Bender bar transducer having stacked encapsulated actuators

A bender bar transducer having stacked encapsulated actuators provides improved acoustic power over a wider frequency range, low applied voltage requirements and consistent part-to-part performance.

PRIORITY

The present application is a U.S. National Stage patent application of International Patent Application No. PCT/US2014/016102, filed on Feb. 12, 2014, the benefit of which is claimed and the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to acoustic transducers and, more specifically, to an acoustic logging tool utilizing stacked encapsulated actuators to produce acoustic radiation.

BACKGROUND

Acoustic well logging is a well-developed art, and details of acoustic logging tools and techniques are set forth in A. Kurkjian, et al., “Slowness Estimation from Sonic Logging Waveforms”, Geoexploration, Vol. 277, pp. 215-256 (1991); C. F. Morris et al., “A New Sonic Array Tool for Full Waveform Logging,” SPE-13285, Society of Petroleum Engineers (1984); A. R. Harrison et al., “Acquisition and Analysis of Sonic Waveforms From a Borehole Monopole and Dipole Source . . . ” SPE 20557, pp. 267-282 (September 1990); and C. V. Kimball and T. L. Marzetta, “Semblance Processing of Borehole Acoustic Array Data”, Geophysics, Vol. 49, pp. 274-281 (March 1984). An example of an acoustic logging tool is provided in U.S. Pat. No. 6,661,737 entitled “ACOUSTIC LOGGING TOOL HAVING PROGRAMMABLE SOURCE WAVEFORMS,” owned by the Assignee of the present disclosure, Halliburton Energy Services, Inc. of Houston, Tex.

An acoustic logging tool typically includes an acoustic source (transducer), and a set of receivers (the receiver array) that are spaced several inches or feet apart. An acoustic signal is transmitted by the acoustic source and received at the receivers of the borehole tool which are spaced apart from the acoustic source. Measurements are repeated every few inches as the tool passes along the borehole. The acoustic signal from the source travels through the formation adjacent the borehole to the receiver array, and the arrival times and perhaps other characteristics of the receiver responses are recorded.

Typically, compressional wave (“P-wave”), shear wave (“S-wave”), and Stoneley wave arrivals and waveforms are detected by the receivers and are processed. The processing of the data is often performed on the surface, although it may also be performed real time in the tool itself. Regardless, the information that is recorded is typically used to determine formation characteristics, such as formation slowness (the inverse of acoustic speed) and anisotropy, from which pore pressure, porosity, and other formation property determinations can be made. With some tools, the acoustic signals have been used to image the formation.

Acoustic logging tools are used for both wireline logging and logging while drilling applications. In wireline logging, a probe, or “sonde”, housing multiple logging tools is lowered into the borehole after some or all of the well has been drilled. The sonde is attached to a conductive wireline that carries power from the surface to the tools in the sonde, and that carries telemetry information to the surface. The sonde may be transported through the borehole by the wireline, or a separate transport mechanism may be provided. For example, in “pipe-conveyed” logging, the sonde is mounted on a tubing string. The rigidity of the tubing string allows the sonde to be transported through highly deviated and horizontal boreholes.

One problem with obtaining downhole measurements via wireline is that the drilling assembly must be removed or “tripped” from the drilled borehole before the desired borehole information can be obtained. This can be both time-consuming and extremely costly, especially in situations where a substantial portion of the well has been drilled. In this situation, thousands of feet of tubing may need to be removed and stacked on the platform (if offshore). Typically, drilling rigs are rented by the day at a substantial cost. Consequently, the cost of drilling a well is directly proportional to the time required to complete the drilling process. Removing thousands of feet of tubing to insert a wireline logging tool can be an expensive proposition.

As a result, there is a strong incentive to minimize the number of wireline logging trips. One way to do this involves collection of data during the drilling process. Designs for measuring conditions downhole, including the movement and location of the drilling assembly contemporaneously with the drilling of the well, have come to be known as “measurement-while-drilling” techniques, or “MWD”. Similar techniques, concentrating more on the measurement of formation parameters, commonly have been referred to as “logging while drilling” techniques, or “LWD”. While distinctions between MWD and LWD may exist, the terms MWD and LWD often are used interchangeably. For the purposes of this disclosure, the term LWD will be used with the understanding that this term encompasses both the collection of formation parameters and the collection of information relating to the movement and position of the drilling assembly.

LWD tools are generally located as close to the drill bit as possible, so as to minimize the delay between reaching a formation and measuring its properties. When implemented as LWD tools, acoustic logging tools must overcome a number of obstacles to perform successfully. These obstacles include drilling noise, and acoustic properties of the thick tool body.

Bender bars are utilized in acoustic logging tools to detect and/or generate acoustic vibrations or seismic waves. Bender bars can be utilized in both the transmitter portion and the receiver portion of the acoustic logging tool. However, current bender bars can have difficulties with low frequency responses, resulting in difficulties in producing high quality logs for large hole and soft formation applications. Additionally, traditional bender bars have been constructed with an actuator that is a single layer thick to allow for simpler construction. However, the single-layer design also requires the use of higher actuation voltages.

Accordingly, there is a need in the art for an improved bender bar that overcomes these and other limitations.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIGS. 1A and 1Billustrate a bender bar transducer100. As shown in the cross-sectional view ofFIG. 1A, transducer100includes ferroelectric elements104aand104bmounted on an inert element102. Inert element102may be, for example, aluminum or some other suitable non-piezoelectric element. As shown inFIG. 1B, ferroelectric elements104aand104bare slabs of mater that are mounted on inert element102. As shown inFIG. 1A, the ferroelectric elements of ferroelectric elements104aand104bare electrically coupled to electronics106. Electronics106may include driver circuits or receiver elements such as that illustrated, for example, in U.S. Pat. No. 6,661,737. As described therein, this illustrative embodiment of transducer100provides a bi-polar acoustic wave as it is driven by electronics106.

