Double-signal noise reduction device and method for small-displacement mud pulse

Abstract

The invention discloses a small-displacement slurry pulse double-signal noise reduction device and method, and aims to solve the problem that a data processing method that only one path of pressure sensor is mounted on a slurry pipeline to collect one path of signal cannot meet the requirement of high-speed slurry pulse signal transmission, so that two paths of pressure signals are collected by using two paths of pressure sensors; the mud pulse is subjected to noise reduction processing by using a time delay difference algorithm, and the problem of mud pump noise overlapped with a pulse signal frequency domain can be solved by using double sensors; according to noise reduction in a ground signal processing process, a method for extracting pulse signals when pulse signal frequencies and noise signal frequencies are overlapped is provided by combining noise characteristics in mud pulse signals and a mud pump noise generation mechanism, and the noise reduction effect is improved by adopting a time delay difference noise reduction algorithm based on double pressure sensors.

Description

Technical Field

[0001] This invention belongs to the field of geological core drilling technology, specifically relating to a dual-signal noise reduction device and method for small-volume mud pulses. Background Technology

[0002] Driven by my country's demand for deep resource extraction, measurement-while-drilling (MWD) technology is widely used in geological drilling processes due to its ability to acquire downhole information parameters in real time. Mud pulse MWD technology, as a cost-effective downhole information transmission technology, is widely applied for real-time acquisition of downhole parameters. The bottom-hole pulse generator encodes downhole information into pressure waves, which are then transmitted to the surface via the mud medium. Surface receiving equipment processes the collected data to recover the downhole information. However, downhole signals suffer significant attenuation after long-distance transmission, and the mud channel contains a large amount of noise, all of which pose significant challenges to surface processing of mud pressure signals.

[0003] Signal denoising is a crucial part of surface processing of mud pulse signals. After long-distance transmission, the amplitude of mud pulse signals attenuates significantly, and other factors within the mud pipeline, such as mechanical vibrations and pressure fluctuations caused by bubble bursts, interfere with the mud pulses. The mud pump has a particularly significant impact on the downhole mud pulse generator. All of these factors result in very weak signal waveforms received by surface sensors, drowning out useful signals. Accurately extracting useful pulse signals from a background of complex and strong noise has always been a research challenge in measurement-while-drilling (MWD) signal processing. Unlike the large-capacity mud pumps used in oil extraction, the geological industry typically uses small-capacity mud pumps due to limitations in the construction environment, cost, and borehole diameter. This makes mud signals more susceptible to noise and more difficult to extract effective information.

[0004] Currently, the most commonly used noise reduction methods in China are based on single pressure sensors, such as digital low-pass filters, wavelet denoising, and EMD decomposition denoising. These methods can effectively remove interference noise when the noise signal spectrum of the mud pump and the mud pulse signal spectrum do not overlap. However, when the noise signal of the mud pump and the mud pulse signal overlap, these methods cannot solve the problem well. Summary of the Invention

[0005] This invention provides a dual-signal noise reduction device and method for small-displacement mud pulses, which solves the problem that the existing data processing method of installing only one pressure sensor on the mud pipeline to collect one signal can no longer meet the requirements of high-speed mud pulse signal transmission.

[0006] To solve the above problems, the technical solution provided by the present invention is as follows:

[0007] This invention provides a dual-signal noise reduction device for small-volume mud pulses, including an industrial control computer (1), a mud pump (2), an air chamber (3), a downhole pulse generator (4), an A-channel pressure sensor (5), and a B-channel pressure sensor (6). The industrial control computer (1) is connected to the A-channel pressure sensor (5) and the B-channel pressure sensor (6) via cables. The mud pump (2) is connected to the downhole pulse generator (4) via a mud pipe (7). The A-channel pressure sensor (5) and the B-channel pressure sensor (6) are connected via mud pipes of the same diameter, with a distance between them equal to a preset transmission length. The B-channel pressure sensor (6) is located close to the mud pump. (2) Setting: In the mud pipe section between the A-line pressure sensor (5) and the B-line pressure sensor (6), the pulse signal is generated by the downhole pulse generator (4) and transmitted through the mud pipe. The direction of pulse signal propagation is from the A-line pressure sensor (5) to the B-line pressure sensor (6). The pump noise is generated by the mud pump (2) and transmitted from the B-line pressure sensor (6) to the A-line pressure sensor (5). On the one hand, the air compensation chamber (3) can buffer the interference pressure pulsation generated by the piston movement of the mud pump (2) into the main channel. On the other hand, it reduces the amplitude of mud pressure attenuation during short-distance transmission in the mud pipe (7) with a constant diameter, which facilitates the simplification of the subsequent delay model.

