Low-frequency monopole acoustic logging transducers, acoustic logging instruments and systems

Abstract

This invention provides a low-frequency monopole acoustic logging transducer, acoustic logging instrument, and system, belonging to the field of geological exploration technology. The low-frequency monopole acoustic logging transducer includes: a circumferential frame and an even number of dipole triplet plates, which are vertically mounted on the circumferential frame in a circumferential array. Each dipole triplet plate includes: a metal substrate, a first piezoelectric material element, and a second piezoelectric material element. The first piezoelectric material element is disposed on the upper surface of the metal substrate, and the second piezoelectric material element is disposed on the lower surface of the metal substrate relative to the upper surface. The even number of dipole triplet plates arranged in a circumferential array allows the overall circumferential monopole logging transducer to expand and contract radially to generate a symmetrical sound field. By using dipole triplet plates to reduce the fundamental frequency of vibration through axial space, a low-frequency acoustic signal is obtained, thereby more accurately acquiring Stoneley wave information from the formation and increasing the detection depth.

Description

Technical Field

[0001] This invention relates to the field of geological exploration technology, specifically to a low-frequency monopole acoustic logging transducer, an acoustic logging instrument, and an acoustic logging system. Background Technology

[0002] Sonic logging technology is an important technology in oilfield exploration and development. By measuring and analyzing downhole waveform data, important parameters such as formation physical properties and rock mechanics can be obtained, which are used for reservoir delineation, rock porosity calculation, and wellbore stability evaluation.

[0003] The acoustic logging transducer is the core component of an acoustic logging instrument. It utilizes the piezoelectric effect to convert acoustic energy into electrical energy, transmitting acoustic energy into the formation and receiving the returned acoustic signal. The acoustic waves emitted from the acoustic logging transducer propagate a short distance in the well fluid before reaching the wellbore. Some of the energy is reflected back into the wellbore, while some propagates through the formation.

[0004] In the study of acoustic logging response characteristics in fractured formations, P-waves, S-waves, and Stoneley waves all exhibit different response characteristics. Among these, the response characteristics of Stoneley waves show much greater variation than those of P-waves and S-waves, making them easier to observe. Furthermore, Stoneley waves are more sensitive to permeable formations or fractures, thus offering a greater advantage in fracture evaluation. The energy and velocity attenuation of Stoneley waves are frequency-dependent; at high frequencies, energy and velocity attenuation is rapid, while at low frequencies, energy attenuation is minimal. Low-frequency Stoneley waves are highly sensitive to formation permeability. As acoustic waves pass through permeable fractures and lost circulation formations, viscous diffusion causes amplitude attenuation and increases slowness. At fracture sites, Stoneley waves are both reflected and attenuated. High-quality low-frequency Stoneley wave signals can quantitatively evaluate fractures, effectively invert formation permeability, and solve the challenge of predicting the planar distribution of small-scale fractured-vuggy reservoirs. Typically, Stoneley waves are separated from full-waveform array acoustic logging data.

[0005] Monopole acoustic logging transducers are symmetrical sound sources, mainly used to generate and receive acoustic signals in all directions. Monopole acoustic logging transducers are primarily used to excite longitudinal waves. However, the transmission resonant frequency of existing monopole acoustic logging transducers is usually around 10 kHz. At such a high transmission frequency, it is difficult to separate Stoneley waves from the received full-waveform array acoustic waves. Summary of the Invention

[0006] To address the aforementioned technical deficiencies, this invention provides a low-frequency monopole acoustic logging transducer, an acoustic logging instrument, and a system. The low-frequency monopole acoustic logging transducer utilizes an even number of dipole triple laminations arranged in a circular array to form a circumferential monopole logging transducer. This even-numbered arrangement of the dipole triple laminations allows the overall circumferential monopole logging transducer to expand and contract radially in an axisymmetric manner, generating a symmetrical sound field to uniformly radiate acoustic energy in all directions towards the wellbore. Furthermore, the use of dipole triple laminations reduces the fundamental vibration frequency, resulting in a low-frequency acoustic signal, thereby more accurately acquiring formation Stoneley wave information and increasing the detection depth.

[0007] The first aspect of the present invention provides a low-frequency monopole acoustic logging transducer, comprising: a circumferential frame and an even number of dipole triple laminations, wherein the even number of dipole triple laminations are vertically mounted on the circumferential frame in a circumferential array to form a cylindrical structure; The dipole triplet includes: a metal substrate, a first piezoelectric material element, and a second piezoelectric material element. The first piezoelectric material element is disposed on the upper surface of the metal substrate, and the second piezoelectric material element is disposed on the lower surface of the metal substrate.

