Piezoelectric transducer and acoustic logging while drilling equipment

Abstract

The piezoelectric transducer comprises piezoelectric ceramic, a metal substrate, an insulating layer and a sealing layer, the piezoelectric ceramic is lead zirconate titanate piezoelectric ceramic with the Curie temperature higher than 350 DEG C, the mechanical quality factor larger than 450 and the dielectric loss smaller than 0.5%, and the metal substrate is a metal substrate with the Curie temperature higher than 350 DEG C, the mechanical quality factor larger than 450 and the dielectric loss smaller than 0.5%. The outer cambered surface of the piezoelectric ceramic is fixed on the inner cambered surface of the metal substrate through an adhesive, the insulating layer wraps the outer side of an integral structure formed by bonding the piezoelectric ceramic and the metal substrate, the sealing layer wraps the outer side of the insulating layer, and the positive electrode and the negative electrode of the piezoelectric ceramic are respectively led out of the sealing layer through wires. The piezoelectric transducer meets the actual requirements of low frequency, high emission response, high temperature (150 DEG C) resistance, high pressure (140 MPa) resistance, impact resistance and vibration resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of acoustic logging while drilling, and in particular relates to a piezoelectric transducer and acoustic logging while drilling equipment. Background Art

[0002] Acoustic logging is one of the fastest growing and most widely used logging technologies in recent years. It uses acoustic wave transmitting (receiving) transducers with different spectra to purposefully excite (receive) longitudinal waves, shear waves and Stoneley waves in the formation to obtain the required physical parameters of the rock formation, thereby detecting oil and gas resources.

[0003] The latest logging technology developed in recent years - multipole acoustic logging while drilling technology, can complete the logging work while drilling, which can greatly save costs, reduce the exposure time of the formation, and is not affected by mud invasion. Therefore, the logging results obtained can be closer to the actual situation of the formation. Under geological conditions such as high-pressure formations, thin oil layers or concealed oil and gas reservoirs, logging while drilling is the only optional logging method. In international offshore drilling business, the use rate of logging while drilling has reached more than 90%, and the output value of the drilling business has accounted for more than 30% of the total logging service output value. China has also listed logging while drilling technology as one of the key technologies for future oil and gas exploration in my country.

[0004] The piezoelectric transducer used to transmit and receive sound waves is the core component of the acoustic logging instrument. It must not only meet the acoustic characteristics of acoustic logging, but also be able to work stably under high temperature and high pressure. When used in while-drilling acoustic logging instruments, piezoelectric elements must also withstand the harsh environment of strong vibration and high impact. It can be said that high-performance piezoelectric transducers are the foundation of high-end acoustic logging instruments and equipment manufacturing, and are the key to implementing "deep drilling".

[0005] In foreign countries, there are many reports on the application theory and simulation of multipole acoustic logging while drilling (LWD) transducers, but there are few reports on the structural design, materials, and preparation process of transducers. In terms of the application theory and simulation of transducers, the existing technology has established a 1:12 LWD model laboratory to study the influence of drill collar waves on formation wave judgment, and found that choosing the best working frequency is very important, especially in anisotropic formations. This method can effectively eliminate the influence of drill collar waves, and formation shear waves can be obtained regardless of whether dipoles or quadrupoles are used. The existing technology simulates the characteristics of monopoles, dipoles, and quadrupoles in LWD, and concludes that in dipole LWD with severe drill collar wave interference, the formation flexural wave velocity is very different from the shear wave velocity. Since the quadrupole wave velocity in slow formations at low frequencies is consistent with the shear wave velocity of the formation, quadrupole LWD is more suitable for determining the formation shear wave velocity. In terms of the structural design of the transducer, the prior art proposes a solution to change the frequency and radiation energy of the monopole while drilling by using different materials and different electrode methods. However, the monopole transducer in the solution is a continuous ring, and there is no mention of how to install the continuous ring on the drill collar.

[0006] In China, in recent years, a number of relevant professional research institutions and units have carried out research and development work on multipole acoustic logging while drilling, but most of the research work is based on computer simulations based on foreign research or expansion based on laboratory models.

