure wave signal collected by the wellhead receiving end to eliminate the influence of noise on the system. In some preferred embodiments, a noise elimination method can be adopted, which is to learn the pump noise frequency through a pump stroke sensor and generate an analog pump noise waveform, and subtract the analog pump noise waveform from the waveform of the received mud pressure wave signal.

[0085] In addition, for channel attenuation, in the MWD system while drilling, as the well depth increases, the attenuation of the useful signal amplitude increases, and this fading belongs to frequency-selective fading; among them, the channel fading is related to the elastic properties of the drill pipe, the friction between particles in the mud, the compression coefficient of the mud, etc. For the influence of channel fading on the data signal, the useful data signal received by the wellhead pressure sensor will be distorted, and it can be eliminated by means such as equalization at the wellhead, and the present invention does not limit this. For the synchronization signal, since the frequency of the LFM signal changes uniformly from f1 to f2, the attenuation of different frequencies is different, and the channel produces non-linear distortion to the LFM signal, which will also affect the signal synchronization effect. By separating the signal and noise through the following fractional Fourier transform, the influence of this non-linear distortion on the synchronization peak can also be weakened.

[0086] Step S3: Perform preliminary synchronization on the waveform signal after preliminary noise elimination and the local waveform signal;

[0087] The idea of this step is to process the waveform data after denoising in the previous step frame by frame with the local waveform signal through a synchronization algorithm to obtain the synchronization position, thereby completing the rough synchronization of the signal data between the downhole and the surface. As mentioned above, step S2 is the preliminary filtering of channel interference. Therefore, the preliminary synchronization link involved here can be understood as "rough synchronization", aiming to obtain the synchronization position of the waveform signals on the surface and downhole, providing technology for subsequent fractional-order processing to separate pump noise.

[0088] The specific synchronization process involved does not fall within the focus of the present invention. A traditional or improved signal synchronization mechanism can be considered, and the present invention will not elaborate or limit it.

[0089] Step S4: On the surface, perform a fractional Fourier transform on the original waveform signal according to the preliminary synchronization result, and perform separation filtering processing frame by frame in the fractional domain to complete denoising;

[0090] Specifically, in some embodiments of the present invention, it may refer to obtaining the initial synchronization position according to the preliminary synchronization result (here referring to the rough "head position"), and then based on the initial synchronization position and the established frame structure of the waveform signal, obtaining the synchronization header region of the current frame (referring to the data segment plus the redundant region between the two ends of the rough synchronization signal. Therefore, the "synchronization header region" refers to the data segment with the redundant region added between the head and the tail), and performing a fractional Fourier transform on the data segment of the waveform signal corresponding to this synchronization header region, so as to separate the synchronization signal (involving the original waveform signal) from at least the pump noise (and other signal components). Among them, other signal components include the remaining frequency component signals caused by the nonlinear distortion generated at the transmitting end, the multipath components generated by refraction and reflection in the channel, and the nonlinear distortion of the LFM signal caused by the frequency-selective fading characteristic of the mud continuous wave channel.

[0091] Combined with the above conceptual framework, in actual operation, step S4 can be specifically expanded into the following implementation links:

[0092] First, according to the synchronization position obtained from the preliminary synchronization result, determine the start position and the end position of the synchronization signal according to the frame structure; add a preset redundant interval before and after the start position and the end position respectively to obtain the synchronization header region to be processed twice.

[0093] Secondly, when performing a fractional Fourier transform on the synchronization head area, a peak search can be performed for the waveform signal at each angle, wherein the maximum peak value represents the fractional domain where the LFM signal is located, and the signals at the remaining angles can all be judged as noise; it can also be added here that the specific transformation means are not limited in actual operation, that is, it can be obtained by different discrete fractional Fourier transforms, such as the Ozaktas algorithm, the Pei algorithm, etc.; in addition, depending on the medium used, a sparse fractional Fourier transform can also be used. In addition, considering the computational complexity and the amount of calculation, the present invention also proposes another method of directly deriving the angle where the LFM signal peak is located according to the LFM signal setting in the frame structure. Specifically, separating the synchronization signal from the pump noise includes: performing a fractional Fourier transform on the synchronization head area, deriving the fractional domain plane angle according to the downhole LFM signal setting, and all the remaining plane signals are considered to be noise, and only performing a fractional Fourier inverse transform on the angle signal to obtain the synchronization signal after fractional domain denoising.

