Acoustic transducer with trapezoidal irregularly spaced or widened transducer elements

Abstract

A downhole acoustic measurement tool includes a transducer operable to transmit and / or receive an acoustic signal to perform a downhole measurement. The transducer includes a plurality of piezoelectric elements. Each piezoelectric element may have a first axial end and a second axial end, and the second axial end may be wider than the first axial end in a direction along a circumference of the transducer. The piezoelectric elements may be irregularly spaced azimuthally around one or more portions of a circumference of the transducer. The piezoelectric elements are spaced apart not more than a distance defined by W1 * f1 / FUL, where FUL is the upper limit of the frequency band of interest, W1 is the width of the inter-transducer element spacing that produces a parasitic mode at frequency f1.

Description

Background Art

[0001] Acoustic downhole imaging tools are used in oil and gas exploration and production (E&P) in both cased and uncased ("open hole") wellbores. For example, when used in a cased wellbore, such acoustic imaging is performed to inspect the casing and the cement that holds the casing in the wellbore. When used in an open wellbore, acoustic imaging can be performed to obtain an image of the wellbore surface, such as to identify cavities, fractures, textures, and acoustic properties of the subsurface formations penetrated by the wellbore. Summary of the invention

[0002] This Summary is provided to introduce a series of concepts that will be further described in the Detailed Description below. This Summary is neither intended to identify essential features of the claimed subject matter nor to be used to help limit the scope of the claimed subject matter.

[0003] The present disclosure introduces an apparatus including a downhole acoustic measurement tool with a transducer. The transducer is operable to transmit and / or receive acoustic signals for downhole measurement. The transducer includes piezoelectric elements, each of which has a first axial end and a second axial end. The second axial end is wider than the first axial end in a direction along the circumference of the transducer.

[0004] The present disclosure also introduces an apparatus, the apparatus comprising a downhole acoustic measurement tool, the downhole acoustic measurement tool comprising a transducer operable to transmit and / or receive acoustic signals to perform downhole measurements. The transducer comprises piezoelectric elements that are irregularly spaced (pitched) in azimuth around one or more portions of the circumference of the transducer.

[0005] The present disclosure also introduces an apparatus, the apparatus comprising a downhole acoustic measurement tool, the downhole acoustic measurement tool comprising a transducer operable to transmit and / or receive acoustic signals to perform downhole measurements. The transducer comprises a piezoelectric element separated at a controlled distance by a spacer made of an electrically insulating and mechanically compliant material (e.g., a resin or an elastomer or a composite thereof).

[0006] These and other aspects of the present disclosure are set forth in the following description and / or may be learned by one of ordinary skill in the art by reading the materials herein and / or practicing the principles described herein.At least some aspects of the present disclosure may be realized by the methods recited in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present disclosure can be understood when the following detailed description is read in conjunction with the accompanying drawings. It should be emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, for the sake of clarity of discussion, the size of various features may be arbitrarily increased or reduced.

[0008] Figure 1 is a schematic diagram of at least a portion of an exemplary embodiment of an apparatus according to one or more aspects of the present disclosure.

[0009] Figure 2 yes Figure 1 A perspective view of an exemplary embodiment of a portion of a device is shown in FIG.

[0010] Figure 3 yes Figure 2 A perspective view of another exemplary embodiment of the device shown in FIG.

[0011] Figure 4 and Figure 5 are diagrams depicting one or more aspects of the disclosure.

[0012] Figure 6 yes Figure 3 An expanded view of an exemplary embodiment of a portion of the device shown in FIG.

[0013] Figure 7 yes Figure 6 End view of the device shown in .

[0014] Fig. 8A yes Figure 6 An expanded view of another exemplary embodiment of the device shown in FIG.

[0015] Figure 8B yes Fig. 8A A general matrix array shape of an implementation of the transducer in FIG.

[0016] Fig. 9 are diagrams depicting one or more aspects of the disclosure.

[0017] Fig.10 yes Figure 6 A perspective view of an exemplary embodiment of the device shown in FIG.

[0018] Fig.11 yes Fig.10 A perspective view of another exemplary embodiment of the device shown in FIG.

[0019] Fig.12 yes Fig.10 A perspective view of another exemplary embodiment of the device shown in FIG. DETAILED DESCRIPTION

[0020] It should be understood that the following disclosure provides many different embodiments or examples for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. Of course, these are merely examples and are not intended to be limiting. In addition, the present disclosure may repeat figure numerals and / or letters in various examples. This repetition is for simplicity and clarity purposes, and does not itself determine the relationship between the various embodiments and / or configurations discussed. In addition, in the following description, the description of the first feature contacting the second feature may include an embodiment in which the first feature and the second feature are in direct contact, and may also include an embodiment in which an additional feature may be inserted between the first feature and the second feature so that the first feature and the second feature may not be in direct contact.