[0008] In this embodiment of the invention, the length of the metal substrate is greater than the length of the first piezoelectric material element and greater than the length of the second piezoelectric material element.

[0009] In this embodiment of the invention, the circumferential skeleton includes: a first mounting plate and a second mounting plate disposed opposite to each other, a first end of the metal substrate being mounted on the first mounting plate, and a second end of the metal substrate being mounted on the second mounting plate.

[0010] In this embodiment of the invention, the first mounting plate and the second mounting plate are made of metal.

[0011] In this embodiment of the invention, the first piezoelectric material element is bonded to the upper surface of the metal substrate by high-temperature adhesive, and the second piezoelectric material element is bonded to the lower surface of the metal substrate by high-temperature adhesive.

[0012] In this embodiment of the invention, the first piezoelectric material element and the second piezoelectric material element are made of the same material, and both the first piezoelectric material element and the second piezoelectric material element are piezoelectric ceramic sheets.

[0013] In this embodiment of the invention, the piezoelectric ceramic sheet is made of one or more combinations of barium titanate, lead titanate, modified lead titanate, lead zirconate titanate, modified lead zirconate titanate, and lead metaniobate.

[0014] In this embodiment of the invention, the fundamental frequency of the low-frequency monopole acoustic logging transducer is determined by the variation in length of the first piezoelectric material element, the second piezoelectric material element, and the metal substrate.

[0015] A second aspect of the present invention provides an acoustic logging instrument, comprising: a transmitting acoustic system sub-section and a transmitting circuit sub-section, wherein the transmitting acoustic system sub-section comprises a low-frequency monopole acoustic logging transducer as described above; The transmitting circuit subsection is connected to the low-frequency monopole acoustic logging transducer and is used to provide voltage to the low-frequency monopole acoustic logging transducer, so that the low-frequency monopole acoustic logging transducer generates acoustic signals.

[0016] A third aspect of the present invention provides an acoustic logging system, comprising: a surface logging device and an acoustic logging instrument as described above.

[0017] The low-frequency monopole acoustic logging transducer provided by this invention forms a circumferential monopole logging transducer by arranging an even number of dipole triple laminations in a circular array. This even-numbered array allows the overall circumferential monopole logging transducer to expand and contract radially in an axisymmetric manner, generating a symmetrical sound field and uniformly radiating acoustic energy in all directions towards the wellbore. Furthermore, the use of dipole triple laminations reduces the fundamental frequency of vibration, resulting in a low-frequency acoustic signal. This allows for more accurate acquisition of Stoneley wave information from the formation, increasing the detection depth.

[0018] Other features and advantages of the technical solution of the present invention will be described in detail in the following detailed embodiments section. Attached Figure Description

[0019] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the structure of a conventional single-pole acoustic logging transducer provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the vibration modes of a conventional monopole acoustic logging transducer provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of the low-frequency monopole acoustic logging transducer provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the dipole triple lamination provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the vibration modes of a low-frequency monopole acoustic logging transducer provided in an embodiment of the present invention; Figure 6This is a numerical simulation spectrum of the acoustic pressure of the low-frequency monopole acoustic logging transducer provided in this embodiment of the invention; Figure 7 This is a schematic diagram of the structure of the acoustic logging instrument provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the vibration modes of the second dipole triple lamination provided in an embodiment of the present invention; Figure 9 This is a schematic diagram of the acoustic logging system provided in an embodiment of the present invention.

[0020] Explanation of reference numerals in the attached figures 1-Dipole triple lamination, 11-Metal substrate, 12-First piezoelectric ceramic sheet, 13-Second piezoelectric ceramic sheet, 2-First mounting plate, 3-Second mounting plate. Detailed Implementation

[0021] To make the technical solutions and advantages of the embodiments of the present invention clearer, the exemplary embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not an exhaustive list of all embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0022] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "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 only for the convenience of describing this invention 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 invention.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0024] In this invention, unless otherwise explicitly specified and limited, terms such as "installation," "connection," "linking," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0025] In the process of realizing this invention, the inventors discovered that acoustic logging technology is an important technology in oilfield exploration and development. By measuring and analyzing downhole waveform data, important parameters such as formation physical properties and rock mechanics can be obtained, which can be used for reservoir division, rock porosity calculation, wellbore stability evaluation, etc.