[0094] Finally, only the signal at the angle corresponding to the maximum peak is retained, and a fractional-order inverse Fourier transform is performed to obtain the signal after denoising in the fractional domain.

[0095] Here is a further supplement, when performing the aforementioned peak search, it can also be expanded to: Perform a lookup for the variable and find the peak on the u-axis for the FRFT result of the LFM signal Therefore, it is assumed that the peak position obtained by two-dimensional search is the rotation angle , then finally only The angle signal is inversely transformed by fractional Fourier transform.

[0096] That is, compared with the traditional electromagnetic wave, there is no transmission distortion, only multiple components in the fractional domain caused by multipath / unintentional intermodulation interference. The present invention proposes a signal-to-noise separation scheme based on fractional Fourier transform for the special noise and its special fractional domain characteristics existing in the MWD system while drilling. In order to fully understand the technical implementation concept of the separation of synchronization signal and pump noise based on fractional Fourier transform proposed by the present invention, a complete and specific introduction will be given below:

[0097] If a point is represented by a rectangular coordinate system, this point can be regarded as (a, b). Then, this point can be regarded as represented by the coefficient a multiplied by the unit vector in the x-axis direction (i.e. basis function 1) plus the coefficient b multiplied by the unit vector in the y-axis direction (i.e. basis function 2), that is, transforming this point into a linear combination represented by the basis function.

[0098] Similarly, the Fourier transform can be viewed as a set of bases A new coordinate system is formed. The process of representing a signal using this new coordinate system is the Fourier transform, and the basis functions of the Fourier transform are a cluster of exponential functions. Taking a rectangular wave as an example, the Fourier transform is to approximately represent the rectangular wave by the linear superposition of an infinite number of sine functions (sine waves).

[0099] Based on this, if a three-dimensional rectangular coordinate system is established with time t as the x-axis, frequency f as the y-axis, and signal amplitude as the z-axis, then the time-domain representation of the signal can be regarded as a two-dimensional representation method with the x-axis as the abscissa and the z-axis as the amplitude; the frequency-domain representation of the signal (i.e., the Fourier transform of the signal) can be regarded as a two-dimensional representation method with the y-axis as the abscissa and the z-axis as the amplitude. In such a coordinate system, taking the cos signal as an example, its waveform in the time domain and in the frequency domain is as Figure 4 shown.

[0100] It can be known from the properties of the Fourier transform that:

[0101] (8)

[0102] (9)

[0103] (10)

[0104] Therefore, in this coordinate system, the Fourier transform can be regarded as rotating the two-dimensional plane representing the signal counterclockwise by 90 degrees around the coordinate origin with the z-axis as the rotation axis. Performing the Fourier transform successively in these four directions can respectively obtain , , and , as Figure 5 shown.

[0105] From this perspective of rotation, the fractional Fourier transform (FRFT) can be regarded as an extension of the Fourier transform. The Fourier transform rotates the two-dimensional plane representing the signal by an integer multiple of 90 degrees, while the FRFT rotates the two-dimensional plane representing the signal by an arbitrary angle. Assuming this rotation angle is , the x-axis becomes the u-axis after rotation, and the y-axis becomes the v-axis after rotation. At this time, the FRFT domain where the u-axis is located is called the fractional domain. Then the FRFT schematic diagram can refer to Figure 6 .

[0106] If the Fourier transform is understood as performing a 90-degree transformation on a function, then the FRFT can be understood as performing a Fourier transform on a function by a non-integer multiple of 90 degrees. It can be seen from the figure that when , the FRFT is the time-domain expression of the signal ; When the coordinate axis rotates counterclockwise , the FRFT is the frequency-domain representation of the signal ; When the coordinate axis rotates counterclockwise , the FRFT is ; When the coordinate axis rotates counterclockwise , the FRFT is ; When the coordinate axis rotates counterclockwise , the FRFT is . Therefore, the FRFT includes the Fourier transform, that is, the FRFT is an extension of the Fourier transform - changing the rotation angle to an arbitrary angle, rather than limiting the rotation angle to an integer multiple of ninety degrees. The mathematical definition of the FRFT is:

[0107] (11) (12)

[0108] Wherein, , is an integer, represents the FRFT operator, represents the rotation angle of the FRFT.

