Surface received electromagnetic wave signal interference filtering device and method for a downhole well

Abstract

The application provides a ground-received oil and gas well downhole electromagnetic wave signal interference filtering device and method, the filtering device comprises a signal receiving and frequency domain transformation module, an interference component estimation module, an interference component reconstruction module and an interference filtering judgment module, wherein the signal receiving and frequency domain transformation module is configured to receive an electromagnetic wave signal and perform frequency domain transformation; the interference component estimation module is configured to estimate harmonic parameters of an interference component in the signal transformed by the signal receiving and frequency domain transformation module; the interference reconstruction module is configured to reconstruct the harmonic parameters of the interference component estimated by the interference component estimation module to obtain a power frequency harmonic signal; and the interference filtering judgment module is configured to subtract the power frequency harmonic signal from the received electromagnetic wave signal to obtain an effective signal, and judge whether the interference is filtered in the effective signal. The application has the advantages of being capable of estimating power frequency fundamental frequency and harmonic parameters thereof, reconstructing an interference signal, removing power frequency interference and guaranteeing effective identification of a signal.

Description

Technical Field

[0001] This invention relates to the field of oil and gas well information and control engineering technology, specifically to an interference filtering device and method for receiving downhole electromagnetic wave signals from oil and gas wells on the surface. Background Technology

[0002] Communication between oil and gas wells and the surface is a key technology for establishing digital oilfields in the future. While methods for downhole-to-surface communication have been largely established, surface electromagnetic noise, particularly power frequency interference (e.g., electromagnetic fields and leakage currents emitted by equipment at the well site), severely impacts signal reception. Power frequency interference is mainly distributed around 50Hz and its harmonics, as well site power is primarily 50Hz. Since harmonics vary significantly across different well sites and times, the interference is highly complex. Lower carrier frequencies allow for longer signal transmission distances, making it suitable for deeper wells. Therefore, electromagnetic carrier frequencies below 10Hz are generally chosen for downhole-to-surface signal transmission. Because the signal transmitted from downhole is relatively small, with the power frequency amplitude being three orders of magnitude larger than the effective signal, the signal is completely overwhelmed by noise, making it impossible to observe the effective signal directly from the spectrum. Therefore, to receive the effective signal, it is essential to suppress power frequency and harmonic interference signals.

[0003] For this type of narrowband interference, notch filters are typically used in engineering to filter it out. However, notch filters are usually implemented using infinite impulse response (IIR) filters. Because the phase response of IIR filters is not linear, it can cause significant distortion to normal communication signals. Moreover, the frequency of power frequency interference is unlikely to change with different well sites, making notch filters unsuitable for this scenario.

[0004] To ensure that the filter does not interfere with the effective signal, the phase shift of the filter at different frequencies must be linear. Therefore, we can only use a finite impulse response (FIR) filter. However, this low-pass filter has an attenuation of about 2dB for signals below 10Hz, and the attenuation varies slightly for different frequency components. Therefore, this filter will introduce distortion into the effective signal.

[0005] Considering that the main energy of power frequency interference signals at the well site is concentrated in the fundamental frequency and its harmonics, if the parameters of the fundamental frequency and its harmonics can be estimated, the interference signal can be reconstructed and directly subtracted from the received signal. This can eliminate power frequency interference while minimizing distortion to the effective signal. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to solve one or more of the problems existing in the prior art. For example, one objective of the present invention is to provide an interference filtering method capable of estimating the fundamental frequency and its harmonic parameters, reconstructing interference signals, removing power frequency interference from the received signal, and ensuring effective signal identification of electromagnetic wave signals received from oil and gas wells on the surface. Another objective of the present invention is to provide an interference filtering method capable of estimating the fundamental frequency and its harmonic parameters, reconstructing interference signals, removing power frequency interference from the received signal, and ensuring effective signal identification of electromagnetic wave signals received from oil and gas wells on the surface.

[0007] To achieve the above objectives, the present invention provides an interference filtering device for receiving downhole electromagnetic wave signals from oil and gas wells on the surface. The filtering device includes a signal receiving and frequency domain transformation module, an interference component estimation module, an interference component reconstruction module, and an interference filtering judgment module.

[0008] The signal receiving and frequency domain transformation module is configured to receive electromagnetic wave signals and perform frequency domain transformation.

[0009] The interference component estimation module is configured to estimate the harmonic parameters of the interference components in the signal after it has been transformed by the signal receiving and frequency domain transformation modules.

[0010] The interference reconstruction module is configured to reconstruct the harmonic parameters of the interference components estimated by the interference component estimation module to obtain the power frequency harmonic signal.

