Synchronizing signal and pump noise separation method based on fractional Fourier transform

Abstract

The invention discloses a synchronous signal and pump noise separation method based on fractional Fourier transform, and relates to the technical field of drilling. The method specifically comprises the steps that after a slurry pressure wave signal is formed underground, the slurry pressure wave signal transmitted by a slurry channel is subjected to preliminary noise elimination treatment on the ground, and coarse synchronization is conducted on the signal subjected to preliminary noise elimination and a local signal; in combination with a coarse synchronization result, only fractional order Fourier transform is adopted, and separation of a synchronization signal and a noise signal is carried out through different feature expressions of different signals in a fractional domain; and then fine synchronization processing is carried out, so that the purpose of improving the signal-to-noise ratio and the synchronization precision of the synchronization signal of the ground receiving end is achieved, and finally, the signal subjected to preliminary noise elimination is analyzed. According to the invention, multi-round synchronization and multi-round denoising processing are carried out aiming at special noise and special fractional domain characteristics of a measurement while drilling system, so that the accuracy and stability of synchronization of measurement while drilling signals are effectively improved, and the reliability and transmission performance of the whole system are greatly optimized.

Description

Technical Field

[0001] The invention relates to the technical field of drilling, and in particular to a method for separating a synchronization signal from pump noise based on fractional-order Fourier transform. Background Art

[0002] In recent years, in order to further improve 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 the low data transmission rate and has become a technical bottleneck restricting the further development of the MWD system. In order to meet the increasing demand for information, the industry has proposed a technical solution to achieve mud continuous wave using shear valves. 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 interception effect on the mud through the continuous movement of the motor rotor to form a continuous pressure wave. The swing frequency of the motor rotary valve rotor can reach 40Hz, and various modulation methods such as OOK, FSK, PSK are used for carrier modulation, so that a transmission rate of 40bps can be achieved. Compared with the maximum transmission rate of 5bps of the positive and 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 sinusoidal signal and a non-standard linear frequency modulation (LFM) signal, that is, the transmitter generates nonlinear distortion. 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, which leads to the gradual deterioration of the synchronization accuracy of the system, further causing the system bit error rate to increase, 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 multipath effects, which will generate multiple synchronization peaks when received on the ground, and the superimposed noise influence is prone to missynchronization. Summary of the invention

[0005] In view of the above, the present invention aims to provide at least a method for separating synchronization signals from pump noise based on fractional Fourier transform, so as to improve the accuracy and stability of synchronization and significantly 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 a synchronization signal from pump noise based on fractional-order Fourier transform, comprising:

[0008] The mud pressure wave signal is formed through encoding and modulation in the well;

[0009] The well performs preliminary noise elimination processing on the mud pressure wave signal transmitted through the mud channel;

[0010] Preliminarily synchronizing the waveform signal after preliminary noise elimination with the local waveform signal;

[0011] Inoue performs fractional Fourier transform on the waveform signal based on the preliminary synchronization result, and performs separation filtering processing frame by frame in the fractional domain to complete noise elimination;

[0012] Perform secondary synchronization on the separated and denoised waveform signal;

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

[0014] In at least one possible implementation, the step of performing fractional Fourier transform on the waveform signal according to the preliminary synchronization result, and performing separation filtering processing frame by frame in the fractional domain to complete noise reduction includes:

[0015] 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;

[0016] 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.

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

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

[0019] A preset redundant interval is added 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, separating the synchronization signal from the pump noise includes:

[0021] When performing fractional Fourier transform on the synchronization head region, a peak search is performed on the waveform signal at each angle;

[0022] 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.

[0023] In at least one possible implementation, the preliminary noise elimination process 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] In a fourth aspect, the present invention provides a computer-readable storage medium, which stores a computer program, which, when executed on a computer, enables the computer to execute the method as described in the first aspect or any possible implementation of the first aspect.