FIGS. 2A, 2B, 2C, and 2Dillustrate certain illustrative embodiments of a bender bar transducer200according to aspects of the present disclosure. As shown inFIG. 2A, bender bar transducer200includes an inert element210. Multiple ferroelectric slabs are mounted in layers on each side of inert element210to form a stacked bender bar. As shown in the particular example illustrated inFIG. 2A, ferroelectric elements202aand202bare mounted on opposite sides of inert element210. Ferroelectric element204ais mounted on ferroelectric element202aand ferroelectric element204bis mounted on ferroelectric element202b. Ferroelectric element206ais mounted on ferroelectric element204aand ferroelectric element206bis mounted on ferroelectric element204b. Ferroelectric element208ais mounted on ferroelectric element206aand ferroelectric element208bis mounted on ferroelectric element206b.

FIGS. 2A, 2B, 2C and 2Dspecifically illustrate an example embodiment with three pairs of stacked ferroelectric elements—ferroelectric elements204aand204b,206aand206b, and208aand208b. Alternatively, any number of pairs of ferroelectric elements can be utilized, as the example illustrated inFIGS. 2A, 2B, 2C, and 2Dare illustrative only.

Inert element210can be any element that is not ferroelectric in nature. For example, inert element120can be Al, brass, titanium, or any metal or alloy. Ferroelectric elements202a,202b,204a,204b,206a,206b,208a, and208bcan be any ferroelectric elements, for example lead zirconate titanate (PZT), barium titanate (BaTiO3), Gallium orthophosphate (GaPO4), Tourmaline, Quartz, or other ferroelectric material. The term ferroelectric material is used to refer to any ferroelectric or relaxor ferroelectric material that exhibits a coupling between voltage and mechanical motion. The ferroelectric material can be a ceramic or a polymer. Without limitation, the ferroelectric material can be described as an electrostrictor, a piezoceramic, piezopolymer, magnetostrictor, or a shape memory ceramic. As shown inFIG. 2A, pairs of ferroelectric elements—ferroelectric elements202a,202b;204a,204b;206a,206b, and208a,208b—are stacked. Each layer of ferroelectric element in the stacking can have different thicknesses and can have differing widths and lengths. For purposes of this disclosure, thickness refers to the dimension perpendicular to the largest planar surface of inert element210, the surfaces on which ferroelectric element202aand202bare mounted, and the length and width refer to dimensions in the plane of inert element210. The various layers of ferroelectric element are differently sized and may be of different types of ferroelectric elements in order to better control the response of transducer200.

FIG. 2Billustrates an illustrative stacking arrangement of transducer200. As shown inFIG. 2B, each of ferroelectric elements202a,204a,206a, and208aare rectangular bars with each of them of different lengths but similar widths. As shown inFIG. 2B, ferroelectric element202ais mounted to inert element210in a symmetric fashion. Ferroelectric element204ais symmetrically mounted on ferroelectric element202a. Ferroelectric element206ais symmetrically mounted on ferroelectric element204a, ferroelectric element208ais symmetrically mounted on ferroelectric element206a, while ferroelectric elements202b,204b,206b, and208bare similarly stacked on the opposite side of inert element210, as is shown inFIG. 2A.

FIG. 2Cillustrates another example of a stacking arrangement of transducer200. As shown inFIG. 2C, each of ferroelectric elements202a,204a,206a, and208aare rectangular bars having differing dimensions in both length and width. As shown inFIG. 2C, ferroelectric element202ais symmetrically mounted on inert element210. Ferroelectric element204ais symmetrically mounted on ferroelectric element202a; ferroelectric element206ais symmetrically mounted on ferroelectric element204a; and ferroelectric element208ais symmetrically mounted on ferroelectric element206a. Ferroelectric elements202b,204b,206b, and208bare the same sizes as ferroelectric elements202a,204a,206a, and208aand are similarly arranged on the opposite side of inert element210.

FIG. 2Dillustrates another example of a stacking arrangement of transducer200. As shown inFIG. 2D, only ferroelectric element202ais rectangular in shape. Ferroelectric elements204a,206a, and208aare elliptical, or disc-shaped, slabs in shape, with the minor and major axis of the ellipse corresponding to width and length directions, respectively. As shown inFIG. 2D, each of the elliptical layers204a,206a, and208aare of different sizes. Further, ferroelectric element202ais symmetrically mounted on inert element210. Ferroelectric element204ais symmetrically mounted on ferroelectric element202a; ferroelectric element206ais symmetrically mounted on ferroelectric element204a; and ferroelectric element208ais symmetrically mounted on ferroelectric element206a. Ferroelectric elements202b,204b,206b, and208bare the same sizes and shapes as ferroelectric elements202a,204a,206a, and208aand similarly arranged on the opposite side of inert element210.

The stacked ferroelectric element pairs204aand204b,206aand206b, and208aand208bcan provide mass loading to the dipole at the center of maximum bending. This mass loading forces the frequency response of transducer200toward lower frequencies and lowers the quality factor Q, as was disclosed in U.S. Pat. No. 7,692,363; however, the mass loading proposed in that disclosure was not capable of being driven. In accordance with one or more illustrative embodiments of the present disclosure, each of ferroelectric element pairs202aand202b,204aand204b,206aand206b, and208aand208bcan be independently driven with controlled pulses to enhance further the low frequency response of transducer200.

FIG. 3illustrates a schematic of a driver300for driving each bipolar element, a bipolar element being formed by each of the ferroelectric element pairs. In some embodiments, individual (unipolar) elements (formed by individual ones of ferroelectric elements) can be driven separately by driver circuit300to achieve asymmetric acoustic radiation.

The embodiment of driver circuit300illustrated inFIG. 3is a bipolar driver where individual ferroelectric pairs (ferroelectric element202aand202b;204aand204b;206aand206b; and208aand208b) are driven simultaneously and synchronously. As shown inFIG. 3, driver300includes a controller302that controls pulse generators304,306,308, and310. Pulse generator304is coupled through a driver312to produce signal S1, which is coupled to drive ferroelectric element202aand202b. Pulse generator306is coupled through a driver314to produce signal S2, which is coupled to drive ferroelectric element204aand204b. Pulse generator308is coupled through a driver316to produce signal S3, which is coupled to drive ferroelectric element206aand206b. Pulse generator310is coupled through a driver318to produce signal S4, which is coupled to drive ferroelectric element208aand208b.

