A demodulation method for a modulation signal transmitted by an acoustic wave of an oil pipe string

Abstract

The invention discloses a demodulation method for a modulation signal of acoustic wave transmission of an oil pipe string, and belongs to the technical field of acoustic wave transmission. The method comprises: receiving an acoustic wave signal transmitted from the oil pipe string, wherein the acoustic wave signal comprises a pilot signal and a data frame; performing segmentation processing on the received acoustic wave signal by using a sliding window technology to determine the position of the pilot signal; performing spectrum analysis on the pilot signal with the determined position, and recording N frequency band information that meets the signal-to-noise ratio requirement; performing demodulation processing on each bit in the data frame; judging and obtaining the demodulation value of N small windows of each bit according to the result of the demodulation processing; comprehensively analyzing and comparing the demodulation values ​​of the N small windows of each bit, and outputting the demodulation value of each bit, so as to realize complete demodulation of the acoustic wave modulation signal transmitted in the oil pipe string; the invention improves the reliability of demodulation of underground broadband modulation signals, and ensures the success rate of automatic frequency selection of an acoustic wave two-way communication system of oil and gas wells.

Description

Technical Field

[0001] The invention relates to a demodulation method for a modulation signal of acoustic wave transmission of an oil pipe column, and belongs to the technical field of acoustic wave transmission. Background Art

[0002] The prior art designs a two-way acoustic modulation data communication system between the oil and gas well underground and the ground. The system consists of the following components: Figure 1 shown.

[0003] The system uses the steel tubing string in the wellbore of the oil and gas well as the acoustic wave transmission channel. Since the tubing string in the wellbore is composed of a cascade of tubing and couplings (such as Figure 2 As shown in Figure 2), the oil pipe string shows the characteristics of a comb filter for the transmission of sound waves (as shown in Figure 2). Figure 3 Figure 1 shows the actual test result for a well shown in Figure 1), i.e., the stopband and passband appear alternately.

[0004] In addition, due to the different wellbore structures (different well depths, different wellbore trajectories, different oil casing specifications, etc.), the resistance band distribution of acoustic wave transmission in the tubing string is not the same between different oil and gas wells. Even for the same well, the change of the liquid level in the wellbore or the change of the fluid characteristics in the tubing will cause the acoustic wave transmission resistance band characteristics of the tubing string to change dynamically. Furthermore, the acoustic wave transmission resistance band distribution characteristics of the uplink channel (downhole to the ground) and the downlink channel (ground to downhole) are not necessarily symmetrical, that is, the uplink channel and the downlink channel need to use different frequency points (frequency bands) for modulation communication.

[0005] Therefore, if reliable acoustic wave modulation two-way data communication between the oil and gas wells and the ground is to be achieved, it is not possible to simply use fixed acoustic wave frequency (frequency band) modulation for two-way communication. The communication system must dynamically and automatically find the appropriate acoustic wave frequency (frequency band) according to the changes in the acoustic wave transmission resistance band of the oil pipe string, so as to achieve reliable acoustic wave communication between the well and the ground. Figure 3 As shown in the well, the system should be able to automatically find the optimal frequency band of 2200~2300Hz as the frequency band for uplink communication. The process method of automatic frequency selection has been described in another patent.

[0006] In one step of the automatic frequency selection process, the surface equipment receives the linear frequency sweep signal sent from the underground, completes the spectrum analysis and finds the optimal uplink channel frequency (band), and then needs to send the optimal uplink channel frequency (band) and modulation mode to the underground equipment through broadband linear frequency sweep modulation. The underground equipment needs to successfully demodulate the received information to complete the underground transmission configuration.

[0007] Therefore, a key problem needs to be solved here, that is, how to effectively demodulate the broadband linear swept frequency modulated acoustic wave signal of the downlink channel after it is transmitted through the oil pipe string; that is, the demodulation problem of the broadband acoustic wave signal after passing through the comb filter.