[0021] Figure 1 is a schematic diagram of at least a portion of an exemplary embodiment of a wellsite system 100 to which one or more aspects of the present disclosure may be applied. The wellsite system 100 may be onshore (as depicted) or offshore. Figure 1 In the exemplary wellsite system 100 shown in FIG. 1 , a downhole tool string 104 is conveyed in a wellbore 108 via a wireline, a slickline, and / or other conveying device 112. The exemplary wellsite system 100 may be used to evaluate the wellbore 108, cement 116 securing a casing 120 within the wellbore 108, tubulars (not shown) secured within the casing 120 (e.g., production service pipe), and / or a subterranean formation 124 penetrated by the wellbore 108 at a casing section 150 and / or an open hole section 155. Although Figure 1 The majority of the wellbore 108 depicted in FIG. 1 is depicted as being cased, but a majority of the wellbore may be uncased (“open hole,” without casing 120 and cement 116 ).

[0022] The tool string 104 is suspended in the wellbore 108 from the lower end of the conveying device 112. The conveying device 112 may be a single-core or multi-core steel wire or wireline logging cable wound on a drum 113 of a drawworks 115 at a surface 128 of a wellsite from which the wellbore 108 extends. The wellsite surface 128 is a generally planar terrain surface (i.e., the surface of the earth), a drilling rig platform (not shown) at the wellsite, or other equipment at the wellsite that is vertically penetrated by the wellbore 108. Operation of the drawworks 115 rotates the drum 113 to reel in the conveying device 112 and thereby pull the tool string 104 in the uphole direction 101 in the wellbore 108, and to unroll the conveying device 112 and thereby move the tool string 104 in the downhole direction 102 in the wellbore 108. The transport device 112 may include at least one or more conductors (not shown) that facilitate data communication between the downhole tool string 104 and the surface equipment 132 disposed at the surface 128 of the well site, including by electrically connecting the one or more conductors of the transport device 112 to the surface equipment 132 through one or more slip rings, cables, and / or (in Figure 1 The conveyor 112 may alternatively transport the downhole tool string without the conductors inside the cable but with at least one module that can autonomously acquire and / or process downhole measurements and / or store downhole measurements in a downhole memory without human intervention or communication with the surface equipment 132.

[0023] Despite Figure 1 It is not shown like this in the figure, but the winch 115 can be set on the service vehicle or fixed slide rail / platform. The service vehicle or fixed slide rail / platform can also contain at least a part of the ground equipment 132.

[0024] The downhole tool string 104 includes a plurality of modules 136, one or more of which may include an elongated housing, mandrel, chassis, and / or structure that carries various electronic and / or mechanical components. For example, at least one module 136 may be or include at least a portion of an apparatus for measuring characteristics and / or properties of the wellbore 108, casing 120, tubulars (not shown) installed in the casing 120, cement 116, and / or formation 124, and / or at least a portion of an apparatus for obtaining sidewall or inline core and / or fluid (liquid and / or gas) samples from the wellbore 108 and / or formation 124. Figure 1 While not including the exemplary embodiment depicted in FIG. 1 , other embodiments of the downhole tool string 104 within the scope of the present disclosure may include additional or fewer components or modules 136 .

[0025] The wellsite system 100 also includes a data processing system, which may include at least a portion of one or more of the surface equipment 132, control devices and / or other electrical and / or mechanical devices (such as a downhole controller 140) in one or more of the modules 136 of the downhole instrument string 104, a remote computer system (not shown), communication equipment, and / or other equipment. The data processing system may include one or more computer systems or devices and / or may be a distributed computer system. For example, the collected data or information may be stored, distributed, communicated to human wellsite operators, and / or processed locally (downhole or on the surface) and / or remotely.

[0026] The data processing system may perform the methods and / or processes described below, or portions thereof, alone or in combination with other system components. For example, according to one or more aspects of the present disclosure, the data processing system may include processor capabilities for collecting caliper, acoustic, ultrasonic, and / or other data associated with the evaluation of cement 116, casing 120, tubulars (not shown) installed in casing 120, and / or formation 124. The methods and / or processes within the scope of the present disclosure may be implemented by one or more computer programs running in a processor located in, for example, one or more modules 136 of the downhole tool string 104 and / or the surface equipment 132. Such a program may utilize data received from the downhole controller 140 and / or other modules 136 and may transmit control signals to operating elements of the downhole tool string 104, wherein such communication may be performed through one or more electrical conductors or optical conductors of the conveyor 112. The program may be stored on a tangible, non-transitory computer-usable storage medium associated with one or more processors of the downhole controller 140, other modules 136 of the downhole tool string 104, and / or the surface equipment 132, or may be stored on an external tangible, non-transitory computer-usable storage medium electrically coupled to such a processor. The storage medium may be one or more known or future developed storage media, such as a magnetic disk, an optically readable disk, a flash memory, or another computer-readable device, including a remote storage device coupled via one or more wired and / or wireless communication links, as well as other examples.

[0027] like Figure 1 At least one of the modules 136, as indicated by reference numeral 138, may be or include a downhole acoustic measurement tool operable to obtain acoustic measurements characterizing the wellbore 108, the casing 120, a tubular (not shown) installed in the casing 120, the cement 116, and / or the formation 124. The downhole acoustic measurement tool 138 includes a phased array module 139 of acoustic transducers ("active elements"), each of which may operate as an acoustic transmitter and / or receiver. Exemplary embodiments of the downhole acoustic measurement tool 138 within the scope of the present disclosure are described below.

