A method, device and computer storage medium for generating a low-frequency limited acoustic beam in a well

Abstract

A method for generating low-frequency limited acoustic beams in a well, the method comprising: determining a transducer aperture according to a downhole borehole size, calculating a nonlinear action region of a radiated acoustic field based on the transducer aperture and a distance parameter; selecting a sound source design modulation theory model according to the nonlinear action region, determining sound source parameters of the transducer based on the sound source design modulation theory model and the transducer aperture; carrying out nonlinear radiated acoustic field simulation according to the sound source parameters, determining a critical propagation distance corresponding to a maximum value of a difference frequency sound source level, and extracting nonlinear acoustic wave signal characteristics at the distance, generating a loadable modulation signal based on the characteristics; measuring and comparing signal characteristics of the transducer under a loadable modulation signal loading state and under a natural radiated modulation signal loading state, and determining the loadable modulation signal with a larger difference frequency sound source level. The present application can generate nonlinear acoustic wave signals containing larger low-frequency components at a smaller radiated distance, and the difference frequency conversion efficiency of the generated nonlinear radiated signals is high.

Description

Technical Field

[0001] This invention relates to the field of acoustics, and more particularly to a method, apparatus, device, and computer storage medium for generating low-frequency finite sound beams in a well. Background Technology

[0002] In geophysical acoustic logging technology, when acoustic signals are emitted from the wellbore, the generated acoustic signals will couple from the mud fluid filling the well into the formation and propagate further. By deploying acoustic signal receiving devices in the well and processing and interpreting the received acoustic signals, parameters such as lithology, porosity, and permeability of the formation medium outside the well can be obtained. It is also possible to obtain reflectors and fractures within a certain range away from the wellbore, or to identify the distribution location of oil, gas, and water layers.

[0003] Existing wellbore acoustic logging technologies primarily employ three types of sound sources: monopoles, dipoles, and phased array sources. Monopoles, emitting sound waves at frequencies between 8 and 10 kHz, enable acoustic logging instruments to image and measure reflectors such as fractures, faults, and formation interfaces within a range of approximately 3 to 10 meters outside the wellbore. Dipole sources, with relatively lower emission frequencies (primary frequency approximately 1.0 to 3 kHz), generate dipole shear waves within the formation. The measured information can reflect geological reflectors such as faults, fractures, and formation interfaces within tens of meters of the wellbore, providing crucial technical support for well testing design. However, a current unresolved challenge with this measurement technology is the 180-degree uncertainty inherent in dipole detection. To overcome the azimuth limitations of dipole shear wave imaging logging, acoustic phased array source technology has also been applied to well-reflected wave imaging. This measurement method mainly targets the phase and amplitude control of formation P-waves radiating into the formation. However, P-waves have relatively high frequencies and attenuate rapidly, which can easily lead to the risk of reflected signals being obliterated by direct wave information. Phased acoustic wave technology can image the formation outside the well with an angular resolution of approximately 22.5°, and its radial detection distance is usually comparable to that of monopole acoustic source emission technology.

[0004] Therefore, in wellbore acoustic long-range detection technology, the characteristics of the sound source radiation are the decisive factors for the instrument's detection distance and azimuth resolution. However, instrument measurement technologies based on the above-mentioned sound sources do not yet simultaneously possess radial detection range of external formations and more accurate circumferential azimuth identification capabilities. To address this, considering the super-directivity and low-frequency broadband characteristics of parametric array technology based on nonlinear acoustic wave mixing, patent application publication number 201180027274.4 proposes a method for generating parallel sound beams in the wellbore, referencing... Figure 1This method proposes loading a high-frequency original frequency signal onto a transmitting transducer 101. After passing through a nonlinear material 102 positioned in front of the transducer, the resulting low-frequency parallel sound beam 103 propagates to an acoustic reflector 104 located in front of it. The acoustic reflector then reflects the sound beam 106 into the formation outside the well. 101 and 104 are coaxially mounted in a metal casing 105. When encountering a reflector 107 in the formation outside the well, the signal 108 from the reflector returns to the wellbore. A receiving transducer 109 placed in the wellbore transmits the signal to an electronic device 110, where data processing allows the acquisition of parameters from the formation outside the well. In this patent, the basis for forming a parallel sound beam from the transmitting sound source is parametric array technology, the main problem of which is:

[0005] (1) The installation and operation of the nonlinear material are inconvenient. After the transmitting transducer is loaded with a high-frequency original frequency signal, a low-frequency parallel sound beam can only be formed after passing through the nonlinear material placed in front of it. Although the nonlinear material is a material with optimized characteristics such as low sound velocity and high nonlinear coefficient, it still needs to meet certain size requirements to form a low-frequency signal capable of detecting formation information outside the well. For example, even if FC-43 with high nonlinear parameters is used as the nonlinear material in the embodiment, a space of at least 12cm*6cm in length and width is still required to form a parallel sound beam of 20-120kHz. If the frequency is lower, the space required for the nonlinear material is even larger, making its assembly and operation in wells with limited dimensions inconvenient. In addition, when the nonlinear material is a solid material, how to ensure the coupling between the transducer and the nonlinear material in the high-temperature and high-pressure downhole working environment is also a challenging problem.