[0008] In one optional embodiment of the present invention, the air compensation chamber has an elliptical structure and is connected to the mud pipe via a straight pipe.

[0009] This invention provides a dual-signal noise reduction method for mud pulses, comprising the following steps:

[0010] Step 1: Determine the noise signal model of the mud pump based on its performance parameters.

[0011] The mud pump generates the power for mud circulation through the movement of three pistons. The three cylinders are 120° out of phase. When the mud pump rotates one cycle, all three cylinders rotate one cycle. The mud displacement variation function is a half-wave sine wave, which can be mathematically viewed as the sum of three sine signals with a 60° phase difference. The periodic angle change of the pump flow rate of the three-cylinder pump is 2π / 3. The noise signal model is as follows:

[0012] ;

[0013] Step 2: Acquire and parameterize the signals from pressure sensors A and B to obtain the mud pulse signal model.

[0014] Both the downhole pulse signal and the mud pump noise are finite bandwidth signals, and the amplitude attenuation of the pulse signal after passing through the two sensors is very small, which can be considered as no attenuation. Therefore, the transmission characteristics between the two pressure sensors can be regarded as a distortion-free transmission system, and the transmission coefficient between the two sensors is assumed to be constant. Then the system frequency domain transfer function between the two sensors is: (1); where: Assuming a unit gate function, and considering the transmission characteristics of pressure sensors A and B as a linear system, its frequency response is: (2); where: Let the magnitude of the transfer function between pressure sensor A and pressure sensor B be the modulus. Angular frequency; For delay The resulting phase shift;

[0015] Therefore, the signals received by the two pressure sensors can be represented as follows:

[0016] (3);

[0017] In the formula, s(t) is the downhole pulse signal; n(t) is the Gaussian noise in the mud pipe; p(t) is the mud pump noise signal; h(t) is the time-domain transfer function between the two sensors; and the signal received by the B-channel pressure sensor... Perform convolution operation, the convolution factor is ,get:

[0018] (4);

[0019] In equations (3) and (4) Representing convolution operation, since the pipeline between pressure sensors A and B is considered as a linear system, the left side of equation (3) above represents the convolution operation of the pressure sensor signals. After another unit impact response is In a linear system, the response between pressure sensors A and B includes a delay caused by the signal passing through the conduits of pressure sensors A and B. ;in, The preset transmission length between pressure sensor A and pressure sensor B is in meters. The speed at which the pressure signal travels in the mud medium is expressed in m / s.

[0020] In equation (3) Subtracting equation (4) from the result, the downhole delayed differential detection mud pulse signal model is shown in the following equation:

[0021] (5);

[0022] Step 3: Based on the noise signal model in Step 1 and the mud pulse signal model in Step 2, the mud pulse is denoised using a time-delay differential algorithm to obtain an effective mud pulse signal.

[0023] In an optional embodiment of the present invention, step 1 further includes: the pressure pulsation generated by the piston movement during the operation of the mud pump is called mud pump noise, which is a major source of interference on the ground. Because it is related to the flow rate, mud pump noise also has periodicity, mainly consisting of multiple periodic signals with the same frequency as the piston movement; the third cylinder of the three-cylinder pump used in drilling... The frequency of a subharmonic can be calculated using the following formula: In the formula, Indicates the first The frequency (Hz) of the subharmonic. This indicates the stroke rate, which is the number of pump strokes generated per minute. This value can be measured by installing a pump stroke sensor on-site. The harmonic order is determined by the operating mode of the mud pump, which causes differences in the intensity of different harmonic orders. The main harmonic order is determined based on the number of cylinders and the operating mode, and the calculation formula is as follows: ;in, This refers to the number of cylinders in the mud pump. This refers to the operating mode of a mud pump, which is single-acting. =1, double action =2; Multiple mud pumps are connected in series on site to increase the total flow rate. In the most reasonable case, different models of mud pumps should be set so that their pumping frequencies are close or equal, so as to avoid generating more strong interference noise in the transmission system.