[0026] The acoustic logging transducer is the core component of an acoustic logging instrument. It utilizes the piezoelectric effect to convert acoustic energy into electrical energy, transmitting acoustic energy into the formation and receiving the returned acoustic signal. The acoustic waves emitted from the acoustic logging transducer propagate a short distance in the well fluid before reaching the wellbore. Some of the energy is reflected back into the wellbore, while some propagates through the formation.

[0027] In the study of acoustic logging response characteristics in fractured formations, P-waves, S-waves, and Stoneley waves all exhibit different response characteristics. Among these, the response characteristics of Stoneley waves show much greater variation than those of P-waves and S-waves, making them easier to observe. Furthermore, Stoneley waves are more sensitive to permeable formations or fractures, thus offering a greater advantage in fracture evaluation. The energy and velocity attenuation of Stoneley waves are frequency-dependent; at high frequencies, energy and velocity attenuation is rapid, while at low frequencies, energy attenuation is minimal. Low-frequency Stoneley waves are highly sensitive to formation permeability. As acoustic waves pass through permeable fractures and lost circulation formations, viscous diffusion causes amplitude attenuation and increases slowness. At fracture sites, Stoneley waves are both reflected and attenuated. High-quality low-frequency Stoneley wave signals can quantitatively evaluate fractures, effectively invert formation permeability, and solve the challenge of predicting the planar distribution of small-scale fractured-vuggy reservoirs. Typically, Stoneley waves are separated from full-waveform array acoustic logging data.

[0028] Commonly used acoustic logging transducers include monopole acoustic logging transducers and dipole acoustic logging transducers. Dipole acoustic logging transducers are asymmetric sound sources, capable of generating and receiving acoustic signals with specific directions. Their transmission resonant frequency is around 2.5 kHz. Dipole acoustic logging transducers can directly excite shear waves for analyzing formation shear wave anisotropy and rock mechanical parameters. Monopole acoustic logging transducers are symmetric sound sources, primarily used to generate and receive acoustic signals in all directions. Their transmission resonant frequency is around 10 kHz. Monopole acoustic logging transducers are mainly used to excite P-waves. In conventional formations, monopole acoustic logging transducers are more stable and reliable, providing accurate P-wave measurement data. Figure 1 This is a schematic diagram of the structure of a conventional monopole acoustic logging transducer provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the vibration modes of a conventional monopole acoustic logging transducer provided in an embodiment of the present invention, as shown below. Figure 1-2 As shown, in existing technology, a conventional monopole acoustic logging transducer includes a cylindrical piezoelectric ceramic element, which is manufactured using materials such as lead zirconate titanate (PZT) or other piezoelectric materials. When the monopole acoustic logging transducer operates in emission mode, a time-varying voltage is applied to the outer surface of the cylindrical piezoelectric ceramic element. Due to the piezoelectric effect, the cylindrical piezoelectric ceramic element undergoes radial mechanical expansion and contraction, thereby driving the surrounding fluid and generating acoustic energy radiation and transmission. Figure 2 As shown, the conventional monopole acoustic logging transducer was subjected to modal analysis using finite element analysis software (COMSOL 6.1) to simulate the motion and displacement of each mode. Figure 2 (a) is a schematic diagram of the first-order vibration mode. The monopole acoustic logging transducer exhibits expansion motion and can radiate acoustic energy. Figure 2 (b) illustrates the second-order vibration mode, where the monopole acoustic logging transducer exhibits a contracting motion, enabling acoustic energy radiation. Conventional cylindrical monopole acoustic logging transducers operate in a radial vibration mode, with the fundamental frequency decreasing as the diameter of the cylindrical tube increases. However, the radial dimension of the cylindrical tube is limited by the spatial constraints in the radial direction of the logging instrument, making it difficult to obtain monopole acoustic logging transducers with lower frequencies. Therefore, the resonant frequency of conventional monopole acoustic logging transducers is typically around 10kHz. At such a high transmission frequency, it is difficult to separate the Stoneley wave from the received full-waveform array acoustic waves.