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

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

[0040] The main design concept of the present invention is to form a mud pressure wave signal through coding and modulation in the well, and perform preliminary noise elimination on the mud pressure wave signal transmitted through the mud continuous wave channel in the well, and perform rough synchronization between the signal after preliminary noise elimination and the local signal; then, combined with the rough synchronization result, only fractional-order 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, and then convert it to the time domain for fine synchronization processing, 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, based on the fine synchronization result, the pressure wave signal after preliminary noise elimination is demodulated and decoded in the well. Compared with the traditional scheme, the present invention performs at least two rounds of synchronization and two rounds of noise elimination for the special noise existing in the MWD system while drilling 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 MWD system. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described below with reference to the accompanying drawings, in which:

[0042] Figure 1 This is a schematic diagram of the rotor of the MWD mud continuous wave system pulser;

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

[0044] Figure 3 A schematic flow chart of a synchronization signal and pump noise separation method based on fractional Fourier transform provided in an embodiment of the present invention;

[0045] Figure 4 It is a schematic diagram of the representation of time domain signals and frequency domain signals in a spatial rectangular coordinate system;

[0046] Figure 5 It is a schematic diagram of Fourier transform on the time-frequency plane;

[0047] Figure 6 It is a schematic diagram of FRFT in the time-frequency plane;

[0048] Figure 7 It is a schematic diagram of two signals on the time-frequency plane;

[0049] Figure 8 For two signals at a rotation angle of Schematic diagram on the fractional domain of ;

[0050] Fig. 9 For two signals at a rotation angle of Schematic diagram on the fractional domain of ;

[0051] Fig.10 A time domain waveform diagram of simulated pump noise provided by an embodiment of the present invention;

[0052] Fig.11 A simulated pump noise spectrum diagram provided by an embodiment of the present invention;

[0053] Fig.12 A schematic diagram of the fractional domain of an LFM signal and a sine signal provided in an embodiment of the present invention;

[0054] Fig.13 A schematic diagram of a synchronization signal and pump noise separation device based on fractional Fourier transform provided in an embodiment of the present invention;

[0055] Fig.14 A schematic diagram of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0056] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

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

[0058] As mentioned above, the MWD mud continuous wave system achieves the interception effect on the mud by the continuous movement of the rotor of the motor-controlled pulser to form a continuous pressure wave. The mud pressure wave signal generated in this way is a non-standard sinusoidal signal and a non-standard linear frequency modulation signal (LFM) signal, that is, the transmitter generates nonlinear distortion. To expand, the fluid flow through the gap between the rotor and the stator can be expressed as: (1)

[0059] in, is the flow coefficient, is the pore area, is the flow rate through the gap, is the density of the liquid, is the pressure difference on both sides of the gap. From the above formula, we can get: (2)

[0060] according to Figure 1 The pulser rotor schematic diagram shows that the maximum area through which the fluid can flow is: (3)

[0061] in, , and is the stator characteristic radius, in units of ; is the gap width between the rotor outer ring and the inner wall of the drill pipe, in units of .

[0062] When the pulser is running, the flow area is: (4)

[0063] in, is the angular velocity of the pulser rotor, in units of , which can be expressed as: (5)

[0064] in, is the rotor rotation frequency, in units of ; is the angle of the rotor blades, in degrees; The speed at which the rotor rotates is the given control signal.

[0065] Therefore, the flow area when the pulser is running is: (6)

[0066] In summary, the pressure signal of the pulser can be obtained .

[0067] From the above formula, it can be concluded that the pressure signal The relationship with the given signal is as follows.

[0068] (7)

[0069] From the above formula, we can see that the pressure signal It has a nonlinear relationship with the given signal. When the given waveform is an LFM signal, the waveform of the pressure wave signal generated by the pulser is as follows: Figure 2 As shown in the figure. This nonlinear relationship causes the peak value of the synchronization curve to decrease when the correlation algorithm is used, which affects the accuracy and reliability of the synchronization of the measurement while drilling system. At the same time, in actual application, the traditional correlation synchronization method is greatly affected by noise. When there is too much residual noise, the synchronization peak will not be obvious, causing the system to miss synchronization or missynchronize. In addition, there are multiple reflections and refractions in the mud channel, resulting in multipath effects. Multiple synchronization peaks will be generated when receiving on the ground, and the superimposed noise influence is prone to missynchronization.