[0024] In an optional embodiment of the present invention, step 2 further includes: theoretically, by acquiring the two pressure signals from pressure sensors A and B, pump interference noise can be completely eliminated from the pressure signal; then, Fourier transform is performed on equation (5) to obtain the following equation:

[0025] (6);

[0026] in, The Fourier transform of the downhole pulse signal and random noise is expressed as follows: (7);

[0027] In the formula: The transfer function of the downhole signal recovery system is obtained through... It can realize the reconstruction of downhole signals;

[0028] Since the attenuation of mud pressure during short-distance transmission in a mud pipe with a constant diameter is very small and almost negligible, the transmission model of the mud pressure signal between pressure sensors A and B can be simplified to a time-domain delay model. This means only considering the phase delay caused by the mud pipe between pressure sensors A and B, with negligible attenuation, and simplifying the system transfer function to a constant. Therefore, the signals collected by the two pressure sensors can be simplified as follows:

[0029] (8);

[0030] (9);

[0031] The duration of the mud pulse signal passing through two pressure sensors, and its magnitude is... .

[0032] In an optional embodiment of the present invention, step 3 includes: step 31, acquiring two signals at a certain frequency at a certain distance; step 32, removing signals outside the frequency domain of the pulse signal using a bandpass filter; step 33, calculating the delay time according to the delay differential algorithm; step 34, performing time delay compensation on one signal and differential processing on the other signal; step 35, adjusting the delay time according to the differential signal result; and step 36, eliminating pump noise aliased in the pulse signal.

[0033] In an optional embodiment of the present invention, step 33 includes: the time delay differential method mainly utilizes the characteristic that the mud pump pressure signal and the pulse pressure signal are transmitted in opposite directions. By installing two pressure sensors to collect the two signals, the principle of wave cancellation is used to remove the mud pump noise signal.

[0034] Where signal r B (t) The signal after time delay τ is r B (t-τ), its expression is:

[0035] r B (t-τ)=s(t- -τ)+p(t-τ) (10);

[0036] The signal r after delay processing B (t-τ) and signal r A (t) Subtract to obtain the delayed differential output:

[0037] (11)

[0038] Therefore, by adjusting the delay time τ, the noise of the mud pump can be completely eliminated, and the final output obtained is: (12);

[0039] As can be seen from the formula, if the delay time can be set accurately... Transmission time of mud pump signal between two pressure sensors Equal values ​​will completely preserve the downhole transmitted signal in the output signal. and its phase shift signal Furthermore, it can be concluded that this method can completely eliminate signals that are opposite to the transmission direction of mud pulse signals and is unaffected by changes in the noise state of mud pumps, which is of great value for adapting to changes in mud pump discharge during field use.

[0040] According to the Fourier transform, any signal can be decomposed into multiple sinusoidal signals. Furthermore, the noise signal from a mud pump is discrete in the frequency domain. One sinusoidal signal can represent the portion of the frequency domain signal where the fundamental wave and pulse signal of the mud pump overlap. Let the frequency of one of these signals be... The mathematical expression corresponding to the signal is: (13);

[0041] Therefore, the optimal output expression for the time-delay differential algorithm is:

[0042] (14);

[0043] From mathematical knowledge, we know that in the above formula, when When the carrier period is 1 / 4, the output amplitude is maximized when the installation distance between the two pressure sensors is one-quarter wavelength of the corresponding sine signal; Equation (14) can be simplified to:

[0044] (15);

[0045] when When the carrier period is half, the output amplitude is minimized when the installation distance between the two pressure sensors is half the wavelength of the corresponding sine signal; Equation (15) can be simplified as follows: (16).