[0011] The interference filtering judgment module is configured to subtract the power frequency harmonic signal from the received electromagnetic wave signal to obtain the effective signal, and to determine whether the interference in the effective signal has been filtered out.

[0012] In one exemplary embodiment of one aspect of the present invention, the filtering device may further include a demodulation module configured to demodulate the effective signal after filtering out interference.

[0013] In one exemplary embodiment of this invention, the interference components are distributed near the power frequency and its harmonics, and the downhole electromagnetic wave signal of the oil and gas well is selected with a frequency below 10Hz.

[0014] Another aspect of the present invention provides an interference filtering method for receiving downhole electromagnetic wave signals from oil and gas wells on the surface, the interference filtering method may include the following steps:

[0015] The frequency domain transformation of the electromagnetic wave signal received from the ground is performed to estimate the harmonic parameters of the interference components to be initially filtered out.

[0016] The power frequency interference signal is reconstructed based on the harmonic parameters of the interference components, and the power frequency interference signal components are subtracted from the received electromagnetic wave signal to obtain the effective signal.

[0017] Determine whether the power frequency interference signal in the valid signal is filtered out successfully. If the filtering is successful, demodulate the valid signal to restore the downhole electromagnetic wave signal. If the filtering is unsuccessful, repeat the interference filtering operation on the valid signal until the filtering is successful.

[0018] In an exemplary embodiment of another aspect of the present invention, the filtering of qualified items may include the following steps:

[0019] Determine whether the proportion of the energy of the effective signal in the received signal energy is greater than 50%. If it is greater than 50%, it means that the strength of the effective signal is greater than the strength of the interference signal, and the effective signal enters the demodulation module for demodulation.

[0020] In an exemplary embodiment of another aspect of the present invention, the harmonic parameters for filtering out interference components may include the frequency, amplitude, and phase of the interference components, and are obtained through the following steps:

[0021] The received signal is sampled to determine its expression. A DFT transformation is then performed on the signal, and the amplitude and phase in the expression are solved using either a direct solution method or a difference method.

[0022] In another exemplary embodiment of the present invention, the expression for the power frequency interference signal can be:

[0023] x(n)=Acos(2nπf / f s +θ), n=0, 1,…,N-1 (1)

[0024] Where x(n) represents a sinusoidal sampling sequence of length N, f is the frequency, and s -1 ;f s S is the sampling rate. -1 A represents amplitude, with units consistent with the measured signal; θ represents phase, in rad.

[0025] remember:

[0026] f / f s = (K+Δ) / N, 0≤Δ<1, and K is an integer. Equation (1) can be rewritten as:

[0027]

[0028] In an exemplary embodiment of another aspect of the present invention, the DFT transformation may include the steps of:

[0029] Equation (2) is transformed by DFT to obtain:

[0030]

[0031] remember:

[0032] δ - (k)=K+Δ-k (4)

[0033] δ + (k)=K+Δ+k (5)

[0034] We can obtain:

[0035] δ + (k)+δ - (k)=2(K+Δ) (6)

[0036] δ + (k)-δ - (k)=2k (7)

[0037] Using δ - δ - (k), δ + δ + (k), Substituting equations (4) and (5) into equation (3), and expanding by series, we get:

[0038]

[0039] We can obtain:

[0040]

[0041] Expanding the exponential form, the real and imaginary parts of X(k) can be written in the following forms:

[0042]

[0043]

[0044] In another exemplary embodiment of the present invention, the method may further include the steps of:

[0045] remember:

[0046] f + (k)=ctgπδ-(k) / N+ctgπδ + (k) / N (11)

[0047] f - (k)=ctgπδ - (k) / N-ctgπδ + (k) / N (12)

[0048] Among them, signal parameter items It is a constant independent of the spectral line position k, and can be obtained by elimination using the proportional method:

[0049]

[0050] Based on the trigonometric formula:

[0051]

[0052] Substituting equation (14) into equation (13), we get:

[0053]

[0054] Equation (15) contains only one unknown term, K+Δ, so K and Δ can be solved using equation (15).

[0055] In another exemplary embodiment of the present invention, the method may further include the steps of:

[0056] remember:

[0057]

[0058] g(k) = cos(2πk / N); k i =k1,k2 (17)

[0059] X Δ =cos(2π(K+Δ) / N) (18)

[0060] Substituting into equation (15), we get:

[0061]

[0062] Since 0 ≤ Δ < 1, we can solve for:

[0063]

[0064]

[0065] The [] symbol indicates rounding down;

[0066] Substituting equations (20) and (21) into equations (9) and (10), we get:

[0067]

[0068]

[0069] By combining equations (22) and (23), the amplitude A and phase θ can be solved.