[0070] Based on the above analysis of the current situation, the present invention believes that this nonlinear distortion can be separated and filtered from the fractional domain, so as to achieve the effect of denoising the received mud pressure wave signal. In addition, due to the multipath effect caused by multiple reflections and refractions in the mud channel, multiple synchronization peaks will be generated when receiving on the ground. When there is too much residual noise, the synchronization peak will not be obvious, which is prone to missynchronization. Similarly, this multipath effect changes into 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.

[0071] It should be mentioned here that the mud continuous wave measurement while drilling system is mainly divided into two parts: downhole and surface. Downhole, the system is mainly composed of continuous wave generator, motor drive circuit, downhole central control unit and power supply modules; surface, the system is mainly composed of ground sensors, ground data processing unit, decoding unit and control unit modules.

[0072] Different from the past, the downhole part can control the mud (drilling fluid) pressure to generate the expected waveform. The waveform signal is transmitted to the surface through the mud. The surface part processes the waveform transmitted from the downhole via the ground sensor and decodes and restores the data. This process can be broken down into the following: Figure 3 The process scheme shown in the figure has one of the main concepts of separation of synchronization signal and pump noise based on fractional Fourier transform, which includes:

[0073] Step S1, forming a mud pressure wave signal through encoding and modulation in the well;

[0074] The downhole transmitter of the MWD mud continuous wave system will control the motor to rotate the rotor according to the protocol encoding method, frame structure, modulation method, data rate and other agreements, so that the mud flow between the rotor and the stator will change regularly, and finally reflect the change of the mud pressure wave. This has been explained in the previous article and will not be repeated here.

[0075] Step S2: performing preliminary noise elimination processing on the mud pressure wave signal transmitted through the mud channel on the well;

[0076] What can be expanded 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, in terms of interference processing, the MWD system while drilling is mainly affected by interference such as pump noise, drill bit reflection, motor noise, etc. Therefore, the present invention proposes that digital signal processing can be performed on the well before subsequent synchronization is implemented to reduce the influence of interference on useful signal decoding, so as to obtain relatively more useful downhole data as much as possible.

[0077] Therefore, it is possible to consider using data signal processing technology on the well to perform preliminary filtering on the mud pressure wave signal collected by the well receiving end to eliminate the influence of noise on the system. In some preferred embodiments, a noise elimination method can be adopted in which the pump noise frequency is learned through a pump stroke sensor and a simulated pump noise waveform is generated, and the simulated pump noise waveform is subtracted from the waveform of the received mud pressure wave signal.

[0078] In addition, as for channel attenuation, in the MWD system, as the depth of the well increases, the attenuation of the useful signal amplitude increases, and this attenuation belongs to frequency selective fading; among them, channel attenuation is related to the elastic properties of the drill pipe, the friction between particles in the mud, the compression coefficient of the mud, etc. As for the influence of channel fading on the data signal, the useful data signal received by the uphole pressure sensor will be distorted, which can be eliminated by equalization and other means on the well, 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 nonlinear distortion on the LFM signal, which will also affect the signal synchronization effect. The signal and noise are separated by the following fractional Fourier transform, and the influence of the nonlinear distortion on the synchronization peak can also be weakened.

[0079] Step S3, preliminarily synchronizing the waveform signal after preliminary noise elimination with the local waveform signal;

[0080] The idea of ​​this step is to process the waveform data after noise elimination in the previous step frame by frame with the local waveform signal through the synchronization algorithm to obtain the synchronization position, thereby completing the rough synchronization of the downhole and uphole signal data. As mentioned above, step S2 is the preliminary filtering of channel interference, so the preliminary synchronization link involved here can be understood as "rough synchronization", the purpose of which is to obtain the synchronization position of the uphole and downhole waveform signals, and provide technology for subsequent fractional-order processing to separate pump noise.

