NL9900024A - Prodn. of acoustic sonde for down hole well logging operations - Google Patents

Abstract

Acoustic sonde (12) for down hole well logging operations has housing with an acoustically transparent section (16) defining an internal chamber in which an annular acoustic transducer array (44) is located adjacent the transparent housing section. It has an annular backing element (92) composed of acoustically attenuating material, acoustic transducer elements located externally of the element, and electronic transducer circuits (98) individually electrically coupled to the elements, electronic transmitting/receiving circuitry (62) being coupled in controlling relation with the circuits. Also claimed is a method of mfg. a piezo-electric acoustic array by assembling a tubular acoustic attenuating backing (92) and tubular piezo-electric body (94) adhered to one another, the piezo-electric body defining the outer periphery of the assembly, and making cuts through the body to divide it into spaced piezo-electric transducers, electrically isolated from one another and located peripherally about and supported by the tubular acoustic attenuating backing.

Description

Title: Method and device for bundle control and

Bessel shadows from conformal array

This invention relates generally to a method and apparatus for acoustic borehole recordings in wells, such as for the production of petroleum products, and more particularly describes a methodology for imaging features using a cylindrical array of piezoelectric elements. This method utilizes mechanical and electronic beam focusing, electronic beam control, and amplitude shadows to improve resolution and overcome side lobe effects. Even more particularly, the present invention introduces a new signal reconstruction technique that utilizes independent array element transmission and reception, thereby creating focusing and beam control. The present invention has application in wire line, drilling measurements, pipeline application, and medical applications. The applications of the invention include, but are not limited to, borehole curve measurement, borehole geometry, borehole imaging, coating inspection, cement evaluation, and volumetric probing applications (e.g., fluid, behind the coating, open hole).

This invention relates to methods and equipment for determining the arrangement of earth strata traversed by a borehole, and relates to improved methods and equipment that utilize acoustic pulse energy transmission in fluid-filled boreholes to detect the angular and azimuth direction of the inclination of earth formations.

It is conventional practice to use an inclination meter to determine the angle and azimuthal direction of the inclination of the earth formation layers traversed by a borehole. A conventional shape of an inclination meter simultaneously makes resistance measurements at three or four electrodes with equal distances in a plane perpendicular to the axis of the borehole. The electrodes provide a resistance of the surrounding formation as the electrodes move along the wall of the borehole The records of all the resistance electrodes are correlated to derive the relative displacement along the borehole from the intersections with the plane of the geological inclination of the formation Inertial sensors with the inclination meter provide additional information regarding the direction and slope of the borehole and the rotational position of the tool itself.

Resistance inclination meters, although effective in non-fluid boreholes or in water-filled boreholes, have not been particularly effective in boreholes containing oil-based drilling mud. This is mainly due to the insulating property of the oil-based drilling fluid, since effective resistance recording is dependent on the measurement of conductivity or resistivity as obtained by the drilling fluid and the insulating layer of mud cake adhering to the wall of the borehole. To overcome this problem to some extent, special "scraper" and "hammer" electrodes ("scratcher" and "polier" electrodes) have been used to scrape through the insulating layer of mud cake and then contact the formation in order to to perform the resistance measurement. Such attempts aim to optimize the electrical contact of the electrode with the borehole wall. However, these attempts have met with various measures of success, often producing intermittent inclination information.

Attempts have been made to use acoustic energy in obtaining information to determine inclination measurements of the formation. There is no need for an absolute measurement, but for a well registration that can determine the change or transition from one layer of earth or formation to another. Attempts have been made to transmit acoustic pulse energy into the formation from a transducer in contact with the borehole wall and then to measure the transition time of the acoustic energy through the formation to remote transducers and also in contact with the borehole wall . Other attempts have been made to direct the acoustic pulse energy to the separation between the borehole wall and the formation and to measure the acoustic pulse energy reflected thereby, which would be indicative of the acoustic impedance of the formations. In both cases described above, however, it is not possible to place the acoustic transducer in continuous direct contact with the borehole wall due to the random wall geometry that occurs during drilling, and any penetration of the oil-based drilling fluid between the transducers and the interface between borehole wall and formation will introduce some weakening in the acoustic pulse energy. It has been found that the heavier the "weight" of the oil base mud, the greater is the attenuation of the acoustic energy due to scattering produced by the "weighing" material, such as barite or hematite, and the viscosity of the oil base mud. Moreover, in a pulse-echo configuration, the "noise" generated by the "falling off" of the transmitting transducer complicates the detection and accurate determination of the reflected acoustic pulse energy. If a "delay line" space is built into the transducer design between the transducer crystal and the borehole fluid, such as a "delay line" to delay the transducer call signal, the delay line also introduces additional reflection and transmission losses. Further, in the first case described above, the "travel" of the acoustic pulse through the formation itself to the receiving transducers introduces additional attenuation. In many cases, acoustic transducers are intended to substantially contact the borehole wall and to remain in static position for respective transducer pulses. U.S. Patent No. 5,146,050 to Strozeski, et al. Shows this general type of acoustic recording instrument for formation inclination. In other cases, as shown by U.S. Patent No. 5,001,676 to Broding, an acoustic transducer is rotatably mounted within a transducer housing and is typically rotated 360 ° by a motor and shaft at a rotational speed of 100-400 rpm while the transducer becomes pulsed in the range of approximately 2000 Hz. The use of a rotatable acoustic transducer of this type requires a complicated transducer design, which makes it both expensive to manufacture and difficult to use. Accordingly, it is desirable to provide a borehole recording instrument that has a high pulse rate and yet has a simplified and trouble-free transducer design.

According to one principle of the present invention, there is provided a method and equipment for acoustically recording earth formations that surround a fluid-containing borehole by means of an in-the-down-down ("downhole") recording instrument adapted to longitudinal movement by the borehole. An acoustic transducer system is provided within the recording instrument and includes a cylindrical array of piezoelectric elements, the array being fixed within the housing structure. The method of the preferred embodiment of the present invention utilizes mechanical and electronic beam focusing, electronic beam control, and amplitude shadows to increase resolution and overcome side lobe effects. This invention introduces a new signal reconstruction technique that utilizes independent array element transmission and reception, thereby creating focusing and beam control. Application of the methodology can be used in wire line measurement during drilling, pipe, pipeline applications and medical applications. From the borehole standpoint, applications of the invention include, but are not limited to, borehole caliber, borehole geometry, borehole imaging, liner inspection, cement evaluation, and volumetric scanning (e.g., fluid, behind liner, open hole).

Although the preferred embodiment of the present invention comprises a cylindrical array of linear piezoelectric elements, the present invention is not limited to such a thing. It is to be borne in mind that the scope of this invention is intended to include arrays of multiple piezoelectric elements of different configuration, such as conical, bikonic, curved, etc.

Briefly, this invention describes the methodology for displaying features using a cylindrical or conical array of piezoelectric elements that are formed as, but not limited to, one of the following: cylindrical arrays: (1) A set of N straight lines elements of equal width aligned along the cylinder axis of the system, the length of which is equal to the height of the array, where N is any number of elements.