[0007] In summary, whether it is the international research on the launch-while-drilling transducer or the domestic research on the launch-while-drilling transducer, there is currently no piezoelectric transducer that can work stably in such harsh environments as high temperature, high pressure, strong vibration, and high impact. Summary of the invention

[0008] In order to solve all or part of the above problems, the purpose of the present invention is to provide a piezoelectric transducer and while-drilling acoustic logging equipment. The piezoelectric transducer of the present invention meets the requirements of low-frequency and high-emission response, and has the advantages of high temperature resistance, high pressure resistance, impact resistance and vibration resistance.

[0009] According to one aspect of the present invention, a piezoelectric transducer is provided, comprising a piezoelectric ceramic, a metal substrate, an insulating layer and a sealing layer, wherein the piezoelectric ceramic is a lead zirconate titanate piezoelectric ceramic having a Curie temperature higher than 350°C, a mechanical quality factor greater than 450, and a dielectric loss less than 0.5%, the outer arc surface of the piezoelectric ceramic is fixed to the inner arc surface of the metal substrate by an adhesive, the insulating layer is wrapped around the outside of the overall structure formed by bonding the piezoelectric ceramic and the metal substrate, the sealing layer is wrapped around the outside of the insulating layer, and the positive and negative electrodes of the piezoelectric ceramic are respectively led out to the outside of the sealing layer by wires.

[0010] Furthermore, the cross section of the piezoelectric ceramic perpendicular to its length direction is a 1 / 4 arc ring, a semi-circular arc ring, or an arc structure surrounded by a plurality of arc rings.

[0011] Furthermore, the metal substrate is an aluminum alloy or a titanium alloy, and the thermal expansion coefficient of the aluminum alloy or the titanium alloy is equal to the thermal expansion coefficient of the piezoelectric ceramic.

[0012] Furthermore, the thermal expansion coefficient of the metal substrate is controlled within a range of 6.0×10-6 / °C to 23.0×10-6 / °C.

[0013] Furthermore, the resonance frequency of the overall structure formed by bonding the piezoelectric ceramic and the metal substrate is below 5 kHz.

[0014] Furthermore, the adhesive needs to meet the following requirements: glass transition temperature ≥ 120° C., thermal shrinkage ≤ 0.5%.

[0015] Furthermore, the thickness of the insulating layer is 1.5 mm to 2 mm, and the insulating layer is formed by epoxy resin sprayed on the outer side of the integral structure formed after the piezoelectric ceramic and the metal substrate are bonded, or a polyimide insulating film is bonded.

[0016] Furthermore, the sealing layer is formed by pouring epoxy resin and / or vulcanized rubber on the outside of the insulating layer, and during the pouring of the epoxy resin, bubbles therein are removed by vacuuming, the viscosity of the epoxy resin is less than or equal to 6000mPa·s, and the vulcanized rubber is fluororubber.

[0017] Furthermore, the cross section of the piezoelectric transducer perpendicular to its length direction is an arc ring, and the piezoelectric transducer is a while-drilling quadrupole transmitting transducer or a while-drilling monopole transmitting transducer.

[0018] The present invention also provides a while-drilling acoustic logging equipment, comprising any one of the piezoelectric transducers described above.

[0019] It can be seen from the above technical solution that the piezoelectric transducer and the acoustic logging while drilling equipment provided by the present invention have the following beneficial effects:

[0020] The piezoelectric transducer of the present invention meets the requirements of low-frequency high-emission response;

[0021] The piezoelectric transducer of the present invention has the advantages of high temperature resistance (150° C.), high pressure resistance (140 MPa), impact resistance and vibration resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic structural diagram of a piezoelectric transducer according to an embodiment of the present invention;

[0023] Figure 2 A schematic diagram of a piezoelectric ceramic used in a piezoelectric transducer according to an embodiment of the present invention;

[0024] Figure 3 A schematic diagram of another piezoelectric ceramic used in a piezoelectric transducer according to an embodiment of the present invention;

[0025] Figure 4 is a schematic diagram of a third piezoelectric ceramic used in a piezoelectric transducer according to an embodiment of the present invention;