[0008] The traditional demodulation method for linear swept frequency modulated signals is to use a matched filter (pulse compression) of the same bandwidth at the receiving end, so that the output signal of the filter produces a narrow and sharp high signal-to-noise ratio pulse signal in the middle of each bit. This pulse signal can be easily identified to recover the corresponding bit data.

[0009] However, after the broadband linear frequency sweep modulated acoustic wave signal is transmitted through the tubing string, due to the transmission characteristics of the tubing string comb filter, its time domain signal has signal missing at certain positions of the entire pulse width (corresponding to the frequency domain, that is, there is signal missing in certain frequency bands in the frequency domain, such as Figure 3 As shown in Figure 4 This is the time domain waveform of a single broadband linear swept frequency pulse signal after passing through the tubing string. The above-mentioned signal loss phenomenon can be clearly seen.

[0010] For this kind of signal, if a matched filter with the same bandwidth as the modulated signal is used for processing, its output end cannot produce a single narrow and sharp pulse with a high signal-to-noise ratio at each bit position. In the actual oil and gas well application environment, the environmental noise is usually relatively large and the signal-to-noise ratio is very poor, so data demodulation cannot be achieved reliably. Summary of the invention

[0011] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a demodulation method for a modulation signal transmitted by an oil pipe string through acoustic waves. In the scenario where the oil pipe string is used as an acoustic wave transmission channel, the reliability of downhole broadband modulation signal demodulation is improved, and the success rate of automatic frequency selection of an oil and gas well acoustic two-way communication system is ensured.

[0012] To achieve the above object, the present invention is implemented by adopting the following technical solutions: In a first aspect, the present invention provides a method for demodulating a modulated signal transmitted by an acoustic wave of an oil pipe string, which is applicable to a downhole receiving end, comprising: Receiving an acoustic wave signal transmitted from an oil pipe string, wherein the acoustic wave signal includes a pilot signal and a data frame; The received acoustic wave signal is processed in segments using the sliding window technique to determine the location of the pilot signal; Perform spectrum analysis on the pilot signal of the determined position and record the information of N frequency bands that meet the signal-to-noise ratio requirements; Demodulate each bit in the data frame according to the recorded N frequency band information; According to the result of the demodulation processing, the demodulation value of N small windows of each bit position is determined; The demodulation values ​​of N small windows of each bit are comprehensively analyzed and compared, and the demodulation value of each bit is output to achieve complete demodulation of the acoustic wave modulation signal transmitted in the oil pipe string.

[0013] Furthermore, the pilot signal is a linear frequency sweep signal with a set pulse width, which is used to initialize the downhole receiving device.

[0014] Furthermore, the data frame includes a series of bits modulated by linear frequency sweeping, and each bit is modulated by sending a linear frequency sweeping signal with a set pulse width or by not sending a signal.

[0015] Furthermore, the step of using the sliding window technology to process the received acoustic wave signal in sections to determine the position of the pilot signal includes: The received acoustic wave signal is processed by sliding sampling using a window with the same pulse width as the leading signal, the sampling data in each window is converted into the frequency domain, and the converted frequency domain result is integrated within the bandwidth of the sweep. If the integral value exceeds the threshold and is the maximum, the window position here is used as the position of the leading signal.

[0016] Furthermore, the performing of spectrum analysis on the pilot signal for determining the position and recording N frequency band information that meets the signal-to-noise ratio requirement includes: For the nth frequency band, calculate the starting position and ending position of frequency band n in the time domain pulse, the formula is as follows: Pns = (fn-Bn / 2-fs) / k; Pne = (fn+Bn / 2-fs) / k; Wherein, Pns represents the starting position of frequency band n in the time domain pulse, Pne represents the ending position of frequency band n in the time domain pulse, fn represents the center frequency point of frequency band n, Bn represents the width of frequency band n, fs represents the starting frequency of the linear sweep signal, and k represents the sweep slope of the linear sweep signal; The calculation formula of k is as follows: k = (fe - fs) / T; Wherein, fe represents the end frequency of the linear sweep signal, and T is the pulse width.