[0006] (2) Waveguide interference and energy attenuation caused by the enclosure of the parallel sound beam. In this scheme, an enclosure is required to accommodate the transducer, nonlinear material and reflector. However, since the enclosure forms an acoustic waveguide structure, when the transducer is loaded with an acoustic signal, a guided wave will also be formed in this acoustic waveguide structure. The guided wave will be superimposed with the original frequency wave, difference frequency wave and harmonic wave generated in the nonlinear process, affecting the frequency components of the parallel sound beam. In addition, after the acoustic reflector 104 deflects the sound beam, the enclosure will also reduce the energy of the sound beam 106 radiated to the ground. Summary of the Invention

[0007] To address the aforementioned problems, embodiments of this application provide a method, apparatus, device, and computer storage medium for generating low-frequency finite sound beams in a well.

[0008] Therefore, the following technical solutions are adopted in the embodiments of this application:

[0009] Firstly, a method for generating a low-frequency finite sound beam in a well is provided. This method includes: determining the transducer aperture based on the size of the downhole borehole; calculating the nonlinear region of the radiated sound field based on the transducer aperture and distance parameters; selecting a sound source design modulation theory model based on the nonlinear region; determining the sound source parameters of the transducer based on the sound source design modulation theory model and the transducer aperture; performing simulation calculations of the sound wave in the nonlinear radiated sound field based on the determined sound source parameters; determining the critical propagation distance corresponding to the maximum difference-frequency sound source level; extracting the nonlinear sound wave signal characteristics at the critical propagation distance; generating a loadable modulation signal based on the nonlinear sound wave signal characteristics; measuring the first output signal characteristics of the transducer under the loadable modulation signal loading state; measuring the second output signal characteristics of the transducer under the natural radiation modulation signal loading state; and determining the loadable modulation signal with a larger difference-frequency sound source level by comparing and analyzing the first and second output signal characteristics.

[0010] In one implementation, the sound source design modulation theory model includes Westervelt, Berktay, and Mellen.

[0011] In one implementation, the simulation calculation of sound waves in a nonlinear radiated sound field is accomplished using the KZK equations after integration and normalization.

[0012] In one implementation, the natural radiation modulation signal is a CW amplitude modulation envelope signal or an LFM modulation signal.

[0013] Secondly, according to the method described in the first aspect, a device for generating low-frequency finite sound beams in a well is provided. This device includes: a nonlinear region calculation module, a sound source parameter determination module, a sound field calculation module, a modulation signal measurement module, and a modulation signal analysis module. The nonlinear region calculation module is used to determine the transducer aperture based on the size of the downhole borehole, and calculate the nonlinear action region of the radiated sound field based on the transducer aperture and distance parameters. The sound source parameter determination module is used to select a sound source design modulation theory model based on the nonlinear action region, and determine the sound source parameters of the transducer based on the sound source design modulation theory model and the transducer aperture. The sound field calculation module is used to perform simulation calculations of sound waves in the nonlinear radiated sound field based on the determined sound source parameters, determine the critical propagation distance corresponding to the maximum value of the difference frequency sound source level, extract the nonlinear sound wave signal characteristics at the critical propagation distance, and generate a loadable modulation signal based on the nonlinear sound wave signal characteristics. The modulation signal measurement module is used to measure the first output signal characteristics of the transducer under the loadable modulation signal loading state; and to measure the second output signal characteristics of the transducer under the natural radiation modulation signal loading state. The modulation signal analysis module is used to determine the loadable modulation signal with a large difference frequency sound source level by comparing and analyzing the characteristics of the first output signal and the characteristics of the second output signal.

[0014] Thirdly, an electronic device is provided, comprising a memory and a processor, wherein the memory stores a computer program executable on the processor, and the processor executes the computer program to implement the method described in the first aspect.

[0015] Fourthly, a computer-readable medium having processor-executable non-volatile program code is provided, the program code causing the processor to perform the method described in the first aspect.

[0016] This invention simulates and calculates sound waves in a nonlinear radiated sound field based on sound source parameters, analyzes the simulation results, generates a modulated signal that can be loaded, and measures the modulated signal to select the modulated signal with a higher difference-frequency source level. This invention can generate a nonlinear sound wave signal containing a large low-frequency component even at a short radiation distance, and can be directly applied to a sound source for long-range sound wave detection in wells, directly generating a low-frequency finite sound beam in the well. The generated nonlinear radiated signal has high difference-frequency conversion efficiency, ensuring that the low-frequency signal radiated from the transducer through the wellbore to the formation has a longer detection distance and a higher signal-to-noise ratio in the formation. Attached Figure Description

[0017] The accompanying drawings used in the description of the embodiments or prior art are briefly introduced below.

[0018] Figure 1 This is a schematic diagram of a prior art method for generating parallel sound beams in a wellbore, provided in an embodiment of this application;

[0019] Figure 2 This is a schematic flowchart of a method for generating a low-frequency finite acoustic beam in a well, as provided in an embodiment of this application.

[0020] Figure 3 This is a schematic diagram illustrating the working state and design model partitioning of a parametric matrix provided in an embodiment of this application;

[0021] Figure 4 This is a schematic diagram illustrating the relationship between distance and frequency provided in an embodiment of this application;

[0022] Figure 5 This is a schematic diagram showing the relationship between the original frequency sound source level of a sound source with different apertures and frequency, as provided in the embodiments of this application.

[0023] Figure 6 This is a schematic diagram illustrating the relationship between the difference frequency sound source level and the frequency and difference frequency after the aperture size is changed, as provided in the embodiments of this application.