[0026] Figure 5 The impedance characteristic spectrum of the while-drilling quadrupole transmitting transducer obtained by using the piezoelectric transducer of the embodiment of the present invention;

[0027] Figure 6 The figure is a transmission voltage response curve of the while-drilling quadrupole transmitting transducer obtained by using the piezoelectric transducer according to the embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to better understand the purpose, structure and function of the present invention, a piezoelectric transducer and a while drilling acoustic logging equipment of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0029] like Figure 1 As shown, a piezoelectric transducer according to an embodiment of the present invention is shown, comprising a piezoelectric ceramic 1, a metal substrate 2, an adhesive layer 3 formed by an adhesive, an insulating layer 4 and a sealing layer 5.

[0030] The piezoelectric ceramic 1 is a lead zirconate titanate (PZT) piezoelectric ceramic with a Curie temperature higher than 350°C, a mechanical quality factor greater than 450, and a dielectric loss less than 0.5%. The inner and outer diameters and height of the piezoelectric ceramic are determined by the installation dimensions of the test piece or the fixture and the operating frequency of the transducer. The cross section of the piezoelectric ceramic perpendicular to its length direction can be a 1 / 4 arc ring, such as Figure 2 As shown; it can also be a semicircular arc ring, such as Figure 3 As shown; it can also be an arc structure with a larger arc length surrounded by a number of arc rings with smaller arc lengths, such as Figure 4 shown.

[0031] The outer arc surface of the piezoelectric ceramic 1 is fixed to the inner arc surface of the metal substrate 2 by an adhesive, and the positive and negative electrodes of the piezoelectric ceramic are led out to the outside of the outermost sealing layer by high-temperature and high-voltage resistant wires. Specifically, the outer arc surface of the piezoelectric ceramic corresponds to the negative electrode of the piezoelectric ceramic, that is, the negative electrode of the piezoelectric ceramic is fixed to the inner arc surface of the metal substrate by an adhesive.

[0032] The metal substrate 2 is an aluminum alloy or a titanium alloy, and the thermal expansion coefficient of the aluminum alloy or the titanium alloy is equal to the thermal expansion coefficient of the piezoelectric ceramic; or the thermal expansion coefficient of the metal substrate 2 is controlled between 6.0×10-6 / °C and 23.0×10-6 / °C. The outer diameter and height of the metal substrate are determined by the inner diameter and height of the piezoelectric ceramic, and the thickness of the metal substrate is determined by the resonant frequency of the piezoelectric transducer.

[0033] The resonant frequency of the overall structure formed after the piezoelectric ceramics and the metal substrate are bonded is below 5kHz to meet the practical application needs of obtaining high emission response at low frequencies. The adhesive used for bonding the piezoelectric ceramics and the metal substrate is a high-temperature adhesive, which needs to meet the requirements of glass transition temperature Tg ≥ 120°C and thermal shrinkage rate ≤ 0.5%. The piezoelectric ceramics are bonded to the inner arc surface of the metal substrate, and the arc end, height positioning and thickness of the adhesive layer are controlled by specially designed positioning and pressing tools. When the high-temperature adhesive is cured, it strictly follows the slow heating and cooling mechanism to prevent the various parts of the transducer from expanding and contracting too quickly, resulting in the inability to release stress and causing the piezoelectric ceramics to be cracked. After the high-temperature adhesive is cured, it forms the following Figure 1 Adhesive layer 3.

[0034] In order to prevent the positive and negative poles of the piezoelectric ceramic from short-circuiting and discharging under high voltage, an insulating layer is wrapped around the outside of the overall structure formed by the piezoelectric ceramic and the metal substrate. The thickness of the insulating layer is 1.5 mm to 2 mm. The insulating layer is formed by an epoxy resin with good insulation sprayed on the outside of the overall structure formed after the piezoelectric ceramic and the metal substrate are bonded, or a polyimide insulating film is bonded. In specific implementation, the epoxy resin is, for example, a high-temperature epoxy resin.

[0035] In order to ensure the water tightness of the transducer and meet the requirements of anti-vibration, anti-impact and anti-corrosion working conditions, it is also necessary to wrap a sealing layer on the outside of the insulating layer. The sealing layer is formed by pouring epoxy resin and / or vulcanized rubber on the outside of the insulating layer; in specific implementation, for example, high-temperature epoxy resin is poured on the outside of the insulating layer to form a sealing layer, for example, vulcanized rubber is poured on the outside of the insulating layer to form a sealing layer, and for example, high-temperature epoxy resin is first poured on the outside of the insulating layer and then vulcanized rubber is poured to form a sealing layer. Among them, the pouring of epoxy resin needs to remove the bubbles therein by vacuuming. In order to ensure thorough vacuum degassing, the viscosity of the high-temperature epoxy resin is required to be below 6000mPa·s; the vulcanized rubber adopts corrosion-resistant and high-temperature resistant fluororubber.

[0036] The cross section of the piezoelectric transducer of the embodiment of the present invention perpendicular to its length direction is an arc ring, such as Figure 1 And the aforementioned piezoelectric transducer can be a while-drilling quadrupole transmitting transducer or a while-drilling monopole transmitting transducer used in the while-drilling logging.

[0037] The piezoelectric transducer of the embodiment of the present invention meets the practical needs of low-frequency high-transmission response, high temperature resistance (150° C.), high pressure resistance (140 MPa), impact resistance, and vibration resistance.

[0038] The piezoelectric transducer of the embodiment of the present invention is further explained below by taking a while-drilling quadrupole transmitting transducer as an example.

[0039] It also consists of piezoelectric ceramics, metal substrate, adhesive layer 3 formed by adhesive, insulating layer and sealing layer. The index parameters of piezoelectric ceramics are: Curie temperature higher than 350℃, mechanical quality factor greater than 450, dielectric loss less than 0.5%. The piezoelectric ceramics used are as follows Figure 2 The 1 / 4 arc ring shown, the positive and negative electrodes of the piezoelectric ceramic are led out with high temperature and high voltage wires, and are cleaned and degreased for use. The metal substrate is processed into a 1 / 4 arc ring that matches the arc of the piezoelectric ceramic using a titanium alloy with a thermal expansion coefficient close to that of the piezoelectric ceramic. The bonding surface is roughened by a mechanical method and cleaned and degreased for use. The piezoelectric ceramic and the metal substrate are bonded together with a high-temperature adhesive to form a bending vibration transducer with a resonant frequency below 5KHz. The high-temperature adhesive requires a glass transition temperature Tg ≥ 120°C and a thermal shrinkage rate ≤ 0.5%. The piezoelectric ceramic is bonded to the inner arc of the metal substrate. The arc end, the height direction positioning and the thickness of the adhesive layer are controlled by a specially designed positioning and pressing tool. When the high-temperature adhesive is cured, it is strictly in accordance with the slow heating and slow cooling mechanism to prevent the various parts of the transducer from expanding and contracting too quickly, and the stress cannot be released, causing the piezoelectric ceramic to be cracked. After the high-temperature bonding is completed, a high-temperature epoxy resin with good insulation properties is evenly sprayed on the outside of the bending vibration transducer to form an insulating layer to prevent short circuits between the positive and negative electrodes and discharge under high voltage. After the insulating layer 4 is completed, in order to ensure the water tightness of the transducer and meet the requirements of anti-vibration, anti-impact, and anti-corrosion working conditions, a high-temperature epoxy resin is poured outside the insulating layer 4, and the bubbles in the sealing layer are removed by vacuuming. To ensure that the vacuum is completely removed, the viscosity of the high-temperature epoxy is required to be below 6000mPa·s. After the epoxy resin is poured, a pre-designed mold is used on the outside to uniformly vulcanize a layer of fluororubber by high temperature and high pressure to form a sealing layer 5 composed of a combination of high-temperature epoxy resin rubber and vulcanized rubber.