In some embodiments of the present disclosure, output signals produced by transducer200can be detected by sensors320. Signals from sensors320can be input to controller302, which can then adjust the signals S1, S2, S3, and S4supplied to transducer200to provide desirable results. One such desirable result can be, for example, enhancing the dipole nature of transducer200and the suppression of other modes of vibration.

FIGS. 4A, 4B, and 4Cillustrate the results of different driving pulses for S1, S2, S3, and S4. As shown inFIG. 4A, signals S1, S2, S3, and S4that are in phase with one another will add to the effect and produce a large signal.FIG. 4Billustrates the effects of shifting signals S1, S2, S3, and S4in phase with respect to one another. As shown inFIG. 4B, the resulting output signal is broader. As shown inFIG. 4C, as the phase between the impulses S1, S2, S3, and S4are increased, the resulting output signal becomes more diffuse.

Some embodiments of transducer200can experience larger displacements due to the stacking of ferroelectric elements, resulting in mass loading as well as the ability to drive multiple pairs of ferroelectric elements. The overall thickness of the stacking and resulting mass loading can also result in a lower frequency response and a lower Q. Controlling the pulses to each of the ferroelectric element pairs in frequency, amplitude, and shape can produce much lower or higher frequency responses with larger displacements. The displacements, as illustrated above, can be controlled by adjusting the phasing between individual signals supplied to the ferroelectric element pairs. In some embodiments, controlling pulse signals to individual pairs of ferroelectric elements can also be used to equalize the dipole displacement at both sides and thereby minimize Stoneley mode generation (generation of waves that travel along the wellbore). This effectively enhances a pure dipole signal output signal and increases the dipole signal-to-noise (S/N). In some embodiments of the present disclosure, numerous adaptive pulse controls produced by monitoring the output signals can be added to improve the dipole quality of the output signals produced by transducer200.

Performance of a basic bender bar100with an embodiment of a stacked bender bar200was modeled and compared with utilizing a WaveSonic™ (Halliburton Acoustic logging tool) dipole source, which could have included transmitter driving circuit board Part No. 101507949 and Wireline Tool part no 101378058 manufactured by Halliburton Energy Services, Inc. The performance of the bender bar100was modeled and analyzed utilizing a multiphysics modeling package by COMSOL, Inc. (COMSOL) and a second package by Simulia, Inc., called the ABAQUS software packages (ABAQUS). Both COMSOL and ABAQUS are finite element multi-physics modeling packages.

It was found that the COMSOL package is not stable and could not produce any dynamic response. As a result, only ABAQUS modeling results are presented in this disclosure. The software package ABAQUS is capable of performing several kinds of analysis to give insight to the performance of a bender bar. These analyses include Natural Frequency Extraction, Direct-Solution Steady-State Dynamic Analysis, and Implicit Dynamic Analysis using Direct Integration. The response was modeled without loading (no surrounding medium). The proposed concepts of this discloser are verifiable utilizing this software and the results are provided below.

FIG. 5illustrates a particular example of bender bar100that was utilized for analysis as discussed above. In this analysis, bender bar100is a PZT bender bar. Specifically, inert element102is a brass plate of thickness 0.125 inch, length 7.7 inch, and width 1.1 inch. Ferroelectric elements104aand104bare PZT crystal (C5400 or PZT-4 that may be purchased, for example, from Channel Industries or Piezo Technologies). Each of Ferroelectric elements104aand104bhas a thickness of 0.125 inch, length of 4.0 inch, and width of 1.0 inch. Ferroelectric elements104aand104bare bonded to inert element102, for example, with epoxy or a resin.

Natural Frequency Extraction (Modal analysis) is performed utilizing the particular example of bender bar100illustrated inFIG. 5to calculate the natural frequencies and the corresponding mode shapes of bender bar100. The ABAQUS model utilizes an eigenvalue analysis to find the various modes and mode frequencies. For the WaveSonic™ bender bar model shown inFIG. 5, 14 vibrational modes between 0 and 10 kHz where found. Those modes are listed in Table 1. The more important modes are the symmetric modes, which for bender bar100ofFIG. 5are listed as mode 1 at 383.6 Hz, mode 5 at 2622.8 Hz, and mode 9 at 5887.7 Hz, which are themselves illustrated inFIGS. 6A, 6B, and 6C, respectively. The harmonic displacement of the center point is illustrated inFIG. 7as a function of frequency.

Bender bar100can have several types of mode shapes. The various types of bending include, for example, twisting, swinging sidewise, and swinging lengthwise. Among these, only certain symmetric bending modes provide substantial pressure when bender bar100is coupled to an acoustic medium.FIGS. 6A, 6B, and 6Cshow symmetric bending modes corresponding to the modes at 363.6 Hz, 2622.8 Hz, and 5887.7 Hz, respectively.FIGS. 6A, 6B, and 6Care not to scale and are provided to emphasize the mode shapes only.FIG. 6Ashows a mode having no internal nodes.FIG. 6Billustrates a mode having two internal nodes.FIG. 6Cshows a mode having 4 internal nodes.

FIG. 7shows the harmonic displacement in Z-direction of the center point of the bar. In this model, illustrated inFIG. 7, there is no loading (i.e., no surrounding medium).FIG. 7illustrates peaks702,704, and706, corresponding to mode 1, mode 5, and mode 9 of Table 1, respectively. The results illustrated inFIG. 7are based on a theoretical model of the ABAQUS system.FIG. 7illustrates that peaks702,704, and706are observed at the symmetrical modes 1, 5, and 9 shown inFIGS. 6A, 6B, and 6C, respectively.