[0028] like Figure 1 As indicated by reference numeral 142, another (or more) of the modules 136 may be or include an orientation module that allows for measuring the azimuth of the downhole acoustic measurement tool 138. Such a module 142 may include, for example, one or more of a relative bearing (RB) sensor or a gravity / acceleration sensor, a magnetometer, and a gyroscope sensor.

[0029] like Figure 1 As indicated by reference numeral 146 in the figure, another (or more) of the modules 136 may be or include a centralizer module. For example, the centralizer module 146 includes an electric motor driven by a controller (also not shown) and / or other means for actively extending (“opening”) and retracting (“closing”) the plurality of centralizing arms 147. Although in Figure 1 Only two centralizing arms 147 are depicted in the exemplary embodiment shown in , but other embodiments within the scope of the present disclosure may have more than two centralizing arms 147. Extension of the centralizing arms 147 helps push the downhole acoustic measurement tool 138 to a central location within the casing 120, another tubular, or the wellbore 108 being investigated by the downhole acoustic measurement tool 138. Embodiments of a downhole tool string within the scope of the present disclosure may include more than one instance of the downhole acoustic measurement tool 138 and / or more than one instance of the centralizer module 146. The module 136 may be delivered in either or both of the open hole section 150 and the cased wellbore section 155, including embodiments in which the centralizer module 146 and the phased array module 138 may be configured or configurable for use in either or both of the two sections. The downhole tool string 104 may also not include the centralizer module 146, or may include another type of centralizer module, such as a passive centralizer module.

[0030] Figure 2 is a perspective view of at least a portion of an example implementation of an active element 202 of a phased array 200 as part of an acoustic measurement tool 138 according to one or more aspects of the present disclosure. The phased array 200 is Figure 1 An exemplary implementation of the phased array module 139 is shown in FIG. The phased array 200 allows azimuthal measurements relative to the wellbore to be obtained, possibly without mechanical rotation of the downhole acoustic measurement tool 138 .

[0031] Figure 2The exemplary phased array 200 depicted in FIG. 1 includes active elements 202 arranged in one or more rows 204 and a plurality of columns 206 extending about a central axis 208. However, embodiments of the phased array 200 and other phased arrays within the scope of the present disclosure may include a different number (including one) of rows 204 and / or columns 206. The phased array 200 may be configured such that the transducer elements 202 are collectively arranged in azimuth around a substantial portion (e.g., greater than 50%) of the tool (perhaps the entire periphery of the tool), such as Figure 2 However, the phased array 200 may include one or more segments 210 composed of a plurality of elements 202, such as Figure 3 . The number of azimuthal and axial elements 202 shown in one segment 210 is the same as an example. Other embodiments with different numbers of elements 202 in the azimuthal and axial directions are also within the scope of the present disclosure. The phased array 201 can be composed of multiple segments 210 including different numbers of elements, which is also within the scope of the present disclosure. The minimum number of elements 202 in a segment 210 is 1 in a direction orthogonal to the azimuthal or axial phased array. The segments 210 can also be adjacent to each other, but they can also be spaced apart in the azimuthal and / or axial directions and have overlapping or non-overlapping elements in the axial or azimuthal directions, respectively. The shape of the segment 210 is not necessarily as shown. Figure 3 The circumferential rectangle shown.

[0032] The active portion of the acoustic transducer is composed of a piezoelectric material. The shape of this piezoelectric element determines the characteristics of the transducer in transmitting and receiving signals. However, in addition to the intended signal, the element may also generate parasitic signals that may be inherent to the shape of the element. These parasitic signals may hinder the application of the transducer. Other potential parasitic signals may originate from the characteristics of the phased array 200 or the segment 210 of which the piezoelectric element may be a part, or from the characteristics of the general 3D structure of the phased array or segment, as described later in Fig.10 as shown in .

[0033] In the application of casing thickness and annulus impedance measurement for well integrity assessment, the frequency content of the signal from the transducer is preferably broadband and stable over a predefined frequency range. The piezoelectric elements are designed so that their transmit and receive signal sensitivity increases over a predefined frequency range due to their thickness mode resonance. To achieve such efficient transmission and reception, the thickness of each element is preferably close to half the wavelength of the acoustic wave in the thickness direction near the casing thickness resonance frequency.

[0034] The other dimensions of the elements are determined by the desired spatial resolution, signal strength, and / or available space for the transducer and / or the number of drive circuit switches and connectors available in the acoustic measurement tool 139. In a multi-element phased array transducer, a certain number of elements are required and their relative spacing (pitch) is determined by acoustics. These "secondary" primary dimensions, combined with the material properties of the piezoelectric elements, may excite unwanted signals at frequencies within the bandwidth of interest, and this may cause problems in reversing the signals from the sleeve 120 or another tubular 108 when the frequency bands of the signals from the sleeve or the other tubular 108 are substantially close to each other. The present disclosure introduces aspects that can be used to mitigate parasitic modes.