(2) A set of N x M linear elements of equal length and width aligned along the cylinder axis of the array, where N is the number of elements around the array, and M is the number of elements along the axis of the array.

(3) A set of N curved transducer elements of equal width, having a geometric radius R parallel to the axis of the array (and thereby creating a focal length F), aligned along the axis of the array, the length of which is equal to the height of the array.

(4) A set of N x M linear elements of unequal size aligned along the cylinder axis of the array, where N is the number of elements around the array, and M is the number of elements along the axis of the array.

(5) A set of N x M curved transducer elements of unequal length and width, with a geometric radius R parallel to the axis of the array (and thereby creating a focal length F), aligned along the axis of the array, the length of which is aware of the array.

(6) A set of N x M curved transducer elements of unequal length and width, with a geometric radius R parallel to the axis of the array (and thereby creating a focal length F), aligned along the axis of the array and mounted such, that their surface is on the geometric surface with radius R, the length of which is equal to the height of the array.

(7) A set of N x M linear transducer elements arranged so that the long dimension of each element is perpendicular to the axis of the array, where N is the number of elements arranged around the axis of the array, and M is the number of elements along the axis of the array.

(8) A set of N x M curved transducer elements of unequal length and width and arranged so that the long dimension is perpendicular to the axis of the array, where N and M are defined in (7) above. The curvature of the array defines a physical focus in the direction perpendicular to the axis of the array.

Conical arrays (The cylindrical array described above is a special case of the more general conical array). The surface of the cylindrical array can be described by a surface of revolution of a circle with radius R about the axis of the array, the radius being perpendicular to the surface of the array. The conical array surface is a truncated cone (hereinafter referred to as "cone") and is described by a surface of revolution about the axis of the array described by a circle of radius R, the radius not perpendicular to the axis of the array state. A linear surface can be described by an infinitely large radius R. The conical transducer arrays include: (1) A set of N linear elements of equal width and located on the surface of the cone, aligned along the cylinder axis of the array, of which the length is equal to the height of the array, where N is any number of elements.

(2) A set of N x M linear elements of equal length and width and located on the surface of the cone aligned along the cylinder axis of the array, where N is the number of elements around the array, and M is the number of elements along the axis of the array.

(3) A set of N curved transducer elements of equal width, located on the surface of the cone with a geometric radius R parallel to the axis of the array (and thereby creating a focal length F), aligned along the axis of the array, whose length is equal to the height of the array.

(4) A set of N x M linear elements of unequal size, located on the surface of the cone, aligned along the cylinder axis of the array, where N is the number of elements around the array, and where M is the number of elements along the axis of the array.

(5) A set of N x M curved transducer elements of unequal length and width, with a geometric radius R parallel to the axis of the array (and thereby creating a focal length F), located on the surface of the cone and aligned along the axis of the array, the lengths of which are equal to the height of the array.

(6) A set of N x M curved transducer elements of unequal length and width, with a geometric radius R parallel to the axis of the array (and thereby creating a focal length F), located on the surface of the cone, aligned along the axis of the array and mounted such that their surface is on the geometric surface of radius R, the length of which is equal to the height of the array.

(7) All of the above, wherein the elements are trapezoidal with widths increasing along the conical surface, thereby maintaining an equal distance between elements.

(8) A set of N x M linear transducer elements located on the surface of the cone, arranged so that the long dimension of each element is perpendicular to the axis of the array, where N is the number of elements that is arranged around the axis of the array, and M is the number of elements along the axis of the array.

(9) A set of N x M curved transducer elements of unequal length and width, located on the surface of the cone and arranged so that their long dimension is perpendicular to the axis of the array, N and M being defined in (7) above. The curvature defines physical focusing in the direction perpendicular to the local surface axis of the cone.

The system will be used in the following configurations: (1) Single array.

(2) Dual array (a) cylindrical (b) bi-conic, with the tip of the cones facing other conical array.

(c) bi-conical, the point of the cones pointing away from another conical array.

(3) Multiple arrays, of any combination of (1) and (2) above.

In the following discussion, "axial direction" means the direction along the axis of the array, and "orthogonal direction" means a plane orthogonal to the axis of the array. In the case of the conical arrays, the orthogonal surface described is a conical or conical surface that is perpendicular to the surface of the conical section (at the center thereof, if the element surface is bent).

Mechanical focusing:

The array can be focused in either the axial or orthogonal direction, or by the cylindrical curvature of the elements, or by acoustic lenses for all arrays.

N x M arrays may or may not be equipped with mechanical focusing.

Electronic focusing:

Focusing in the arrays will be accomplished electronically by developing a virtual focal plane by providing proper delays to the electrical stimuli of each element of the array. Focusing the array can be either axial or orthogonal, or in the case of N x M, arrays can be electronically focused in both the axial and the orthogonal directions. In the case of axial or orthogonal focusing, the orthogonal or axial axis can be mechanically focused.

Mechanical control:

Mechanically focused arrays will not have variable control options in the direction controlled by the mechanical focus. A single steering direction must be defined by mechanical shape in the axial direction or orthogonal direction. A cylindrical array will transmit acoustic pulse signals perpendicular to the axis of the array. A conical array will emit over a surface perpendicular to the surface of the cone, at an angle to the axis of the array defined by the slope of the conical surface (for curved conical elements, the angle is defined at the center of the elements ).

Electronic control:

Steering in the arrays will be accomplished electronically by developing a virtual focal plane by providing the correct delays to the electrical stimuli from each element of the system to the point the output signal in the desired control direction. The control of the array can be either axial or orthogonal or, in the case of N x M, can be controlled in all directions. In the case of axial or orthogonal steering, the orthogonal or axial axis can be mechanically steered to a fixed surface.

In order for the manner in which the aforementioned features, advantages and objects of the present invention are achieved to be achieved in detail, a more detailed description of the invention briefly summarized above is given with reference to embodiments thereof which are included in the accompanying drawings. are illustrated.

It should be noted, however, that the accompanying drawings only illustrate typical embodiments of this invention and, therefore, should not be construed as limiting the scope, since the invention can also be applied in other equally effective embodiments.

FIG. 1 is a schematic illustration of a method and apparatus for beam control and Bessel shading of a conformal array according to the teachings of the present invention.

FIG. 2 is a cross-sectional view of a portion of the acoustic well recording probe of FIG. 1, showing a cylindrical array with a plurality of piezoelectric elements incorporated within a sub-housing of the probe.

FIG. 3 is an isometric illustration of a 32-element cylindrical piezoelectric array as contained within the sub-housing of the probe of FIG. 2.

FIG. 4 is an exploded isometric illustration similar to that of FIG. 3, illustrating an initial state in the manufacture of a 64-element cylindrical piezoelectric array constructed in accordance with the present invention.

FIG. 5 is a plan view of the 64-element array of FIGS. 4 and 6.

FIG. 6 is an isometric illustration of a 64-element piezoelectric array upon completion of its manufacturing process.

FIG. 7 is a plan view of a piezoelectric transducer array embodying the present invention and including piezoelectric transducers of uneven size.