FIG. 8illustrates a particular example of a stacked bender bar200on which frequency calculations can be performed. In the embodiment shown inFIG. 8, stacked bender bar200includes inert element210, ferroelectric elements202aand202band ferroelectric elements204aand204b. Inert element210and ferroelectric elements202aand202bare the same elements and dimensions as inert element102and ferroelectric elements104aand104billustrated inFIG. 5. In other words, inert element210is a brass plate of thickness 0.125 inch, length 7.7 inch, and width 1.1 inch. Ferroelectric elements202aand202bare PZT crystal (C5400 or PZT-4, which may be purchased, for example, from Channel Industries or Piezo Technologies). Each of Ferroelectric elements202aand202bhas a thickness of 0.125 inch, length of 4.0 inch, and width of 1.0 inch. Ferroelectric elements202aand202bare bonded to inert element210with an epoxy or resin. Ferroelectric elements204aand204bare half sized of ferroelectric elements202aand202b, having thickness of 0.125 inch, length of 2.0 inch, and width of 1.0 inch. Ferroelectric elements204aand204bare bonded to ferroelectric elements202aand202b, respectively, with epoxy or resin.

The calculated natural frequencies for stacked bender bar200shown inFIG. 8are given in Table 2. Modes 1, 5, and 10 correspond to three symmetric mode shapes, which are illustrated inFIGS. 9A, 9B, and 9C, respectively.FIG. 10illustrates the harmonic displacement in Z direction of bender bar200illustrated inFIG. 8compared to those of bender bar100illustrated inFIG. 5.

FIGS. 9A, 9B, and 9Cshow Symmetric bending modes of the example of bender bar200illustrated inFIG. 8. In accordance with Table 2,FIG. 9Aillustrates mode 1 at 367.53 Hz,FIG. 9Billustrates mode 5 at 3463.9 Hz, andFIG. 9Cillustrates mode 10 at 6593.3 Hz. These modes represent the lower frequency symmetric modes of bender bar200, with mode 1 of bender bar200having 0 nodes illustrated inFIG. 9A, with mode 5 of bender bar200having 2 nodes illustrated inFIG. 9B, and with mode 10 of bender bar200having 4 nodes illustrated inFIG. 9C.

FIG. 10illustrates the harmonic displacement in the Z-direction of the center point of the example bender bar200illustrated inFIG. 8in comparison with bender bar100as illustrated inFIG. 5. Peaks702,704, and706corresponding to modes 1, 5, and 9, respectively, of bender bar100ofFIG. 5are illustrated. Peaks1002,1004, and1006corresponding to modes 1, 5, and 10, respectively, of bender bar200ofFIG. 8are illustrated. As shown inFIG. 10and Tables 1 and 2, peaks1004and1006are shifted to higher frequencies while peak1002is shifted to a slightly lower frequency.

The stacked bender bar computed results illustrated inFIG. 10show that the addition of the additional ferroelectric element204aand204b, which provides extra mass, did not reduce the frequency response, and instead adjusted the frequency of most of the symmetric modes to higher frequency. The frequency (f) of the modes of a mechanical system is governed by the relation:

where k=stiffness and m=mass. If the mass m increases compared to stiffness k, the frequency will be lower. However, as shown inFIG. 10, it seems the stiffness k is increasing more than the mass m, resulting in an increase in frequency. Therefore, embodiments of the disclosure as illustrated inFIGS. 2A, 2B, 2C, and 2Dand inFIG. 8can be utilized to shift operating frequencies of bender bars to higher frequencies.

FIGS. 11A, 11B, and 11Cillustrate a bender bar transducer1100according to some embodiments of the present disclosure that may lower the frequency and may provide more power. As shown inFIG. 11, transducer1100includes an inert element1102. Transducer1100also includes pairs of ferroelectric elements, ferroelectric elements1104aand1104band ferroelectric elements1106aand1106b, bonded to inert element1102such that there are gaps1108aand1108bat the center point of inert element1102. Bender bar1100is similar to bender bar100, except that the stiffness k is reduced by stripping off portions of ferroelectric elements104aand104bfrom the middle of bender bar100to form ferroelectric elements1104aand1104band1106aand1106b.

In a particular example as shown inFIG. 11C, inert element inert element1102is a brass plate of thickness 0.125 inch, length 7.7 inch, and width 1.1 inch. Ferroelectric elements1104aand1104band ferroelectric elements1106aand1106bare PZT crystal (C5400 or PZT-4 purchased from Channel Industries or Piezo Technologies). Each of ferroelectric elements1104aand1104band ferroelectric elements1106aand1106bhas a thickness of 0.125 inch, width of 1.0 inch, and length of 2 inch. Ferroelectric element1104aand ferroelectric element1106aare positioned symmetrically on one side of inert element1102such that a 0.063 inch gap is formed along a center line of inert element1102. Similarly, ferroelectric element1104band1106bare positioned symmetrically on the other side of inert element1102such that a 0.063 inch gap is formed on the center line of inert element1102. Ferroelectric elements1104aand1104band ferroelectric elements1106aand1106bare bonded to inert element1102with an epoxy or resin.

The calculated natural frequencies of bender bar1100as illustrated inFIG. 11Cwith the dimensions described above are shown in Table 3.FIGS. 12A, 12B, and 12Cillustrate the three symmetric mode shapes indicated by mode 1 at 352.39 Hz, mode 5 at 2035.7 Hz, and mode 9 at 5654.2 Hz in Table 3. As discussed above, the displacements shown inFIGS. 12A, 12B, and 12Care not to scale.

FIG. 13illustrates the harmonic displacement in Z-direction of the center point of bender bar1100illustrated byFIG. 11Cin comparison with the harmonic displacement bender bar100as illustrated byFIG. 5. As shown inFIG. 13, peak702corresponds to mode 1 of bender bar100, peak704corresponds to mode 5 of bender bar100, and peak706corresponds to mode 9 of bender bar100. The mode frequencies for bender bar100are illustrated in Table 1. In comparison, mode 1 of bender bar1100results in peak1302, mode 5 of bender bar1100results in peak1304, and mode 9 of bender bar1100results in peak1306. From these calculated results, it is clear that the split bender bar1100shifts lower the natural frequency of the symmetric modes of bender bar1100compared to that of the un-split bender bar100.