[0046] Compared with existing single-sensor detection and noise reduction schemes, this invention provides a dual-signal noise reduction device and method for small-displacement mud pulses, which has the following beneficial effects: (1) This invention utilizes dual sensors to solve the mud pump noise that overlaps with the frequency domain of the pulse signal. (2) The method of this invention has good noise reduction effect and can better retain the effective signal. It can completely remove the mud pump noise signal, retain the frequency domain component of the original pulse signal, and can eliminate all noise signals that are opposite to the transmission direction of the pulse signal without being affected by the signal-to-noise ratio. (3) Compared with wavelet decomposition, EMD decomposition and other methods, this invention does not require the selection of parameters and other information. The steps are simple, easy to use, and highly adaptable. (4) The method of this invention has high computational efficiency and strong real-time performance, and can realize real-time processing under low computing power at the work site. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments or prior art, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of a dual-signal noise reduction device for small-displacement mud pulses provided in an embodiment of this application.

[0049] Figure 2 A flowchart illustrating a dual-signal noise reduction method for mud pulses provided in this application embodiment.

[0050] Figure 3 This is a schematic diagram of the signal simulation output of a dual-signal noise reduction method for mud pulses provided in an embodiment of this application.

[0051] Figure 4 This is a flowchart of a time delay differential processing method provided in an embodiment of this application.

[0052] Figure 5 A schematic diagram of a time delay differential algorithm provided in an embodiment of this application. Detailed Implementation

[0053] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The terms "upper," "lower," "front," "rear," "left," and "right," etc., used when describing the installation position or direction of the structure or components in this embodiment are based on the orientation shown in the accompanying drawings. They are merely for convenience of description, used to distinguish the relative positions of various components or directions, and do not represent the orientation of the device or functional component in this embodiment during use.

[0054] Mud pulses utilize drilling fluid (drilling mud) as the transmission medium. Downhole instruments (mud pulse generators) modulate the pressure or frequency of the mud to generate specific pressure wave signals. These signals are transmitted to the surface via the mud column. Surface equipment receives and decodes these signals to obtain data such as temperature, pressure, azimuth, and formation characteristics measured by downhole tools.

[0055] like Figure 1 As shown, this embodiment of the invention provides a dual-signal noise reduction device for small-displacement mud pulses, including an industrial control computer 1, a mud pump 2, an air chamber 3, a downhole pulse generator 4, an A-channel pressure sensor 5, and a B-channel pressure sensor 6. The industrial control computer 1 is connected to pressure sensors A and B via cables. The mud pump 2 is connected to the downhole pulse generator 4 via a mud pipe 7. A mud pipe 7 of the same diameter is used between pressure sensors A and B, with a preset distance L between them. Pressure sensor B is positioned closer to mud pump 2. In the mud pipe section between pressure sensors A and B, the pulse signal is generated by the downhole pulse generator 4 and transmitted through the mud pipe 7, with the pulse signal propagating from pressure sensor A to pressure sensor B. Pump noise is generated by mud pump 2 and transmitted from pressure sensor B to pressure sensor A. The air compensation chamber 3 serves two purposes: firstly, it buffers the interference pressure pulsations generated by the piston movement of mud pump 2 from entering the main channel; secondly, it reduces the attenuation of mud pressure during short-distance transmission within the constant diameter mud pipe 7, facilitating the simplification of the subsequent delay model. The air compensation chamber 3 has an elliptical structure and is connected to the mud pipe 7 via a straight pipe.

[0056] like Figure 2 and Figure 3 As shown, this embodiment of the invention provides a dual-signal noise reduction method for mud pulses, comprising the following steps:

[0057] Step 1: Determine the noise signal model of the mud pump based on its performance parameters.

[0058] A mud pump powers the mud circulation pipeline. A reciprocating three-cylinder pump is typically used. However, mud pumps used in geological drilling sites have relatively small displacements, generally around 10 L / s, resulting in significant interference. The mud pump generates the power for mud circulation through the movement of three pistons. The three cylinders are 120° out of phase; when the mud pump completes one cycle, all three cylinders have completed one cycle. The mud displacement variation function is a half-wave sine wave, and its ideal waveform is shown below. Figure 3 The simulation output is shown. Mathematically, the model can be viewed as the sum of three sinusoidal signals with a 60° phase difference. The periodic angle change of the pump flow rate of the three-cylinder pump is 2π / 3. The noise signal model is as follows:

[0059] .