[0024] Figure 7This is a schematic diagram illustrating the relationship between the original frequency acoustic signal and the propagation distance, provided in an embodiment of this application.

[0025] Figure 8 This is a schematic diagram illustrating the relationship between the difference frequency acoustic signal and the propagation distance, provided in an embodiment of this application.

[0026] Figure 9 This is a schematic diagram illustrating the relationship between the original frequency sound source level and the difference frequency sound source level as distance increases, provided in an embodiment of this application.

[0027] Figure 10 This is a schematic diagram of a natural radiation experimental measurement device provided in the embodiments of this application;

[0028] Figure 11 This is a schematic diagram of a CW frequency modulation signal measurement result provided in an embodiment of this application;

[0029] Figure 12 This is a schematic diagram of a preferred frequency modulation signal measurement result provided in an embodiment of this application;

[0030] Figure 13 This is a schematic diagram of a transducer structure provided in an embodiment of this application;

[0031] Figure 14 This is a schematic diagram of another transducer structure provided in the embodiments of this application;

[0032] Figure 15 This is a schematic diagram of a device for generating low-frequency finite sound beams in a well, as provided in an embodiment of this application. Detailed Implementation

[0033] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0034] In the description of this application, the terms “center,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” and “outer,” etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0035] The terms "first" and "second," etc., used in the specification and claims herein are used to distinguish different objects, not to describe a specific order of objects. For example, "first operational amplifier" and "second operational amplifier," etc., are used to distinguish different operational amplifiers, not to describe a specific order of operational amplifiers.

[0036] In the description of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, contact connections, or integral connections. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. In the embodiments of this application, "contact" or "coupling" can refer to direct contact between components or contact between components through adhesives or thermally conductive colloids.

[0037] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0038] Figure 2 This is a schematic flowchart illustrating a method for generating a low-frequency finite acoustic beam in a well, as provided in an embodiment of this application. Figure 2 As shown, the method for measuring low-frequency finite-beam acoustic signals in a well includes the following steps:

[0039] Step S101: Determine the transducer aperture based on the size of the downhole borehole, and calculate the nonlinear action region of the radiated sound field based on the transducer aperture and distance parameters.

[0040] Specifically, the transducer aperture refers to the physical region or array structure within which it effectively transmits or receives sound waves, determining key performance characteristics such as directivity, resolution, and beamwidth. By optimizing the sound source parameters, the transducer can find an optimal solution between physical limitations, engineering constraints, and application requirements. The transducer aperture can be designed based on the size of the downhole borehole. Furthermore, the nonlinear region of the radiated sound field can be calculated first, and a sound source modulation theory model can be selected based on this nonlinear region. Then, the transducer's sound source parameters can be optimized based on this sound source modulation theory model.

[0041] Specifically, the borehole diameter parameters of the sound source can be determined based on the existing downhole borehole dimensions. The downhole borehole dimensions are directly determined by the drill bit, and the standardized design of existing drill bit dimensions and performance balances construction efficiency, cost, and safety. For example, if the drill bit has an outer diameter of 216 mm (equivalent to 8.5 in), and assuming the sound source is a piston or rectangular sound source, the radius of its transducer can be set between 40 mm and 80 mm.

[0042] The nonlinear region of the radiated sound field can be calculated based on the transducer aperture and distance parameters. Specifically, the low-frequency finite beam proposed in this scheme is a difference-frequency wave based on the nonlinear effects during sound wave propagation. To maximize the emission energy of the low-frequency finite beam, the source parameters need to be optimized. The focus of this optimization design is to ensure that a high-energy low-frequency finite beam can be generated in the well by designing the source parameters under the environmental parameters of the actual application. Before designing the source parameters, the nonlinear region of the radiated sound field needs to be calculated. The distance parameters can include the acoustic absorption distance, Rayleigh distance, and impact distance of the original frequency wave (frequency f0).

[0043] Specifically, the acoustic absorption distance R of the original frequency wave (frequency f0) A Rayleigh distance R o and impact distance R s These are three key distance parameters in parametric array design. Their relative ratios are related to the boundary of the nonlinear interaction region and the nonlinear operating state of the parametric array. Furthermore, the transducer aperture directly affects the boundary of the nonlinear interaction region; increasing the transducer aperture linearly expands the nonlinear region. Essentially, the parametric array utilizes the nonlinear interaction of sound waves propagating in a medium, and the nonlinear interaction region is the critical spatial range within which the original frequency wave energy is converted into a difference frequency wave during this process.

[0044] Sound absorption distance R of the original frequency A =1 / α, where α = (α1+α2) / 2, α1 and α2 are the sound absorption coefficients of the two original frequency waves f1 and f2 respectively, or the sound absorption coefficients corresponding to the point of the average frequency (f1+f2) / 2 of the two original frequencies. When the distance is greater than the sound absorption distance of the original frequency, the high-frequency original frequency sound wave is completely attenuated, and only the difference frequency sound wave continues to propagate forward in the sound field.

[0045] Rayleigh distance is defined as R F =S / λ, where λ is the wavelength of the two primary frequency waves, and S is the acoustic signal radiation area of ​​the parametric array. The acoustic signal radiation area is determined by the transducer aperture. Within the Rayleigh distance, the primary frequency wave is approximately a collimated plane beam, maintaining a high intensity. Therefore, the conversion efficiency is relatively high when the primary frequency interaction generates the difference frequency wave within this range.