FIGS. 14A, 14B, 14C, and 14Dillustrate a stacked and split embodiment bender bar1400. The example embodiment illustrated inFIG. 14A, for example, includes inert element1410with multiple layers of ferroelectric elements on each side, arranged such that gaps1420aand1420bare formed in the stacked ferroelectric elements at a center line of bender bar1400. Any number of layers can be utilized. The particular example illustrated inFIG. 14Ashould not be considered limiting.

As shown inFIG. 14A, ferroelectric elements1402aand1402band ferroelectric elements1412aand1412bare bonded to inert element1410in such a fashion that a gap1420ais formed between ferroelectric element1402aand1412aand a gap1420bis formed between ferroelectric element1402band1412b. Ferroelectric element1402aand1402band ferroelectric element1412aand1412bcan all be of the same size and shape and are positioned such that loading of inert element1410is symmetrical around the center line at gap1420band1420a.

Similarly, ferroelectric elements1404ais bonded on ferroelectric element1402a, ferroelectric element1404bis bonded on ferroelectric element1402b, ferroelectric element1414ais bonded on ferroelectric element1412a, and ferroelectric element1414bis bonded on ferroelectric element1412bso that the loading is symmetrical and that the gaps1420aand1420bare maintained. Similarly, ferroelectric element1406ais bonded on ferroelectric element1404a, ferroelectric element1416ais bonded on ferroelectric element1414a, ferroelectric element1406bis bonded on ferroelectric element1404band ferroelectric element1416bis bonded on ferroelectric element1414b. Additionally, ferroelectric element1408ais bonded on ferroelectric element1406a, ferroelectric element1418ais bonded on ferroelectric element1416a, ferroelectric element1408bis bonded on ferroelectric element1406b, and ferroelectric element1418bis bonded on ferroelectric element1416b. As a consequence, stacks of ferroelectric element are formed on inert element1410in such a way that gaps1420aand1420bare formed between the ferroelectric elements. In some embodiments, this arrangement adds to the mass loading m of bender bar1400, it does not increase the stiffness k, resulting in lowered operating frequencies.

FIG. 14Billustrates some embodiments of bender bar1400as illustrated inFIG. 14A, where each of ferroelectric elements1402a,1404a,1406a, and1408aand ferroelectric elements1412a,1414a,1416a, and1418a(and correspondingly1402b,1404b,1406b, and1408band ferroelectric elements1412b,1414b,1416b, and1418b) are rectangular and have the same width, but differing lengths. Each layer may also have a different thickness.

FIG. 14Dillustrates some embodiments where each of ferroelectric elements1402aand1412a(and correspondingly1402band1412b) are rectangular and ferroelectric elements1404a,1406a, and1408aand ferroelectric elements1412a,1414a,1416a, and1418a(and correspondingly1404b,1406b, and1408band ferroelectric elements1414b,1416b, and1418b) are semi-elliptical slabs and of differing major and minor axis lengths. In such case, ferroelectric elements1404aand1414atogether form a whole ellipse with a cut in the center at gap1420a; ferroelectric elements1406aand1416aform a whole ellipse with a cut in the center at gap1420a; and ferroelectric elements1408aand1418aform a whole ellipse with a cut in the center at gap1420a. Again, thicknesses may differ between layers.

FIG. 15illustrates a particular example of bender bar1400. The particular example of bender bar1400ofFIG. 15includes ferroelectric elements1402aand1402b, ferroelectric elements1404aand1404b, ferroelectric elements1412aand1412b, and ferroelectric elements1414aand1414bto form a two-layered stack. The results of calculations of the natural frequencies of such a system are provided in Table 4. In that calculation, Inert element1410and ferroelectric elements1402aand1402band ferroelectric elements1412aand1412bare the same elements and dimensions as inert element1100and ferroelectric elements1104aand1104band ferroelectric elements1106aand1106billustrated inFIG. 5. In other words, inert element1410is a brass plate of thickness 0.125 inch, length 7.7 inch, and width 1.1 inch. Ferroelectric elements1402a,1402b,1404a,1404b,1412a,1412b,1414a, and1414bare PZT crystal (C5400 or PZT-4, which can be purchased, for example, from Channel Industries or Piezo Technologies).

The results of the calculation on bender bar1400as illustrated inFIG. 15(e.g., a stacked and split bender bar) are shown in Table 4. Illustrates of the first three symmetric modes, modes 1, 5, and 8, are illustrated inFIGS. 16A, 16B, and 16C, respectively.FIG. 17illustrates a comparison of the frequencies of modes 1, 5, and 8 of bender bar1400with those of bender bar100as illustrated inFIG. 5. As shown inFIG. 17, mode 1 at 321.08 Hz is illustrated as peak1702, mode 5 at 2013.6 Hz is illustrated as peak1704, and mode 8 at 5500.7 Hz is illustrated as peak1706.

FIG. 18illustrates a narrow band pulse for driving ferroelectric elements with different center frequency. The main objective is to study the displacement of the mid-point of the bender element. Note that, since there is no loading of the system, the response would be dominated by the harmonic displacements as described in static models discussed above. To show the effects of the multiple driving pulse shapes in different PZT type ferroelectric elements, we use 1000 Hz and 750 Hz narrow pulses with different voltages applied to the stacked elements. The results are shown in theFIG. 19. As such, the illustrative waveform illustrated inFIG. 18was applied to the ferroelectric elements of the bender bars in the above identified calculations.

FIG. 19illustrates dynamic modeling results between driving stacked element with the same driving pulses1902with 1000 Hz center frequency and different driving pulses1904(1000 Hz pulse applied to the longer PZT element and 750 Hz to the shorter PZT element of bender bar200ofFIG. 8). As shown inFIG. 19, plot (a) indicates a Time response, plot (b) indicates the Instantaneous frequency (note that there is a spike in the instantaneous frequency for the same driving pulse), and plot (c) indicates the frequency response.

The results indicated inFIG. 19show that the two different driving pulse shapes change the output responses. Note that these results are used only for two stacked elements. Multiple elements with different driving pulses could produce even better preferred responses. In summary, the controlled driving voltages and pulse shapes with multiple PZT elements could provide a desired response that is proposed in this disclosure.