[0017] Further, the demodulating each bit in the data frame according to the recorded N frequency band information includes: Extract sampling data of N small windows according to the obtained N Pns / Pne; For each small window, a matched filter corresponding to the linear frequency sweep signal is automatically generated according to its corresponding frequency band parameters fn and Bn; The sampled data in the N small windows are respectively convolved with the corresponding N matched filters to obtain N convolution calculation results.

[0018] Further, the determining, based on the result of the demodulation processing, to obtain the demodulation value of the N small windows of each bit position includes: According to the convolution calculation results of the N small windows in each bit position, the demodulation values ​​of the N small windows in each bit position are comprehensively determined; If the peak value of the convolution output of a small window is greater than the set threshold and the peak position is within the central set range of the time window, the demodulation output of the small window is judged to be "1", otherwise it is judged to be "0".

[0019] Furthermore, the comprehensive analysis and comparison of the demodulation values ​​of the N small windows of each bit position, outputting the demodulation value of each bit position, and realizing the complete demodulation of the acoustic wave modulation signal transmitted in the oil pipe string include: Compare the demodulated values ​​of N windows in each bit position, output the demodulated value of each bit position, and realize the complete demodulation of the acoustic wave signal transmitted in the oil pipe string; Among them, if the number of "1" in the N window demodulation outputs is greater than N / 2, the bit is demodulated to "1"; conversely, if the number of "0" in the N demodulation outputs is greater than N / 2, the bit is demodulated to "0".

[0020] Furthermore, the method also includes: using a weighted method to perform weighted accumulation of the demodulation values ​​of the N windows of each bit position according to the quality of the signal-to-noise ratio of each window, wherein the demodulation value weight coefficient of the window with a good signal-to-noise ratio is high, and the demodulation value weight coefficient of the window with a poor signal-to-noise ratio is low, and the weighted accumulation result determines the final demodulation value of the bit position.

[0021] Furthermore, the method also includes: after completing the demodulation of all bits, performing synchronization, verification and extraction processing of the data frame.

[0022] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a demodulation method for a modulation signal transmitted by an oil pipe string acoustic wave, which improves the reliability of downhole broadband modulation signal demodulation and ensures the success rate of automatic frequency selection of an oil and gas well acoustic wave two-way communication system when the oil pipe string is used as an acoustic wave transmission channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the composition of a two-way acoustic wave modulation data communication system between the underground and surface of an oil and gas well provided by an embodiment of the present invention; Figure 2 It is a schematic diagram of the structure of an oil pipe string in an oil and gas wellbore provided by an embodiment of the present invention; Figure 3 It is a spectrum analysis result diagram of a received signal after a linear frequency sweeping acoustic wave signal provided by an embodiment of the present invention is transmitted through an oil pipe string in an oil and gas wellbore. The result diagram can clearly reflect the characteristics of a comb filter presented by the oil pipe string for acoustic wave transmission, that is, acoustic wave stop bands and pass bands appear alternately; Figure 4 It is a schematic diagram of a time domain waveform of a received signal after the linear frequency sweeping acoustic wave signal provided by an embodiment of the present invention is transmitted through an oil pipe string in an oil and gas wellbore; Figure 5 is a schematic diagram of signal composition provided by an embodiment of the present invention; Figure 6 It is a schematic diagram of realizing acoustic wave modulation of a data frame bit stream provided by an embodiment of the present invention through a linear up-sweep OOK method; Figure 7 is a schematic diagram of N frequency band data for demodulation processing in each bit position of a data frame provided by an embodiment of the present invention (in this example, N=3); Figure 8 Schematic diagram of the corresponding starting positions and ending positions of N frequency bands for demodulation processing in each bit of a data frame provided by an embodiment of the present invention in the time domain (N=3 in this example); Fig. 9 Schematic diagram of a process of capturing a pilot broadband linear frequency sweep pulse signal provided by an embodiment of the present invention; Fig.10 It is a schematic diagram of a demodulation process of each bit of a data frame provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0025] Embodiment 1: This embodiment introduces a demodulation method for a modulation signal transmitted by an acoustic wave of an oil pipe string, which is applicable to a downhole receiving end, and includes: Receiving an acoustic wave signal transmitted from an oil pipe string, wherein the acoustic wave signal includes a pilot signal and a data frame; The received acoustic wave signal is processed in segments using the sliding window technique to determine the location of the pilot signal; Perform spectrum analysis on the pilot signal of the determined position and record the information of N frequency bands that meet the signal-to-noise ratio requirements; Demodulate each bit in the data frame according to the recorded N frequency band information; According to the result of the demodulation processing, the demodulation value of N small windows of each bit position is determined; The demodulation values ​​of N small windows of each bit are comprehensively analyzed and compared, and the demodulation value of each bit is output to achieve complete demodulation of the acoustic wave modulation signal transmitted in the oil pipe string.