[0046] The impact distance is Rs = 1 / (βkM), where β is the nonlinear coefficient of the medium, and the wave number k = 2π / λ. The sound Mach number is the ratio of the mass vibration velocity of the medium near the transducer surface to the velocity of the small signal sound. In the formula, u is the particle velocity, I is the sound source intensity, ρ is the density of the radiating medium, and c0 is the velocity of the small amplitude wave sound.

[0047] The relative magnitudes of the absorption distance, Rayleigh distance, and impact distance determine the three operating states of the parametric array: original frequency acoustic absorption limitation, original frequency spread limitation, and impact limitation. For a detailed explanation of the relationship between distance magnitude and operating state, please refer to [link to relevant documentation / reference]. Figure 3 .

[0048] Step S102: Select the sound source design modulation theory model according to the nonlinear action region, and determine the sound source parameters of the transducer based on the sound source design modulation theory model and the transducer aperture.

[0049] The sound source design modulation theory model can be selected based on the nonlinear action region, and then the sound source parameters of the transducer can be optimized based on the selected sound source design modulation theory model and the transducer aperture.

[0050] Specifically, the sound source design modulation theory model can provide sufficiently accurate parametric array design and performance analysis results. However, since each mathematical model has its own applicable range, the applicability of the design model must be fully considered when designing specific transducers in different application fields.

[0051] For example, based on different definitions and calculation formulas for distance, this scheme calculates the variation relationships of three distances respectively, for reference. Figure 4 A set of calculation results is presented. These results compare the absorption distance, Rayleigh distance, and impact distance with the original frequency for transducer apertures of 0.02, 0.05, and 0.08 m. In the figure, R... A Rs represents the absorption distance corresponding to different original frequencies, Rs represents the impact distance, and R0_0.02m, R0_0.05m and R0_0.08m represent the Rayleigh distances corresponding to sound source radii of 0.02m, 0.05m and 0.08m, respectively.

[0052] from Figure 4 The calculation results show that the absorption distance R A The impact distance Rs is unaffected by the transducer aperture and depends only on the original frequency, while the Rayleigh distance's trend with the original frequency is related to the transducer aperture. In this example, if the transducer aperture is 0.05m, then Rs exists in the range below 400kHz. o <R s <R A The relationship is that the transducer is in an extended restricted state, and its parameter design model should adopt the Berktay model.

[0053] The purpose of parametric array optimization design is to rationally design technical specifications while fully considering existing technology and actual operating conditions, ensuring the effective generation of nonlinear effects in the parametric array's radiated sound field and maximizing the difference frequency source level. The sound source design mainly involves two parts: optimization design of the original frequency technical specifications and optimization design of the difference frequency technical specifications. In specific detection applications, an optimal design scheme needs to be developed by considering the comprehensive influencing factors of parameters such as the original frequency source level, the difference frequency source level, the gain, and the critical and cavitation source levels. Based on the calculation of the parametric array's operating state, the Berketay theoretical model needs to be used to design the parameter specifications for the original frequency and difference frequency.

[0054] First, there's the original frequency sound source level design:

[0055] The formula for calculating the sound source level of the original frequency signal is as follows:

[0056] SL0 = (P e ·η e )+DI(ref.dB / μPa@1m))

[0057] Among them, P e For the transmitter to output electrical power, η e For electroacoustic conversion efficiency, DI is the original frequency directivity index of the integrated transmitter array, and ref.dB / μPa@1m refers to the sound pressure level in decibels at a distance of 1 meter from the sound source, with 1 micropascal as the reference sound pressure.

[0058] As can be seen from the formula, the magnitude of the original frequency sound source level is significantly related to the electrical power applied by the transmitter. The original frequency directivity index of the transmitter array is a characteristic parameter used to measure the directivity of the transducer array or the sharpness of the main beam. It is usually defined as the ratio of the sound intensity at a certain point along the far-field acoustic axis to the average sound intensity in all directions over a uniform distance, and can also be calculated using the following formula:

[0059]

[0060] In the formula, S is the effective radiation area of ​​the transducer array, and λ0 is the original wavelength.

[0061] The following analysis examines the relationship between the original frequency source level and various parameters. Assuming transducer apertures are 0.08m, 0.05m, and 0.02m, the variation of the original frequency source level with frequency f0 is calculated. The calculation results are as follows: Figure 5 As shown, from Figure 5 As can be seen, the original frequency sound source level increases continuously with the increase of frequency; at the same frequency, the sound source level increases with the increase of the radius of the radiating sound source.

[0062] Next is the difference frequency sound source level design:

[0063] In a parametric array, the source level of the difference frequency reflects the magnitude of the difference frequency energy. Based on parametric gain, original frequency, etc., the formula for calculating the source level of the difference frequency can be derived:

[0064] SL d =2SL0+20log(f d )+20logΔ-287

[0065] In the formula, SL0 is the original frequency sound source level, f d The frequency of the difference frequency is Δ=E1(2αR0f0 / f d )exp(2αR0f0 / f d ), f d / f0 is the ratio of the difference frequency to the original frequency, also known as the drop ratio.