[0109] In summary, the FRFT can be regarded as a new coordinate system composed of a set of basis , and the process of representing the signal using this coordinate system is the FRFT.

[0110] From the characteristics of the basis function, for the Fourier transform, if the input is a linear combination of complex sinusoidal signals, such as the cosine function or the sine function, then there will be impulses in the frequency domain. Similarly, for the FRFT, if the input is a complex LFM signal, then there will be an impulse in a certain fractional domain. For example, the LFM signal in the mud continuous waveform signal involved in the present invention has good aggregation characteristics, making it convenient to separate signals in the fractional domain. Thus, assuming that the chirp rates of all signals are different, then in the u domain where the signal has an impulse, other signals will not have peaks. Here, taking two signals as an example, the distributions of signal 1 and signal 2 in the time-frequency plane are as Figure 7 shown. Then, for the u domains where signal 1 and signal 2 can obtain peaks, reference can be made to Figure 8 and Figure 9 respectively for illustration.

[0111] Based on the above analysis and introduction, in the MWD system while drilling concerned by the present invention, since the pressure sensor at the surface receiving end is installed near the mud pump and is several kilometers away from the signal transmitting end (downhole instrument), among the signals collected by this pressure sensor, the pressure fluctuation generated when the mud pump is working has the strongest amplitude energy. This pressure pulsation caused by the operation of the mud pump is called mud pump noise (pump noise), which will seriously interfere with the measurement accuracy and signal quality of the MWD system, and corresponding signal processing and filtering technologies need to be adopted to suppress it.

[0112] When operating on a drilling platform, the interference frequency of the nth harmonic introduced by the mud pump can be expressed as the following model, which is composed of the linear superposition of multiple single-component sine signals.

[0113] (13)

[0114] In the formula, n is the harmonic order, represents the fundamental frequency, that is, the operating frequency of the mud pump (Hz).

[0115] Through practice, the present invention believes that the energy of the harmonic multiple of the number of cylinders of the mud pump is the strongest. In view of this characteristic of pump noise in the measurement while drilling scenario, it is proposed that the pump noise can be simulated. Here, taking the time-domain waveform and frequency spectrum diagram of simulating the pump noise of a 5-cylinder pump as an example, as Figure 10 and Figure 11 shown.

[0116] Combined with the pump noise simulation results, in the mud pressure wave signal, since the sine signal can be regarded as an LFM signal with a modulation frequency of 0, the energy of the pump noise only exists on the plane of α = π / 2. Based on the analysis of this characteristic, the present invention believes that the pump noise signal and the LFM signal can be filtered and separated in the fractional domain.

[0117] Since the pump noise signal can be regarded as the linear combination of multiple sine signals, the following analysis takes the sine signal as an example.

[0118] Specifically, in the MWD system while drilling, the LFM signal is used as the pilot signal, expressed as follows:

[0119] (14)

[0120] Taking a single-component sine signal as an example for derivation, it is expressed as the following formula:

[0121] (15)

[0122] Among them, and are the amplitudes of the LFM signal and the sine signal respectively, and The starting frequency and the frequency modulation rate are respectively, and T is the duration of the two signals.

[0123] (1) LFM signal:

[0124] ① When :

[0125] When , the LFM signal achieves the best energy concentration in the fractional domain. At this time, its fractional spectrum is:

[0126] (16)

[0127] Among them, .

[0128] Then,

[0129] (17)

[0130] Then the maximum value is:

[0131] (18)

[0132] Therefore, the LFM signal shows an impulse characteristic in the fractional domain of , and the impulse position is at . The bandwidth of the nth zero-crossing in this fractional domain is .

[0133] ② When :

[0134] (19)

[0135] Among them,

[0136] (20)

[0137] (21)

[0138] (22)

[0139] (23)

[0140] Among them, and are both Fresnel integrals. Therefore,

[0141] (24)

[0142] Therefore, the bandwidth of this LFM signal in the fractional domain of is .

[0143] Since in practical applications, the bandwidth is most likely much greater than 1, therefore:

[0144] (25)

[0145] (2) Sine signal:

[0146] The sine signal can be regarded as when the LFM signal, substitute into the above derivation.