[0060] Step 2: Acquire and parameterize the signals from pressure sensors A and B to obtain the mud pulse signal model.

[0061] Both the downhole pulse signal and the mud pump noise are finite bandwidth signals, and the amplitude attenuation of the pulse signal after passing through the two sensors is very small, which can be considered as no attenuation. Therefore, the transmission characteristics between the two pressure sensors can be regarded as a distortion-free transmission system, and the transmission coefficient between the two sensors is assumed to be constant. Then the system frequency domain transfer function between the two sensors is: (1); where: Assuming a unit gate function, and considering the transmission characteristics of pressure sensors A and B as a linear system, its frequency response is: (2); where: Let the magnitude of the transfer function between pressure sensor A and pressure sensor B be the modulus. Angular frequency; For delay The resulting phase shift;

[0062] Therefore, the signals received by the two pressure sensors can be represented as follows:

[0063] (3);

[0064] In the formula, s(t) is the downhole pulse signal; n(t) is the Gaussian noise in the mud pipe; p(t) is the mud pump noise signal; h(t) is the time-domain transfer function between the two sensors; and the signal received by pressure sensor B... Perform convolution operation, the convolution factor is ,get:

[0065] (4);

[0066] In equations (3) and (4) Representing convolution operation, since the pipeline between pressure sensors A and B is considered as a linear system, the left side of equation (3) above represents the convolution operation of the pressure sensor signals. After another unit impact response is In a linear system, the response between pressure sensors A and B includes a delay element resulting from the signal passing through pipes A and B. ;in, The preset transmission length between pressure sensor A and pressure sensor B is in meters. The speed at which the pressure signal travels in the mud medium is expressed in m / s.

[0067] In equation (3) Subtracting equation (4) from the result, the downhole delayed differential detection mud pulse signal model is shown in the following equation:

[0068] (5);

[0069] Step 3: Based on the noise signal model in Step 1 and the mud pulse signal model in Step 2, the mud pulse is denoised using a time-delay differential algorithm to obtain an effective mud pulse signal.

[0070] Step 1 also includes: The pressure pulsations generated by the piston movement during the operation of the mud pump are called mud pump noise, which is a major source of interference on the ground. Because it is related to the flow rate, mud pump noise also has a periodicity, mainly composed of multiple periodic signals with the same frequency as the piston movement; the third cylinder pump used in drilling... The frequency of a subharmonic can be calculated using the following formula: In the formula, Indicates the first The frequency (Hz) of the subharmonic. This indicates the stroke rate, which is the number of pump strokes generated per minute. This value can be measured by installing a pump stroke sensor on-site. The harmonic order is determined by the operating mode of the mud pump, which causes differences in the intensity of different harmonic orders. The main harmonic order is determined based on the number of cylinders and the operating mode, and the calculation formula is as follows: ;in, This refers to the number of cylinders in the mud pump. This refers to the operating mode of a mud pump, which is single-acting. =1, double action =2; Multiple mud pumps are connected in series on site to increase the total flow rate. In the most reasonable case, different models of mud pumps should be set so that their pumping frequencies are close or equal, so as to avoid generating more strong interference noise in the transmission system.

[0071] Step 2 also includes: theoretically, by acquiring the two pressure signals from pressure sensors A and B, pump interference noise can be completely eliminated from the pressure signal; then, Fourier transform is performed on equation (5) to obtain the following equation:

[0072] (6);

[0073] in, The Fourier transform of the downhole pulse signal and random noise is expressed as follows: (7);

[0074] In the formula: The transfer function of the downhole signal recovery system is obtained through... It can realize the reconstruction of downhole signals;

[0075] Since the attenuation of mud pressure during short-distance transmission in a mud pipe with a constant diameter is very small and almost negligible, the transmission model of the mud pressure signal in the mud pipe section between pressure sensors A and B can be simplified to a time-domain delay model. This means only considering the phase delay caused by the mud pipe between pressure sensors A and B, with negligible attenuation, and simplifying the system transfer function to a constant. Therefore, the signals collected by the two pressure sensors can be simplified as follows:

[0076] (8);

[0077] (9);

[0078] The duration of the mud pulse signal passing through two pressure sensors, and its magnitude is... .