FIG. 8 is an isometric illustration similar to that of FIGS. 3 and 6 and showing a curved piezoelectric array.

FIG. 9 is a cross-section along the line 9-9 of FIG.

8.

FIG. 10 is an isometric illustration of a cylindrical piezoelectric array located within a generally cylindrical acoustic window provided with a mechanical focusing capability.

FIG. 11 is a section along the line 11-11 of FIG. 10.

FIG. 12 is a section along the line 12-12 of FIG. 11.

FIG. 13 is an isometric illustration of a generally cylindrical piezoelectric acoustic array in which are stacked up circularly oriented radiators of piezoelectric elements arranged around a background substrate.

FIG. 14 is an isometric illustration of a convexly curved array of piezoelectric elements arranged to provide an array of convex configuration for the purpose of mechanical focusing.

FIG. 15 is an isometric illustration of a generally cone-shaped piezoelectric array that has a plurality of piezoelectric elements arranged to provide an external shape of conical configuration.

FIG. 16 is an isometric illustration showing a tapered convexly curved piezoelectric array with ends of different sizes.

FIG. 17 is an isometric illustration showing a plurality of piezoelectric elements arranged in a generally conical configuration with the larger dimension defining the upper end of the array.

FIG. 18 is an isometric illustration showing a piezoelectric array constructed in accordance with the present invention and having curved upper and intermediate surfaces that are spaced apart by a generally cylindrical section and an array concept define with focusing as a goal.

FIG. 19 is an isometric illustration of a piezoelectric array constructed in accordance with the present invention and having a plurality of emitters of piezoelectric elements, each in the form of an octagon.

FIG. 20 is a plan view of the piezoelectric array of FIG. 19.

FIG. 21 is an isometric illustration of a piezoelectric array that has a plurality of radiators of piezoelectric elements that define an eight-sided array structure that provides conventionally curved external signal focusing surfaces.

FIG. 22 is a plan view of the piezoelectric array of FIG. 21.

FIG. 23 is an exploded isometric illustration of a transformer block that has multiple transformers and can be used as shown in FIG.

FIG. 24 is a section along the line 24-24 of FIG. 23.

FIG. 25 is a partial sectional view of a transformer that can be tuned.

FIG. 26 is a top view of a transformer block, similar to that of FIG. 4.

Referring now to the drawings, and first to FIG.

1, reference numeral 10 generally designates the data-transmitting and data-receiving systems for an acoustic downhole recording probe. The acoustic borehole recording probe is generally designated by reference numeral 12, and is generally defined by a probe housing 14 which has an acoustically transparent section or "window" section 16 through which acoustic signals are sent to the borehole wall 18 and the surrounding earth formation 20 traversed by the borehole. As shown, the probe 12 is supported by a wire line cable 22 which extends around cable disks 24 and 26 to a cable drum 28. The electrical conductors 30 of the wire line cable establish a data transfer coupling with a receiving system 32 and a data acquisition system 34. The data acquisition system is provided with an output 36 to which a data recording system such as a tape system 38 is coupled for magnetically recording output signals from the acquisition system, a graphic system 40 for providing a hard copy of the output signals, and a cathode ray tube 42 for providing a real-time visual image of the data collected by the acquisition system.

The probe 12 to be lowered into a hole comprises in its internal electronic circuits and an array 44 of acoustic transducers, a preferred embodiment of which is shown in Figs. 3 and 4 to 6. The transducer array 44 is provided with a plurality of array switches 46 coupled to array receivers 48 and array transmitters 50 under the control of an array timing circuit 52. The output signals from the array transmitters 50 are processed by an amplitude / receive control 54 under the control of a signal processing circuit 56. The output signals from the array receivers are then processed by analog-to-digital converter circuits 58 so that an array memory circuit 60 is provided with a digitized array reception signal. The data from the array memory 60 is processed by an array processing circuit 62 and provided to an input buffer 63 and to the signal processor 56. The output signal from the signal processor 56 is supplied to an output buffer 64, which has controlled data transmission from a data transmission chain 66 which provides data to the receiving system circuit 32.

The circuitry of FIG. 1 allows each of the many acoustic transmitters of the transmitter array 44 to fire one by one into a controlled sequence for transmission of acoustic signals from the probe to the borehole wall and into the formation. The array timing circuit also allows time-controlled reception of acoustic reflections from the surrounding formation. The array timing circuit 52 together with the signal processor 56 also provides the probe to be lowered into the hole with the ability to provide directionally controlled or focused acoustic signals for beam control and Bessel shading of the conformal array. Referring now to Fig. 2, which is a cross-sectional view illustrating a portion of the probe 12, the probe housing 14 as defined above defines an internally threaded mating connector 68 which receives the externally threaded end 70 from an elongated connector portion 72 of a housing connector subsystem 74. The elongated housing connector 72 defines an internal bore 76, which defines a dry wire passage for a plurality of electrical conductors individually connected to piezoelectric elements of the array, as will be described below . The connector protrusion 72 is sealed with respect to the housing section 78 of the housing 14 by circular seals 80 which are contained within respective sealing grooves of the connector protrusion.

The length of the connector protrusion cooperates with the housing section 78 to define an annular recess or receptacle (82), which is closed by an annular, mechanically focused, acoustically transparent window 84, which is provided with an inter-focusing section 86 with a concave curvature. The focusing window 84 is sealed with respect to the housing sections 78 and 74 by means of circular seals 88 and 90 which are received within respective annular sealing grooves of the housing sections. Although the acoustically transparent window 84 has a curved section to mechanically focus acoustic signals emitted by the straight transducers, it should be borne in mind that the transducers themselves may be curved to achieve signal focusing, and the window may not -focusing type. Within the annular recess or receptacle 82 there is an annular support portion 92 that is surrounded by a plurality of piezoelectric elements 94 with substantially equal mutual spacing, which may be separate from the support portion or may be attached to the support portion if desired. Within the recess or receptacle 82 is a connector block 96 which is provided with a plurality of connector pins 98 extending through respective passages of the housing section 74, with end portions thereof exposed for connection within a conventional and non-shown bus connector. Each of the connector pins 98 is coupled by an electrical conductor to an individual piezoelectric element 94 and is arranged to conduct fire pulses to the respective piezoelectric element to excite it, and to conduct reflected acoustic signals from the piezoelectric element. electrical elements for processing through the circuit of Figure 1 together with acquisition of acoustic data representing the environment of the formation at the bottom of the hole.