FIG. 20illustrates yet another illustrative embodiment of the present disclosure wherein the bender bar includes stacked encapsulated ferroelectric elements utilized to produce and detect acoustic forces (dipole, for example) along a wellbore. Bender bar transducer2000includes an inert element2010, as previously described herein. First and second encapsulated ferroelectric elements2002and2004, respectively, are mounted on each side of inert element2010to form a stacked encapsulated bender bar. However, in other embodiments, first and second encapsulated ferroelectric elements2002,2004may only be mounted on one side of inert element2010.

Inert element2010may be, for example, aluminum or some other suitable non-piezoelectric element. In certain embodiments, inert element2010is a plate having a length, width and thickness, the plate being attached on two or more sides. In others, inert element2010is a beam attached at one or both ends. The inert element provides a structure to which the encapsulated active elements2002,2004are bonded. The different attachment techniques provide different levels of coupling with the surrounding fluid. If the beam is attached on all of its sides, then the beam will be stiffer and better suited towards a surrounding fluid with a high bulk modulus. If the inert element2010is a cantilevered beam, then the bender bar transducer would have higher deflections and lower forces (aka, lower stiffness) than when the inert element2010is a plate attached on two or more sides. The lower stiffness bender bar transducer would be better suited towards operating when the surrounding fluid has a low bulk modulus, such as gas.

First and second encapsulated ferroelectric elements2002,2004each include ferroelectric layers2008a,band2012a,bstacked atop one another. Ferroelectric layers2008,2012are encapsulated by material2014which may be, for example, a polymer. Material2014applies a compressive force to ferroelectric layers2008,2012along the length or width of the layers. In certain embodiments, the thickness of material2014may be, for example, 0.005 inches to 0.020 inches. In some cases, the compressive stress may be 25 MPa at room temperature. In other applications, the compressive stress may be 50 MPa at the operating temperature. In all cases, it is desired for the compressive stress to be less than 400 MPa in order to avoid compressive failure of the piezoceramic. In addition to this planar compressive force, a tri-axial compressive force may also be applied to layers2008,2012by material201. Once encapsulated, first and second encapsulated ferroelectric elements2002,2004are coupled to inert element2010using a variety of methods, such as, for example, a two-part epoxy.

The use of material2014provides a pre-compression to ferroelectric layers2008,2012, thus making bender bar transducer2000more robust. As a result, first and second encapsulated ferroelectric elements2002,2004can handle more bending strain without breaking layers2008,2012. In addition, encapsulation of layers2008,2012make them easier to handle and easier to attach electrical connections thereto. The encapsulation also allows for load transfer in instances when layers2008,2012are fractured during use. Moreover, the encapsulation also minimizes electrical arching around the edges of layers2008,2012.

The illustrative transducers described herein may be manufactured in a variety of ways. In one method, for example, the inert elements and the encapsulated ferroelectric elements have different coefficients of thermal expansion. In such cases, both elements may be heated. After heating, the inert element and encapsulated ferroelectric elements are coupled to one another, and then allowed to cool thereafter. Because they have different amounts of thermal expansion, a compression will occur, as previously described.

The use of multilayered, encapsulated ferroelectric elements as described herein provides a high force output with low voltage requirements. The free-strain output from a piezoelectric ceramic, for example, is proportional to:
ε=d31·(V/t)·n,Eq. (2),
where ε is the free-strain, d31is the piezoelectric coefficient for the ceramic, V is the applied voltage, t is the thickness of the piezoceramic layer, and n is the number of piezoelectric ceramic layers. Based upon this, we also see that that more layers will produce more displacement. When the movement of the piezoceramic is blocked by being bonded to a substantially stiffer structure, the force imparted by the piezoceramic is shown by:
F=EεAEq. (3),

where F is the blocked force, E is the modulus, ε is the free strain, and A is the cross-sectional area. Thus:
F=E(d31(V/t))(t·n)wEq. (4),

where w is the width of the piezoceramic,
F=d31Vn(Ew)  Eq. (5),

when the constants E and w are removed,
F=∝d31VnEq. (6),

By removing the constants, we see that it is linearly proportional to these variables. which means that more layers will produce more force and that the thickness of the layers is less important. Therefore, if the applied voltage is kept constant, a greater force can be applied by having more layers of ferroelectric ceramic, n>1. The tradeoff for more layers is that the applied current will also increase, but this is typically not a limiting factor in logging instruments using bender-bars for acoustic logging.

The applied voltage in acoustic logging instruments is often limited by the electronic components that can be used in wellbore environmental conditions, such as the electrical feed-through connectors. Higher voltages need more insulation and thus intrinsically, larger diameter electrical feed-through connectors. Higher applied voltages also need higher-voltage, supply electronics, which is often difficult to design for the higher operating temperatures within a wellbore. Typically, required current for bender bars for acoustic logging has been less of a design limitation than voltage with wellbore logging instruments. Therefore, the use of multilayer ferroelectric ceramic actuators in the present disclosure is an improvement over traditional bars because we can achieve a higher force output with lower voltage.

FIG. 21illustrates another illustrative embodiment of the present disclosure wherein the bender bar includes a plurality of single-layered encapsulated ferroelectric elements. Bender bar2100is somewhat similar to bender bar2000described with reference toFIG. 20and, therefore, may be best understood with reference thereto. Bender bar transducer2100includes an inert element2110, as previously described herein. Unlike bender bar2000, however, bender bar2100includes a plurality of single-layered encapsulated ferroelectric elements stacked atop one another. First and second encapsulated ferroelectric elements2102a,band2104a,b, respectively, are mounted on each side of inert element2110to form a stacked encapsulated bender bar. However, in other embodiments, first and second encapsulated ferroelectric elements2102,2104may only be mounted on one side of inert element2110.