[0079] like Figure 4 As shown, step 3 includes: step 31, acquiring two signals at a certain frequency at a certain distance; step 32, removing signals outside the frequency domain of the pulse signal using a bandpass filter; step 33, calculating the delay time according to the delay differential algorithm; step 34, performing time delay compensation on one signal and differential processing on the other signal; step 35, adjusting the delay time according to the differential signal result; and step 36, eliminating pump noise aliased in the pulse signal.

[0080] like Figure 5As shown, step 33 includes: The time delay differential method mainly utilizes the characteristic that the mud pump pressure signal and the pulse pressure signal are transmitted in opposite directions. By installing two pressure sensors to collect the two signals, the principle of wave cancellation is used to remove the mud pump noise signal.

[0081] Where signal r B (t) The signal after time delay τ is r B (t-τ), its expression is:

[0082] r B (t-τ)=s(t- -τ)+p(t-τ) (10);

[0083] The signal r after delay processing B (t-τ) and signal r A (t) Subtract to obtain the delayed differential output:

[0084] (11)

[0085] Therefore, by adjusting the delay time τ, the noise of the mud pump can be completely eliminated, and the final output obtained is: (12);

[0086] As can be seen from the formula, if the delay time can be set accurately... Transmission time of mud pump signal between two pressure sensors Equal values ​​will completely preserve the downhole transmitted signal in the output signal. and its phase shift signal Furthermore, it can be concluded that this method can completely eliminate signals that are opposite to the transmission direction of mud pulse signals and is unaffected by changes in the noise state of mud pumps, which is of great value for adapting to changes in mud pump discharge during field use.

[0087] According to the Fourier transform, any signal can be decomposed into multiple sinusoidal signals. Furthermore, the mud pump noise signal studied in this paper is discrete in the frequency domain. One sinusoidal signal can represent the portion of the frequency domain signal where the fundamental wave and pulse signal of the mud pump overlap. Let the frequency of one of these signals be... The mathematical expression corresponding to the signal is: (13);

[0088] Therefore, the optimal output expression for the time-delay differential algorithm is:

[0089] (14);

[0090] From mathematical knowledge, we know that in the above formula, when When the carrier period is 1 / 4, the output amplitude is maximized when the installation distance between the two pressure sensors is one-quarter wavelength of the corresponding sine signal; Equation (14) can be simplified to:

[0091] (15);

[0092] when When the carrier period is half, the output amplitude is minimized when the installation distance between the two pressure sensors is half the wavelength of the corresponding sine signal. Equation (15) can be simplified as follows: (16).

[0093] The present invention addresses the limitation that the data processing method of installing only one pressure sensor on the mud pipeline to collect one signal is insufficient to meet the requirements of high-speed mud pulse signal transmission. Therefore, the present invention uses two pressure sensors to collect two pressure signals and uses a time-delay differential algorithm to denoise the mud pulse. The dual sensors can solve the problem of mud pump noise that overlaps with the frequency domain of the pulse signal. In the noise reduction process of ground signal processing, combined with the noise characteristics in the mud pulse signal and the generation mechanism of mud pump noise, a method is proposed to extract the pulse signal when the frequency of the pulse signal overlaps with the frequency of the noise signal. A time-delay differential noise reduction algorithm based on dual pressure sensors is used to improve the noise reduction effect.