[0029] To address the aforementioned problems, this invention provides a low-frequency monopole acoustic logging transducer, comprising: a circular frame and an even number of dipole triple laminations. The even number of dipole triple laminations are vertically mounted on the circular frame in a circular array to form a circular logging transducer. Each dipole triple lamination includes: a metal substrate, a first piezoelectric material element, and a second piezoelectric material element. The first piezoelectric material element is disposed on the upper surface of the metal substrate, and the second piezoelectric material element is disposed on the lower surface of the metal substrate relative to the upper surface. The low-frequency monopole acoustic logging transducer, through the even number of dipole triple laminations arranged in a circular array, forms a circular monopole logging transducer. This even-numbered array arrangement allows the overall circular monopole logging transducer to expand and contract radially in an axisymmetric manner, generating a symmetrical sound field and uniformly radiating acoustic energy in all directions towards the wellbore. Furthermore, a dipole tri-laminated structure is employed to achieve vibration. The vibration principle of the dipole tri-laminated structure is as follows: as the length increases, the fundamental frequency of vibration gradually decreases, thereby obtaining low-frequency acoustic signals using the dipole tri-laminated structure. This allows for more accurate acquisition of formation Stoneley wave information and increases the detection depth. Unlike the piezoelectric circular tube design of conventional monopole acoustic logging transducers, this invention uses an even number of dipole tri-laminated structures arranged in a circular array. The bending vibration of the dipole tri-laminated structures allows the overall circular monopole logging transducer to expand and contract radially in an axisymmetric manner, generating a symmetrical sound field and uniformly radiating acoustic energy in all directions towards the wellbore. By using dipole tri-laminated structures to reduce the fundamental frequency of vibration through axial space, low-frequency acoustic signals are obtained, thus enabling more accurate acquisition of formation Stoneley wave information and increasing the detection depth.

[0030] Figure 3 This is a schematic diagram of the structure of the low-frequency monopole acoustic logging transducer provided in an embodiment of the present invention. Figure 4 This is a schematic diagram of the structure of the dipole triple lamination 1 provided in an embodiment of the present invention. Figure 3-4 As shown in the figure, this embodiment provides a low-frequency monopole acoustic logging transducer, comprising: a circumferential frame and an even number of dipole triple laminations 1. The circumferential frame includes: a first mounting plate 2 and a second mounting plate 3. Each dipole triple lamination 1 includes: a metal substrate 11, a first piezoelectric material element, and a second pressure material element. The dipole triple laminations 1 are vertically mounted on the circumferential frame in a circumferential arrangement to form a cylindrical structure. Each dipole triple lamination 1 vibrates under the action of a voltage field, and the even number of circumferentially arranged dipole triple laminations 1 generate a symmetrical acoustic field under the piezoelectric effect.

[0031] In this embodiment, the first piezoelectric material element is disposed on the upper surface of the metal substrate 11, and the second piezoelectric material element is disposed on the lower surface of the metal substrate 11 relative to the upper surface. Both the first and second piezoelectric material elements vibrate under voltage, and the fundamental frequency of the vibration decreases as the length of the first and second piezoelectric material elements and the metal substrate increases. Therefore, by limiting the length of the metal substrate 11 and the piezoelectric material elements bonded thereon, a low-frequency acoustic signal can be obtained.

[0032] In this embodiment, there are eight dipole triple laminations 1, which are arranged in a circular array and mounted on a circular skeleton.

[0033] In other embodiments of the invention, the number of dipole triple laminations 1 is six.

[0034] Furthermore, in this embodiment, the length of the metal substrate 11 is greater than the length of both the first and second piezoelectric material elements. Both the first and second piezoelectric material elements are located at the center of the metal substrate 11. The first end of the first piezoelectric material element is shorter than the first end of the metal substrate 11, and the second end of the second piezoelectric material element is shorter than the second end of the metal substrate 11. The length of the second piezoelectric material element is the same as the length of the first piezoelectric material element, and the first end of the second piezoelectric material element is flush with the first end of the first piezoelectric material element.

[0035] In this embodiment, the metal substrate 11 serves two purposes: one is as a carrier for the movement of the transducer, and the other is as a conductive electrode that couples voltage to the piezoelectric ceramic element. The metal substrate 11 is also used to ensure the stiffness required for the vibration of the dipole triplex plate 1. Therefore, the metal substrate 11 is made of alloy steel.