[0147] ① When :

[0148] When , the sine signal achieves the best aggregation performance in this fractional domain, that is, the frequency domain, and there is:

[0149] (26)

[0150] Then the peak value is:

[0151] (27)

[0152] The sine signal in the fractional domain (i.e., the frequency domain) of the nth zero-crossing bandwidth is .

[0153] ② When :

[0154] When , then there is:

[0155] (28)

[0156] Among them,

[0157] (29)

[0158] (30)

[0159] Therefore, there is:

[0160] (31)

[0161] The bandwidth of the sine signal in the fractional domain is .

[0162] From the above analysis, it can be concluded that when , the LFM signal has a peak value in the fractional domain, and at this time the maximum value of the sine signal is ; When the sine signal has a peak and at this time, the maximum value of the LFM signal is . Based on this, Figure 12 a schematic can be obtained.

[0163] Therefore, the signal separation can be performed by utilizing the energy concentration characteristics of the LFM signal and the sine signal in different fractional domains.

[0164] In the fractional domain, that is, the frequency domain, the sine signal is the useful signal and the LFM signal is the interference signal. The signal-to-interference ratio is:

[0165] (32)

[0166] In the fractional domain, the LFM signal is the useful signal and the sine signal is the interference signal. The signal-to-interference ratio is:

[0167] (33)

[0168] As mentioned above, another implementation step of step S4 is as follows:

[0169] S41. Perform a fractional Fourier transform on the synchronization header area.

[0170] S42. Derive the plane angle in the fractional domain where the LFM signal is located according to the LFM signal setting in the downhole frame structure. Only the signal at this angle is the useful LFM signal, and all other plane signals are considered as noise.

[0171] S43. Only perform an inverse fractional Fourier transform on the signal in the fractional domain of this angle to obtain the synchronized signal after noise cancellation in the fractional domain.

[0172] Continuing from the previous text, step S5: Perform secondary synchronization on the waveform signal after fractional domain separation and noise cancellation;

[0173] Similarly, the specific synchronization process is not the focus of the present invention. A traditional or improved signal synchronization mechanism can be considered, and the present invention will not elaborate and limit this.

[0174] Step S6: Perform demodulation and decoding on the waveform signal after preliminary noise cancellation based on the secondary synchronization result.

[0175] That is to say, the previously mentioned signal after preliminary noise cancellation is used for both coarse synchronization and the final demodulation and decoding process; while the signal targeted by the fractional Fourier transform in the intermediate link is the synchronization region segment obtained from the original waveform or the coarse synchronization result of the waveform after preliminary noise cancellation, and the output of the secondary synchronization result is also the synchronization position information.

[0176] Finally, demodulation can be performed in ways such as coherent demodulation or non - coherent demodulation. Then, the 01 codeword is obtained through decision - making. Next, the corresponding parameter values are obtained according to the established protocols such as the aforementioned encoding method and frame structure composition. For example, in some embodiments, coherent demodulation and hard - decision decoding methods can be used, but the present invention does not make limitations or elaborations on this.

[0177] In summary, the main design concept of the present invention is as follows: forming a mud pressure wave signal through encoding and modulation underground, performing preliminary noise reduction processing on the mud pressure wave signal transmitted through the mud continuous - wave channel on the wellhead, and performing coarse synchronization between the preliminarily noise - reduced signal and the local signal; then, combining the coarse - synchronization result, only using the fractional - order Fourier transform, separating the synchronization signal and the noise signal through different characteristic performances of different signals in the fractional domain, and then performing fine - synchronization processing after converting to the time domain, so as to achieve the purpose of improving the signal - to - noise ratio and synchronization accuracy of the synchronization signal at the ground receiving end. Finally, signal - to - noise separation is completed, and finally, based on the secondary - synchronization result, the waveform signal after preliminary noise elimination is demodulated and decoded on the wellhead. Compared with the traditional scheme, the present invention aims at the special noise and special fractional - domain characteristics existing in the MWD system while drilling, eliminates the signal components of noise / interference / distortion at other angles, and only retains the LFM signal at the angle with the largest peak value, thereby effectively improving the accuracy and stability of the synchronization of the measurement signal while drilling, and greatly optimizing the reliability and transmission performance of the entire MWD system.