[0070] In another exemplary embodiment of the present invention, the method may further include the steps of:

[0071] Transform equations (9) and (10) into difference form:

[0072]

[0073]

[0074] According to the trigonometric formula, we can obtain:

[0075]

[0076] In equation (26), only the first term of the denominator is a function of k, denoted as g(k) in equation (17). According to equation (23), the following difference proportion form can be obtained:

[0077]

[0078] We obtain the quadratic equation:

[0079] (1-D)X Δ 2 +[D(g(k1)+g(k2))-(g(k3)+g(k4))]X Δ +g(k3)g(k4)-Dg(k1)g(k2)=0 (28) where,

[0080]

[0081] XΔ can be solved using equation (28), and K and Δ can be solved by substituting it into equations (20) and (21);

[0082] Substituting the values ​​of K and Δ into the difference formulas (23) and (24), we get:

[0083]

[0084]

[0085] By combining equations (30) and (31), we can obtain A and θ.

[0086] Compared with the prior art, the beneficial effects of the present invention may include at least one of the following:

[0087] (1) The present invention provides a method for filtering out ground power frequency interference when receiving downhole signals. It can estimate the power frequency fundamental frequency and its harmonic parameters, thereby reconstructing the interference signal and removing the power frequency interference to ensure effective signal identification.

[0088] (2) The present invention solves the problem that the existing method of using an infinite impulse response filter (IIR) to filter received signals is not suitable because the phase response of the IIR filter is not linear, which will cause significant distortion to the normal communication signal. Moreover, the frequency of power frequency interference may change with different well sites. Therefore, it is not suitable when notch filters are not applicable.

[0089] (3) The interference filtering method of the present invention improves the sensitivity of signal reception by more than 65dB, which is more than 10dB higher than the traditional filtering method. This is basically consistent with the simulation results. The sensitivity improvement in the actual test results is slightly less than that in the simulation results because the actual signal contains a small amount of other noise interference. Attached Figure Description

[0090] The above and other objects and features of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which:

[0091] Figure 1 A schematic flowchart of an interference filtering method for receiving downhole electromagnetic wave signals from oil and gas wells on the ground according to an exemplary embodiment of the present invention is shown.

[0092] Figure 2 A time-domain waveform diagram of a simulated signal during a simulation test according to an exemplary embodiment of the present invention is shown.

[0093] Figure 3 The time-domain waveform of the recovered signal obtained by filtering method during simulation testing according to an exemplary embodiment of the present invention is shown.

[0094] Figure 4 The diagram shows the time-domain waveform of the recovered signal obtained by the signal interference filtering method during simulation testing according to an exemplary embodiment of the present invention.

[0095] Figure 5 The diagram shows the time-domain waveform of the recovered signal obtained by filtering during a field test according to an exemplary embodiment of the present invention.

[0096] Figure 6 The diagram shows the time-domain waveform of the recovered signal obtained by a signal interference filtering method during a field test according to an exemplary embodiment of the present invention.

[0097] Figure 7 A schematic diagram of an interference filtering device for receiving downhole electromagnetic wave signals from oil and gas wells on the ground is shown according to an exemplary embodiment of the present invention. Detailed Implementation

[0098] The interference filtering apparatus and method for receiving downhole electromagnetic wave signals from oil and gas wells on the surface according to the present invention will be described in detail below with reference to exemplary embodiments.

[0099] Figure 7 A schematic diagram of an interference filtering device for receiving downhole electromagnetic wave signals from oil and gas wells on the ground is shown according to an exemplary embodiment of the present invention.

[0100] In a first exemplary embodiment of the present invention, as Figure 7 As shown, the interference filtering device for receiving downhole electromagnetic wave signals from oil and gas wells on the ground includes a signal receiving and frequency domain transformation module, an interference component estimation module, an interference component reconstruction module, and an interference filtering judgment module.

[0101] The signal receiving and frequency domain transformation module is configured to receive electromagnetic wave signals and perform frequency domain transformation on the received signals. The interference component estimation module is configured to estimate the harmonic parameters of the interference components in the signal transformed by the signal receiving and frequency domain transformation module. After the frequency domain transformation is completed, the interference component estimation module searches for the harmonic parameters of the interference components in the frequency domain, that is, calculates the power frequency interference harmonic parameters around the frequency f = 50nHz (n = 1, 2, 3…). The received signal can also be a mechanical wave or other signal.

[0102] In this embodiment, the interference reconstruction module is configured to reconstruct the harmonic parameters of the interference components estimated by the interference component estimation module to obtain the power frequency harmonic signal (i.e., the interference component signal). For example, the power frequency interference can be reconstructed using the following formula:

[0103]

[0104] Where P(n) represents the interference signal function with a dominant frequency of f, which is dimensionless; A k The amplitude of the k-th harmonic is represented by the unit consistent with the measured signal; f represents the dominant interference frequency, s. -1 ;f s Indicates the sampling rate, s -1 ;θ k The phase of the kth harmonic is represented in rad.