[0081] The specific synchronization process is not the focus of the present invention. A traditional or improved signal synchronization mechanism may be considered, and the present invention will not elaborate on or limit this.

[0082] Step S4: Inoue performs a fractional Fourier transform on the original waveform signal according to the preliminary synchronization result, and performs separation filtering processing frame by frame in the fractional domain to complete noise elimination;

[0083] Specifically, in some embodiments of the present invention, it may refer to obtaining the initial synchronization position (here, the rough "head end position") according to the preliminary synchronization result, and then obtaining the synchronization header area of ​​the current frame (referring to the data segment between the two ends of the rough synchronization signal plus the redundant area, so the "synchronization header area" refers to the data segment between the two ends plus the redundant area) based on the initial synchronization position and the established frame structure of the waveform signal, and performing a fractional Fourier transform based on the data segment of the waveform signal corresponding to the synchronization header area, 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 nonlinear distortion generated by 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 characteristics of the mud continuous wave channel.

[0084] In combination with the above conceptual framework, in actual operation, step S4 can be specifically expanded into the following implementation steps:

[0085] First, the start and end positions of the synchronization signal can be determined based on the synchronization position obtained from the preliminary synchronization result and the frame structure; preset redundant intervals are added before and after the start and end positions to obtain the synchronization header area that requires secondary processing.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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:

[0090] 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.

[0091] Similarly, the Fourier transform can be viewed as a set of bases The process of using the new coordinate system to represent the signal is called Fourier transform, and the basis function of Fourier transform is a cluster of exponential functions. Taking a rectangular wave as an example, the Fourier transform approximates the rectangular wave by linearly superposing an infinite number of sinusoidal functions (sine waves).

[0092] Based on this, if we use time t as the x-axis, frequency f as the y-axis, and signal amplitude as the z-axis to establish a spatial rectangular coordinate system, then the time domain representation of the signal can be regarded as a two-dimensional representation method with the x-axis as the horizontal axis 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 horizontal axis and the z-axis as the amplitude. In such a coordinate system, taking the cosine signal as an example, its waveform in the time domain and its waveform in the frequency domain are as follows: Figure 4 shown.

[0093] From the properties of Fourier transform, we know that:

[0094] (8)

[0095] (9)

[0096] (10)

[0097] Therefore, in this coordinate system, the Fourier transform can be regarded as rotating the two-dimensional plane representing the signal in the spatial rectangular coordinate system 90 degrees counterclockwise with the origin as the center and the z-axis as the rotation axis. Performing Fourier transform in these four directions can respectively obtain , , and ,like Figure 5 shown.

[0098] From this rotation perspective, the fractional Fourier transform (FRFT) can be seen as an extension of the Fourier transform. The Fourier transform is to rotate the two-dimensional plane representing the signal by an integer multiple of ninety degrees, while the FRFT is to rotate the two-dimensional plane representing the signal by an arbitrary angle. Assume that the 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 diagram can be referred to Figure 6 .

[0099] If the Fourier transform is understood as a 90-degree transformation of a function, then the FRFT can be understood as a Fourier transform of a function that is not an integer multiple of 90 degrees. , FRFT is the time domain expression of the signal ; When the coordinate axis rotates counterclockwise , FRFT is the frequency domain expression of the signal ; When the coordinate axis rotates counterclockwise When ; When the coordinate axis rotates counterclockwise When ; When the coordinate axis rotates counterclockwise When Therefore, FRFT includes Fourier transform, that is, FRFT is an extension of Fourier transform - the rotation angle becomes an arbitrary angle, and the rotation angle is no longer limited to integer multiples of ninety degrees. The mathematical definition of FRFT is:

[0100] (11) (12)

[0101] in, , is an integer, represents the FRFT operator, Represents the rotation angle of FRFT.