[0066] Figure 6 (a, b, c) show the variation of the difference frequency source level with the original frequency at different difference frequencies (5.0kHz to 30.0kHz, in 5.0kHz intervals) for transducer apertures of 0.02m, 0.05m, and 0.08m. Figure 6 As shown, for a sound source with a fixed transducer aperture, the source level of the difference frequency first increases and then decreases with the increase of the original drilling frequency, regardless of the difference frequency. When the aperture is fixed, the source level of the difference frequency increases with the increase of the difference frequency at a certain original frequency. When the transducer aperture is changed, the source level of the difference frequency changes in the same way as the original frequency and the difference frequency, but its value increases with the increase of the transducer aperture.

[0067] As can be seen from the difference frequency sound source level, the difference frequency sound source level is mainly determined by four parameters: transducer array aperture (referring to the overall effective size or distribution range of the array composed of multiple transducer array elements), original frequency, original frequency sound source level, and difference frequency. Increasing the transducer array aperture, increasing the original frequency sound source level, decreasing the downshift ratio, and increasing the difference frequency are all beneficial to improving the difference frequency sound source level. However, the parametric array design must fully consider the specific requirements of the actual engineering and the feasibility of implementation. In addition, to obtain a higher original frequency sound source level, it can be achieved by increasing the transducer array aperture and increasing the original frequency sound power. However, the requirement for system portability means that the array aperture cannot be too large. These all require trade-off optimization design during array design.

[0068] In this embodiment, by calculating the original frequency and difference frequency sound source levels and combining the constraints of the critical sound source level and the cavitation sound source level, the optimal transducer aperture, original frequency, difference frequency and other parameters of the parametric array suitable for well detection can be optimized.

[0069] The low-frequency component of the low-frequency finite beam in this scheme is mainly the difference frequency component of the parametric array. Since the propagation distance of sound waves in the same medium depends primarily on their frequency, the lower the frequency, the greater the propagation distance. Therefore, the magnitude of the difference frequency determines its detection distance in the formation outside the well. In designing the difference frequency of the parametric array, the relationship between the sound wave frequency of the transmitting source and the detection distance in existing acoustic long-range sound detection is referenced. For example, existing monopole acoustic source long-range sound detection instruments have a center frequency of around 15.0 kHz, and their radial detection distance in the formation outside the well is generally no greater than 10.0 m; existing dipole acoustic source long-range sound detection instruments, when the center frequency of the sound source is around 3.0 kHz, have a radial detection distance in the formation outside the well of 50–60 m. Therefore, the range of the difference frequency formed by the sound source can be designed with reference to the frequency range of the sound source used in existing in-well acoustic long-range sound detection, i.e., the range of 2.0–20.0 kHz. Using a descent ratio of 10, the estimated original frequency is approximately 20.0–200.0 kHz.

[0070] Sound beamwidth parameter design:

[0071] The beamwidth directly affects the azimuth resolution and must meet the following requirements:

[0072]

[0073] Where λ is the wavelength of the sound wave, D is the transducer aperture, and k is the beamforming coefficient (usually taken as 0.5 to 1).

[0074] Based on the above embodiments, the sound source parameters of the transducer that need to be optimized include, but are not limited to, the original frequency and sound source level, the difference frequency and sound source level, and the beamwidth.

[0075] In one implementation, one of three sound source design modulation theory models—Westervelt, Berktay, and Mellen—can be selected to determine the sound source parameters of the transducer.

[0076] Step S103: Based on the determined sound source parameters of the transducer, perform simulation calculations of the sound wave in the nonlinear radiated sound field, determine the critical propagation distance corresponding to the maximum value of the difference frequency sound source level, extract the nonlinear sound wave signal characteristics at the critical propagation distance, and generate a modulated signal based on the nonlinear sound wave signal characteristics.

[0077] Specifically, the determined source parameters of the transducer and environmental parameters are input into the model simulating the nonlinear radiated sound field. The source parameters of the transducer include, but are not limited to, the original frequency and source level, the difference frequency and source level, and the beamwidth. The critical propagation distance corresponding to the maximum value of the difference frequency source level is determined based on the model's output. Nonlinear acoustic signal characteristics at the critical propagation distance are then extracted from the model's output. These signal characteristics include, but are not limited to, time-domain characteristics, frequency-domain characteristics, phase characteristics, and directivity. Finally, based on the extracted signal characteristics, a loadable modulation signal to drive the transducer is designed.

[0078] In one implementation, the simulation calculation of sound waves in a nonlinear radiated sound field is accomplished using the KZK equations after integration and normalization.

[0079] Specifically, based on the parameter design given in step S101, it is necessary to mathematically describe the conversion process of the original frequency and the difference frequency during the process of the sound source radiating sound waves loaded onto the transmitting transducer. In this embodiment, the KZK equation is used to analyze the propagation process of nonlinear sound waves in the medium.

[0080] The KZK equations describing a nonlinear sound field are:

[0081]

[0082] Integrating both sides of the equation, we get:

[0083]

[0084] Normalizing the integral equation, we get:

[0085]

[0086] Where A is the absorption parameter and N is the nonlinear parameter. P, σ, and τ are the normalized sound pressure, axial distance, and time variables, respectively. The above equations fully consider the three processes involved in sound wave propagation: diffraction, absorption, and nonlinear effects.