[0105] In this embodiment, the interference filtering judgment module is configured to subtract the power frequency harmonic signal from the received electromagnetic wave signal to obtain the effective signal, and to determine whether the interference in the effective signal has been filtered out.

[0106] In this exemplary embodiment, the filtering device may further include a demodulation module configured to demodulate and acquire the effective signal after interference filtering.

[0107] In this exemplary embodiment, the interference components are mainly distributed at the power frequency (e.g., 50Hz) and its harmonics, and the downhole electromagnetic wave signal of the oil and gas well can be selected from frequencies below 10Hz.

[0108] Figure 1A schematic flowchart of an interference filtering method for receiving downhole electromagnetic wave signals from oil and gas wells on the ground according to an exemplary embodiment of the present invention is shown.

[0109] In a second exemplary embodiment of the present invention, as Figure 1 As shown, the interference filtering method for receiving downhole electromagnetic wave signals from oil and gas wells on the surface may include the following steps:

[0110] The electromagnetic wave signal received from the ground is subjected to frequency domain transformation, and the transformed electromagnetic wave signal is sampled to estimate the harmonic parameters of the interference components that are initially filtered out.

[0111] The power frequency interference signal is reconstructed based on the harmonic parameters of the interference components, and the power frequency interference signal components are subtracted from the received electromagnetic wave signal to obtain the effective signal.

[0112] Determine whether the power frequency interference signal in the valid signal is filtered out successfully. If the filtering is successful, demodulate the valid signal to restore the downhole electromagnetic wave signal. If the filtering is unsuccessful, repeat the interference filtering operation on the valid signal until the filtering is successful.

[0113] In this exemplary embodiment, the filtering of qualified samples may include the following steps:

[0114] Determine whether the proportion of the energy of the effective signal in the received signal energy is greater than 50%. If it is greater than 50%, it means that the strength of the effective signal is greater than the strength of the interference signal, and the effective signal enters the demodulation module for demodulation.

[0115] In this exemplary embodiment, the harmonic parameters for filtering out interference components may include the frequency, amplitude, and phase of the interference components, and are obtained through the following steps:

[0116] The received signal is sampled, the interference frequency f is determined first, and a DFT transformation is performed on it. The frequency, amplitude and phase of each harmonic of the interference frequency are solved using the direct solution method or the difference method.

[0117] In another exemplary embodiment of the present invention, the expression for the power frequency interference signal can be:

[0118] x(n)=Acos(2nπf / f s +θ), n=0, 1,…,N-1 (1)

[0119] Where x(n) represents a sinusoidal sampling sequence of length N, f is the frequency, and s -1 ;f s S is the sampling rate. -1 A represents amplitude, with the unit consistent with the measured signal; θ represents phase, in rad.

[0120] Note f / f s = (K+Δ) / N, 0≤Δ<1, and K is an integer. Equation (1) can be rewritten as:

[0121]

[0122] In an exemplary embodiment of another aspect of the present invention, the DFT transformation may include the steps of:

[0123] Equation (2) is transformed by DFT to obtain:

[0124]

[0125] remember:

[0126] δ - (k)=K+Δ-k (4)

[0127] δ + (k)=K+Δ+k (5)

[0128] We can obtain:

[0129] δ + (k)+δ - (k)=2(K+Δ) (6)

[0130] δ + (k)-δ - (k)=2k (7)

[0131] Using δ - δ - (k), δ + δ + (k), Substituting equations (4) and (5) into equation (3), and expanding by series, we get:

[0132]

[0133] We can obtain:

[0134]

[0135] Expanding the exponential form, the real and imaginary parts of X(k) can be written in the following forms:

[0136]

[0137]

[0138] In another exemplary embodiment of the present invention, the method may further include the steps of:

[0139] remember:

[0140] f+ (k)=ctgπδ - (k) / N+ctgπδ + (k) / N (11)

[0141] f - (k)=ctgπδ - (k) / N-ctgπδ + (k) / N (12)

[0142] Among them, signal parameter items It is a constant independent of the spectral line position k, and can be obtained by elimination using the proportional method:

[0143]

[0144] Based on the trigonometric formula:

[0145]

[0146] Substituting equation (14) into equation (13), we get:

[0147]

[0148] Equation (15) contains only one unknown term, K+Δ, so K and Δ can be solved using equation (15).