[0102] In summary, FRFT can be regarded as a set of basis The new coordinate system formed by this coordinate system is the process of using this coordinate system to represent the signal.

[0103] From the characteristics of the basis function, it can be obtained that for Fourier transform, if the input is a linear combination of complex sinusoidal signals, such as cos function or sin function, then there will be an impulse in the frequency domain. Similarly, for FRFT, if the input is a complex LFM signal, then an impulse will be formed 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, which makes it easy to separate signals in the fractional domain. Therefore, assuming that the modulation frequency of all signals is are not the same, then in the signal In the u domain where the impulse appears, other signals will not have peaks. Here we take two signals as an example. The distribution of signal 1 and signal 2 in the time-frequency plane is as follows: Figure 7 As shown, then, for the u domain where signal 1 and signal 2 can obtain peak values, we can refer to Figure 8 and Fig. 9 Hint.

[0104] Based on the analysis and introduction in the previous article, in the MWD system that the present invention focuses on, since the pressure sensor at the uphole receiving end is installed close to the mud pump and is several thousand meters away from the signal transmitting end (downhole instrument), the signal collected by the pressure sensor has the strongest amplitude energy, which is the pressure fluctuation generated by the mud pump when it is working. 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.

[0105] 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 formed by the linear superposition of multiple single-product sinusoidal signals.

[0106] (13)

[0107] Where n is the harmonic order, Indicates the fundamental frequency, that is, the operating frequency of the mud pump (Hz).

[0108] The present invention believes that the harmonic energy of the cylinder multiple of the mud pump is the strongest. In view of the characteristics of pump noise in the drilling measurement scenario, it is proposed to simulate the pump noise. Here, the time domain waveform and spectrum diagram of the simulated 5-cylinder pump noise are taken as an example. Fig.10 and Fig.11 shown.

[0109] Combined with the pump noise simulation results, in the mud pressure wave signal, since the sinusoidal signal can be regarded as an LFM signal with a frequency modulation of 0, the energy of the pump noise only exists on the plane of α=π / 2. Based on the analysis of this feature, the present invention believes that the pump noise signal and the LFM signal can be filtered and separated in the fractional domain.

[0110] Since the pump noise signal can be regarded as a linear combination of multiple sinusoidal signals, the following analysis takes the sinusoidal signal as an example.

[0111] Specifically, in the MWD system, the LFM signal is used as the pilot signal, which is expressed as follows:

[0112] (14)

[0113] Taking a single-component sinusoidal signal as an example, the derivation is expressed as follows:

[0114] (15)

[0115] in, and are the amplitudes of the LFM signal and the sinusoidal signal, and are the starting frequency and modulation frequency respectively, and T is the duration of the two signals.

[0116] (1) LFM signal:

[0117] ① When hour:

[0118] when When , the LFM signal reaches the best energy concentration in the fractional domain, and its fractional spectrum is:

[0119] (16)

[0120] in, .

[0121] So,

[0122] (17)

[0123] The maximum value is:

[0124] (18)

[0125] Therefore, the LFM signal is The fractional domain of the impulse characteristic is shown, and the impulse position is The bandwidth of the nth zero-crossing point in this fractional domain is .

[0126] ② When hour:

[0127] (19)

[0128] in,

[0129] (20)

[0130] (twenty one)

[0131] (twenty two)

[0132] (twenty three)

[0133] in, and are all Fresnel integrals. Therefore,

[0134] (twenty four)

[0135] Therefore, this LFM signal is The bandwidth on the fractional domain of .

[0136] Since in practical applications, the bandwidth is likely to be much greater than 1, therefore:

[0137] (25)

[0138] (2) Sinusoidal signal:

[0139] The sinusoidal signal can be considered as The LFM signal at Bring in the above derivation.