Reference is now made to Fig. 3, where an isometric illustration of a cylindrical array consisting of 32 elements is illustrated which is representative of the piezoelectric array module of Fig. 2. An acoustically attenuating support section 92 preferably consists of a suitable elastomer filled with high density metal shavings, such as tungsten shavings. The support section 92 is selected to preferably provide an acoustic attenuation of about 30 db / cm, and when filled with the high-density tungsten shavings, provides an acoustic impedance of about 13.3 mega-rays, MKS. This is a desired impedance adjustment for the multiple piezoelectric transducer elements that may consist of lead-metaniobate ceramic with an acoustic impedance of 21.7 mega-rays, MKS, since a ratio of 2: 1 is desired. In the preferred embodiment, the array transducer is embedded in a module with a high structural strength, which is acoustically transparent (window) at the outer transmitting surface of the array, and acoustically attenuating on the inner surface (supporting portion) of the array. The module must be able to withstand pressures of 20 kpsi, and temperatures of around 200 ° C, without significant radial deformation due to the compression forces created by the printing environment. The acoustic properties of the outer surface must allow sufficient thickness in the window to provide the radial compression strength, at a thickness of 1/4 of a wavelength of the primary component of transmitted frequency. The module must be hermetically sealed and compatible with the stainless steel and / or titanium components to which it is attached. The outer surface of the module must be resistant to the corrosive environments that are common in the wiring industry. The thermal expansion coefficient of the module material should be as close as possible to the thermal expansion properties of the transducers. The multiple transducer array, including its acoustically transparent window, can be an integral unit that is retained by the housing structure and sealed to the housing by O-rings or other suitable sealing elements. To enable the transducer array to withstand the hydrostatic pressure conditions that will be typical for deep wells, the transducer array will be or wound with a carbon fiber material, so that its carbon fibers will add structural resistance to radial compression. The resulting annular transducer array structure can then be easily installed within the housing of a recording probe to be lowered into a hole by a simple "plug-in" construction. This feature would allow the transducer array package to be exchanged easily and efficiently even under field conditions in the event that such a thing becomes suitable.

A preferred embodiment of the structure of the array mounting material for the module is a carbon composite material, which is designed to be acoustically transparent at the window surface, and "loaded" with (tungsten or other materials), powder and shavings on the back of the transducer to provide acoustic attenuation. The carbon composite material can be metallized with a thin corrosion-resistant metal with sufficient thickness to prevent a loss of hermiticity due to normal scraping and wear. The metallization material can be chosen to allow periodic re-metallization.

In an alternative embodiment of the aforementioned mounting structure, ceramic materials can be used instead of carbon composite.

The piezoelectric transducer elements 94 are preferably made from lead metaniobate; however, other transducer materials may be used for other operating frequencies, such as (non-limiting) lead, zirconate, titanate (all forms), barium titanate, lithium sulfate, quartz, lithium niobate, and PVDP. The space 96 between the elements as shown in Fig. 3 will be filled with acoustically damping materials, such as, for example (non-limiting) tungsten powder-laden epoxy, tungsten powder-laden carbon composite, and tungsten powder-loaded ceramics. With backward and inter-element attenuation, the acoustic pulses are transmitted unidirectionally from the array in the radially outward direction. The supporting structures, weakening and window systems will be designed to prevent electrical short circuits between array elements.

The nominal operating frequency range of the piezoelectric array representing the preferred embodiment will be in the range of 200-500 kHz. Other applications may include frequencies that are much lower (10 kHz) or much higher (a few MHz). For image scanning of a well bore, or evaluation of the coating / cement, the preferred embodiment will take the form of a mechanically vertically focused, orthogonal scanning array of 32-128 elements operating at a frequency of about 250 kHz. For image scanning of a well bore, a high-resolution vertical embodiment may be preferred. This array will be mechanically focused in the horizontal direction, and focused and scanned in the vertical direction. A preferred embodiment would have eight horizontally focused elements on each of the eight planes of an octagonal parallelepiped. This mode allows a vertical scan with high resolution.

For volumetric procedures behind the cladding, the preferred embodiment will typically take the form of a mechanically vertically focused, horizontally sensing conical array of 32 to 128 elements designed to engage the borehole wall at an angle of about 10 ° to 35 ° and at preferably about 20 °. For volumetric fluid procedures, a preferred embodiment may take the form of bikonic dual array embodiments. This bi-conical dual array will have oppositely directed conical array sections that may be separated by an intermediate spacer. If desired, the intermediate "spacer" may conveniently take the form of a cylindrical transducer array of the general nature as indicated in Figures 4 to 6. The tips of the conical arrays will face each other. The preferred array embodiment for this feature is the mechanically vertically focused, orthogonal scanning array. The space between the array elements will be designed to allow reflections from the wellbore, liner or pipe to be received on the other array. Interchangeable spacers will be provided to allow use in well bores, linings, and pipe of various diameters.

Another embodiment of the present invention for volumetric scanning may conveniently take the form of a bikonic dual array as shown in Fig. 18, with curved or tapered, frusto-conical ends, except that the array will be mechanically focused in the horizontal position, and electronically focused and scanned in the vertical direction. It is anticipated that this embodiment would have eight horizontally focused elements on each of the eight planes of an octagonal "cone".

Another embodiment consists of a full scanning array, with electronic focusing and control in both horizontal directions. This array of conical variations could be used in all the above applications.

Additional embodiments include synthetic multiple transmitters and receivers. For example, an octogonal arrangement of orthogonally focused, vertically controlled array elements could be designed to fire all elements around the octagon in parallel, and thereby vertically controlled, monopole, dipole, crossed dipole, segmented dipole, quadrapole, crossed quadrapole, octapole acoustic radiation fields, and combination modes. The receiver of the acoustic signals could be the transmitting array in a pulse echo mode, or a second array could be configured to receive the pulse echo signals. Another alternative to the pulse echo system is continuous wave transmission with a second receiver.

Direct measurements of formation density using bi-conical arrays can take the following general forms: ARRAY-ELECTRONICS:

Transmitter:

The array transmitters 50 consist of piezoelectric elements, inductors, tuning inductors, transformers, multiplexers, drive electronics, and voltage control electronics.

Array driver:

The array drivers are designed using conventional pulsechoo or continuous wave piezoelectric drivers, with at least one driver per active element, and as much as one driver per element. The number of floats can be minimized using conventional multiplexing techniques. The drive pulses will be formed to minimize harmonic distortion in the acoustic pulse waveform, and to minimize excitation of unwanted harmonic modes within the transducer element. Typical pulse formation will be (non-limiting) semi-sinusoidal, single pulses, up to multiple half periods of a sine wave.

The power of the pulse echo signal can be increased by using a plurality of fire pulses with a pulse frequency equal to the characteristic frequency of the transducer. The pulses driving the transducer can be unipolar or bi-polar. The output stages of the amplifier can also be "push-pull".

Array transformer:

The array drivers are connected to each transducer element through transformers, inductors and tuning inductors.

In a preferred embodiment, an array of transformers, inductors, and tuning inductors is made from a single ferrite substrate, creating a module that contains one transformer, one inductor, and one tuning inductor per array element. The array transformer can be subdivided into smaller subgroups, as desired by spatial geometry constraints and magnetic element sizes. The preferred embodiment of the array transformers would place the magnetic components in a circular ring with an outer diameter equal to the diameter of the array, and an inner diameter approximately equal to the inner diameter of the array. If the size of the magnetic elements were too large for this arrangement, alternative embodiments would allow the rings to be placed on both ends of the array, and optionally multiple rings could be used. The inductor and tuning elements are desired to optimize the response to the drive signal.

An alternative and preferred array transformer would be a linear array of about 2 inches by 2 inches. The actual size will depend on the chosen ferrite and the detailed design of the transformer, the inductor and the tuner.