First and second encapsulated ferroelectric elements2102,2104include a single ferroelectric layer2108a-d. Although described here as ferroelectric elements, other solid state transducers could also be utilized, such as, for example, ferroelectrics and relaxor ferroelectrics, including piezoceramics, piezopolymers, electrostrictors, shape memory ceramics, magnetostrictors, etc., as will be understood by those ordinarily skilled in the art having the benefit of this disclosure. Ferroelectric layers2108a-dare each encapsulated by material2114which may be, for example, a polymer. Material2114applies a compressive force to ferroelectric layers2108,2112along the length or width of the layers. In certain embodiments, the thickness of material2014may be, for example, 0.005 inches to 0.020 inches. In addition to this compressive force, a hydrostatic force may also be applied to layers2108,2112by material2014, all as previously described. Once encapsulated, first and second encapsulated ferroelectric elements2102,2104are coupled to inert element2010using a variety of methods, such as, for example, glue.

The stacked encapsulation of the embodiments ofFIGS. 20 and 21may be combined with the other features described herein. For example, the bender bar transducer200ofFIGS. 2A-2D and 3may include one or more encapsulated ferroelectric layers202. Layers202may be encapsulated individually or two or more layers202may be jointly encapsulated. The encapsulation may also be applied to shaped the ferroelectric layers202shown inFIGS. 2C and 2D. In another example, bender bar transducer1100ofFIGS. 11A and 11Bmay include encapsulated ferroelectric elements1104. In yet another example, bender bar transducer1400ifFIGS. 14A and 14Bmay also include one or more encapsulated ferroelectric elements. In such embodiments, gaps1420a,bwould still be present, as the encapsulation material would only cover the ferroelectric elements on either side of the gaps. In other words, for example, element1418awould be encapsulated alone or in conjunction with layer1416a. However, element1418awould not be encapsulated with element1408a, thus maintaining gaps1420a,b. Furthermore, one or more of the shaped ferroelectric layers ofFIGS. 14C and 14Dmay also be encapsulated as previously described.

In addition, the bender bars described herein may be utilized in a variety of environments, including, for example, downhole well applications. As a result, acoustic forces (dipole, for example) may be produced and/or detected through drilling, production, completion, or other downhole fluids.

Moreover, the concept of multilayer encapsulated piezoceramics described herein, which may be utilized on one or both sides of a rounded substrate, are useful in creating a more versatile Piezo-Disc Bender. Commonly referred to as a bimorph or a unimorph transducers, possible applications for a such a Piezo-Disc Bender created with multilayer encapsulated piezoceramics include buzzers, alarms, and speakers in appliance, electronics, and toys, as well as, transmitter and/or receivers used in downhole logging tools or telemetry systems. As described herein, the term transducer refers to a device that may work as either a transmitter or receiver, or as both a transmitter and receiver.

FIGS. 22A-Billustrate acoustic transducers utilized in a drilling and wireline application, respectively, according to illustrative embodiments of the present disclosure.FIG. 22Aillustrates a drilling platform2equipped with a derrick4that supports a hoist6for raising and lowering a drill string8through various formations19. Hoist6suspends a top drive11suitable for rotating drill string8and lowering it through well head13. Connected to the lower end of drill string8is a drill bit15. As drill bit15rotates, it creates a wellbore17that passes through various formations19. A pump21circulates drilling fluid through a supply pipe22to top drive11, down through the interior of drill string8, through orifices in drill bit15, back to the surface via the annulus around drill string8, and into a retention pit24. The drilling fluid transports cuttings from the borehole into pit24and aids in maintaining the integrity of wellbore16. Various materials can be used for drilling fluid, including, but not limited to, a salt-water based conductive mud.

An acoustic logging tool10is integrated into the bottom-hole assembly near the bit15. In this illustrative embodiment, logging tool10is an LWD tool utilizing a bender bar acoustic transducer as described herein; however, in other illustrative embodiments, logging tool10may be utilized in a wireline or tubing-convey logging application. Moreover, in certain illustrative embodiments, logging tool10may be adapted to perform logging operations in both open and cased hole environments.

Still referring toFIG. 22A, as drill bit15extends wellbore17through formations19, logging tool10collects acoustic measurement signals relating to various formation properties, as well as the tool orientation and various other drilling conditions. In certain embodiments, logging tool10may take the form of a drill collar, i.e., a thick-walled tubular that provides weight and rigidity to aid the drilling process. A telemetry sub28may be included to transfer images and measurement data/signals to a surface receiver30and to receive commands from the surface. In some embodiments, telemetry sub28does not communicate with the surface, but rather stores logging data for later retrieval at the surface when the logging assembly is recovered.

Still referring toFIG. 22A, logging tool10includes a system control center (“SCC”), along with necessary processing/storage/communication circuitry, that is communicably coupled to one or more acoustic transmitters and/or receivers (not shown) utilized to acquire formation measurement signals reflecting formation parameters. In certain embodiments, once the measurement signals are acquired, the SCC calibrates the measurement signals and communicates the data back uphole and/or to other assembly components via telemetry sub28. In an alternate embodiment, the system control center may be located at a remote location away from logging tool10, such as the surface or in a different borehole, and performs the processing accordingly. These and other variations within the present disclosure will be readily apparent to those ordinarily skilled in the art having the benefit of this disclosure.

FIG. 22Billustrates an alternative embodiment of the present invention whereby an acoustic transducer is utilized in a wireline application. At various times during the drilling process, drill string8may be removed from the borehole as shown inFIG. 24B. Once drill string8has been removed, logging operations can be conducted using a wireline logging sonde34, i.e., a probe suspended by a cable41having conductors for transporting power to the sonde34and telemetry from sonde34to the surface. The wireline logging sonde34includes the acoustic logging tool10as described herein to transmit and/or receiver acoustic forces. A logging facility43collects measurements from the logging sonde34, and includes a computer system45for processing and storing the measurements gathered by the transmitter/receivers.

Through use of the illustrative embodiments of the present disclosure, bender bars are improved in a number of ways. First, for example, a larger acoustic output (increased pressure) is provided. Second, since lower voltages are needed, smaller electrical and feed-through connectors may be utilized. Third, an acoustic output with a wider frequency band (i.e., broadband signal) may be produced. As a result, the bender bar has a broader frequency response which allows for sweeping of the entire acoustic transmission frequency. Fourth, a more consistent acoustic output is provided, all while maintaining a high modal purity (large dipole/monopole & dipole/quadrupole ratios, for example).