[0087] For example, suppose the signal loaded onto the sound source is a CW amplitude-modulated envelope signal, its expression can be expressed as:

[0088] P(t)=p0E(t)sin(2πf0t)

[0089] Where, E(t)=sin(2πf c t) is the envelope signal, f c Let p0 be the initial sound pressure level of the sound source, and f0 be the carrier frequency. Then, the difference frequency formed by the byte strips during propagation is f0. d =2f c .

[0090] In this example, the carrier frequency is set to 216kHz, the envelope frequency to 21.6kHz, and the sound source level applied to the sound source to be 224dB. The propagation process of the signal in the nonlinear medium FC-43 solution is simulated and analyzed. The velocity of the FC solution is 646m / s, the density is 1850kg / m3, and the nonlinear coefficient is 7.6.

[0091] Figure 7 The graph illustrates the change in the time-domain waveform of a loaded sound source propagating in FC-43 solution along its axial direction as the propagation distance increases. The horizontal axis represents time, the vertical axis represents amplitude, and the z-value above each waveform represents the propagation distance. The time on the horizontal axis is obtained by transforming the dimensionless time and subtracting the time delay of the sound wave at different propagation distances z. The waveform amplitude on the vertical axis is normalized to the maximum amplitude of the input waveform. The propagation distance z0 represents the Rayleigh distance, expressed as z0 = S / λ, where S is the radiating area of ​​the transmitting transducer and λ is the wavelength of the original frequency.

[0092] Figure 8 The waveform of the difference frequency sound wave obtained after filtering the waveform in the range of 10 to 50 kHz varies with the propagation distance. Figure 8 The waveforms show that as the propagation distance increases, the waveform applied to the transducer gradually becomes distorted, exhibiting obvious nonlinear "sawtooth wave" characteristics, with its relative amplitude continuously decreasing. The corresponding difference frequency wave characteristics show a process where the difference frequency wave starts almost nonexistent, then rapidly increases in energy, and gradually flattens out.

[0093] By comparing the changes in the source level of the original frequency and difference frequency waves with distance, we can obtain... Figure 9 The comparison results in the figure more intuitively illustrate the changes and conversion processes of the original frequency and difference frequency signals with distance. It can be seen that when the propagation distance is approximately 0.5 times the Rayleigh distance, the amplitude of the difference frequency wave reaches its peak, and then gradually tends towards a stable state after 1.0 times the Rayleigh distance. Therefore, the difference frequency component contained in the nonlinear acoustic signal radiated at this location is the largest, meaning this location is the critical propagation distance corresponding to the maximum value of the difference frequency sound source level. Finally, the nonlinear acoustic signal characteristics at this critical propagation distance are extracted. These characteristics include harmonic components, waveform distortion characteristics, time-frequency joint characteristics, and nonlinear coefficients. Based on these nonlinear acoustic signal characteristics, a modulated signal can be designed, such as synthesizing the fundamental frequency and higher harmonics according to the extracted ratio to generate a pre-distorted signal; designing time-varying amplitude modulation based on the extracted envelope shape (e.g., exponential decay, asymmetric peak); and designing a phase modulation function using the extracted phase nonlinear characteristics.

[0094] In practical applications, it is necessary to combine the impedance characteristics, frequency response parameters, acoustic-to-electric conversion efficiency, critical sound source level, cavitation sound source level and other parameters of the transducer itself, as well as the parameters of the original frequency and difference frequency and their detection performance requirements, to adjust the sound source level of the input signal.

[0095] Furthermore, the CW modulation signal used in this example can be replaced with an LFM modulation signal or other similar forms. The nonlinear fluid FC-43 used in the calculation can also be replaced with other nonlinear materials with low velocity and high nonlinear coefficients. These nonlinear materials can be liquids, solids, or other mixtures.

[0096] Step S104: Measure the first output signal characteristics of the transducer under the loadable modulation signal loading state, and measure the second output signal characteristics of the transducer under the natural radiation modulation signal loading state.

[0097] Specifically, the main application of the effective acoustic beam signal generated by this scheme is that after sound waves are radiated in the well, they can be coupled into the formation through the fluid in the well and used to identify features such as reflectors and fractures far from the wellbore. Therefore, the difference frequency signal in the generated effective acoustic beam signal, due to its low-frequency characteristics, can propagate effectively over long distances and interact with the formation; thus, improving the difference frequency conversion efficiency is crucial.

[0098] The transmitting transducer can be fabricated based on the theoretical analysis results and methods in steps S101 and S102, and the modulation signal selected in step S103 is used as the transmitting signal loaded onto the transducer. The first output signal characteristics of the transducer under the loading state of the modulated signal are measured. At the same time, the same experimental measurement was carried out using the CW modulation signal to measure the second output signal characteristics of the transducer under the loading state of the natural radiation modulation signal.

[0099] For example, this example demonstrates how the energy of the original frequency and difference frequency signals in the received signal varies with distance under the two loading signal conditions described above.

[0100] Figure 10 This is a schematic diagram of the apparatus used in this example experiment. The modulation signal source in the diagram includes two scenarios: one is a direct input of the CW signal to the transducer, and the other is a modulation signal optimized in step S102. The modulation signal is amplified and then applied to the transmitting transducer placed in the water tank. After propagating through the water, receiving transducers at different locations can receive different acoustic signals. The received signals are then acquired by the acquisition system and simultaneously displayed on an oscilloscope for observation.