[0149] In another exemplary embodiment of the present invention, the method may further include the steps of:

[0150] remember:

[0151]

[0152] g(k) = cos(2πk / N); k i =k1,k2 (17)

[0153] X Δ =cos(2π(K+Δ) / N) (18)

[0154] Substituting into equation (15), we get:

[0155]

[0156] Since 0 ≤ Δ < 1, we can solve for:

[0157]

[0158]

[0159] The [] symbol indicates rounding down;

[0160] Substituting equations (20) and (21) into equations (9) and (10), we get:

[0161]

[0162]

[0163] By combining equations (22) and (23), the amplitude A and phase θ can be solved.

[0164] In another exemplary embodiment of the present invention, the method may further include the steps of:

[0165] Transform equations (9) and (10) into difference form:

[0166]

[0167]

[0168] According to the trigonometric formula, we can obtain:

[0169]

[0170] In equation (26), only the first term of the denominator is a function of k, denoted as g(k) in equation (17). According to equation (23), the following difference proportion form can be obtained:

[0171]

[0172] We obtain the quadratic equation:

[0173] (1-D)X Δ 2 +[D(g(k1)+g(k2))-(g(k3)+g(k4))]X Δ +g(k3)g(k4)-Dg(k1)g(k2)=0 (28)

[0174] in,

[0175]

[0176] XΔ can be solved using equation (28), and K and Δ can be solved by substituting it into equations (20) and (21).

[0177] Substituting the values ​​of K and Δ into the difference formulas (23) and (24), we get:

[0178]

[0179]

[0180] By combining equations (30) and (31), we can obtain A and θ.

[0181] Specifically, such as Figure 1 As shown, the received signal is first transformed in the frequency domain to search for power frequency harmonic interference components, i.e., calculating power frequency interference parameters around the frequency f = 50nHz (n = 1, 2, 3 = ). Then, the power frequency interference is reconstructed based on these parameters, and the interference signal is subtracted from the received signal. This eliminates one interference signal component. Next, it is determined whether the energy of the effective signal (e.g., a signal around 5Hz) accounts for more than 50% of the energy of the received signal. If the effective signal energy accounts for more than half, the signal can proceed to the demodulation module; if the effective signal energy accounts for less than half, the resulting signal undergoes the interference cancellation process again, and n = n + 1 is set to continue eliminating the next interference signal.

[0182] As can be seen from the above process, the key to this method lies in estimating the harmonic parameters of the interference components, that is, estimating the frequency, amplitude and phase parameters of the nth harmonic.

[0183] Specifically, for a sinusoidal sampling sequence x(n) of length N, its expression is as follows:

[0184] x(n)=Acos(2nπf / f s +θ); n=0, 1,…,N-1 (1)

[0185] Where x(n) represents a sinusoidal sampling sequence of length N, f is the frequency, and s -1 ;f s S is the sampling rate. -1 A represents amplitude, with the unit consistent with the measured signal; θ represents phase, in rad.

[0186] Note f / f s = (K+Δ) / N, 0≤Δ<1, and K is an integer, so equation (1) can be written as:

[0187]

[0188] The DFT transform expression for this signal is as follows:

[0189]

[0190] remember:

[0191] δ - (k)=K+Δ-k (4)

[0192] δ + (k)=K+Δ+k (5)

[0193] then,

[0194] δ+ (k)+δ - (k)=2(K+Δ) (6)

[0195] δ + (k)-δ - (k)=2k (7)

[0196] For ease of representation and without causing confusion, δ will be used below. - δ - (k), δ + δ + (k). Substituting equations (4) and (5) into equation (3), and using the series expansion:

[0197]

[0198] We can obtain:

[0199]

[0200] Expanding the exponential form, the real and imaginary parts of X(k) can be written in the following forms:

[0201]

[0202]

[0203] The above two equations are the basic formulas for the DFT transformation of sinusoidal signals. From equation (9), it can be seen that the real part of X(k) consists of the sum of two terms. The first term is entirely determined by the signal parameters and is a constant in the frequency domain; the arctangent function in the second term is related to the spectral line position parameter k, determining the shape of the real part of X(k) in the frequency domain. From equation (10), it can be seen that the imaginary part of X(k) is expressed as a product, and the spectral line position k is also included in the arctangent function.

[0204] For ease of representation, the following definition is provided:

[0205] f + (k)=ctgπδ - (k) / N+ctgπδ + (k) / N (11)

[0206] f - (k)=ctgπδ - (k) / N-ctgπδ + (k) / N (12)

[0207] Because f + (k) and f -(k) contains only the signal frequency parameter K+Δ. If we separate them from the basic formula, we can solve for the signal frequency parameter and then complete the solution for the other parameters. Analyzing the imaginary part expression (10) of X(k), we can directly use the proportional method to find f - (k) can be separated. Similarly, for the real part expression (9), the difference operation is performed first, and then the proportion method is used to separate f. + Similarly, (k) can be used to solve for signal parameters.