[0178] Corresponding to the above - mentioned various embodiments and preferred solutions, the present invention also provides an embodiment of a synchronization signal and pump - noise separation device based on the fractional - order Fourier transform, as Figure 13 shown, which may specifically include the following components:

[0179] A signal generation module 131, which is used to form a mud pressure wave signal through encoding and modulation underground;

[0180] A preliminary noise reduction module 132, which is used to perform preliminary noise elimination processing on the mud pressure wave signal transmitted through the mud channel on the wellhead;

[0181] A coarse synchronization module 133, which is used to perform preliminary synchronization between the preliminarily noise - reduced waveform signal and the local waveform signal;

[0182] A signal - to - noise separation module 134, which is used to perform fractional - order Fourier transform on the waveform signal on the wellhead according to the preliminary synchronization result, and perform separation filtering processing frame by frame in the fractional domain to complete noise reduction;

[0183] A fine synchronization module 135, which is used to perform secondary synchronization on the waveform signal after separation and noise reduction;

[0184] A signal analysis module 136, which is used to perform demodulation and decoding on the waveform signal after secondary synchronization on the wellhead.

[0185] It should be understood that the above Figure 13 The division of each component in the synchronous signal and pump noise separation device based on the fractional Fourier transform shown is only a division of logical functions. In actual implementation, it can be fully or partially integrated into a physical entity, or physically separated. And these components can all be implemented in the form of software called by processing elements; some components can also be implemented in the form of software called by processing elements, and some components can be implemented in the form of hardware. For example, a certain above-mentioned module can be a separately established processing element, or can be integrated in a certain chip of an electronic device. The implementation of other components is similar. In addition, these components can be integrated together in whole or in part, or can be independently implemented. In the implementation process, each step of the above method or each of the above components can be completed through the integrated logic circuit of the hardware in the processor element or the instructions in the form of software.

[0186] For example, these above components can be one or more integrated circuits configured to implement the above method, such as: one or more application specific integrated circuits (ASIC), or, one or more digital signal processors (DSP), or, one or more field programmable gate arrays (FPGA), etc. Again, these components can be integrated together and implemented in the form of a system-on-a-chip (SOC).

[0187] Based on the above embodiments and their preferred solutions, those skilled in the art can understand that in actual operation, the technical concept involved in the present invention can be applied to various implementation manners. The present invention uses the following carriers as illustrative explanations:

[0188] (1) An electronic device. Specifically, the device may include: one or more processors, a memory, and one or more computer programs, wherein the one or more computer programs are stored in the memory, and the one or more computer programs include instructions. When the instructions are executed by the device, the device executes the steps / functions of the foregoing embodiments or equivalent implementation manners.

[0189] Specifically, the electronic device can be an electronic device related to a computer, such as but not limited to various computing terminals and electronic products, etc.

[0190] Specifically, the processor, communication interface, and memory can all communicate with each other via a communication bus. Among them, the processor may be a central processing unit (CPU), a digital signal processor (DSP), a microcontroller, or a digital signal processor. It may also include a graphics processing unit (GPU), an embedded neural-network processor (hereinafter referred to as: NPU), and an image signal processor (hereinafter referred to as: ISP). The processor may also include an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiments of the present invention. In addition, the processor may have the function of operating one or more software programs, and the software programs may be stored in a storage medium such as a memory. The aforementioned memory / storage medium may include: non-volatile memory, such as a non-removable disk, a USB flash drive, a mobile hard disk, an optical disc, etc., as well as a read-only memory (hereinafter referred to as: ROM), a random access memory (hereinafter referred to as: RAM), etc.

[0191] Even though the present invention does not limit the specific form of the electronic device, for the purpose of schematic introduction, Figure 14 As shown, the present invention provides a schematic structural diagram of an embodiment of an electronic device. Specifically, the electronic device 900 includes a processor 910 and a memory 930. Among them, the processor 910 and the memory 930 can communicate with each other through an internal connection path to transmit control and / or data signals. The memory 930 is used to store a computer program, and the processor 910 is used to call and run the computer program from the memory 930. The above-mentioned processor 910 and the memory 930 may be integrated into a processing device, and more commonly, they are independent components. The processor 910 is used to execute the program code stored in the memory 930 to implement the above functions. Specifically, in implementation, the memory 930 may also be integrated in the processor 910, or independent of the processor 910.