[0101] First, the transmission response of a CW-modulated acoustic signal with an original frequency of 216kHz as the excitation source was measured in the water tank. The receiving distance ranged from 0.2m to 1.8m, and the receiving spacing was 0.2m. Figure 11 (a) shows the time-domain waveform of the original wave. As the propagation distance increases, the sound pressure intensity does not increase continuously, but rather exhibits a process of first increasing and then decreasing. The arrival time of the sound wave is clear and distinct, with only a small amount of signal interference in the received wave train. By comparing and analyzing the amplitude of this time-domain signal, its trend as the source distance increases can be obtained, such as... Figure 11 As shown in (b), filtering the received signal yields a low-frequency difference signal. Since the energy of the difference signal is significantly reduced compared to the original frequency wave, the amplitude of the low-frequency signal in the time-domain waveform is small, as shown in (b). Figure 11 As shown in (c), analyzing the variation of the difference frequency with the source distance yields Figure 11(d). Figure 11 As shown in (d), by comparing the amplitudes of the original frequency and the difference frequency signals under the same source distance, it can be seen that the amplitude of the difference frequency is between 1 / 55 and 1 / 50 of the original frequency.

[0102] Furthermore, to compare the propagation characteristics of the selected modulation signal after the parametric array sound source simulated by the KZK equation in step S102 propagates in the medium, another set of tests was conducted. During the tests, all test conditions remained unchanged except for the input sound source signal. Similarly, the characteristics of the original frequency signal received by the receiving transducer after inputting the signal were first observed. From... Figure 12 From the time-domain waveform of (a), the arrival point of the signal is clear, and there are some low-frequency fluctuations in the signal during propagation; the amplitude of the original frequency signal changes with the measurement distance as follows: Figure 12 As shown in (b), within the measured location range, its amplitude decreased by more than two times; while for the difference frequency signal, it can be seen that... Figure 12 (c) Compared with the case of a sound source with a direct input CW modulated signal, the wave of the difference frequency signal is clearer and the signal-to-noise ratio of the relative noise is greatly improved. Figure 12 The analysis results shown in (d) regarding the amplitude variation of the difference frequency wave with distance indicate that the amplitude variation of the difference frequency wave with distance is relatively stable. Under the same propagation distance, the amplitude of the difference frequency signal is approximately between 1 / 13 and 1 / 10 of that of the original frequency signal.

[0103] The experimental measurements conducted above verified the advantages of using the nonlinear signal with a large difference frequency source level obtained in step S103 as the input signal: a nonlinear acoustic signal containing a large low-frequency component can be generated even with a small radiation distance, which can be directly applied to the transmitting sound source for long-range acoustic detection in the well, and a low-frequency finite sound beam can be directly generated in the well; the generated nonlinear radiation signal has high difference frequency conversion efficiency, which can ensure that after the signal on the transmitting transducer is radiated to the formation through the well hole, the generated low-frequency signal has a larger detection distance and a higher signal-to-noise ratio in the formation.

[0104] Step S105: By comparing and analyzing the characteristics of the first output signal and the characteristics of the second output signal, the modulated signal with the highest difference frequency conversion efficiency is obtained.

[0105] Specifically, based on the measurement results of step S104, the output characteristics of the preferred modulation signal and the output characteristics of the CW signal are compared to obtain the loadable modulation signal with the highest difference-frequency conversion efficiency.

[0106] Figure 13 This illustration shows a schematic diagram of a transducer structure provided in an embodiment of this application. The transducer can be configured according to... Figure 2 The transducer aperture obtained in the method shown is used to design the transducer with optimized acoustic source parameters.

[0107] Specifically, such as Figure 13 As shown, the transducer 10 can be a composite rod structure consisting of a piezoelectric ceramic stack 11, a rear mass block 12, a front radiating block 13, and a through pin 14, with the overall structural domain being cylindrical.

[0108] This transducer employs a longitudinally vibrating composite rod structure to achieve its performance parameters. Utilizing the thickness-direction stretching vibration mode of piezoelectric ceramics, it achieves high-power, high-energy unidirectional acoustic radiation through high acoustic impedance back radiation suppression and low acoustic impedance front radiation. The transducer's original frequency is determined based on theoretical calculations and is achieved by adjusting the transducer's material and structural parameters according to the longitudinal vibration principle. The transducer's vibration modes, harmonic responses, and acoustic radiation performance are calculated through numerical simulations.

[0109] Figure 14 This illustration shows another transducer structure provided in an embodiment of this application, which can be based on... Figure 2 The transducer aperture obtained in the method shown is used to design the transducer with optimized acoustic source parameters.

[0110] Specifically, such as Figure 14As shown, the transducer 20 is disc-shaped, preferably with a radius of 0.05 m. Applying a higher average electrical power results in a higher emission source level for the original frequency sound wave. The design of the original frequency and difference frequency of this sound source will be ultimately determined based on simulation optimization results. The disc-shaped transducer 20 operates through the stretching and contracting vibration of the piezoelectric material in the thickness direction. The piezoelectric material is preferably a 100 mm diameter PZT piezoelectric ceramic disc. The upper and lower planes of the piezoelectric ceramic are coated with silver electrodes, with the polarization direction along the thickness direction.

[0111] Figure 15 The diagram shows a schematic of a device for generating a low-frequency finite sound beam in a well according to the present invention. The device for generating a low-frequency finite sound beam in a well according to the present invention includes the following modules:

[0112] The nonlinear region calculation module 201 is used to determine the transducer aperture based on the size of the downhole borehole, and to calculate the nonlinear action region of the radiated sound field based on the transducer aperture and distance parameters.