Embodiments described herein further relate to any one or more of the following paragraphs:

1. An acoustic transducer for use in a wellbore, the transducer comprising: an inert element; and a first encapsulated ferroelectric element coupled to the inert element, the first encapsulated ferroelectric element having two or more layers stacked atop one another, wherein the first encapsulated ferroelectric element produces and detects acoustic forces along the wellbore.

2. A transducer as defined in paragraph 1, wherein the inert element comprises: a plate having a first side, a second side opposite the first side, and a first and second end; and a beam attached at the first end, the second end, or both.

3. A transducer as defined in any of paragraphs 1 or 2, wherein the first encapsulated ferroelectric element is coupled to the first side of the plate, the transducer further comprising a second encapsulated ferroelectric element coupled to the second side of the plate, the second encapsulated ferroelectric element also having two or more layers stacked atop one another.

4. A transducer as defined in any of paragraphs 1 to 3, wherein a material utilized to encapsulate the first encapsulated ferroelectric element applies a compressive force to the stacked layers.

5. A transducer as defined in any of paragraphs 1 to 4, wherein the compressive force comprises at least one of a compressive force along a length of the first encapsulated ferroelectric element; a compressive force along a width of the first encapsulated ferroelectric element; and a tri-axial compressive force applied to the first encapsulated ferroelectric element.

6. A transducer as defined in any of paragraphs 1 to 5, wherein a material utilized to encapsulate the first encapsulated ferroelectric element comprises a polymer.

7. A transducer as defined in any of paragraphs 1 to 6, wherein the wellbore contains drilling, production or completion fluid.

8. A transducer as defined in any one of paragraphs 1 to 7, wherein the acoustic forces are dipole acoustic forces.

9. A transducer as defined in any one of paragraphs 1 to 8, wherein the transducer is part of an acoustic logging tool or acoustic telemetry system.

10. A method for manufacturing an acoustic transducer for use in a wellbore, the method comprising: providing an inert element; and coupling a first encapsulated ferroelectric element to the inert element, the first encapsulated ferroelectric element having two or more layers stacked atop one another, wherein the first encapsulated ferroelectric element produces and detects dipole acoustic forces along the wellbore.

11. A method as defined in paragraph 10, wherein providing the inert element further comprises providing the inert element as: a plate having a first side, a second side opposite the first side, and a first and second end; a beam attached at both ends; or a beam attached at one end.

12. A method as defined in any of paragraphs 10 or 11, wherein the first encapsulated ferroelectric element is coupled to the first side of the plate, the method further comprising coupling a second encapsulated ferroelectric element to the second side of the plate, the second encapsulated ferroelectric element also having two or more layers stacked atop one another.

13. A method as defined in any one of paragraphs 10 to 12, wherein coupling the first encapsulated ferroelectric element further comprises compressing the first encapsulated ferroelectric element.

14. A method as defined in any of paragraphs 10 to 13, wherein the inert element and the first encapsulated ferroelectric element have different coefficients of thermal expansion; and compressing the first encapsulated ferroelectric element comprises: heating the inert element and the first encapsulated ferroelectric; coupling the first encapsulated ferroelectric element to the inert element; and after the coupling, cooling the inert element and the first encapsulated ferroelectric element.

15. A method as defined in any of paragraphs 10 to 14, wherein compressing the first encapsulated ferroelectric elements further comprises at least one of: applying a compressive force along a length of the first encapsulated ferroelectric element; applying a compressive force along a width of the first encapsulated ferroelectric element; and applying a tri-axial compressive force to the first encapsulated ferroelectric element.

16. A method utilizing an acoustic transducer within a wellbore, the method comprising: deploying the transducer into the wellbore, the transducer comprising an inert element; and an encapsulated ferroelectric element coupled to the inert element, the encapsulated ferroelectric element having two or more layers stacked atop one another; and producing an acoustic force along the wellbore utilizing the first encapsulated ferroelectric element and the inert element.

17. A method as defined in paragraph 16, wherein producing the acoustic force further comprises producing a dipole acoustic force.

18. A method as defined in any of paragraphs 16 or 17, wherein a material utilized to encapsulate the encapsulated ferroelectric element applies a compressive force to the stacked layers.

19. A method as defined in any of paragraphs 16 to 18, wherein producing the acoustic force along the wellbore further comprises producing the acoustic force through a drilling or completion fluid.

20. A method as defined in any of paragraphs 16-19, wherein the transducer is deployed along a wireline or as part of a logging-while-drilling or measurement-while drilling assembly.

21. An acoustic transducer for use in a wellbore, the transducer comprising: an inert element; a first encapsulated ferroelectric element coupled to the inert element, the first encapsulated ferroelectric element having a single layer; and a second encapsulated ferroelectric element stacked atop the first encapsulated ferroelectric element, the second encapsulated ferroelectric element having a single layer, wherein the first and second encapsulated ferroelectric elements produce and detect acoustic forces along the wellbore.

22. A transducer as defined in paragraph 21, wherein the inert element comprises: a plate having a first side, a second side opposite the first side, and a first and second end; a beam attached at both ends; or a beam attached at one end.

23. A transducer as defined in any of paragraphs 21 or 22, wherein a material utilized to encapsulate the first and second encapsulated ferroelectric elements applies a compressive force to the layers.

24. A transducer as defined in any of paragraphs 21 to 23, wherein the wellbore contains drilling, production or completion fluid.

25. A transducer as defined in any of paragraphs 21 to 24, wherein the acoustic forces are dipole acoustic forces.

Although various embodiments and methodologies have been shown and described, the disclosure is not limited to such embodiments and methodologies and will be understood to is include all modifications and variations as would be apparent to one skilled in the art. For example, in addition to logging tools, the acoustic transducers described herein may also be utilized in acoustic telemetry systems. Therefore, it should be understood that the disclosure is not intended to be limited to the particular forms disclosed. Rather, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims.