Low-frequency noise elimination method and device for distributed optical fiber data in well

Abstract

The invention provides a low-frequency noise elimination method and device for distributed optical fiber data in a well, and belongs to the field of seismic exploration. The method comprises the steps of converting input DAS time domain data into DAS frequency domain data, and then carrying out threshold-adjustable notch filtering processing on the DAS frequency domain data. According to the method, the DAS data are processed by adopting the notch filtering method with the adjustable threshold, low-frequency noise of the DAS data can be effectively eliminated, and the signal-to-noise ratio of the DAS data is improved.

Description

Technical Field

[0001] The invention belongs to the field of seismic exploration, and in particular relates to a method and a device for eliminating low-frequency noise of distributed optical fiber data in a well. Background Art

[0002] As an emerging transformative technology, distributed optical fiber sensing (DAS) has developed rapidly in the fields of oil and gas exploration and development, engineering monitoring, etc., but there are still some problems that need to be solved urgently.

[0003] When DAS data is collected, various human activities are inevitable on the ground above the wellhead. These activities, as passive seismic sources, will generate strong surface waves that propagate along the surface to the shallow optical cable, and the generation time lasts for a long time. The noise is mainly low-frequency, but the energy is strong, and the frequency band range has a large overlap with the effective wave, which cannot be removed by conventional bandpass filtering methods.

[0004] Therefore, there is an urgent need to find a method to eliminate low-frequency noise in DAS data. Summary of the invention

[0005] The purpose of the present invention is to solve the above-mentioned problems existing in the prior art and to provide a method and device for eliminating low-frequency noise of distributed optical fiber data in a well, which can effectively eliminate the low-frequency noise of DAS data.

[0006] One of the purposes of the present invention is to provide a method for eliminating low-frequency noise of distributed optical fiber data in a well.

[0007] A second object of the present invention is to provide a low-frequency noise elimination device for distributed optical fiber data in a well.

[0008] A third object of the present invention is to provide a computer-readable storage medium.

[0009] A fourth object of the present invention is to provide a computer device.

[0010] The present invention is achieved through the following technical solutions:

[0011] The first aspect of the present invention provides a method for eliminating low-frequency noise in distributed optical fiber data in a well, converting input DAS time domain data into DAS frequency domain data, and then performing notch filtering with an adjustable threshold on the DAS frequency domain data.

[0012] A further improvement of the present invention is:

[0013] The method comprises:

[0014] Step S1, input DAS time domain data and perform spectrum analysis on the data;

[0015] Step S2, converting DAS time domain data into frequency domain data;

[0016] Step S3, performing notch filtering with an adjustable threshold on the DAS frequency domain data;

[0017] Step S4: Convert the DAS frequency domain data to the time domain.

[0018] A further improvement of the present invention is:

[0019] In step S1, the data is subjected to spectrum analysis, and the specific operations include:

[0020] For the input DAS time domain data, the low-frequency noise development part is selected and spectrum analysis is performed to obtain the frequency band range of the low-frequency noise [f1, f2].

[0021] A further improvement of the present invention is:

[0022] In step S2, the DAS time domain data is converted into frequency domain data, and the specific operations include:

[0023] For the input DAS time domain data, Fourier transform is used to transform the data from time domain to frequency domain.

[0024] A further improvement of the present invention is:

[0025] In step S3, the DAS frequency domain data is subjected to notch filtering with an adjustable threshold, and the specific operations include:

[0026] Step S31, taking the DAS frequency domain data of a channel, and calculating the amplitude spectrum of the DAS frequency domain data of the channel, wherein the amplitude spectrum is calculated by performing Fourier transform on the data to the frequency domain, and calculating the modulus value corresponding to each frequency, which is an existing general technology and will not be described in detail here;

[0027] Step S32, from the calculated amplitude spectrum, select all amplitude values ​​within the frequency band range [f1, f2], and then calculate the arithmetic mean to obtain the mean Am;

[0028] Step S33, calculating the filtering threshold fp=Am×p, where p is the filtering threshold percentage;

[0029] Step S34, for the DAS frequency domain data of the channel, compare the amplitude value Ai corresponding to each frequency in the frequency band [f1, f2] with the size of the filtering threshold. If Ai>fp, reassign Ai to Ai=fp. If Ai≤fp, do nothing.

[0030] A further improvement of the present invention is:

[0031] The step S3 further comprises:

[0032] Step S35, repeating steps S31 to S34, and performing notch filtering with an adjustable threshold on the DAS frequency domain data of all channels in turn.

[0033] A further improvement of the present invention is:

[0034] In step S4, the DAS frequency domain data is transferred to the time domain, and the specific operations include:

[0035] The DAS frequency domain data after the notch filtering with an adjustable threshold in step S3 is subjected to an inverse Fourier transform to be converted into DAS time domain data.

[0036] A second aspect of the present invention provides a low-frequency noise elimination device for distributed optical fiber data in a well, comprising:

[0037] Input module, used to input DAS time domain data and perform spectrum analysis on the data;

[0038] A first conversion module, used to convert DAS time domain data into frequency domain data;

[0039] The filter processing module performs notch filtering with an adjustable threshold on the DAS frequency domain data;

[0040] The second conversion module is used to convert the DAS frequency domain data after notch filtering into the time domain.

[0041] According to a third aspect of the present invention, a computer-readable medium is provided, wherein the computer-readable storage medium stores at least one computer-executable program, and when the at least one program is executed by the computer, the computer executes the steps in the method for eliminating low-frequency noise of distributed optical fiber data in a well as described above.

[0042] A fourth aspect of the present invention provides a computer device comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the method for eliminating low-frequency noise in distributed optical fiber data in a well as described above.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The present invention uses a notch filter method with an adjustable threshold to process DAS data, which can effectively eliminate low-frequency noise of the DAS data and improve the signal-to-noise ratio of the DAS data. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a flow chart of a method for eliminating low-frequency noise of distributed optical fiber data in a well according to the present invention;

[0046] Figure 2 It is the data of vertical seismic profile (VSP) acquired by DAS before denoising;

[0047] Figure 3 yes Figure 2 Spectrum of

[0048] Figure 4 The method of the present invention is used to Figure 2 DAS data after removing low-frequency noise from the data;

[0049] Figure 5 yes Figure 4 spectrum. DETAILED DESCRIPTION

[0050] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0051] Aiming at the problem that when collecting distributed optical fiber sensing (DAS) data in a well, strong low-frequency noise is generated on the shallow channel of optical fiber data due to the influence of ground activities above the wellhead, and the low-frequency noise has a wide frequency band and overlaps with the effective signal, which is difficult to eliminate by conventional bandpass filtering and other methods, the present invention proposes a method for eliminating the low-frequency noise of distributed optical fiber data in a well, and uses a notch filtering method with an adjustable threshold to process DAS data, which can effectively eliminate the low-frequency noise of DAS data and improve the signal-to-noise ratio of DAS data.

[0052] [Example 1]

[0053] An embodiment of the present invention provides a method for eliminating low-frequency noise of distributed optical fiber data in a well, the method comprising the following steps:

[0054] Step S1, input DAS time domain data and perform spectrum analysis on the data;

[0055] For the input DAS time domain data, the low-frequency noise development part is selected and spectrum analysis is performed to obtain the frequency band range of the low-frequency noise [f1, f2].

[0056] The DAS time domain data may be the original DAS collected data, or may be the data that has been pre-processed but without processing the low-frequency interference data.

[0057] Spectrum analysis refers to performing Fourier transform on data to the frequency domain to calculate the amplitude spectrum, and then reading the frequency range of various noises on the amplitude spectrum. Spectrum analysis is a common existing technology and will not be described in detail here.

[0058] Step S2, converting DAS time domain data into frequency domain data;

[0059] For the input DAS time domain data, Fourier transform is used to transform the data from time domain to frequency domain.

[0060] Fourier transform is an existing conventional technology and will not be described in detail here.

[0061] Step S3, performing notch filtering with an adjustable threshold on the DAS frequency domain data;

[0062] Specific operations include:

[0063] Step S31, taking the DAS frequency domain data of a channel, and calculating the amplitude spectrum of the DAS frequency domain data of the channel, wherein the amplitude spectrum is calculated by performing Fourier transform on the data to the frequency domain, and calculating the modulus value corresponding to each frequency, which is an existing general technology and will not be described in detail here;

[0064] Step S32, from the calculated amplitude spectrum, select all amplitude values ​​within the frequency band range [f1, f2], and then calculate the arithmetic mean to obtain the mean Am;

[0065] Step S33, calculating the filter threshold fp=Am×p, where p is the filter threshold percentage, which is a set value;

[0066] The filter threshold percentage p value can be determined by the application effect, that is, by selecting several groups of different p values, applying the entire process of the method of the present invention to filter the DAS data respectively, and according to the filtering effect, taking the p with the best effect as the final determined p;

[0067] Step S34: for the DAS frequency domain data of the channel, compare the amplitude value Ai (i refers to the frequency number) corresponding to each frequency in the frequency band [f1, f2] with the size of the filtering threshold. If Ai>fp, reassign Ai to Ai=fp. If Ai≤fp, do not process.

[0068] Step S35, repeating steps S31 to S34, and performing notch filtering with an adjustable threshold on the DAS frequency domain data of all channels in turn.

[0069] Step S4, converting the DAS frequency domain data after notch filtering to the time domain;

[0070] Specific operations include:

[0071] The DAS frequency domain data after the notch filtering (referring to the DAS frequency domain data corresponding to the amplitude value Ai finally determined in step S3) is subjected to inverse Fourier transform and converted into the time domain.

[0072] Inverse Fourier transform is a prior art method and will not be described in detail here.

[0073] Step S5: output the DAS time domain data after notch filtering.

[0074] Figure 2 This is the data of a vertical seismic profile (VSP) collected by DAS before denoising. From the data, we can see that there is strong low-frequency noise in the shallow channel, and the noise exists in all time periods;

[0075] Figure 3 for Figure 2 In the spectrum diagram, the black circle indicates the frequency band of low-frequency noise, which is 10 to 40 Hz. The amplitude value is relatively high within this range.

[0076] Figure 4 Yes Figure 2 After using this method to remove low-frequency noise from the DAS data, it can be seen that the low-frequency noise in the shallow channel of the denoised DAS data has been effectively suppressed.

[0077] Figure 5 yes Figure 4 Spectrum diagram. In the spectrum diagram, the black circle indicates that the amplitude of the low-frequency noise is greatly attenuated.

[0078] Compared with the traditional notch filtering method, the method of the present invention not only retains the effective signal, but also removes the noise within a specific frequency range, thereby improving the signal-to-noise ratio of DAS data. The traditional notch filtering method will remove all the effective signals and noise within a specific frequency range without distinction.

[0079] [Example 2]

[0080] The embodiment of the present invention provides a low-frequency noise elimination device for distributed optical fiber data in a well, comprising:

[0081] Input module, used to input DAS time domain data and perform spectrum analysis on the data;

[0082] For the input DAS time domain data, the low-frequency noise development part is selected and spectrum analysis is performed to obtain the frequency band range of the low-frequency noise [f1, f2].

[0083] The DAS time domain data may be the original DAS collected data, or may be the data that has been pre-processed but without processing the low-frequency interference data.

[0084] A first conversion module, used to convert DAS time domain data into frequency domain data;

[0085] The filter processing module performs notch filtering with an adjustable threshold on the DAS frequency domain data;

[0086] Perform notch filtering with adjustable threshold on DAS frequency domain data. The specific operations include:

[0087] Step S31, taking the DAS frequency domain data of a channel, and calculating the amplitude spectrum of the DAS frequency domain data of the channel, wherein the amplitude spectrum is calculated by performing Fourier transform on the data to the frequency domain, and calculating the modulus value corresponding to each frequency, which is an existing general technology and will not be described in detail here;

[0088] Step S32, from the calculated amplitude spectrum, select all amplitude values ​​within the frequency band range [f1, f2], and then calculate the arithmetic mean to obtain the mean Am;

[0089] Step S33, calculating the filtering threshold fp=Am×p, where p is the filtering threshold percentage;

[0090] Step S34: for the DAS frequency domain data of the channel, compare the amplitude value Ai (i refers to the frequency number) corresponding to each frequency in the frequency band [f1, f2] with the size of the filtering threshold. If Ai>fp, reassign Ai to Ai=fp. If Ai≤fp, do not process.

[0091] Step S35, repeating steps S31 to S34, and performing notch filtering with an adjustable threshold on the DAS frequency domain data of all channels in turn.