[0026] The demodulation method of the oil pipe string acoustic wave transmission modulated signal provided in this embodiment specifically involves the following steps: Signal structure design The signal is composed of a leading broadband linear up-sweep signal pulse (for example, a pulse width of 10s) + a group of data frames using linear up-sweep modulation (the modulation method can be OOK, that is, bit "1" sends a linear up-sweep signal with a pulse width of 200ms, bit "0" does not send a signal, and the duration is 200ms). The signal composition is shown in the figure below. Figure 5 As shown; An example of linear up-sweep OOK modulation is as follows: Figure 6 As shown; Since the wider the pulse, the greater its energy, the easier it is to be detected by the downhole receiver. Therefore, the role of the initial wide pulse signal is to allow the downhole receiving device to first capture the wide pulse signal and perform spectrum analysis on the wide pulse linear sweep signal to find the passband position of the received signal.

[0027] Leading wide pulse capture and spectrum analysis The receiving end of the downhole device caches the collected acoustic wave receiving signals, and its core processor uses a window with the same time width as the wide pulse to slide the received acoustic wave sampling signals. The sampling data in each window is first converted into the frequency domain, and then the frequency domain results are integrated within the bandwidth of the sweep. If the integral value exceeds the threshold and is the maximum, the window position is the position of the wide pulse.

[0028] Once the window position is locked, the data in the window is further spectrally analyzed, and the first N frequency band data that meet the signal-to-noise ratio requirements are recorded in order of signal-to-noise ratio (where the frequency band data of the nth frequency band is marked as: center frequency fn, bandwidth Bn).

[0029] Definition: Pns represents the starting position of frequency band n in the time domain pulse, and Pne represents the ending position of frequency band n in the time domain pulse.

[0030] Assuming that the starting frequency of the linear sweep signal is fs, the ending frequency is fe, and the pulse width is T seconds, the sweep slope is: k = (fe - fs) / T; For the nth frequency band: Pns = (fn-Bn / 2-fs) / k; Pne = (fn+Bn / 2-fs) / k; The sampling data in the wide pulse window is extracted into N small windows of sampling data according to the N Pns / Pne obtained above (for example Figure 7 (where N=3).

[0031] For each small window, the matched filter corresponding to the linear swept frequency signal is automatically generated according to its corresponding frequency band parameters fn and Bn, and the sampling data of the small window is convolved with the matched filter. If the peak value of the output is greater than the set threshold and the peak position is near the center of the small window, it is confirmed that the sampling data in the small window is a section of the linear swept frequency signal sent down.

[0032] If most of the N small windows can get the above confirmation, the downhole device determines that the wide pulse is successfully captured, and records the frequency band information of the N frequency bands for demodulation of the subsequent linear sweep frequency modulation signal of the signal group.

[0033] The capture process of the leading wide pulse is as follows: Fig. 9 shown.