[0140] ① When hour:

[0141] when When , the sinusoidal signal achieves the best aggregation performance in the fractional domain, that is, the frequency domain, and we have:

[0142] (26)

[0143] The peak value is:

[0144] (27)

[0145] The sinusoidal signal The bandwidth of the nth zero-crossing point in the fractional domain (i.e., frequency domain) is .

[0146] ② When hour:

[0147] when When , we have:

[0148] (28)

[0149] in,

[0150] (29)

[0151] (30)

[0152] Therefore, we have:

[0153] (31)

[0154] The sinusoidal signal The bandwidth on the fractional domain of .

[0155] From the above analysis, it can be concluded that when When , the LFM signal has a peak in the fractional domain , at this time the maximum value of the sinusoidal signal is ;when When the sinusoidal signal has a peak , at this time the maximum value of the LFM signal is . Based on this, we can get Fig.12 Hint.

[0156] Therefore, the energy aggregation characteristics of LFM signals and sinusoidal signals in different fractional domains can be used for signal separation.

[0157] exist In the fractional domain, that is, in the frequency domain, the sinusoidal signal is a useful signal and the LFM signal is an interference signal. The signal-to-interference ratio is:

[0158] (32)

[0159] exist In the fractional domain, the LFM signal is a useful signal and the sinusoidal signal is an interference signal. The signal-to-interference ratio is:

[0160] (33)

[0161] As mentioned above, another implementation of step S4 is as follows:

[0162] S41. Perform fractional-order Fourier transform on the synchronization header region.

[0163] S42. The fractional domain plane angle is derived according to the LFM signal setting in the downhole frame structure. Only the signal at this angle is a useful LFM signal, and the rest of the plane signals are considered as noise.

[0164] S43, performing fractional-order inverse Fourier transform only on the signal in the fractional domain of the angle to obtain a synchronization signal after noise elimination in the fractional domain.

[0165] Continuing from the above, step S5, performing secondary synchronization on the waveform signal after noise removal by fractional domain separation;

[0166] Similarly, the specific synchronization process is not the focus of the present invention, and a traditional or improved signal synchronization mechanism may be considered, which will not be elaborated or limited in the present invention.

[0167] Step S6: performing uphole demodulation and decoding on the waveform signal after preliminary noise elimination based on the secondary synchronization result.

[0168] That is, the signal after the aforementioned preliminary denoising is used for both coarse synchronization and the final demodulation and decoding process; and the signal targeted by the fractional-order Fourier transform involved in the intermediate link is the synchronization area segment obtained by the coarse synchronization result of the original waveform or the waveform after preliminary denoising, and the secondary synchronization result output is also the synchronization position information.

[0169] Finally, demodulation can be carried out by coherent demodulation or incoherent demodulation, and then the 01 code word is obtained by judgment, and then the corresponding parameter value is obtained according to the established protocols such as the aforementioned encoding method, frame structure composition, etc. For example, in some embodiments, coherent demodulation and hard decision decoding methods can be adopted, and the present invention does not limit or elaborate on this.

[0170] In summary, the main design concept of the present invention is to form a mud pressure wave signal through coding and modulation in the well, and perform preliminary noise elimination on the mud pressure wave signal transmitted through the mud continuous wave channel in the well, and perform rough synchronization on the signal after preliminary noise elimination with the local signal; then, combined with the rough synchronization result, only fractional Fourier transform is used to separate the synchronization signal and the noise signal through the different characteristic performances of different signals in the fractional domain, and then converted to the time domain for fine synchronization processing, 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 complete the signal-to-noise separation, and finally demodulate and decode the waveform signal after preliminary noise elimination in the well based on the secondary synchronization result. Compared with the traditional scheme, the present invention eliminates the noise / interference / distortion signal components at other angles for the special noise and its special fractional domain characteristics of the MWD system while drilling, and only retains the LFM signal at the maximum peak angle, 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 MWD system.