[0094] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A dual-signal noise reduction device for small-volume mud pulses, characterized in that, The system includes an industrial control computer (1), a mud pump (2), an air chamber (3), a downhole pulse generator (4), an A-channel pressure sensor (5), and a B-channel pressure sensor (6). The industrial control computer (1) is connected to the A-channel pressure sensor (5) and the B-channel pressure sensor (6) via cables. The mud pump (2) is connected to the downhole pulse generator (4) via a mud pipe (7). The A-channel pressure sensor (5) and the B-channel pressure sensor (6) are connected via mud pipes of the same diameter, with a distance between them equal to a preset transmission length. The B-channel pressure sensor (6) is positioned close to the mud pump (2). Between the A-line pressure sensor (5) and the B-line pressure sensor (6), the pulse signal is generated by the downhole pulse generator (4) and transmitted through the mud pipe. The pulse signal propagates from the A-line pressure sensor (5) to the B-line pressure sensor (6). The pump noise is generated by the mud pump (2) and transmitted from the B-line pressure sensor (6) to the A-line pressure sensor (5). On the one hand, the air compensation chamber (3) can buffer the interference pressure pulsation generated by the piston movement of the mud pump (2) into the main channel. On the other hand, it reduces the amplitude of mud pressure attenuation during short-distance transmission in the mud pipe (7) with a constant diameter, which facilitates the simplification of the subsequent delay model.

2. The dual-signal noise reduction device for small-volume mud pulses according to claim 1, characterized in that, The air compensation chamber has an elliptical structure and is connected to the mud pipe via a straight pipe.

3. A dual-signal noise reduction method for mud pulses, characterized in that, Includes the following steps: Step 1: Determine the noise signal model of the mud pump based on its performance parameters. The mud pump generates the power for mud circulation through the movement of three pistons. The three cylinders are 120° out of phase. When the mud pump rotates one cycle, all three cylinders rotate one cycle. The mud displacement variation function is a half-wave sine wave, which can be mathematically viewed as the sum of three sine signals with a 60° phase difference. The periodic angle change of the pump flow rate of the three-cylinder pump is 2π / 3. The noise signal model is as follows: ； Step 2: Acquire and parameterize the signals from pressure sensors A and B to obtain the mud pulse signal model. Both the downhole pulse signal and the mud pump noise are finite bandwidth signals, and the amplitude attenuation of the pulse signal after passing through the two sensors is very small, which can be considered as no attenuation. Therefore, the transmission characteristics between the two pressure sensors can be regarded as a distortion-free transmission system, and the transmission coefficient between the two sensors is assumed to be constant. Then the system frequency domain transfer function between the two sensors is: (1); where: Assuming a unit gate function, and considering the transmission characteristics of pressure sensors A and B as a linear system, its frequency response is: (2); where: Let the magnitude of the transfer function between pressure sensor A and pressure sensor B be the modulus. Angular frequency; For delay The resulting phase shift; Therefore, the signals received by the two pressure sensors can be represented as follows: (3)； In the formula, s(t) is the downhole pulse signal; n(t) is the Gaussian noise in the mud pipe; p(t) is the mud pump noise signal; h(t) is the time-domain transfer function between the two sensors; and the signal received by the B-channel pressure sensor... Perform convolution operation, the convolution factor is ,get: （4）； In equations (3) and (4) Representing convolution operation, since the pipeline between pressure sensors A and B is considered as a linear system, the left side of equation (3) above represents the convolution operation of the pressure sensor signals. After another unit impact response is In a linear system, the response between pressure sensors A and B includes a delay caused by the signal passing through the conduits of pressure sensors A and B. ;in, The preset transmission length between pressure sensor A and pressure sensor B is in meters. The speed at which the pressure signal travels in the mud medium is expressed in m / s. In equation (3) Subtracting equation (4) from the result, the downhole delayed differential detection mud pulse signal model is shown in the following equation: （5）； Step 3: Based on the noise signal model in Step 1 and the mud pulse signal model in Step 2, the mud pulse is denoised using a time-delay differential algorithm to obtain an effective mud pulse signal.