[0034] Demodulation of Wideband Linear Frequency-Sweep Modulation Signal Frames When the downhole device successfully captures the leading broadband linear sweep pulse signal in the received signal, since the time structure of the entire signal is fixed, it means that the time slices of each bit of the subsequent data modulation frame are also fixed. Therefore, it is easy to extract the acoustic wave receiving data corresponding to each bit using the bit-width time window for subsequent processing.

[0035] Because each bit of the data modulation frame is modulated by a linear swept frequency signal with the same bandwidth as the pilot signal, the frequency passband distribution in each bit time slice is the same as that of the pilot signal. However, due to the different pulse widths, we need to recalculate the N Pns / Pne in each bit time slice in order to extract N small window data for demodulation in each bit time slice.

[0036] As mentioned above, the modulation method adopts the linear sweep OOK method, that is, bit "1" sends a linear sweep signal with a pulse width of 200ms, and bit "0" does not send a signal, and the duration is 200ms.

[0037] For each small window in each bit time slice, a matched filter corresponding to the linear frequency sweep signal is automatically generated according to its corresponding frequency band parameters fn and Bn, and the received data in the small window is convolved with the matched filter. If the peak value of its output is greater than the set threshold and the peak position is near the center of the small window, the demodulation output of the window is judged to be "1"; conversely, if the matched filter calculation output cannot detect a peak value greater than the threshold, the demodulation output of the window is judged to be "0".

[0038] The demodulation output results of the N windows of each bit time slice are compared, and the final demodulation value of the bit is output.

[0039] The comparison method is that if the number of "1"s in the N window demodulation outputs is greater than N / 2, the bit is demodulated as "1"; conversely, if the number of "0"s in the N window demodulation outputs is greater than N / 2, the bit is demodulated as "0".

[0040] In addition, since the signal-to-noise ratios of the received signals of the N windows are different, a weighted method can also be used to accumulate the demodulation values ​​of the N windows according to the quality of the signal-to-noise ratio of each window, that is, the output result weight coefficient of the window with a high signal-to-noise ratio is high, and the output result weight coefficient of the window with a low signal-to-noise ratio is low, and the weighted accumulation result determines the final demodulation value of the bit.

[0041] The above demodulation process is as follows Fig.10 shown.

[0042] After the processor completes the demodulation of each bit in turn, it can process the data frame, including frame synchronization, frame error checking, and extraction of each data in the frame. At this point, the demodulation of the broadband linear frequency sweep modulated acoustic wave data frame transmitted through the oil pipe string is completed.

[0043] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for demodulating a modulated signal transmitted by an acoustic wave of an oil pipe string, suitable for a downhole receiving end, characterized in that: include: Receiving an acoustic wave signal transmitted from an oil pipe string, wherein the acoustic wave signal includes a pilot signal and a data frame; The received acoustic wave signal is processed in segments using the sliding window technique to determine the location of the pilot signal; Perform spectrum analysis on the pilot signal of the determined position and record the information of N frequency bands that meet the signal-to-noise ratio requirements; Demodulate each bit in the data frame according to the recorded N frequency band information; According to the result of the demodulation processing, the demodulation value of N small windows of each bit position is determined; The demodulation values ​​of N small windows of each bit are comprehensively analyzed and compared, and the demodulation value of each bit is output to achieve complete demodulation of the acoustic wave modulation signal transmitted in the oil pipe string.

2. The method for demodulating a modulation signal transmitted by an acoustic wave of an oil pipe string according to claim 1, characterized in that: The pilot signal is a linear frequency sweep signal with a set pulse width, which is used to initialize the downhole receiving device.

3. The method for demodulating a modulation signal transmitted by an acoustic wave of an oil pipe string according to claim 2, characterized in that: The data frame includes a series of bits modulated by linear frequency sweeping, and each bit is modulated by sending a linear frequency sweeping signal with a set pulse width or by not sending a signal.