Aligning:

The array will be electrically tuned by the combination of the inductances in the coupling transformer, a fixed inductor and a tuning inductor. The array transformers, inductor and tuning elements will be designed to allow the array and the transformers, fixed inductor and tuning inductor to be removed as a unit, allowing replacement of a transducer without re-tuning.

Check the transmit amplitude:

The firing voltage for each element can be variable and controlled by the electronics. The fire voltage will be controlled by conventional voltage control electronics.

Element shadows:

Electronic shading will be provided by making each array element driving voltage variable, and thus allowing side lobe suppression using, for example, (non-limiting) Bessel shadows, cosine shadows, or Gaussian shadows. Shading is accomplished by adjusting the firing voltage on each element of the array by reducing the driving voltage (relative to the central element if the number of active elements is odd, or relative to the central pair if the number of elements is even). After each element according to the function described by the selected shadow technique and the distance of the element from the central peak. Shading in the case of Bessel or cosine shading may include shading from the central peak after the first zero, or out to multiple zeros and peaks.

Transmission temperature control:

Electronic focusing and control will be provided by conventional array timing technology.

Receiver:

The array transmitters consist of piezoelectric elements, inductors, tuning inductors, transformers, multiplexers, and electronic amplifiers and gain factor control electronics and analog-to-digital converters.

Array receiver:

The array receivers are designed using conventional pulse echo or continuous wave piezoelectric receivers, with at least one receiver per active element, and as many as one receiver per element. The number of floats can be minimized using conventional multiplexing techniques. Filtering will be accomplished by using conventional, active, electronic filters.

Control of the gain factor in the receiver:

The gain factor will be selectable using conventional electronics for variable gain factor.

Element shadows:

The gain factors of the receiving elements can be adjusted using variable gain factor techniques using conventional electronics. The shading will use Bessel shadows, cosine shadows, or Gaussian shadows as described above in connection with the transmission section.

Timer control in the receiver:

Electronic focusing and control will be provided by conventional array timing technology.

Dynamic transducer damping:

Dynamic transducer damping will be accomplished by providing a feedback drive system to cancel the harmonic motion of the transducer by driving the transducer to cancel motion generated by the oscillation of the transducer. The feedback output signal can also be used as a pick-up signal from the receiver. The feedback signal will maintain a zero voltage at all times on the transducer electrodes, except for the fire pulse. The electronics will be designed to prevent overvoltage conditions on the receiving section of the array electronics, and to allow maximum application of driving voltage power.

In the case of firing sequences for multiple pulse transducers, the following will be used in conjunction with the feedback technique described above: following the activation pulse sequences, an adjacent pulse sequence of equal length or less, 180 ° out of phase with the activation pulse sequence, will drive the transducer. The optimum number of out-of-phase signals for providing active attenuation will be determined for the array following fabrication. The purpose of the active attenuation is to reduce the transducer excitation voltage in the control range of the active feedback electronics described above.

Array processors: ---------------- The array electronics will include a number of dedicated signal processors of conventional design for real-time processing of the array data at a high data rate.

Signal reconstruction:

A unique real-time signal processing algorithm can be used in array electronics. This technique requires individual firing of each element, and receiving the pulse echo of the signal simultaneously on the selected active array elements. The reception signal is mathematically reconstructed in the array processors by applying the correct timing shifts and gain adjustments. In this technique, for example, with an array of 64 vertical elements, each element would be fired once to produce 64 transmit data sets per revolution. Each data set would contain the results of the analog-to-digital conversion of the pulse echo signal received on each receiving element. For example, if 8 receiver elements were active, there would be 8 digitized pulse echo waveforms for each of the 64 receivers in the array, or 512 data sets per revolution. The signal is reconstructed in the following method. Each pulse echo signature is digitally shifted to the correct tempering as calculated for focusing and controlling travel time with fluid velocity and a gain factor term is generated for each pulse echo signature as calculated by the shadow technique and compensation for fluid attenuation. Each data point in the signature is multiplied by its correct gain factor (or attenuation factor). The array signature is then constructed by summing the phase and gain adjusted signatures of each element combination of firing and receiving elements. The number of signatures available for this reconstruction is N squared, where N is the number of active elements for the phased array. This should result in a signal improvement of up to 20 * logiN ^) dB; for N equal to 8 this is 36 dB and a signal / noise improvement of 20 * log (N2) dB, for N equal to 8 this is 18 dB. The table below illustrates for 8 active elements the transmit / receive combinations that can be used to reconstruct the waveform. Each Xij is an array of M samples of signature data. The number of samples in the signature will depend on the characteristic frequency and sample rates of the analog-to-digital converters as indicated by the following example:

Tl T2 T3 Τ4 Τ5 Τ6 Τ7 Τ8 R1 XII Χ12 Χ13 Χ14 Χ15 Χ16 Χ17 Χ18 R2 Χ21 Χ22 Χ23 Χ24 Χ25 Χ26 Χ27 Χ28 R3 Χ31 Χ32 Χ33 Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ Χ55 Χ56 Χ57 Χ58 R6 Χ61 Χ62 Χ63 Χ64 Χ65 Χ67 Χ67 R7 Χ71 Χ72 Χ73 Χ74 Χ75 Χ76 Χ77 Χ78 R8 Χ81 Χ82 Χ83 Χ84 Χ85 Χ86 Χ87 Χ88

A weighing array can be developed to compensate for shadows and signal attenuation due to different path lengths of each of the signals, as indicated by the following: .......-............. ............. Tl ........................- 12 -........- ...... T3 .................... T4 ..................... T5 ............................... T6 .................. ...... T7 ................... T8 .......-.......- R1 W12 W13 W14 W15 W16 W17 W18 R2 W21 W23 W24 W25 W26 W27 W28 W3 W31 W32 W33 W34 W35 W36 W37 W38 R4 W41 W42 W43 W44 W45 W46 W47 W48 R5 W51 W52 W53 W54 W55 W56 W57 W58 R6 W61 W62 W63 W64 W65 W66 W67 W68 W73 W74 W75 W76 W77 W78 R8 W81 W82 W83 W84 W85 W86 W87 W88

The weighing array is multiplied on a signature-for-signature basis, which provides the following product array:

Tl T2 T3 Τ4 Τ5 Τ6 Τ7 Τ8 R1 W11X11 W12X12 W13X13 W14X14 W15X15 W16X16 W17X17 W18X18 R2 W21X21 W22X22 W23X23 W24X24 W25X25 W26X26 W27X27 W28X28 R3 W31X31 W32X32 W33X33 W34X34 W35X35 W36X36 W37X37 W38X38 R4 W41X41 W42X42 W43X43 W44X44 W45X45 W46X46 W47X47 W48X48 R5 W51X51 W52X52 W53X53 W54X54 W55X55 W56X56 W57X57 W58X58 R6 W61X61 W62X62 W63X63 W64X64 W65X65 W66X66 W67X67 W68X68 R7 W71X71 W72X72 W73X73 W74X74 W75X75 W76X76 W77X77 W78X78 R8 W81X81 W82X82 W83X83 W85X86 W88X88 W88 W88 W88 W88 W88 W88 W88 W88