[0171] Corresponding to the above embodiments and preferred solutions, the present invention also provides an embodiment of a synchronization signal and pump noise separation device based on fractional Fourier transform, such as Fig.13 As shown, it may specifically include the following components:

[0172] The signal generation module 131 is used to generate mud pressure wave signals through encoding and modulation in the well;

[0173] A preliminary noise elimination module 132 is used to perform preliminary noise elimination processing on the mud pressure wave signal transmitted through the mud channel on the well;

[0174] A coarse synchronization module 133, used for performing preliminary synchronization between the waveform signal after preliminary noise elimination and the local waveform signal;

[0175] The signal-to-noise separation module 134 is used to perform fractional Fourier transform on the waveform signal according to the preliminary synchronization result, and perform separation filtering processing frame by frame in the fractional domain to complete noise elimination;

[0176] A fine synchronization module 135 is used to perform secondary synchronization on the separated and denoised waveform signal;

[0177] The signal analysis module 136 is used to perform uphole demodulation and decoding on the waveform signal after the secondary synchronization.

[0178] It should be understood that the above Fig.13 The division of the various components in the synchronization signal and pump noise separation device based on fractional Fourier transform shown is only a division of logical functions. In actual implementation, they can be fully or partially integrated into one physical entity, or they can be physically separated. And these components can all be implemented in the form of software calling through processing elements; some components can also be implemented in the form of software calling through processing elements, and some components can be implemented in the form of hardware. For example, one of the above modules can be a separately established processing element, or it can be integrated in a chip of an electronic device. The implementation of other components is similar. In addition, all or part of these components can be integrated together, or they can be implemented independently. In the implementation process, each step of the above method or the above components can be completed by the hardware integrated logic circuit in the processor element or the instructions in the form of software.

[0179] For example, the above components may be one or more integrated circuits configured to implement the above methods, such as one or more application specific integrated circuits (ASIC), or one or more microprocessors (DSP), or one or more field programmable gate arrays (FPGA). For another example, these components may be integrated together to be implemented in the form of a system-on-a-chip (SOC).

[0180] 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 a variety of implementations. The present invention uses the following carrier as a schematic illustration:

[0181] (1) An electronic device. The device may specifically 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, and when the instructions are executed by the device, the device performs the steps / functions of the aforementioned embodiment or equivalent implementation.

[0182] The electronic device may specifically be electronic device related to computers, such as but not limited to various computing terminals and electronic products.

[0183] Specifically, the processor, communication interface, and memory can all communicate with each other through a communication bus. Among them, the processor may be a central processing unit CPU, DSP, microcontroller or digital signal processor, and may also include GPU, embedded neural network processor (Neural-network Process Units; hereinafter referred to as: NPU) and image signal processor (Image Signal Processor; hereinafter referred to as: ISP). The processor may also include a specific integrated circuit ASIC, or one or more integrated circuits configured to implement the embodiment of the present invention, etc. 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; and the aforementioned memory / storage medium may include: non-volatile memory (Non-Volatile Memory), such as a non-removable disk, U disk, mobile hard disk, optical disk, etc., as well as read-only memory (Read-Only Memory; hereinafter referred to as: ROM), random access memory (RandomAccess Memory; hereinafter referred to as: RAM), etc.

[0184] Although the present invention does not limit the specific form of the electronic device, for the purpose of illustrative introduction, Fig.14 As shown, the present invention provides a schematic diagram of the structure of an embodiment of an electronic device. Specifically, the electronic device 900 includes a processor 910 and a memory 930. 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 can be combined into a processing device, and more commonly, they are independent components from each other. The processor 910 is used to execute the program code stored in the memory 930 to implement the above-mentioned functions. In specific implementation, the memory 930 can also be integrated in the processor 910, or, independent of the processor 910.

[0185] 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, and the audio circuit may further include a speaker 982, a microphone 984, etc. The display unit 970 may include a display screen.

[0186] Furthermore, the electronic device 900 may also include a power supply 950 for providing electrical energy to various devices or circuits in the electronic device 900 .