[0040] The impedance characteristic experiment was carried out using the while drilling quadrupole transmitting transducer according to the embodiment of the present invention, and the impedance characteristic spectrum obtained is as follows: Figure 5 As shown, from Figure 5 It can be seen that the quadrupole transmitting transducer while drilling in the embodiment of the present invention has a conductivity response at 1.9 kHz in addition to the conductivity response at 11.4 kHz and 15.9 kHz, and according to Figure 5It can be seen that the conductance of the while drilling quadrupole transmitting transducer of the embodiment of the present invention at 11.4kHz is 1.27mS (milliSiemens), the conductance of the while drilling quadrupole transmitting transducer of the embodiment of the present invention at 15.9kHz is 6.62mS (milliSiemens), and the conductance of the while drilling quadrupole transmitting transducer of the embodiment of the present invention at 1.9kHz is 73.2μS (microSiemens).

[0041] The transmitting voltage response experiment was carried out using the while drilling quadrupole transmitting transducer according to the embodiment of the present invention, and the obtained transmitting voltage response curve is as follows: Figure 6 As shown, from Figure 6 It can be seen that the while drilling quadrupole transmitting transducer of the embodiment of the present invention generates a bending vibration mode near 2 kHz, and the transmitting voltage response near 3 kHz is greater than 104 dB.

[0042] Combination Figure 5 and Figure 6 Description: The while-drilling quadrupole transmitting transducer of the embodiment of the present invention meets the requirements of low-frequency high transmitting response.

[0043] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0044] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A piezoelectric transducer, characterized in that: It includes a piezoelectric ceramic, a metal substrate, an insulating layer and a sealing layer, wherein the piezoelectric ceramic is a lead zirconate titanate piezoelectric ceramic with a Curie temperature higher than 350°C, a mechanical quality factor greater than 450, and a dielectric loss less than 0.5%. The outer arc surface of the piezoelectric ceramic is fixed to the inner arc surface of the metal substrate by an adhesive, the insulating layer is wrapped around the outer side of the overall structure formed by bonding the piezoelectric ceramic and the metal substrate, the sealing layer is wrapped around the outer side of the insulating layer, and the positive and negative electrodes of the piezoelectric ceramic are respectively led out to the outside of the sealing layer by wires.

2. The piezoelectric transducer according to claim 1, characterized in that: The cross section of the piezoelectric ceramic perpendicular to its length direction is a 1 / 4 arc ring, a semi-circular arc ring, or an arc structure surrounded by a plurality of arc rings.

3. The piezoelectric transducer according to claim 1, characterized in that: The metal substrate is an aluminum alloy or a titanium alloy, and the thermal expansion coefficient of the aluminum alloy or the titanium alloy is equal to the thermal expansion coefficient of the piezoelectric ceramic.

4. The piezoelectric transducer according to claim 1, characterized in that: The thermal expansion coefficient of the metal substrate is controlled within a range of 6.0×10-6 / °C to 23.0×10-6 / °C.

5. The piezoelectric transducer according to claim 1, characterized in that: The resonance frequency of the overall structure formed by bonding the piezoelectric ceramic and the metal substrate is below 5 kHz.

6. The piezoelectric transducer according to claim 1, characterized in that: The adhesive needs to meet the following requirements: glass transition temperature ≥ 120° C., and thermal shrinkage ≤ 0.5%.

7. The piezoelectric transducer according to claim 1, characterized in that: The thickness of the insulating layer is 1.5 mm to 2 mm, and the insulating layer is formed by epoxy resin sprayed on the outer side of the integral structure formed after the piezoelectric ceramic and the metal substrate are bonded together, or by a polyimide insulating film bonded thereto.

8. The piezoelectric transducer according to claim 1, characterized in that: The sealing layer is formed by pouring epoxy resin and / or vulcanized rubber on the outside of the insulating layer, and during the pouring of the epoxy resin, bubbles therein are removed by vacuuming. The viscosity of the epoxy resin is less than or equal to 6000 mPa·s, and the vulcanized rubber is fluororubber.

9. The piezoelectric transducer according to claim 1, characterized in that: The cross section of the piezoelectric transducer perpendicular to its length direction is an arc ring, and the piezoelectric transducer is a while-drilling quadrupole transmitting transducer or a while-drilling monopole transmitting transducer.

10. A while drilling acoustic logging equipment, characterized in that: A piezoelectric transducer comprising any one of claims 1 to 9.

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