[0092] The second conversion module is used to convert the DAS frequency domain data after notch filtering into the time domain.

[0093] Furthermore, the device also includes an output module for outputting the DAS time domain data after notch filtering.

[0094] [Example 3]

[0095] An embodiment of the present invention provides a computer-readable medium, wherein the computer-readable storage medium stores at least one program executable by a computer, and when the at least one program is executed by the computer, the computer executes the following steps:

[0096] The steps are specifically as follows:

[0097] Step S1, input DAS time domain data and perform spectrum analysis on the data;

[0098] For the input DAS time domain data, the low-frequency noise development part is selected and spectrum analysis is performed to obtain the frequency band range of the low-frequency noise [f1, f2].

[0099] The DAS time domain data may be the original DAS collected data, or may be the data that has been pre-processed but without processing the low-frequency interference data.

[0100] Step S2, converting DAS time domain data into frequency domain data;

[0101] For the input DAS time domain data, Fourier transform is used to transform the data from time domain to frequency domain.

[0102] Step S3, performing notch filtering with an adjustable threshold on the DAS frequency domain data;

[0103] Specific operations include:

[0104] Step S31, taking the DAS frequency domain data of a channel, and calculating the amplitude spectrum of the DAS frequency domain data of the channel, wherein the amplitude spectrum is calculated by performing Fourier transform on the data to the frequency domain, and calculating the modulus value corresponding to each frequency, which is an existing general technology and will not be described in detail here;

[0105] Step S32, from the calculated amplitude spectrum, select all amplitude values ​​within the frequency band range [f1, f2], and then calculate the arithmetic mean to obtain the mean Am;

[0106] Step S33, calculating the filtering threshold fp=Am×p, where p is the filtering threshold percentage;

[0107] Step S34: for the DAS frequency domain data of the channel, compare the amplitude value Ai (i refers to the frequency number) corresponding to each frequency in the frequency band [f1, f2] with the size of the filtering threshold. If Ai>fp, reassign Ai to Ai=fp. If Ai≤fp, do not process.

[0108] Step S35, repeating steps S31 to S34, and performing notch filtering with an adjustable threshold on the DAS frequency domain data of all channels in turn.

[0109] Step S4, converting the DAS frequency domain data after notch filtering to the time domain;

[0110] Specific operations include:

[0111] The DAS frequency domain data after notch filtering is inversely transformed into the time domain by Fourier transformation.

[0112] Step S5: output the DAS time domain data after notch filtering.

[0113] [Example 4]

[0114] An embodiment of the present invention provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the following steps:

[0115] The steps are specifically as follows:

[0116] Step S1, input DAS time domain data and perform spectrum analysis on the data;

[0117] For the input DAS time domain data, the low-frequency noise development part is selected and spectrum analysis is performed to obtain the frequency band range of the low-frequency noise [f1, f2].

[0118] The DAS time domain data may be the original DAS collected data, or may be the data that has been pre-processed but without processing the low-frequency interference data.

[0119] Step S2, converting DAS time domain data into frequency domain data;

[0120] For the input DAS time domain data, Fourier transform is used to transform the data from time domain to frequency domain.

[0121] Step S3, performing notch filtering with an adjustable threshold on the DAS frequency domain data;

[0122] Specific operations include:

[0123] Step S31, taking the DAS frequency domain data of a channel, and calculating the amplitude spectrum of the DAS frequency domain data of the channel, wherein the amplitude spectrum is calculated by performing Fourier transform on the data to the frequency domain, and calculating the modulus value corresponding to each frequency, which is an existing general technology and will not be described in detail here;

[0124] Step S32, from the calculated amplitude spectrum, select all amplitude values ​​within the frequency band range [f1, f2], and then calculate the arithmetic mean to obtain the mean Am;

[0125] Step S33, calculating the filtering threshold fp=Am×p, where p is the filtering threshold percentage;

[0126] Step S34: for the DAS frequency domain data of the channel, compare the amplitude value Ai (i refers to the frequency number) corresponding to each frequency in the frequency band [f1, f2] with the size of the filtering threshold. If Ai>fp, reassign Ai to Ai=fp. If Ai≤fp, do not process.

[0127] Step S35, repeating steps S31 to S34, and performing notch filtering with an adjustable threshold on the DAS frequency domain data of all channels in turn.