[0036] In this embodiment, the first mounting plate 2 and the second mounting plate 3 of the circumferential skeleton are arranged opposite to each other to fix the two ends of the plurality of dipole triple laminations 1 respectively. Specifically, the first ends of the plurality of dipole triple laminations 1 are all mounted on the first mounting plate 2 by screws. The second ends of the plurality of second dipole triple laminations 1 are all mounted on the second mounting plate 3 by screws.

[0037] In this embodiment, the first piezoelectric material element and the second piezoelectric material element are the same, both being piezoelectric ceramic sheets. Further, in this embodiment, the first piezoelectric material element is a first piezoelectric ceramic sheet 12, and the second piezoelectric material element is a second piezoelectric ceramic sheet 13. The first piezoelectric ceramic sheet 12 is bonded to the upper surface of the metal substrate 11 using a resin-based high-temperature adhesive, and the second piezoelectric ceramic sheet 13 is bonded to the lower surface of the metal substrate 11 using a resin-based high-temperature adhesive.

[0038] In other embodiments of the present invention, the metal substrate 11 is an electrical insulator. When the metal substrate 11 is an electrical insulator, a first electrode is disposed on the upper surface of the electrical insulator substrate, and a second electrode is disposed on the lower surface of the electrical insulator substrate. The first electrode provides voltage to the first piezoelectric ceramic sheet 12, and the second electrode provides voltage to the second piezoelectric ceramic sheet 13.

[0039] In this embodiment, the first piezoelectric ceramic sheet 12 and the second piezoelectric ceramic sheet 13 are made of lead zirconate titanate.

[0040] In this embodiment, the fundamental vibration frequency of the low-frequency monopole acoustic logging transducer varies according to the lengths of the first piezoelectric material element, the second piezoelectric material element, and the metal substrate. Specifically, in this embodiment, the cylindrical structure of the low-frequency monopole acoustic logging transducer is placed horizontally inside the logging instrument, thus the fundamental vibration frequency of the low-frequency monopole acoustic logging transducer varies along the axial length of the logging instrument. Furthermore, as the axial length increases, the fundamental vibration frequency of the low-frequency monopole acoustic logging transducer decreases.

[0041] Figure 5 This is a schematic diagram of the vibration modes of a low-frequency monopole acoustic logging transducer provided in an embodiment of the present invention, as shown below. Figure 5 As shown, modal analysis was performed using finite element analysis software (COMSOL 6.1) to simulate the motion and displacement of each mode. Figure 5 (a) is a schematic diagram of the first-order vibration mode. Each dipole triplet 1 unit exhibits the arched motion of the first-order vibration mode, causing the low-frequency monopole acoustic logging transducer of the triplet circular array structure to exhibit radial mechanical expansion motion as a whole, which can radiate acoustic energy. Figure 5 (b) is a schematic diagram of the second-order vibration mode. Each dipole triplet 1 unit exhibits the W-shaped motion of the third-order vibration mode, causing the low-frequency monopole acoustic logging transducer of the triplet circular array structure to exhibit radial mechanical contraction motion as a whole, which can radiate acoustic energy, thereby driving the surrounding fluid to move and generating acoustic energy radiation and transmission.

[0042] Figure 6 This is a numerical simulation spectrum of the acoustic pressure of the low-frequency monopole acoustic logging transducer provided in an embodiment of the present invention, such as... Figure 6As shown in the figure, the low-frequency monopole acoustic logging transducer provided in this embodiment, under 1V time-varying voltage excitation, numerically simulates the sound pressure value at 1m in water, as shown by the thin solid line. The existing conventional cylindrical monopole acoustic logging transducer, under 1V time-varying voltage excitation, numerically simulates the sound pressure value at 1m in water, as shown by the thick solid line. Figure 2 In the modes shown, the corresponding vibration modes of a conventional monopole acoustic logging transducer correspond to the natural frequencies of the transducer structure. At these frequencies, the conversion from electrical energy to mechanical energy reaches its maximum, allowing for effective net acoustic energy radiation. It can be observed that the dominant frequency of a conventional monopole acoustic logging transducer is 12700Hz, the fundamental frequency is 5550Hz, and below 2000Hz, it cannot effectively radiate detectable acoustic energy. Figure 5 In the modes shown, the low-frequency monopole acoustic logging transducer provided in this embodiment achieves its maximum conversion from electrical energy to mechanical energy at the frequencies corresponding to the first and second modes, effectively radiating net acoustic energy. The main frequencies of the low-frequency monopole acoustic logging transducer with a triple-layer circular array structure are 750Hz and 4400Hz. Significant acoustic energy radiation is generated in and around the resonance of the first-order vibration mode (500Hz-1000Hz) and the second-order vibration mode (4000Hz-5000Hz). This is very intuitively demonstrated from... Figure 6 The spectrum shown indicates that, compared to conventional monopole acoustic logging transducers, the low-frequency monopole acoustic logging transducer with a triple-layer circular array structure has a lower frequency and a wider bandwidth, enabling it to measure lower-frequency Stoneley waves and compensate for the limitations of conventional monopole acoustic logging transducers in detecting low-frequency energy regions.