Each of the weighting factors is a combination of the desired shading for each transmit / receive pair, the variations in signal strength due to the different path lengths and resulting attenuation in the propagation media, and certain geometric considerations. One of the geometric considerations is the "direct" reflection path from the transducer to itself. For elements located near the center of the array, the direct reflection path may be desired, while for elements remote from the array center, the direct reflection path may produce unwanted and unwanted direct reflections. Similarly, neighboring elements near the center may have desired reflection paths, while those pairs at some distance from the center may produce unwanted reflection paths. For geometric reasons, elements along the diagonal (Wii) generally have desired reflection paths unless they are near the center of the array, while the elements on the anti-diagonal (Wi, 9-1) have all desired reflection paths. Elements near the anti-diagonal are more desirable than those further away. If the distance is calculated from the geometric target center for each direct reflection point for each array pair to the desired focal point of the array, the calculated distance can be used to calculate the geometric weighting for each transmit / receive pair. For example, if the energy profile of the focused beam perpendicular to the beam, at the target point, would follow a Gaussian profile with the peak of the Gaussian curve at the focal point, then a Gaussian weight distribution could be applied to the weighing array to reduce unwanted direct reflections from each element. For example, the following geometric weighing could be used:

T1 T2 T3 T4 T5 T6 T7 T8 R1 0 .1 .2 .4 .6 .8 .9 1 R2 .1 .2 .4 .6 .8 .9 1 .8 R3 .2 .4 .6 .8 .9 1 .9 .8 R4 .4 .6 .8 .9 1 .9 .8 .6 R5 .6 .8 .9 1.9 .8 .6 .4 R6 .6 .9 1 .9 .8 .6 .4. 2 R7 .9 1 .9 .8 .6 .4 .2 .1 - R8 ---- 1 ---------. 9 -----. 8 -----. 6- --------. 4 ------------- .2 --------------. 1 0 -

The approach is to reduce the amplitude of reflected signals outside the desired focal size by reducing the weighting of these reflections. The weighing can be Gaussian, but is not limited to Gaussian weight distributions.

Dynamic signature compensation for the transmission characteristic, pulsecho mode:

Since the characteristic signature of an acoustic transmitter is very repeatable, even though it may be complicated, dynamic signature compensation for the transducer characteristic can be realized even in the presence of various signals. Since the contribution of pulse echo in each actual measuring system is time variable in amplitude and phase, the average over a sufficient number of pulse echo signals will produce a data set with an average of 0 and a low variance. In order to compensate for acoustic signals activated by the transmitter that are not a return echo, the signature must be determined for each transmitter. Each signature or waveform is calculated from a set of N

firings of single transducer elements which are received simultaneously on N separate transducer chains. For example, when each of the 64 transducers of an acoustic transducer array is fired, 8 of the transducers will be in a receive mode so that multiple signals are received when firing each transducer. These multiple signals are then processed electronically according to the present invention. The signature for a given array firing position is determined by the superposition of these single element signatures, each signature being delayed by the proper focus and control delay so that the output waveform is described by

wherein the delay is (quantized to the sampling rate of the waveform),

Wj> Jc is the shadow weight, and g-j ^ k is the geometric shadow, and

at which

Wj / k = wj, k * 9j, k

The signature can be compensated according to:

wherein the element-by-element is average of the digitized signature of a single element.

If an amplitude profile of a transmitter, including all pulse echo returns, is digitized, stored and averaged, with a sufficient averaging time or filtered using a low-frequency low-pass filter, the remaining signal will be a good approximation of the transducer voltage measured would be in the absence of pulsecho. For each transducer in the array that is activated as both a transmitter and a receiver (or any transducer in general), the average signature of the transmitter can be subtracted from the received waveform on a point by point basis, resulting in a " pure "pulse chorse response. The same compensation technique can be used to eliminate signature cross-talk between transmitting elements and their neighboring elements.

Signature processor:

The signal processor will be a conventional signal processor, using standard design techniques for a signal processor.

Array compensation and calibration:

The array instrument will have an assigned transducer for measuring fluid inertia and attenuation. The tool will be designed to be self-calibrating continuously. This will be achieved by introducing into the acoustic path a propagation medium with calibrated acoustic properties and geometry. The "call calibration" will be calibrated over temperature and pressure variations to allow polynomial models for improved call calibration. The results of these measurements will be used to compensate for the array tempering and amplitudes.

Amplitude control:

The signal processor will calculate the coefficients of the weighing matrix and send the coefficients to the array processors. The signal processor will adjust the amplitude control matrices for changes in fluid attenuation, and track length variations if the control attenuation indicates changes in track length.

Tempering control:

The signal processor must also determine the centering and eccentricity of the borehole. The results of the centering and eccentricity will be used to compensate for variations in signal amplitude due to eccentricity and centering, and can be used to modify the selected array elements to be used to generate the wellbore scan. For example, if the tool is outside the center, and the target point is not "before" the normal array center, the array center could move one or more elements to minimize the unwanted effects of surface angles.

Array focusing:

The focal point of the array can be dynamically adjusted by the signal processor based on the eccentricity and off-center calculations. The signal processor will produce a modified timing arrays to be sent to the signal processors to allow for variations in distance to the target points.

Compensation for fluid in the array borehole:

Attenuation (self-calibration):

An assigned transducer will be used in pulse echo mode. Use will be made of conventional pulse echo signal generation and reception amplification and digitization. An additional material of known calibrated acoustic properties, attenuation, thickness, and acoustic impedance can be added to the acoustic path between the transducer and a reflective surface exposed to the wellbore fluid. By measuring the amplitude of the returning signals from the plane of the callibration unit, as well as the reflective surface through the wellbore fluid and the distance traveled in the calibrator and the wellbore fluid, the fluid attenuation can be calculated. The callibration can be performed in software in the signal processor and used to compensate for the signal amplitudes for each element in the array transducer.

Travel time (self-calibration):

The same transducer and electronics as described above can be used in pulse echo mode to measure fluid velocity. The calibrator block of known thickness and acoustic speed can be used as a reference for the time of flight measurements in the butbore fluids. The travel time to each surface in the trass docenthide will be measured, the distance across the calibration unit and the gap exposed to the wellbore fluids will be measured. The distances traveled in each medium and the travel time will be used to provide a calibrated mud speed. The fluid inertia will be calculated in the signal processor and used to compensate for tempering of the array transducers.

Referring now to Figs. 4 to 7, a method of manufacturing a generally cylindrical transducer array similar to that of Figs.