[0192] In addition, in order to make the functions of the electronic device 900 more complete, the electronic device 900 may further include one or more of an input unit 960, a display unit 970, an audio circuit 980, a camera 990, and a sensor 901, etc. The audio circuit may also include a speaker 982, a microphone 984, etc. Among them, the display unit 970 may include a display screen.

[0193] Furthermore, the above-mentioned electronic device 900 may further include a power supply 950 for supplying electrical energy to various components or circuits in the electronic device 900.

[0194] It should be understood that Figure 14The electronic device 900 shown can implement each process of the method provided in the foregoing embodiments. The operations and / or functions of each component in the electronic device 900 can respectively implement the corresponding processes in the foregoing method embodiments. For specific reference, see the descriptions of the method, device, and other embodiments in the foregoing text. To avoid repetition, the detailed descriptions are appropriately omitted here.

[0195] It should be understood that Figure 14 The processor 910 in the electronic device 900 shown may be a system-on-chip (SOC). The processor 910 may include a central processing unit (hereinafter referred to as CPU), and may further include other types of processors, such as a graphics processing unit (hereinafter referred to as GPU), etc., which will be introduced in detail later.

[0196] In summary, the various processors or processing units inside the processor 910 can cooperate together to implement the previous method process, and the corresponding software programs of the various processors or processing units can be stored in the memory 930.

[0197] (2) A computer data storage medium, on which a computer program or the foregoing device is stored. When the computer program or the foregoing device is executed, the computer is enabled to execute the steps / functions of the foregoing embodiments or equivalent embodiments.

[0198] In several embodiments provided by the present invention, if any function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer data storage medium. Based on such an understanding, some technical solutions of the present invention, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of the following software products.

[0199] It should be particularly noted that the storage medium may refer to a server or a similar computer device. Specifically, that is, the foregoing computer program or the foregoing device is stored in the storage device in the server or a similar computer device.

[0200] (3) A computer program product (the product may include the foregoing device). When the computer program product runs on a terminal device, the terminal device is enabled to execute the method for separating a synchronization signal and pump noise based on the fractional Fourier transform of the foregoing embodiments or equivalent embodiments.

[0201] As can be seen from the description of the above embodiments, those skilled in the art can clearly understand that all or part of the steps in the above implementation methods can be implemented by means of software plus a necessary general hardware platform. Based on this understanding, the above computer program product may include, but is not limited to, an APP.

[0202] In the embodiments of the present invention, "at least one" means one or more, and "a plurality" means two or more. "And / or" describes the association relationship of associated objects and indicates that there can be three relationships. For example, A and / or B can represent the cases of A existing alone, A and B existing simultaneously, and B existing alone. Among them, A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after. "At least one of the following" and its similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, and c can represent: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, and c can be single or multiple.

[0203] Those skilled in the art can realize that the various modules, units, and method steps described in the embodiments disclosed in this specification can be implemented by a combination of electronic hardware, computer software, and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0204] In addition, the embodiments in this specification are all described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other. In particular, for embodiments such as devices and equipment, since they are basically similar to the method embodiments, the relevant parts can refer to the partial description of the method embodiments. The device, equipment, etc. embodiments described above are only illustrative. The modules, units, etc. described as separate components may or may not be physically separated, that is, they can be located in one place, or they can be distributed to multiple places, such as the nodes of a system network. Specifically, some or all of the modules and units can be selected according to actual needs to achieve the purpose of the above embodiment solutions. Those skilled in the art can understand and implement without creative efforts.

[0205] The structure, features and effects of the present invention have been described in detail based on the embodiments shown in the drawings above. However, the above are only the preferred embodiments of the present invention. It should be noted that for the technical features involved in the above embodiments and their preferred modes, those skilled in the art can reasonably combine and match them into various equivalent solutions without departing from or changing the design concept and technical effects of the present invention. Therefore, the scope of implementation of the present invention is not limited by the drawings shown. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified into equivalent changes, should still be within the protection scope of the present invention as long as they do not exceed the spirit covered by the description and the drawings.