[0208] Both the direct solution method and the difference solution method can be used to determine the harmonic parameters of the interference components.

[0209] As shown in (10), the imaginary part of X(k) is composed of the product of two parts, while the signal parameter term... This is a constant independent of the spectral line position k, which can be eliminated using the proportion method, thus yielding:

[0210]

[0211] According to the trigonometric formula, we can deduce that:

[0212]

[0213] Substituting equation (14) into equation (13) yields:

[0214]

[0215] Equation (15) contains only one unknown term, K+Δ, so K and Δ can be solved using equation (15).

[0216] remember:

[0217]

[0218] g(k) = cos(2πk / N); k i =k1,k2 (17)

[0219] X Δ =cos(2π(K+Δ) / N) (18)

[0220] Therefore, we can solve equation (15) to get:

[0221]

[0222] Since 0 ≤ Δ < 1, therefore:

[0223]

[0224]

[0225] The square brackets [] indicate rounding down.

[0226] Substituting equations (20) and (21) into equations (9) and (10), we get:

[0227]

[0228]

[0229] By combining equations (22) and (23), the amplitude A and phase θ can be solved.

[0230] The direct solution method described above does not consider the influence of other sinusoidal frequency components. If multiple sinusoidal frequency components exist in the analyzed signal, the accuracy of the direct solution method will be affected. Therefore, the following method uses the difference method to eliminate the influence of other sinusoidal signals by performing difference operations on adjacent terms.

[0231] From equations (9) and (10), its difference form can be obtained:

[0232]

[0233]

[0234] According to the trigonometric formula, we can deduce

[0235]

[0236] In equation (26), only the first term of the denominator is a function of k, denoted as g(k) in equation (17). According to equation (23), the following difference proportion form can be obtained:

[0237]

[0238] Therefore, we can obtain the quadratic equation.

[0239] (1-D)X Δ 2 +[D(g(k1)+g(k2))-(g(k3)+g(k4))]X Δ +g(k3)g(k4)-Dg(k1)g(k2)=0 (28)

[0240] in,

[0241]

[0242] Using the quadratic formula, X can be solved from equation (28). Since equation (28) is a quadratic equation, it will yield two roots. Based on the position of the highest spectral line in the frequency domain, a real root that matches the actual signal should be selected and substituted into equations (20) and (21) to solve for K and Δ.

[0243] Finally, substituting the values ​​of K and Δ into the difference formulas (23) and (24), we get:

[0244]

[0245]

[0246] By combining equations (30) and (31), we can solve for A and θ.

[0247] Figure 2 A time-domain waveform diagram of a simulated signal during a simulation test according to an exemplary embodiment of the present invention is shown. Figure 3 The time-domain waveform of the recovered signal obtained by filtering method during simulation testing according to an exemplary embodiment of the present invention is shown. Figure 4 The diagram shows the time-domain waveform of the recovered signal obtained by the signal interference filtering method during simulation testing according to an exemplary embodiment of the present invention. Figure 5 The diagram shows the time-domain waveform of the recovered signal obtained by filtering during a field test according to an exemplary embodiment of the present invention. Figure 6 The diagram shows the time-domain waveform of the recovered signal obtained by a signal interference filtering method during a field test according to an exemplary embodiment of the present invention.

[0248] To better understand the exemplary embodiments of the present invention described above, further explanation is provided below with reference to specific examples.

[0249] To better illustrate the effectiveness of the interference filtering method for receiving downhole electromagnetic wave signals from oil and gas wells using the present invention, a comparative analysis of simulation testing and field experiments is presented. The simulation testing primarily involves adding known power frequency interference components to the communication signal, then using existing filtering methods and parameter estimation methods to eliminate the interference, and comparing the performance of the two methods. The field experiments mainly involve analyzing the signals actually received and acquired at the well site using these two methods, and verifying the effectiveness of the two methods by comparing the waveforms before and after interference elimination.