3, and the basic structure of the transducer array is also described. A support element 98 of a generally cylindrical configuration is provided, which consists of any of the support materials described above. Preferably, the support material of support element 98 will comprise an elastomer filled with high-density metal shavings or high-density tungsten shavings, thereby providing the option of acoustic attenuation and acoustic adjustment. Provided around the support member 98 is a generally cylindrical body 100 consisting of a suitable piezoelectric transducer material, such as lead metaniobate, ceramic, zirconate, titanate, barium titanate, lithium sulfate, quartz, lithium niobate, and PVD. The cylinders 98 and 100 may be attached to each other at cylindrical interface 102 by any suitable adhesive, adhesive, or by any other means to hold them together as a system. Alternatively, the support material 98 can be introduced within the cylinder 100 in an uncured liquid state, and allowed to cure in place. This process will be described in detail below. Attached to respective ends 104 and 106 of the cylindrical assembly comprising the cylinders 98 and 100 are end caps 108 and 110 each having a circumferential groove 112 within which the respective end of the cylindrical assembly is received. The upper and lower end caps 108 and 110 may also be attached to the cylindrical assembly by any suitable adhesive or by any suitable adhesive material. An inner connector or signal return connector 91 resides within the upper extremity of the array cylinder 100 and is with its lower surface 93 in substantial engagement with or in close proximity to the upper end of the body or support material 98. The outer cylinder surface 95 of the inner connector will be received within the upper end of the array cylinder and will be soldered or conductively bonded to the inner surface of the array cylinder. The inner or signal return connector preferably consists of a metal such as copper that is coated to be corrosion resistant, and provides a single electrical connector 97 centrally located therebetween. An outer connector or signal connector 99 provided with a plurality of protruding connector pins 101 spaced apart from one another is located at the upper end of the array cylinder and is covered by and perhaps held in position by the upper end cap 108. The outer signal connector consists of conductive material such as copper and is soldered or conductively bonded to the outer surface of the array cylinder. The connector pins 101 extend through aligned openings 103 in the flat wall 105 of the top end cap for contact with other electronic components. An array transformer blade 107 may be attached to the upper end cap after the cutting operation is completed so that the connector pins 101 make electrical contact with respective of a plurality of transformers within the transformer block. The array transformer block is designed to be attached to the piezoelectric array and electrically connected to the individual array elements and to drive and receiver electronics, either as a single unit or as multiple units. The transformer block 107 can define multiple electronics connectors 109 for contact mph-dfi-xespect instead of connect-pins of the outer connector. Alternatively, the connector pins 101 may be reception spaces and the connectors 103 of the transformer block may take the form of connector pins. The inner connector pin 97 will be exposed at the central opening 111 of the transformer block.

When it is intended to use a non-hardened support material, the array components, including the array cylinder, inner and outer connectors and end caps will be assembled, with an internal separation tube located within the cylinder and with its internal opening aligned with the central openings 113 and 115 of the end caps. The uncured support material, in a liquid or semi-liquid state, is then forced through an end cap opening as shown at 117 and 119, into the annular space between the inner wall of the arra, γ-cylinder and the outer surface of the inner tube. Openings 87 and 89 are respectively defined in the outer connector 105 and the inner connector 91 to allow the uncured support material to flow into the annular space from the end cap opening. When the annular space is full of support material, each feed size will exit at the opposite end cap openings 117 and 119. After the support material has cured to form a solid mass, the internal tube can be left in place in conjunction with the array, or it can be removed.

After the cylindrical assembly of FIG. 4 is completed, and before the transformer block is installed, a plurality of longitudinal parallel cuts are made in the assembly, as shown in FIGS. 5 and 6. These cuts extend completely through the outer transducer layer 100 and inner conductor ring 99 and somewhat into the support layer 98. This separates the annular transducer body into a plurality of electrically insulated transducer and connector systems while the inner conductor remains continuous so that each return conductor of the respective transducers will be short-circuited or electrically connected to the single return connector pin. A suitable means for making these cuts is by angularly oriented saw cuts around the cylinder axis 116. These saw cuts can be made by mounting the cylindrical transducer assembly in a jaw plate for rotation about the axis 116 and by dividing through its periphery so that the saw cuts will reach a desired number of transducer elements of equal width. After the cuts are made, each transducer and its respective electrical connection will be electronically isolated for individual electronic excitation. If transducer elements of unequal width are desired, then the saw cuts can be made suitably so that the dimensions thereof are uneven, as shown in Fig. 7. With regard to Fig. 7, it is noted that the peripheral cuts 118 of the quarter sections 120 and 122 are closer to each other compared to the cuts 124 of quartz segments 126 and 128. However, these particular distances for the cuts are not intended to be limiting to this invention because unequal spacing of any desired nature can be used so that linear piezoelectric elements of unequal width can be used in an acoustic array.

As stated above, for purposes of well recording, it is considered desirable to achieve focusing of acoustic signals at desired points relative to the formation surrounding the borehole. Focusing can be accomplished mechanically, both vertically and horizontally, by checking the configuration of the piezoelectric elements of the array. As shown in Figs. 8 and 9, a piezoelectric array is generally indicated at 130 by isometric illustration, and uses a central acoustic attenuator support member 132 of annular configuration surrounded by a plurality of curved piezoelectric elements 134 with equal mutual distances. As is clear from the cross-section of FIG. 9, the support member 132 and generally defines cylindrical bore 136 that allows the array unit 130 to be mounted on a cylindrical support, such as the connector protrusion 72 of FIG. 2. The support member 132 defines further an external concave surface 138 to which the curved inner surfaces 140 of the curved linear piezoelectric elements 134 are adhered or otherwise attached. These piezoelectric elements have an approximately constant width along their vertical length and thus define external acoustic signal focusing surfaces 142 for mechanically focusing the acoustic signals at the borehole wall or at any other suitable location relative to the transducer array. When acoustic signal focusing is achieved, there is a longer range, deeper penetration of the acoustic signals into the formation and therefore better depth of penetration of the signals into the formation so that a better angular solution is achieved. Electronic focusing in the horizontal direction is used for the purpose of control.

Reference is now made to Figs. 10-12, where an alternative embodiment of the present invention is generally shown at 144, which is provided for vertical mechanical focusing of the acoustic signals. The array array 144 has an external acoustic window 146 with upper and lower cylindrical end segments 148 and 150 between which is an external peripheral acoustic focusing surface 152 that is of concave configuration. The acoustic window thereby achieves focus of acoustic signals emitted by an internal acoustic piezoelectric array. The piezoelectric array is defined by a generally cylindrical support 154 that defines a cylindrical bore 156 for mounting the array array within the probe. The support element 154, which may contain any suitable acoustic signal attenuating material, also defines an external cylindrical surface 158 to which a plurality of spaced-apart linear elements 160 are attached by means of adhesion or by means of any suitable adhesive. The piezoelectric elements 160 define external surface segments 162.

Reference is now made to Fig. 13, where a generally cylindrical piezoelectric array is generally indicated by 164 by means of an isometric illustration, which array comprises an internal and generally cylindrical support element 166 which has an internal bore 168 has. Externally of the signal attenuating support, a set of piezoelectric acoustic elements is provided that includes a set of NxM linear piezoelectric elements of equal length and width aligned along the cylinder axis of the array, where N is the number of elements around the array and M is the number of piezoelectric elements along the cylinder axis of the array. In this particular case, N 64 represents piezoelectric elements arranged around the array, and array presents N 8 piezoelectric elements in each vertical row along the array axis. It must be borne in mind that these are random numbers, where both N and M represent any desired number for intended results. However, it should be borne in mind that each of the individual piezoelectric elements is electrically coupled to a single electrical conductor so that it can be excited individually by an electrical voltage pulse for signal generation. It should also be borne in mind that the piezoelectric elements can be coupled in selected groups with individual electrical conductors so that they can, if desired, be acidified simultaneously for a certain character of the signal generation.