Claims

1. A method for separating synchronous signals and pump noise based on fractional Fourier transform, characterized in that include: The mud pressure wave signal is formed through encoding and modulation in the well; The well performs preliminary noise elimination processing on the mud pressure wave signal transmitted through the mud channel; Preliminarily synchronizing the waveform signal after preliminary noise elimination with the local waveform signal; Inoue performs fractional Fourier transform on the original waveform or the waveform after preliminary noise reduction according to the preliminary synchronization result, and performs separation filtering processing frame by frame in the fractional domain to complete noise reduction; Perform secondary synchronization on the separated and denoised waveform signal; Based on the secondary synchronization result, the waveform signal after preliminary noise elimination is demodulated and decoded on the well.

2. The synchronization signal and pump noise separation method based on fractional Fourier transform according to claim 1, wherein The method of performing fractional Fourier transform on the original waveform or the waveform after preliminary noise elimination according to the preliminary synchronization result, and performing separation filtering processing frame by frame in the fractional domain to complete noise elimination includes: Obtaining a synchronization initial position according to the preliminary synchronization result, and obtaining a synchronization header area of the current frame based on the synchronization initial position and a predetermined frame structure of the waveform signal; A fractional-order Fourier transform is performed on the data segment of the waveform signal corresponding to the synchronization header area, and the synchronization signal is separated from the pump noise through different fractional domain angles.

3. The method for separating a synchronization signal and pump noise based on fractional Fourier transform according to claim 2, wherein The step of obtaining the synchronization header area of the current frame includes: Determine the start position and end position of the synchronization signal according to the preliminary synchronization result and the frame structure; A preset redundant interval is added before and / or after the start position and the end position respectively to obtain the synchronization header area.

4. The method for separating a synchronization signal and pump noise based on fractional Fourier transform according to claim 2, wherein The separation of the synchronization signal from the pump noise comprises: When performing fractional Fourier transform on the synchronization head region, a peak search is performed on the waveform signal at each angle; Only the signal at the angle corresponding to the maximum peak is retained as the required target signal, and a fractional-order inverse Fourier transform is performed to obtain the synchronization signal after fractional domain denoising.

5. The method for separating a synchronization signal and pump noise based on fractional Fourier transform according to any one of claims 1 to 4, characterized in that The preliminary noise elimination process includes: Learn the pump noise frequency through the pump pulse sensor and generate a simulated pump noise waveform; The simulated pump noise waveform is subtracted from the waveform of the received mud pressure wave signal to eliminate the pump noise.

6. A synchronization signal and pump noise separation device based on fractional Fourier transform, characterized in that, include: A signal generation module, used for encoding and modulating mud pressure wave signals in the well; A preliminary noise elimination module is used to perform preliminary noise elimination processing on the mud pressure wave signal transmitted through the mud channel on the well; A coarse synchronization module, used for performing preliminary synchronization between the waveform signal after preliminary noise elimination and the local waveform signal; The signal-to-noise separation module is used for performing fractional Fourier transform on the original waveform or the waveform after preliminary noise elimination according to the preliminary synchronization result, and performing separation filtering processing frame by frame in the fractional domain to complete noise elimination; A precision synchronization module is used to perform secondary synchronization on the waveform signal after separation and noise elimination; The signal analysis module is used to perform uphole demodulation and decoding on the waveform signal after preliminary noise elimination based on the secondary synchronization result.

7. The synchronization signal and pump noise separation device based on fractional Fourier transform according to claim 6, characterized in that, The signal-to-noise separation module comprises: A data segment determination unit to be processed, used to obtain a synchronization initial position according to a preliminary synchronization result, and obtain a synchronization header area of a current frame based on the synchronization initial position and a predetermined frame structure of a waveform signal; The signal-to-noise separation unit is used to perform fractional Fourier transform on the data segment of the waveform signal corresponding to the synchronization header area, and separate the synchronization signal from the pump noise through different fractional domain angles.

8. An electronic device, characterized in that, include: One or more processors, a memory, and one or more computer programs, wherein the one or more computer programs are stored in the memory, and the one or more computer programs include instructions that, when executed by the electronic device, cause the electronic device to perform the fractional Fourier transform-based synchronization signal and pump noise separation method according to any one of claims 1 to 5.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the fractional Fourier transform-based synchronization signal and pump noise separation method according to any one of claims 1 to 5.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the fractional Fourier transform-based synchronization signal and pump noise separation method according to any one of claims 1 to 5.

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