[0128] Step S4, converting the DAS frequency domain data after notch filtering to the time domain;

[0129] Specific operations include:

[0130] The DAS frequency domain data after notch filtering is inversely transformed into the time domain by Fourier transformation.

[0131] Step S5: output the DAS time domain data after notch filtering.

[0132] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the program can be stored in a non-volatile computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0133] The above technical solution is only one implementation mode of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the principles disclosed in the present invention, and it is not limited to the technical solution described in the above specific embodiments of the present invention. Therefore, the above description is only preferred and does not have a restrictive meaning.

Claims

1. A method for eliminating low-frequency noise of distributed optical fiber data in a well, characterized in that: The input DAS time domain data is converted to DAS frequency domain data, and then the DAS frequency domain data is processed by notch filtering with an adjustable threshold.

2. The method for eliminating low-frequency noise of distributed optical fiber data in a well according to claim 1, characterized in that: The method comprises: Step S1, input DAS time domain data and perform spectrum analysis on the data; Step S2, converting DAS time domain data into frequency domain data; Step S3, performing notch filtering with an adjustable threshold on the DAS frequency domain data; Step S4: Convert the DAS frequency domain data to the time domain.

3. The method for eliminating low-frequency noise of distributed optical fiber data in a well according to claim 2, characterized in that: In step S1, the data is subjected to spectrum analysis, and the specific operations include: For the input DAS time domain data, the low-frequency noise development part is selected and spectrum analysis is performed to obtain the frequency band range of the low-frequency noise [f1, f2].

4. The method for eliminating low-frequency noise of distributed optical fiber data in a well according to claim 2, characterized in that: In step S2, the DAS time domain data is converted into frequency domain data, and the specific operations include: For the input DAS time domain data, Fourier transform is used to transform the data from time domain to frequency domain.

5. The method for eliminating low-frequency noise of distributed optical fiber data in a well according to claim 3, characterized in that: In step S3, the DAS frequency domain data is subjected to notch filtering with an adjustable threshold, and the specific operations include: Step S31, taking the DAS frequency domain data of a channel, and calculating the amplitude spectrum of the DAS frequency domain data of the channel, wherein the amplitude spectrum is calculated by performing Fourier transform on the data to the frequency domain, and calculating the modulus value corresponding to each frequency, which is an existing general technology and will not be described in detail here; Step S32, from the calculated amplitude spectrum, select all amplitude values ​​within the frequency band range [f1, f2], and then calculate the arithmetic mean to obtain the mean Am; Step S33, calculating the filtering threshold fp=Am×p, where p is the filtering threshold percentage; Step S34, for the DAS frequency domain data of the channel, compare the amplitude value Ai corresponding to each frequency in the frequency band [f1, f2] with the size of the filtering threshold. If Ai>fp, reassign Ai to Ai=fp. If Ai≤fp, do nothing.

6. The method for eliminating low-frequency noise of distributed optical fiber data in a well according to claim 5, characterized in that: The step S3 further comprises: Step S35, repeating steps S31 to S34, and performing notch filtering with an adjustable threshold on the DAS frequency domain data of all channels in turn.

7. The method for eliminating low-frequency noise of distributed optical fiber data in a well according to claim 2, characterized in that: In step S4, the DAS frequency domain data is transferred to the time domain, and the specific operations include: The DAS frequency domain data after the notch filtering with an adjustable threshold in step S3 is subjected to an inverse Fourier transform to be converted into DAS time domain data.

8. A low-frequency noise elimination device for distributed optical fiber data in a well, characterized in that: include: Input module, used to input DAS time domain data and perform spectrum analysis on the data; A first conversion module, used to convert DAS time domain data into frequency domain data; The filter processing module performs notch filtering with an adjustable threshold on the DAS frequency domain data; The second conversion module is used to convert the DAS frequency domain data after notch filtering into the time domain.

9. A computer-readable medium, characterized in that The computer-readable storage medium stores at least one computer-executable program, and when the at least one program is executed by the computer, the computer executes the steps of the method for eliminating low-frequency noise of distributed optical fiber data in a well as described in any one of claims 1 to 7.

10. A computer device, characterized in that: The method comprises a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the method for eliminating low-frequency noise of distributed optical fiber data in a well as described in any one of claims 1 to 7.

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