[0043] Figure 7 This is a schematic diagram of the structure of the acoustic logging instrument provided in an embodiment of the present invention. Figure 7 As shown in this embodiment, an acoustic logging instrument includes: a transmitting acoustic system subsection and a transmitting circuit subsection, and further includes: a flexible subsection, a receiving acoustic system subsection, and a receiving control and acquisition electronic circuit subsection. The transmitting acoustic system subsection includes, as described above, a low-frequency monopole acoustic logging transducer, two mutually orthogonally distributed dipole acoustic logging transducers, and a quadrupole transmitting transducer. The receiving acoustic system subsection is connected to the receiving control and acquisition electronic circuit subsection; the receiving acoustic system subsection is used to receive acoustic signals returned from the formation.

[0044] In this embodiment, the transmitting circuit section and the receiving control and acquisition electronic circuit section each have their own power supply units.

[0045] In this embodiment, the second dipole triplet 1 has the same structure as the dipole triplet 1.

[0046] Figure 8This is a schematic diagram of the vibration modes of the second dipole triple lamination 1 provided in an embodiment of the present invention, as shown below. Figure 8 As shown, when the dipole acoustic logging transducer operates in emission mode, a time-varying voltage is applied to the first piezoelectric ceramic element and the second piezoelectric ceramic element 13. Due to the piezoelectric effect, the first piezoelectric ceramic element 12 undergoes mechanical expansion in the thickness direction, while the second piezoelectric ceramic element 13 undergoes mechanical contraction in the thickness direction. Conversely, when voltages of opposite polarity are applied to the first piezoelectric ceramic element 12 and the second piezoelectric ceramic element 13, the first piezoelectric ceramic element 12 contracts and the second piezoelectric ceramic element 13 expands. These two alternating movements together drive the metal substrate 11 to bend upward and downward, thereby driving the surrounding fluid to move and generating acoustic energy radiation and transmission.

[0047] like Figure 8 As shown, the dipole acoustic logging transducer was subjected to modal analysis using finite element analysis software (COMSOL 6.1) to simulate the motion and displacement of each mode. Figure 8 (a) is a schematic diagram of the first-order vibration mode. The dipole acoustic logging transducer exhibits an arched motion. It can be seen that the middle position of the dipole acoustic logging transducer bends upward, which can radiate acoustic energy. Figure 8 (b) is a schematic diagram of the second-order vibration mode. The dipole acoustic logging transducer exhibits an S-shaped motion. It can be seen that the middle position of the dipole acoustic logging transducer is not bent. On both sides of the middle position, one side moves upward and the other side moves downward. The displacements at both ends cancel each other out, and there is no net acoustic energy radiation. Figure 8 (c) is a schematic diagram of the third-order vibration mode. The dipole acoustic logging transducer exhibits a W-shaped motion. It can be seen that the middle position of the dipole acoustic logging transducer bends upward, and the two sides with equal middle positions move downward simultaneously, which can perform net acoustic energy radiation.

[0048] Figure 9 This is a schematic diagram of the acoustic logging system provided in an embodiment of the present invention, as shown below. Figure 9 As shown, the third aspect of this embodiment also provides an acoustic logging system, including: a surface logging device and an acoustic logging instrument as described above; the acoustic logging instrument is installed downhole and is connected to the surface logging device via an armored cable.

[0049] Sonic logging systems are used for cable-guided sonic logging operations in wellbores. They can measure the shear wave velocity of formations, evaluate formation anisotropy, and can also be used for lithology identification, productivity prediction, rock mechanical property prediction, wellbore stability prediction, overpressure formation prediction, fracturing effect evaluation, pore fluid type evaluation, and formation permeability estimation.

[0050] The low-frequency monopole acoustic logging transducer provided by the present invention can cover a frequency range of approximately 750Hz to approximately 4500Hz and can effectively excite low-frequency Stoneley waves.