[0113] The sound source parameter determination module 202 is used to select the sound source design modulation theory model according to the nonlinear action region, and determine the sound source parameters of the transducer based on the sound source design modulation theory model and the transducer aperture.

[0114] The sound field calculation module 203 is used to perform simulation calculations of sound waves in a nonlinear radiated sound field based on the determined sound source parameters, determine the critical propagation distance corresponding to the maximum value of the difference frequency sound source level, extract the nonlinear sound wave signal features at the critical propagation distance, and generate a loadable modulation signal based on the nonlinear sound wave signal features.

[0115] The modulation signal measurement module 204 is used to measure the first output signal characteristics of the transducer under the condition of loading a modulated signal, and to measure the second output signal characteristics of the transducer under the condition of loading a natural radiation modulated signal.

[0116] The modulation signal analysis module 205 is used to determine the loadable modulation signal with a large difference frequency sound source level by comparing and analyzing the characteristics of the first output signal and the characteristics of the second output signal.

[0117] The types, quantities, shapes, installation methods, and structures of the components of the well low-frequency limited sound beam generation device provided in this application are not limited to the above embodiments. All technical solutions implemented under the principles of this application are within the protection scope of this solution. Any one or more embodiments or illustrations in the specification, combined in a suitable manner, are within the protection scope of this solution.

[0118] According to another embodiment, a computing device is also provided, including a memory and a processor, wherein the memory stores executable code, and when the processor executes the executable code, it implements a combination... Figure 2 The method described.

[0119] According to another embodiment, a computer-readable storage medium is also provided, on which a computer program is stored, which, when executed in a computer, causes the computer to perform a combination Figure 2 The method described.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application. Those skilled in the art should understand that although this application has been described in detail with reference to the foregoing embodiments, modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to depart from the spirit and scope of the technical solutions in the embodiments of this application.

Claims

1. A method for generating a low-frequency finite acoustic beam in a well, characterized in that, The method includes: The transducer aperture is determined based on the size of the downhole borehole, and the nonlinear region of the radiated sound field is calculated based on the transducer aperture and distance parameters; the distance parameters include the acoustic absorption distance of the original frequency wave, Rayleigh distance, and impact distance. Based on the nonlinear action region, a sound source design modulation theory model is selected, and the sound source parameters of the transducer are determined based on the sound source design modulation theory model and the transducer aperture. Based on the determined sound source parameters, simulation calculations of sound waves in a nonlinear radiated sound field are carried out to determine the critical propagation distance corresponding to the maximum value of the difference frequency sound source level, and nonlinear sound wave signal characteristics at the critical propagation distance are extracted. Based on the nonlinear sound wave signal characteristics, a modulated signal that can be loaded is generated. Measure the first output signal characteristics of the transducer under a loadable modulation signal loading state; measure the second output signal characteristics of the transducer under a natural radiation modulation signal loading state; By comparing and analyzing the characteristics of the first output signal and the characteristics of the second output signal, a modulated signal with a larger difference frequency source level is determined.

2. The method according to claim 1, characterized in that, Sound source design modulation theory models include those by Westervelt, Berktay, and Mellen.

3. The method according to claim 1, characterized in that, The sound source parameters of the transducer that need to be optimized include: original frequency and sound source level, difference frequency and sound source level, and beamwidth.

4. The method according to claim 1, characterized in that, The simulation calculation of sound waves in a nonlinear radiated sound field is completed using the KZK equations after integration and normalization.

5. The method according to claim 1, characterized in that, The natural radiation modulation signal is either a CW amplitude modulation envelope signal or an LFM modulation signal.

6. A device for generating a low-frequency finite sound beam in a well, characterized in that, The apparatus for generating a low-frequency finite beam by means of the method according to any one of claims 1 to 5 comprises: The nonlinear region calculation module is used to determine the transducer aperture based on the size of the downhole borehole, and to calculate the nonlinear region of the radiated sound field based on the transducer aperture and distance parameters. The sound source parameter determination module is used to select a sound source design modulation theory model according to the nonlinear action region, and determine the sound source parameters of the transducer based on the sound source design modulation theory model and the transducer aperture. The sound field calculation module is used to perform simulation calculations of sound waves in a nonlinear radiated sound field based on the determined sound source parameters, determine the critical propagation distance corresponding to the maximum value of the difference frequency sound source level, extract the nonlinear sound wave signal characteristics at the critical propagation distance, and generate a loadable modulation signal based on the nonlinear sound wave signal characteristics. The modulation signal measurement module is used to measure the first output signal characteristics of the transducer under a modulated signal loading state and to measure the second output signal characteristics of the transducer under a natural radiation modulated signal loading state. The modulation signal analysis module is used to determine the loadable modulation signal with a large difference frequency sound source level by comparing and analyzing the characteristics of the first output signal and the characteristics of the second output signal.

7. An electronic device comprising a memory and a processor, wherein the memory stores a computer program executable on the processor, characterized in that, When the processor executes the computer program, it implements the method described in any one of claims 1 to 5.

8. A computer-readable medium having processor-executable non-volatile program code, characterized in that, The program code causes the processor to execute the method according to any one of claims 1 to 5.

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