[0250] ① Simulation test

[0251] To facilitate comparison of algorithm performance, we first use simulation to verify the algorithm's interference suppression effect. The communication signal uses a frequency f cA cosine signal with a fundamental frequency of 5Hz is used to simulate the power frequency interference signal, while a cosine wave with a fundamental frequency of f0 = 49.8Hz and its 5th harmonic are used to simulate the interference signal. The simulated signal can be represented as:

[0252] x(n)=s(n)+p(n) (32)

[0253] The effective signal is represented as:

[0254] s(n)=cos(2nπf c / f s (33)

[0255] Interference signals are represented as:

[0256]

[0257] To ensure that the signal is not distorted during sampling, the signal sampling rate is set to f. s =2000Hz. Based on the energy ratio of each harmonic component in the measured signal, the amplitude and phase of each harmonic are set in the simulation as shown in Table 1. As can be seen from Table 1, the energy of each interference harmonic is much greater than the energy of the effective signal, and the energy of odd harmonics is greater than that of even harmonics. Here, the phase of each harmonic is randomly set. Figure 2 As shown in the figure, the waveform of the simulated signal only shows the 49.8Hz power frequency signal, and the effective signal is completely submerged.

[0258] Table 1 Harmonic Parameters

[0259]

[0260] The parameters of the harmonic components were estimated using both the direct method and the differential method, and the results are shown in Tables 2 and 3. Comparing Tables 2 and 3, it can be seen that the results obtained using the differential method are more accurate. In the absence of white noise interference, the differential method can accurately estimate the parameters of the harmonic components. Therefore, our interference cancellation algorithm uses the differential method to estimate the parameters of the interfering harmonics, and then subtracts the reconstructed interference signal from the received signal to achieve the purpose of interference cancellation.

[0261] Table 2. Estimation results using the direct method

[0262]

[0263] Table 3. Estimation results using the finite difference method

[0264]

[0265] Figure 3 and Figure 4The results of interference cancellation for the aforementioned signal are presented using two methods: a filtering method and the ground power frequency interference filtering method (differential method) for downhole signal reception according to the present invention. Figure 3 As can be seen above, the effective signal can be seen after low-pass filtering, but the filtering method fails to completely remove interference components. However, from... Figure 4 As can be seen above, the interference filtering method completely recovers the effective signal.

[0266] ② On-site experiment

[0267] The previous comparison of the processing results of filtering and interference cancellation methods for simulated signals shows that the power frequency interference filtering method is superior to the filtering method. However, actual signals differ from simulated signals, and actual signals also contain other stray noise. To further verify the effectiveness of the power frequency interference filtering method, both methods were used to process the signals actually acquired at the well site.

[0268] First, the received signal is filtered using a filtering method, and the time-domain result is as follows: Figure 5 As shown in the figure, there is still some 50Hz power frequency interference in the signal, resulting in an unclear waveform. The result obtained using the interference cancellation algorithm is as follows. Figure 6 As shown, from Figure 6 As can be seen, although some white noise still exists in the waveform, the modulated waveform is clearly visible, indicating that the power frequency interference filtering method of this invention is more effective than ordinary filtering methods. Further experimental results show that the power frequency interference filtering method of this invention improves the signal reception sensitivity by more than 65 dB, which is approximately 10 dB higher than the traditional filtering method. This is basically consistent with the simulation results. The slightly smaller sensitivity improvement in the experimental results compared to the simulation results is due to the presence of a small amount of other noise interference in the measured signal.

[0269] In summary, the beneficial effects of the present invention may include at least one of the following:

[0270] (1) The present invention provides a method for filtering out ground power frequency interference when receiving downhole signals. It can estimate the fundamental frequency of the power frequency and its harmonic parameters, thereby reconstructing the interference signal and removing the power frequency interference to ensure effective signal identification.

[0271] (2) The present invention solves the problem that the existing method of using an infinite impulse response filter (IIR) to filter received signals is not suitable because the phase response of the IIR filter is not linear, which will cause significant distortion to the normal communication signal. Moreover, the frequency of power frequency interference may change with different well sites. Therefore, it is not suitable when notch filters are not applicable.

[0272] (3) The interference filtering method of the present invention improves the sensitivity of actual signal reception by more than 65dB, which is more than 10dB higher than the traditional filtering method. This is basically consistent with the simulation results. The sensitivity improvement in the actual test results is slightly less than that in the simulation results because the actual signal contains a small amount of other noise interference.

[0273] Although the invention has been described above in conjunction with exemplary embodiments, those skilled in the art will understand that various modifications and changes can be made to the exemplary embodiments of the invention without departing from the spirit and scope defined by the claims.