4. The method for demodulating a modulation signal transmitted by an acoustic wave of an oil pipe string according to claim 1, characterized in that: The method of using the sliding window technology to process the received sound wave signal in sections to determine the position of the pilot signal includes: The received acoustic wave signal is processed by sliding sampling using a window with the same pulse width as the leading signal, the sampling data in each window is converted into the frequency domain, and the converted frequency domain result is integrated within the bandwidth of the sweep. If the integral value exceeds the threshold and is the maximum, the window position here is used as the position of the leading signal.

5. The method for demodulating a modulation signal transmitted by an acoustic wave of an oil pipe string according to claim 3, characterized in that: The performing spectrum analysis on the pilot signal for determining the position and recording N frequency band information that meets the signal-to-noise ratio requirement includes: For the nth frequency band, calculate the starting position and ending position of frequency band n in the linear frequency sweep time domain pulse, the formula is as follows: Pns = (fn-Bn / 2-fs) / k; Pne = (fn+Bn / 2-fs) / k; Wherein, Pns represents the starting position of frequency band n in the time domain pulse, Pne represents the ending position of frequency band n in the time domain pulse, fn represents the center frequency point of frequency band n, Bn represents the width of frequency band n, fs represents the starting frequency of the linear sweep signal, and k represents the sweep slope of the linear sweep signal; The calculation formula of k is as follows: k = (fe - fs) / T; Wherein, fe represents the end frequency of the linear sweep signal, and T is the pulse width.

6. The method for demodulating a modulation signal transmitted by an acoustic wave of an oil pipe string according to claim 5, characterized in that: The demodulating process is performed on each bit in the data frame according to the recorded N frequency band information, including: Extract sampling data of N small windows according to the obtained N Pns / Pne; For each small window, a matched filter corresponding to the linear frequency sweep signal is automatically generated according to its corresponding frequency band parameters fn and Bn; The sampled data in the N small windows are respectively convolved with the corresponding N matched filters to obtain N convolution calculation results.

7. The method for demodulating a modulation signal transmitted by an acoustic wave of an oil pipe string according to claim 6, characterized in that: The step of determining, based on the result of the demodulation processing, the demodulation values ​​of the N small windows of each bit position comprises: According to the convolution calculation results of the N small windows in each bit position, the demodulation values ​​of the N small windows in each bit position are comprehensively determined; If the peak value of the convolution output of a small window is greater than the set threshold and the peak position is within the central set range of the time window, the demodulation output of the small window is judged to be "1", otherwise it is judged to be "0".

8. The method for demodulating a modulation signal transmitted by an acoustic wave of an oil pipe string according to claim 7, characterized in that: The comprehensive analysis and comparison of the demodulation values ​​of the N small windows of each bit position, outputting the demodulation value of each bit position, and realizing the complete demodulation of the acoustic wave modulation signal transmitted in the oil pipe string include: Compare the demodulated values ​​of N windows in each bit position, output the demodulated value of each bit position, and realize the complete demodulation of the acoustic wave signal transmitted in the oil pipe string; Among them, if the number of "1" in the N window demodulation outputs is greater than N / 2, the bit is demodulated to "1"; conversely, if the number of "0" in the N demodulation outputs is greater than N / 2, the bit is demodulated to "0".

9. The method for demodulating a modulation signal transmitted by an acoustic wave of an oil pipe string according to claim 8, characterized in that: The method further comprises: using a weighted method to perform weighted accumulation of the demodulation values ​​of the N windows of each bit position according to the quality of the signal-to-noise ratio of each window, wherein the demodulation value weight coefficient of the window with a good signal-to-noise ratio is high, and the demodulation value weight coefficient of the window with a poor signal-to-noise ratio is low, and the weighted accumulation result determines the final demodulation value of the bit position.

10. The method for demodulating a modulation signal transmitted by an acoustic wave of an oil pipe string according to claim 1, characterized in that: The method further comprises: after completing the demodulation of all bits, performing synchronization, verification and extraction processing of the data frame.

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