[0035] Figure 4 is a graph showing electrical impedance curves 300 resulting from numerical simulations of rectangular piezoelectric elements (or strips) in which only thickness modes are allowed to exist. Each curve corresponds to an impedance curve of different widths (ww) in increments of 11% of a minimum width 301. The impedance curve 300 varies from a minimum width 301 to a maximum width 302. The resulting impedance plot 300 confirms the idealized response, showing only resonant and anti-resonant peaks associated with thickness resonances over the measurement frequency band of interest, and no apparent change in the shape of the impedance curve with the width of the element, except for a vertical shift caused by an increase in capacitance proportional to the width of the element.

[0036] Figure 5 is a graph depicting an impedance curve 303 obtained from a similar numerical simulation, which also allows for the presence of resonant modes in a "secondary" fundamental dimension, i.e. the width of the element. Parasitic modes 306, 308 are present, particularly in sub-frequency ranges 307, 309 of the frequency range of interest 310. A wider element may reduce the amplitude of one parasitic contribution, for example, a parasitic resonance present in sub-frequency range 307 may be reduced by reducing the width of the element, however, higher order parasitic modes in another sub-frequency band 309 are still present and in these examples are shifted to frequencies closer to the center of the frequency range of interest 306.

[0037] Figure 6 An exemplary embodiment of a multi-element transducer 400 according to one or more aspects of the present disclosure is depicted. The transducer 400 is similar in shape and function to the Figure 3 4. The transducer 400 may be a multi-element rectangular transducer. However, instead of rows 204 and columns 206 of active elements 202, the transducer 210 is presented as multiple columns 406 and a single row 404, which is not limited to having multiple rows along the axial length 408, as in the case of a matrix array. Figure 6 Transducer 400 is depicted unfolded and lying flat on the surface of the page. Figure 74 is an end view of transducer 400, which depicts element 402 as a member extending from backing 406. Thickness 410 is set so that the element excites its thickness mode resonance within a predetermined frequency range. Between element 402 and backing 406, there may be an interface layer 415 composed of one or more materials. The material of the interface layer is, for example, a piezoelectric layer, an electrical conductor, or an acoustic impedance matching layer. The space 418 between piezoelectric elements 402 is an inter-element portion filled with a filler having more compliant mechanical properties than piezoelectric elements 402.

[0038] Under the constraint that the total number of column elements 406 is fixed, parasitic modes can be reduced by slightly tapering the rectangular elements 402, such as Fig. 8A 4. The transducer 420 may be a multi-element rectangular transducer. Again, only a single row is depicted, which is not limited to having multiple rows along the axial length 442 in the direction 440, as is the case with a matrix array. Figure 8B shows the general matrix array shape. Parasitic modes can be eliminated and effectively destroyed, such as Fig. 9 The impedance curve 304 in FIG. 4 is shown in FIG. 4 . In this particular example, the transducer 420 may have Figure 3 The rectangular shape of the segment 210 and the rectangular shapes of all components are shown in FIG.

[0039] In other words, each piezoelectric element 422 of transducer 420 has a first axial end 424 and a second axial end 426, wherein the second axial end 426 is wider than the first axial end 424 in a direction 421 along the circumference of transducer 420 (e.g., across the page in FIG. 8 ). Figure 3 2. The representation of the transducer segments 210 depicted in 2 is used to achieve a rectangular profile. Other basic patterns are also within the scope of the present disclosure, such as patterns that result in non-rectangular profiles. Fig. 9 The impedance curves depicted in FIG. 5 are numerical simulations for different values ​​of a parameter “pp”, which is the difference between the first axial end 424 and the second axial end 426, varying from a minimum pp value of 0 to a maximum value of 66% in increments of 22%, as an example. Fig. 9 The corresponding four impedance curves 430, 431, 432, and 433 are given in the order of pp values. Fig. 9 The impedance curves shown in show that by such reshaping of element 422, the amplitude of the parasitic mode is greatly reduced, comparing the two curves (432, 433) at pp values ​​of 44% and 66% respectively with curve 430 at pp value of 0%.

[0040] The piezoelectric elements 422 may be positioned azimuthally around one or more portions of the circumference of the transducer, similar to Figure 3The piezoelectric elements 422 may also be distributed azimuthally around the entire circumference of the tool, similar to Figure 2 As shown.

[0041] Each piezoelectric element 422 may be elongated in a direction 440 that is parallel to the longitudinal axis of the downhole acoustic measurement tool 138 and / or the central axis 208 of the transducer 420. The axial length 442 of each piezoelectric element 422 may be greater than the average width of the first axial end 424 and the second axial end 426 by a certain multiple. For example, each first axial end 424 may have a width 444 of 50%, and each second axial end 426 may have a width 446 of 150%, such that the average width of each element 422 is 100%. The foregoing dimensions are merely examples, and other dimensions are also within the scope of the present disclosure, such as when combining a trapezoidal shape with the random basic widths presented below, pairs of basic widths that do not average 100% are also within the scope of the present disclosure.