[0051] The low-frequency monopole acoustic logging transducer formed by a dipole triple-layer circular array structure provided in this invention greatly broadens the design ideas and bypasses the constraints of traditional methods. This allows the low-frequency monopole acoustic logging transducer to adopt more diverse structural forms and better low-frequency performance. Compared with conventional monopole acoustic logging transducers, the low-frequency monopole acoustic logging transducer with the triple-layer circular array structure has a lower frequency, greater emission energy, and wider bandwidth, and can more accurately measure formation Stoneley waves and obtain low-frequency energy information.

[0052] This invention converts the bending vibration of the dipole triple lamellar plate 1 into a unipolar breathing vibration to achieve a lower frequency.

[0053] This invention utilizes the spatial advantage of the well axis direction through a dipole triple-layer plate 1 to form a low-frequency monopole acoustic logging transducer that generates effective acoustic energy radiation. The design and development of the low-frequency monopole acoustic logging transducer using dipole vibration modes greatly broadens the design approach, bypassing the constraints of traditional methods. With more diverse structural forms and superior low-frequency performance, this invention ensures the usability of the low-frequency monopole acoustic logging transducer on existing instruments. Compared with conventional monopole acoustic logging transducers, the resulting low-frequency monopole acoustic logging transducer has a lower frequency, higher emission energy, and wider bandwidth, enabling more accurate acquisition of formation Stoneley wave information and increasing the detection depth.

[0054] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0055] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0056] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details described above. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention. Furthermore, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. As long as such combination does not violate the spirit of the embodiments of the present invention, it should also be considered as the content disclosed by the embodiments of the present invention.

Claims

1. A low-frequency monopole acoustic logging transducer, characterized in that, include: A circular skeleton and an even number of dipole triple laminations are vertically mounted on the circular skeleton in a circular array to form a cylindrical structure. The dipole triplet includes: a metal substrate, a first piezoelectric material element, and a second piezoelectric material element, wherein the first piezoelectric material element is disposed on the upper surface of the metal substrate, and the second piezoelectric material element is disposed on the lower surface of the metal substrate.

2. The low-frequency monopole acoustic logging transducer according to claim 1, characterized in that, The length of the metal substrate is greater than the length of the first piezoelectric material element and also greater than the length of the second piezoelectric material element.

3. The low-frequency monopole acoustic logging transducer according to claim 2, characterized in that, The circumferential frame includes a first mounting plate and a second mounting plate disposed opposite to each other, with a first end of the metal substrate mounted on the first mounting plate and a second end of the metal substrate mounted on the second mounting plate.

4. The low-frequency monopole acoustic logging transducer according to claim 3, characterized in that, The first mounting plate and the second mounting plate are made of metal.

5. The low-frequency monopole acoustic logging transducer according to claim 1, characterized in that, The first piezoelectric material element is bonded to the upper surface of the metal substrate by high-temperature adhesive, and the second piezoelectric material element is bonded to the lower surface of the metal substrate by high-temperature adhesive.

6. The low-frequency monopole acoustic logging transducer according to claim 1, characterized in that, The first piezoelectric material element and the second piezoelectric material element are made of the same material, and both the first piezoelectric material element and the second piezoelectric material element are piezoelectric ceramic sheets.

7. The low-frequency monopole acoustic logging transducer according to claim 6, characterized in that, The piezoelectric ceramic sheet is made of one or more of the following materials: barium titanate, lead titanate, modified lead titanate, lead zirconate titanate, modified lead zirconate titanate, and lead metaniobate.

8. The low-frequency monopole acoustic logging transducer according to claim 1, characterized in that, The fundamental vibration frequency of the low-frequency monopole acoustic logging transducer is determined by the variation in length of the first piezoelectric material element, the second piezoelectric material element, and the metal substrate.

9. A sonic logging instrument, characterized in that, include: The transmitting acoustic system section and the transmitting circuit section, wherein the transmitting acoustic system section includes the low-frequency monopole acoustic logging transducer as described in any one of claims 1-8; The transmitting circuit subsection is connected to the low-frequency monopole acoustic logging transducer and is used to provide voltage to the low-frequency monopole acoustic logging transducer, so that the low-frequency monopole acoustic logging transducer generates acoustic signals.

10. A sonic logging system, characterized in that, include: Surface logging equipment and sonic logging instrument as claimed in claim 9.

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