Figures 14 to 17 are graphically representative of horizontally focusing piezoelectric arrays. In Fig. 14, the array generally designated 172 is a curved external configuration that defines a concave external array surface 174 and has an upper-end extremity 176 larger in diameter than the lower extremity 178. The array 72 can be used individually or in combination with other array sections to provide desired horizontal horizontal focusing of acoustic signals emitted for individual piezoelectric elements 180.

As shown in Fig. 16, generally at 182, this invention provides for providing a piezoelectric array of generally truncated conical configuration with a plurality of individual piezoelectric acoustic transmitter elements 184 that collectively have an external conical array surface 186 to define. In the case of FIG.

15, the larger diameter extremity 188 defines the upper end while the smaller extremity 190 defines the lower end of the array.

As shown in Fig. 16, a piezoelectric acoustic array is generally illustrated at 192 with a large upper extremity 194 and a lower lower extremity 196. This array is defined by a plurality of individual piezoelectric elements 198 that extend from the top to the bottom of the array and which are arranged side by side at mutual distance. Each of the piezoelectric elements has a curved configuration such that the transducers collectively define an externally curved concave surface 200 of the array.

As shown in Fig. 17, a piezoelectric acoustic array is generally shown at 202 and has a generally truncated configuration with a large upper end 204 and a smaller lower end 206, and is defined by a multiple of elongated piezoelectric elements 210 having external surfaces that collectively define an external array surface 212 of conical configuration. The individual piezoelectric elements 210 are arranged side by side at a mutual distance, the vertical height thereof defining the height of the array.

Referring to Fig. 18, a tabs or curved, generally bikonic array is generally shown at 212 in relation to a wellbore wall 214. The bikonic array includes upper and lower array sections generally designated A and B, which each having the configuration shown in FIG. 16 and having a plurality of elongated, spaced apart, curved piezoelectric elements, similar to those discussed above in connection with FIG. The array elements A and B are separated by an intermediate section intended for differential fluid flow. Element A can function as a transmitter, each of the piezoelectric elements 218 being suitably excited by electrical pulses. The bikonic extremity B can function as a receiver, each of its piezoelectric elements 220 being electrically coupled in the receiving mode. The transmitted acoustic signals are mechanically focused vertically due to the configuration of the piezoelectric elements as shown by dotted lines. By then adding the acoustic signals from the arrays A plus B, the average velocity of fluid flow can be determined, while by subtracting the acoustic signals A minus B, the differential velocity of the fluid flow can be determined. The piezoelectric elements can be fired element by element, or they can be fired simultaneously, as needed for proper signal transmission and reception. The length of the central spacer 216 can be adjusted to accommodate the use of an array of particular size in well bores, linings, and pipe of various diameters.

Another embodiment suitable for volume scanning is a bikonic dual array as shown in Fig. 18, except that the array is mechanically focused in the horizontal position and electronically focused and scanned in the vertical direction. It is envisaged that such an array would have 8 horizontally focused elements on each of the 8 planes of an octagonal "cone".

Referring to FIGS. 19 and 20, a piezoelectric transducer array is shown generally at 222, which is an unfocused array of octagonal configuration with a plurality of piezoelectric elements defining substantially flat external surfaces 224. The array configuration of Figs. 19 and 20 could best be used for vertical beam control. An embodiment of an octagonal focused array is generally shown at 226 in Figs. 21 and 22, each of the 8 planes of the octagonal configuration being defined by horizontally curved surfaces as shown at 228. These curved surfaces achieve a vertical scan for high resolution inclination measurement of a surrounding earth formation.

As mentioned in connection with FIG. 4, a transformer block 107 can be used to change the voltage applied to the individual piezoelectric transducers. As shown in Figs. 23 and 24, the transducer block can take a form as generally shown at 230, and include a body 232 of ferrite material defining circular recessed portions 234 around integral posts 236 and thus causing the ferrite posts to represent transformer cores. The recessed portions receive transformer winding conductors with a desired number of turns, which represent the input and output windings of the transformer. The winding guides are secured within the respective recessed portions by a preserving material such as a suitable polymer. A closure piece 238, also consisting of ferrite or any other suitable material, is bonded or otherwise fixed to the surface 240 to simultaneously form a closure piece for all of the transformation floors. The electrical input and output lines of the transformer windings will be exposed for electrical connection to an input source and to the connector elements or pins of the transducer.

Each of the transformers can be tuned by a simple transformer tuner as shown in Fig. 25. The central pole or core 236 can be chamfered on one side, as shown at 242. A ferrite tuning element 244 with an adaptation slot 246 and also provided with a core adaptation station 248 is rotatably mounted. The ferrite post 248 is chamfered at its end 250 so that when it is rotated relative to the core post 236, the structure of the transformer core is modified for the purpose of tuning the output signal of the transformer. A transformer array of the general nature shown in Fig. 23 is manufactured and sold by Ceramic Magnetics, Inc. of Fairfield, New Jersey.

As shown in Fig. 26, a ferrite array transformer block of generally circular configuration is shown generally at 254, with a plurality of transformers 252. It may include transformers that are tuned or fixed as desired. It may also include a combination of tuned or fixed transformers as needed for proper operation of the transformer block in conjunction with the acoustic transducer array of the invention. Typically, the transformer block will have the same number of transformers as it has acoustic transducers, the output leads of individual transformers being electrically connected to individual transducer elements.

It will therefore be appreciated that the present invention is well adapted to achieve all of the aforementioned objects and advantages, together with other advantages that will become apparent and inherent from a description of the device itself. It will be appreciated that certain combinations and sub-combinations are useful and can be used without reference to other features and combinations. This is provided by and falls within the scope of this invention.

Since many possible embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that all matters described above or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. .

Claims (5)

A method for electronically focusing the acoustic signals from an electronic transducer array that has a plurality of acoustic transducer elements arranged in a geometric pattern and has an electronic circuit for selective electronic stimulation thereof, comprising: - developing a virtual focusing surface for said electronic transducer array by providing selected delays to the electronic stimuli of each element of said transducer array, said virtual focusing surface being developed in axial direction. Method according to claim 1, characterized by developing said virtual focusing surface in the orthogonal direction. Method for electronically controlling the acoustic signals from an electronic transducer array that has a plurality of acoustic transducer elements arranged in a geometric pattern and has an electronic circuit for selective electronic stimulation thereof to provide an array output signal, comprising: - developing of a virtual focusing surface for said electronic transducer array by providing selected delays to the electronic stimuli of each said transducer array to point the output signal of the transducer array in a desired control direction; wherein said transducer array is stimulated to steer that array in the axial direction. The method of claim 3, characterized by electronically stimulating said transducer array to direct that array in the orthogonal direction. The method of claim 3, characterized by electronically stimulating said transducer array to direct that array in a randomly selected direction.