[0042] In this particular example, each adjacent pair of piezoelectric elements 422 includes a first piezoelectric element 422a and a second piezoelectric element 422b such that a first axial end 424 of each first piezoelectric element 422a is located at an upper end 448 of the transducer 420, and a first axial end 424 of each second piezoelectric element 422b is located at a lower end 450 of the transducer 420. Additionally, in this particular example, each piezoelectric element 422 includes a radially outer edge 452 extending parallel to the longitudinal axis 208 of the transducer 420. Thus, the radially outward surface of each piezoelectric element 422 may form a right-angled trapezoid. Other embodiments having non-parallel edges or inconsistent upper and lower transducer ends are also within the scope of the present disclosure.

[0043] When inspecting casing or production tubing using an acoustic (e.g., ultrasonic) phased array transducer set in the circumference of a cylindrical tool, the phased array elements can be excited in different holes and then several types of measurements can be combined. The piezoelectric element is excited across its thickness to produce the expected signal. By cutting this active area into sub-elements or segments consisting of at least one element, parasitic modes occur in dimensions other than thickness, such as width, in other words, tool circumference or lateral direction. In general, the modes caused by the width of the element may interfere with the modes related to its thickness. This can be addressed by one or more of the aspects described above.

[0044] Other unintended modes are also associated with the modes of the array that are periodic and exhibit interference in addition to that due to the lateral modes of a single element. Such unintended modes may be associated with Lamb and leakage modes (or interface modes) that propagate laterally along the periodic phased array and interface with the well fluid. The characteristic propagation velocity and energy are modulated by the periodicity of the phased array. Such modes may be transmitted into the fluid due to mode conversion at the piezoelectric and inter-element boundaries due to acoustic impedance discontinuities and may degrade the phased array signal used for resonant target characterization, such as downhole cement evaluation applications using casing resonance analysis, as described in U.S. Patent No. 5,216,638. The following description relates to aspects of reducing the effects of such interference by adding "alea," which is defined as a "randomness" or "disturbance" of the spacing and is intended to break the periodicity of the array.

[0045] It is well known that Lamb modes exist in parts with planar or cylindrical plate geometries. These can be symmetric or antisymmetric.

[0046] Fig.10 is similar to Figure 6 and Figure 7 4 is a perspective view of a portion of transducer 500 of transducer 400 shown in FIG. Transducer 500 has a periodic structure in which rectangular piezoelectric elements 502 each have a constant width 504 and thickness 506. Elements 502 are arranged at a constant interval 508. Elements 502 extend from a backing 512. Between elements 502 and backing 512, there may be an interface layer 515 composed of one or more materials.

[0047] The measurement of radial displacement 516 at the front face 514 of the element array 502 shows the deformation of the array when the elements are excited, and shows that this deformation is related to the pattern of spacing 508. Since this pattern is perfectly periodic, very sharp interference may appear in the frequency range 310. This can be solved by modifying the spacing 508 by introducing an "alea" (defined as a small fraction of the spacing, preferably on the order of a few percent to a few tens of percent), which is randomly or deterministically distributed between the elements 502 while maintaining the average spacing 508 in the array. The displacement 516 depicted is only an example and can be determined by the lower limit F and the lower limit F, respectively. LL and upper limit F UL The defined frequency range of interest 310 varies.

[0048] Fig.11An exemplary embodiment of such a transducer 520 is shown, where two elements 502 have 100% of the original rectangular element width 504, two elements 522 have a width of approximately 78% of the original width 504, two elements 524 have a width of approximately 122% of the original width 504, one element 526 has a width of 61% of the original width 504, and one element 528 has a width of 139% of the original width 504. The spacing between each adjacent element remains the same as Fig.10 in. In addition, the average spacing 508 and width 504 of the elements of the array remain the same as Fig.10 shown for the transducer 500.

[0049] The purpose is to randomize the structure or distribute it in a different way to minimize the excitation pattern associated with a periodic array. Since the spacing is no longer aligned with the deformed profile of the Lamb mode, the resulting sharp interference peaks (appearing similar to peaks 434, 436 in sub-frequency ranges 407, 409 for example) will be distributed over a wider band in the spectrum, and thus their impact will be greatly reduced, similar to Fig. 9 the impact on the impedance curve presented in.

[0050] The piezoelectric elements 502, 522, 524, 526, 528 can be irregularly spaced azimuthally around one or more portions of the circumference of the tool, similar to Figure 3 shown, or irregularly spaced completely around the circumference of the tool, similar to Figure 2 shown. The axial length of each piezoelectric element 502, 522, 524, 526, 528 can be a certain multiple larger than the average width of the piezoelectric elements 502, 522, 524, 526, 528. One or more of the piezoelectric elements 502, 522, 524, 526, 528 can be trapezoidal or other non-rectangular, as described above with respect to FIG. 8. As described below, the piezoelectric elements 502, 522, 524, 526, 528 can be spaced apart by a distance that is typically a certain multiple smaller than the element width, as described in detail below.

[0051] As described herein, by using an element-to-element spacing that is narrower than the element-to-element spacing used on transducers where such parasitic modes occur, the parasitic modes visible in the response of the transducer can also be reduced. The presence of parasitic modes in the piezoelectric elements of the transducer interferes with the characterization of the resonance of the casing.

[0052] Fig.10 The value of the element-to-element spacing in the transducer 500 shown in is W1. Fig.12 An exemplary embodiment of a similar transducer 550 is depicted, which has a thinner element-to-element spacing 552 of W2 (W2 < W1), which allows the width of the element 554 to be increased by (W1 - W2), while the spacing and thickness remain unchanged.

[0053] Thinner inter-element spacing reduces the impact of parasitic modes. For example, while wider inter-element spacing may provide clear resonances in the frequency band of interest 310 for processing pulse-echo signals, thinner inter-element spacing may push parasitic modes out of the frequency band of interest.

[0054] If we consider N as a frequency constant associated with this parasitic mode, it can be determined as: N = (d ie )(f ie ).consider Fig.10 In the depicted embodiment, if the inter-element spacing (d ie =W1) at f ie = f1, then N = f1*W1. However, considering Fig.12 In the embodiment depicted in FIG. 1 , a thinner inter-element spacing d having the same constant N is ie =W2 will increase the disturbance frequency to f ie = f1*W1 / W2. In order to push the parasitic mode frequency to the upper limit of the frequency band of interest, F UL In addition, W2 can be determined as W2 <W1*f1 / F UL Such thinner inter-element spacing may also be used with the non-rectangular and / or irregularly spaced embodiments described above.

[0055] Phased arrays can have several configurations. In one or more embodiments, the phased array can include thin inter-element portions located between adjacent piezoelectric elements. The shape of each piezoelectric element can be a right-angled trapezoid, an isosceles trapezoid, or a rectangle. The spacing of the piezoelectric elements can be irregularly spaced in azimuth around one or more portions of the circumference of the transducer, or can be regularly spaced around the circumference of the transducer at predetermined intervals. In one or more embodiments, the piezoelectric elements can be aligned at their edges in a uniform manner or in an uneven manner. In one or more embodiments, the piezoelectric elements can be in 1-dimensional or 2-dimensional form.

[0056] In one non-limiting example, the phased array may include piezoelectric elements having thin inter-element portions therebetween, the piezoelectric elements may have a right-angled trapezoidal shape, the piezoelectric elements may be irregularly spaced in azimuth about one or more portions of the circumference of the transducer, the edges of the piezoelectric elements may be uniformly aligned, and they may be arranged in a 1-D manner. In another embodiment, the piezoelectric elements may be unevenly aligned at their edges.

[0057] In another non-limiting example, the phased array may include rectangular piezoelectric elements that are irregularly spaced in azimuth around one or more portions of the circumference of the transducer, and the edges of the piezoelectric elements may be uniformly aligned at their edges. The piezoelectric elements may be arranged in a 1-dimensional manner. In another embodiment, the piezoelectric elements may be unevenly aligned at their edges.

[0058] In another non-limiting example, the phased array may include rectangular piezoelectric elements that are regularly spaced in azimuth around one or more portions of the circumference of the transducer, and the edges of the piezoelectric elements may be uniformly aligned at their edges. The piezoelectric elements may be arranged in a 1-dimensional manner. In another embodiment, the piezoelectric elements may be unevenly aligned at their edges.

[0059] In another non-limiting example, the phased array may include rectangular piezoelectric elements that are irregularly spaced in azimuth around one or more portions of the circumference of the transducer, and the edges of the piezoelectric elements may be unevenly aligned at their edges. The piezoelectric elements may be arranged in a 1-dimensional manner. In one or more embodiments, the piezoelectric elements may be evenly aligned at their edges.

[0060] In one non-limiting example, the phased array may include piezoelectric elements having thin inter-element portions therebetween, the piezoelectric elements may have a right-angled trapezoidal shape, the piezoelectric elements may be regularly spaced in azimuth about one or more portions of the circumference of the transducer, the edges of the piezoelectric elements may not be uniformly aligned, and they may be arranged in a 1-D manner. In another embodiment, the piezoelectric elements may be uniformly aligned at their edges.

[0061] In one or more embodiments, the piezoelectric elements may include thin inter-element portions having one of an isosceles trapezoidal shape, random spacing or unique spacing, and one of uniform or non-uniform edge alignment. In any of the above examples, the shape of the piezoelectric elements may be an isosceles trapezoid, a right-angled trapezoid, or a rectangle. Furthermore, in any of the above examples, the phased array may include piezoelectric elements arranged in a 2-dimensional manner.

[0062] In one or more embodiments, an apparatus may include a downhole acoustic measurement tool having a transducer. The transducer is operable to transmit and / or receive acoustic signals for downhole measurement. The transducer has a plurality of piezoelectric elements. Each piezoelectric element has a first axial end and a second axial end, and the second axial end is wider than the first axial end or equal to the first axial end in a direction along the circumference of the transducer.

[0063] In one or more embodiments of the above apparatus, the piezoelectric element is azimuthally positioned around one or more portions of the circumference of the transducer.

[0064] In one or more embodiments of the above apparatus, the piezoelectric elements are distributed azimuthally around the circumference of the transducer.

[0065] In one or more embodiments of the above apparatus, each piezoelectric element is elongated in a direction parallel to the longitudinal axis of the downhole acoustic measurement tool, wherein the axial length of each piezoelectric element is greater than the average width of the first axial end and the second axial end. In one or more embodiments of the above apparatus, the piezoelectric elements are irregularly spaced azimuthally around one or more portions of the circumference of the transducer. In one or more embodiments of the above apparatus, the piezoelectric element has a first width L0 at the first end and a width L1 at the second end, wherein L0 is equal to L1, greater than L1, or less than L1.

[0066] In one or more embodiments of the above-mentioned apparatus, each adjacent pair of piezoelectric elements includes a first piezoelectric element and a second piezoelectric element. The first axial end of each first piezoelectric element is located at the upper end of the transducer; and the first axial end of each second piezoelectric element is located at the lower end of the transducer. In one or more embodiments of the above-mentioned apparatus, each piezoelectric element includes a radial outer edge extending parallel to the longitudinal axis of the transducer. In one or more embodiments of the above-mentioned apparatus, the radially outward surface of each piezoelectric element forms a right-angled trapezoid. In one or more embodiments of the above-mentioned apparatus, the piezoelectric elements are spaced apart by no more than W1*f1 / F UL The defined distance, where F UL is the upper limit of the frequency band of interest, and W1 is the width of the spacing between transducer elements that produces a parasitic mode at frequency f1. In one or more embodiments of the above apparatus, the piezoelectric elements are irregularly spaced azimuthally around one or more portions of the circumference of the transducer.

[0067] In another embodiment, the apparatus is a downhole acoustic measurement tool having a transducer. The transducer is operable to transmit and / or receive acoustic signals to perform downhole measurements, and the transducer includes a plurality of piezoelectric elements. The piezoelectric elements are irregularly spaced azimuthally around one or more portions of the circumference of the transducer. The piezoelectric elements are irregularly spaced completely around the circumference of the transducer.

[0068] In one or more embodiments of the above apparatus, each piezoelectric element is elongated in a direction parallel to a longitudinal axis of the downhole acoustic measurement tool, and wherein an axial length of each piezoelectric element is greater than an average width of the piezoelectric element.

[0069] In one or more embodiments of the above apparatus, the piezoelectric elements are azimuthally irregularly spaced around one or more portions of the circumference of the transducer.

[0070] In one or more embodiments of the above device, each pair of adjacent piezoelectric elements includes a first piezoelectric element and a second piezoelectric element; and the first axial end of each first piezoelectric element is located at the upper end of the transducer. The first axial end of each second piezoelectric element is located at the lower end of the transducer.

[0071] In one or more embodiments of the above apparatus, the piezoelectric elements are spaced apart by no more than W1*f1 / F UL The defined distance, where F UL is the upper limit of the frequency band of interest, W1 is the width of the spacing between the transducer elements that produces the parasitic mode at frequency f1. In one or more embodiments of the above apparatus, each piezoelectric element has a first axial end and a second axial end, and wherein the second axial end is wider than or equal to the first axial end in a direction along the circumference of the transducer, each piezoelectric element is elongated in a direction parallel to the longitudinal axis of the downhole acoustic measurement tool, and wherein the axial length of each piezoelectric element is greater than the average width of the piezoelectric element, and wherein the piezoelectric elements are spaced apart by no more than W1*f1 / F UL The defined distance, where F UL is the upper limit of the frequency band of interest, W1 is the width of the inter-element spacing of the transducer that produces a parasitic mode at frequency f1, where the piezoelectric elements are irregularly spaced completely around the circumference of the transducer, or a combination thereof.

[0072] In another embodiment of the apparatus, the apparatus is a downhole acoustic measurement tool comprising a transducer. The transducer is operable to transmit and / or receive acoustic signals for downhole measurement. The transducer comprises a plurality of piezoelectric elements spaced apart by no more than W1*f1 / F UL The defined distance, where F UL is the upper limit of the frequency band of interest, and W1 is the width of the spacing between transducer elements that produces a parasitic mode at frequency f1. In one or more embodiments of the above apparatus, the piezoelectric elements are irregularly spaced azimuthally around one or more portions of the circumference of the transducer.

[0073] The foregoing lists the features of several embodiments so that those of ordinary skill in the art can better understand aspects of the present disclosure. Those of ordinary skill in the art will appreciate that they can easily use the present disclosure as a basis for designing or modifying other processes and structures to perform the same functions and / or achieve the same advantages of the embodiments described herein. Those of ordinary skill in the art will also recognize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that various changes, substitutions, and modifications may be made herein without departing from the spirit and scope of the present disclosure.

[0074] The Abstract at the end of this disclosure is provided to comply with the requirements of 37 CFR §1.72(b) to allow the reader to quickly ascertain the nature of the technical disclosure. It is understood that it will not be used to interpret or limit the scope or meaning of the claims.

Claims

1. A device comprising: A downhole acoustic measurement tool comprising a transducer, wherein: The transducer is operable to transmit and / or receive acoustic signals for downhole measurements; The transducer includes a plurality of piezoelectric elements; and Each piezoelectric element has a first axial end and a second axial end, wherein the second axial end is wider than the first axial end or equal to the first axial end in a direction along the circumference of the transducer.

2. The apparatus of claim 1, wherein the piezoelectric element is azimuthally positioned around one or more portions of a circumference of the transducer.

3. The apparatus of claim 1, wherein the piezoelectric elements are distributed azimuthally around the circumference of the transducer.

4. The apparatus of claim 1, wherein each piezoelectric element is elongated in a direction parallel to a longitudinal axis of the downhole acoustic measurement tool, wherein an axial length of each piezoelectric element is greater than an average width of the first axial end and the second axial end.

5. The apparatus of claim 1, wherein the piezoelectric elements are irregularly spaced azimuthally around one or more portions of a circumference of the transducer. 6 . The device of claim 1 , wherein the piezoelectric element has a first width L0 at a first end and a width L1 at a second end, wherein L0 is equal to L1 , greater than L1 , or less than L1 .

7. The apparatus of claim 1, wherein: Each pair of adjacent piezoelectric elements includes a first piezoelectric element and a second piezoelectric element; The first axial end of each first piezoelectric element is located at an upper end of the transducer; and The first axial end of each second piezoelectric element is located at a lower end of the transducer.

8. The apparatus of claim 6, wherein each piezoelectric element includes a radial outer edge extending parallel to a longitudinal axis of the transducer.

9. The device according to claim 1, wherein a radially outward surface of each piezoelectric element forms a right-angled trapezoid.

10. The apparatus of claim 1, wherein the piezoelectric elements are spaced apart by no more than W1*f1 / F UL The defined distance, where F UL is the upper limit of the frequency band of interest, and W1 is the width of the spacing between the transducer elements that produces the parasitic mode at frequency f1.

11. The apparatus of claim 10, wherein: The piezoelectric elements are azimuthally irregularly spaced around one or more portions of a circumference of the transducer.

12. A device comprising: A downhole acoustic measurement tool comprising a transducer, wherein: The transducer is operable to transmit and / or receive acoustic signals for downhole measurements; The transducer includes a plurality of piezoelectric elements; and The piezoelectric elements are azimuthally irregularly spaced around one or more portions of a circumference of the transducer.

13. The apparatus of claim 12, wherein the piezoelectric elements are irregularly spaced completely around the circumference of the transducer.

14. The apparatus of claim 12, wherein each piezoelectric element is elongated in a direction parallel to a longitudinal axis of the downhole acoustic measurement tool, and wherein an axial length of each piezoelectric element is greater than an average width of the piezoelectric element.

15. The apparatus of claim 12, wherein the piezoelectric elements are azimuthally irregularly spaced around one or more portions of a circumference of the transducer.

16. The apparatus of claim 15, wherein: Each pair of adjacent piezoelectric elements includes a first piezoelectric element and a second piezoelectric element; The first axial end of each first piezoelectric element is located at an upper end of the transducer; and The first axial end of each second piezoelectric element is located at a lower end of the transducer.

17. The apparatus of claim 12, wherein the piezoelectric elements are spaced apart by no more than W1*f1 / F UL The defined distance, where F UL is the upper limit of the frequency band of interest, and W1 is the width of the spacing between the transducer elements that produces the parasitic mode at frequency f1.

18. The apparatus of claim 12, wherein each piezoelectric element has a first axial end and a second axial end, and wherein the second axial end is wider than or equal to the first axial end in a direction along the circumference of the transducer, each piezoelectric element is elongated in a direction parallel to the longitudinal axis of the downhole acoustic measurement tool, and wherein the axial length of each piezoelectric element is greater than the average width of the piezoelectric element, and wherein the piezoelectric elements are spaced apart by no more than W1*f1 / F UL The defined distance, where F UL is the upper limit of the frequency band of interest, W1 is the width of the inter-element spacing of the transducer that produces a parasitic mode at frequency f1, where the piezoelectric elements are irregularly spaced completely around the circumference of the transducer, or a combination thereof.

19. An apparatus comprising: A downhole acoustic measurement tool comprising a transducer, wherein: The transducer is operable to transmit and / or receive acoustic signals for making downhole measurements; and The transducer includes a plurality of piezoelectric elements, the plurality of piezoelectric elements are spaced apart by no more than W1*f1 / F UL The defined distance, where F UL is the upper limit of the frequency band of interest, and W1 is the width of the spacing between the transducer elements that produces the parasitic mode at frequency f1.

20. The apparatus of claim 18, wherein the piezoelectric elements are azimuthally irregularly spaced around one or more portions of a circumference of the transducer.

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