4. The dual-signal noise reduction method for mud pulses according to claim 3, characterized in that, Step 1 also includes: The pressure pulsations generated by the piston movement during the operation of the mud pump are called mud pump noise, which is a major source of interference on the ground. Because it is related to the flow rate, mud pump noise also has a periodicity, mainly composed of multiple periodic signals with the same frequency as the piston movement; the third cylinder pump used in drilling... The frequency of a subharmonic can be calculated using the following formula: In the formula, Indicates the first The frequency (Hz) of the subharmonic. This indicates the stroke rate, which is the number of pump strokes generated per minute. This value can be measured by installing a pump stroke sensor on-site. The harmonic order is determined by the operating mode of the mud pump, which causes differences in the intensity of different harmonic orders. The main harmonic order is determined based on the number of cylinders and the operating mode, and the calculation formula is as follows: ;in, This refers to the number of cylinders in the mud pump. This refers to the operating mode of a mud pump, which is single-acting. =1, double action =2; Multiple mud pumps are connected in series on site to increase the total flow rate. In the most reasonable case, different models of mud pumps should be set so that their pumping frequencies are close or equal, so as to avoid generating more strong interference noise in the transmission system.

5. The dual-signal noise reduction method for mud pulses according to claim 3, characterized in that, Step 2 also includes: theoretically, by acquiring the two pressure signals from pressure sensors A and B, pump interference noise can be completely eliminated from the pressure signal; then, Fourier transform is performed on equation (5) to obtain the following equation: (6)； in, The Fourier transform of the downhole pulse signal and random noise is expressed as follows: (7); In the formula: The transfer function of the downhole signal recovery system is obtained through... It can realize the reconstruction of downhole signals; Since the attenuation of mud pressure during short-distance transmission in a mud pipe with a constant diameter is very small and almost negligible, the transmission model of the mud pressure signal between pressure sensors A and B can be simplified to a time-domain delay model. This means only considering the phase delay caused by the mud pipe between pressure sensors A and B, with negligible attenuation, and simplifying the system transfer function to a constant. Therefore, the signals collected by the two pressure sensors can be simplified as follows: （8）； （9）； The duration of the mud pulse signal passing through two pressure sensors, and its magnitude is... .

6. The dual-signal noise reduction method for mud pulses according to claim 3, characterized in that, Step 3 includes: Step 31, acquiring two signals at a certain frequency at a certain distance; Step 32, removing signals outside the frequency domain of the pulse signal using a bandpass filter; Step 33, calculating the delay time according to the delay differential algorithm; Step 34, performing time delay compensation on one signal and differential processing on the other signal; Step 35, adjusting the delay time based on the differential signal result; Step 36, eliminating pump noise aliased in the pulse signal.

7. The dual-signal noise reduction method for mud pulses according to claim 6, characterized in that, Step 33 includes: The time delay differential method utilizes the characteristic that the mud pump pressure signal and the pulse pressure signal are transmitted in opposite directions. By installing two pressure sensors to collect the two signals, the principle of wave cancellation is used to remove the mud pump noise signal. Where signal r B (t) The signal after time delay τ is r B (t-τ), its expression is: r B (t-τ)=s(t- -τ)+p(t-τ) (10); The signal r after delay processing B (t-τ) and signal r A (t) Subtract to obtain the delayed differential output: （11） Therefore, by adjusting the delay time τ, the noise of the mud pump can be completely eliminated, and the final output obtained is: (12); As can be seen from the formula, if the delay time can be set accurately... Transmission time of mud pump signal between two pressure sensors Equal values ​​will completely preserve the downhole transmitted signal in the output signal. and its phase shift signal Furthermore, it can be concluded that this method can completely eliminate signals that are opposite to the direction of mud pulse signal transmission and is unaffected by changes in mud pump noise status, which is of great value for adapting to changes in mud pump discharge during field use. According to the Fourier transform, any signal can be decomposed into multiple sinusoidal signals. Furthermore, the noise signal from a mud pump is discrete in the frequency domain. One sinusoidal signal can represent the portion of the frequency domain signal where the fundamental wave and pulse signal overlap. Let the frequency of one of these signals be... The mathematical expression corresponding to the signal is: (13); Therefore, the optimal output expression for the time-delay differential algorithm is: （14）； From mathematical knowledge, we know that in the above formula, when When the carrier period is 1 / 4, the output amplitude is maximized when the installation distance between the two pressure sensors is one-quarter wavelength of the corresponding sine signal; Equation (14) can be simplified to: （15）； when When the carrier period is half, the output amplitude is minimized when the installation distance between the two pressure sensors is half the wavelength of the corresponding sine signal; Equation (15) can be simplified as follows: (16).

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