[0187] It should be understood that Fig.14The electronic device 900 shown can implement each process of the method provided in the aforementioned embodiment. The operation and / or function of each component in the electronic device 900 can be respectively to implement the corresponding process in the aforementioned method embodiment. For details, please refer to the description of the embodiments of the method, device, etc. in the previous text. To avoid repetition, the detailed description is appropriately omitted here.

[0188] It should be understood that Fig.14 The processor 910 in the electronic device 900 shown may be a system on chip SOC, which may include a central processing unit (CPU) and may further include other types of processors, such as a graphics processing unit (GPU), etc., which will be described in detail below.

[0189] In summary, the various processors or processing units within the processor 910 can work together to implement the previous method flow, and the corresponding software programs of the various processors or processing units can be stored in the memory 930.

[0190] (2) A computer data storage medium on which a computer program or the above-mentioned device is stored, which, when the computer program or the above-mentioned device is executed, enables a computer to execute the steps / functions of the aforementioned embodiment or equivalent implementation.

[0191] In several embodiments provided by the present invention, any function, if implemented in the form of a software functional unit and sold or used as an independent product, can be stored in a computer data storage medium. Based on this understanding, some technical solutions of the present invention are essentially or part of the technical solution that contributes to the prior art or part of the technical solution can be embodied in the form of the software product described below.

[0192] It should be particularly pointed out that the storage medium may refer to a server or a similar computer device, specifically, a storage device in a server or a similar computer device storing the aforementioned computer program or the aforementioned apparatus.

[0193] (3) A computer program product (which may include the above-mentioned apparatus), which, when running on a terminal device, enables the terminal device to execute the synchronization signal and pump noise separation method based on fractional Fourier transform of the above-mentioned embodiment or an equivalent implementation.

[0194] It can be seen from the above description of the implementation method that those skilled in the art can clearly understand that all or part of the steps in the above implementation method 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 APP.

[0195] In the embodiments of the present invention, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent the existence of A alone, the existence of A and B at the same time, and the existence of B alone. A and B may be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b and c may represent: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, c may be single or multiple.

[0196] Those skilled in the art will appreciate 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 performed in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0197] In addition, each embodiment in this specification is 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 method embodiments, the relevant parts can refer to the partial description of the method embodiments. The embodiments of the devices and equipment described above are merely schematic, wherein the modules, units, etc. described as separate components may or may not be physically separated, that is, they may be located in one place, or they may be distributed in multiple places, such as nodes of a system network. Specifically, some or all of the modules and units may be selected according to actual needs to achieve the purpose of the above-mentioned embodiment scheme. Those skilled in the art can understand and implement it without paying creative labor.

[0198] The above describes in detail the structure, features and effects of the present invention based on the embodiments shown in the drawings, but the above is only a preferred embodiment of the present invention. It should be noted that the technical features involved in the above embodiments and their preferred methods can be reasonably combined and matched into a variety of equivalent schemes by those skilled in the art without departing from or changing the design ideas and technical effects of the present invention; therefore, the present invention is not limited to the scope of implementation shown in the drawings, and all changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which still do not exceed the spirit covered by the specification and drawings, should be within the protection scope of the present invention.

Claims

1. A method for separating synchronization signals from 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 waveform signal based on the preliminary synchronization result, and performs separation filtering processing frame by frame in the fractional domain to complete noise elimination; 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 method for separating synchronization signal and pump noise based on fractional Fourier transform according to claim 1, characterized in that: The Wellhead 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 reduction, including: 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 synchronization signal and pump noise based on fractional Fourier transform according to claim 2, characterized in that: 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 synchronization signal and pump noise based on fractional Fourier transform according to claim 2, characterized in that: 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 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 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; 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, which, when executed by the electronic device, enable the electronic device to perform the synchronization signal and pump noise separation method based on fractional Fourier transform as described in 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, the synchronization signal and pump noise separation method based on fractional Fourier transform described in any one of claims 1 to 5 is implemented.

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

Images