Claims

1. A method for interference filtering of downhole electromagnetic wave signals received from oil and gas wells on the surface, characterized in that, The interference filtering method includes the following steps: The frequency domain transformation of the electromagnetic wave signal received from the ground is performed to estimate the harmonic parameters of the interference components to be initially filtered out. The power frequency interference signal is reconstructed based on the harmonic parameters of the interference components, and the power frequency interference signal components are subtracted from the received electromagnetic wave signal to obtain the effective signal. Determine whether the power frequency interference signal in the valid signal is filtered out successfully. If the filtering is successful, demodulate the valid signal to restore the downhole electromagnetic wave signal. If the filtering is unsuccessful, repeat the interference filtering operation on the valid signal until the filtering is successful. The harmonic parameters for filtering out interference components include the frequency, amplitude, and phase of the interference components, which are obtained through the following steps: The received signal is sampled to determine its expression, which is then subjected to a DFT transformation. The amplitude and phase in the expression are then solved using either a direct solution method or a difference solution method. The mathematical expression for the interference component is: ,n=0,1,…,N-1 (1) Where x(n) represents a sinusoidal sampling sequence of length N, f is the frequency, and s -1 ;f s S is the sampling rate. -1 A represents amplitude, with units consistent with the measured signal; θ represents phase, in rad. remember: 0≤Δ<1, and K is an integer, equation (1) can be rewritten as: （2） The DFT transformation includes the following steps: Equation (2) is transformed by DFT to obtain: （3） remember: （4） （5） but （6） （7） use express , express Substituting equations (4) and (5) into equation (3), and using the series expansion: have to: （8） Expanding the exponential form, the real and imaginary parts of X(k) can be written as follows: （9） （10）。 2. The interference filtering method for receiving downhole electromagnetic wave signals from oil and gas wells on the surface according to claim 1, characterized in that, The process of achieving qualified filtration includes the following steps: Determine whether the proportion of the energy of the effective signal in the received signal energy is greater than 50%. If it is greater than 50%, it means that the strength of the effective signal is greater than the strength of the interference signal, and the effective signal enters the demodulation module for demodulation.

3. The interference filtering method for receiving downhole electromagnetic wave signals from oil and gas wells on the surface according to claim 1, characterized in that, The method further includes the following steps: remember: （11） （12） Among them, signal parameter items It is a constant independent of the spectral line position k, obtained by elimination using the proportional method: （13） Based on the trigonometric formula: （14） Substituting equation (14) into equation (13), we get: （15） Equation (15) contains only one unknown term, K+Δ, so K and Δ can be solved using equation (15).

4. The interference filtering method for receiving downhole electromagnetic wave signals from oil and gas wells on the surface according to claim 3, characterized in that, The method further includes the following steps: remember: ； （16） ； （17） （18） Substituting into equation (15), we get: （19） Since 0 ≤ Δ < 1, we get: （20） （21） The [ ] symbol indicates rounding down; Substituting equations (20) and (21) into equations (9) and (10), we get: （22） （23） By combining equations (22) and (23), the amplitude A and phase θ can be solved.

5. The interference filtering method for receiving downhole electromagnetic wave signals from oil and gas wells on the surface according to claim 4, characterized in that, The method further includes the following steps: Transform equations (9) and (10) into difference form: （24） （25） According to the trigonometric formula: （26） In equation (26), only the first term of the denominator is a function of k, denoted as g(k) in equation (17). Based on equation (23), the following difference proportion form is obtained: （27） We obtain the quadratic equation: （28） in, （29） X is obtained by solving equation (28), and then K and Δ are obtained by substituting X into equations (20) and (21). Substituting the values ​​of K and Δ into the difference formulas (23) and (24), we get: （30） （31） By combining equations (30) and (31), we obtain A and θ.

6. An interference filtering device for receiving downhole electromagnetic wave signals from oil and gas wells on the surface, characterized in that... The device is used to implement the interference filtering method for receiving downhole electromagnetic wave signals from oil and gas wells on the ground as described in any one of claims 1-5, wherein: The filtering device includes a signal receiving and frequency domain transformation module, an interference component estimation module, an interference component reconstruction module, and an interference filtering judgment module, wherein, The signal receiving and frequency domain transformation module is configured to receive electromagnetic wave signals and perform frequency domain transformation. The interference component estimation module is configured to estimate the harmonic parameters of the interference components in the signal after it has been transformed by the signal receiving and frequency domain transformation modules. The interference component reconstruction module is configured to reconstruct the harmonic parameters of the interference components estimated by the interference component estimation module to obtain the power frequency harmonic signal. The interference filtering judgment module is configured to subtract the power frequency harmonic signal from the received electromagnetic wave signal to obtain the effective signal, and to determine whether the interference in the effective signal has been filtered out.

7. The interference filtering device for receiving downhole electromagnetic wave signals from oil and gas wells on the surface according to claim 6, characterized in that, The interference filtering device further includes a demodulation module, which is configured to demodulate the effective signal after interference filtering.

8. The interference filtering device for receiving downhole electromagnetic wave signals from oil and gas wells on the surface according to claim 6, characterized in that, The interference components are distributed near the power frequency and its harmonics, and the downhole electromagnetic wave signal of the oil and gas well is selected with a frequency below 10Hz.

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