NO346079B1 - Piezoelectric transducer and borehole tool for measuring fluid properties - Google Patents

Description

BACKGROUND

1. The scope of the invention

[0001] This invention generally relates to instruments for measuring fluid properties and in particular, a piezoelectric transducer for measuring properties in borehole fluids.

2. Description of associated technology

[0002] US 3,743,869 describes a piezoelectric transducer which is isolated from earth by means of a rigid metallic insulator to improve the high frequency response of the transducer. The insulator is in the form of a ring or sleeve made of aluminum or aluminum alloy and coated with aluminum oxide. The oxide coating is electrically insulating, but hard and rigid to provide a rigid mount for the transducer, making it useful at frequencies up close to its natural resonant frequency. US 4,594,584 deals with a device for determining and/or monitoring a predetermined filling level in a container. US 2002/0178805 A1 relates to a method and an apparatus for downhole fluid characterization using bending mechanical resonators. US 5,139,087 teaches a method for ensuring injectivity for polymer solutions.

[0003] In underground drilling applications, such as oil and gas exploration and recovery, a borehole is drilled into the earth. The drilling process may include taking measurements of fluids in the borehole while drilling the borehole (logging while drilling (LWD)). In some cases, a wireline is used to lower a measuring instrument into the borehole after a step in the drilling process has been completed to measure properties of fluids in the borehole.

[0004] Measured fluid properties can include, for example, the fluid's density and viscosity. The properties can be measured by placing a mechanical oscillator in the fluid path of the fluid. Fluid density is mainly measured by measuring changes in the oscillator's vibrational frequency while viscosity is determined mainly by monitoring the resonance decay time.

[0005] Other properties can be measured either directly or indirectly by using the speed of sound measurements made in the fluid. These measurements are typically referred to as "speed of sound" measurements and can be used, for example, to determine the fluid's gas-to-oil ratio (GOR).

[0006] There are currently devices that can measure two of these three: sound speed, density and viscosity. In particular, there are instruments that can measure density and viscosity or that can measure density and speed of sound. There are no instruments that can be used to measure all three.

SHORT SUMMARY

[0007] The main features of the present invention appear from the independent claims. Further features of the invention are indicated in the independent claims. In accordance with one embodiment, a downhole tool is described which comprises a body which includes a sample port through which a sample fluid can be drawn into the downhole tool and a sample channel passing through the body in fluid communication with the sample port and through which the sample fluid passes. In this embodiment, the sample channel comprises a sample chamber having an inlet and an outlet located along the sample channel, the sample chamber comprising three cylindrical chambers comprising a central resonator cavity surrounded by two outer resonator cavities, one of the two outer resonator cavities comprising a sensor inlet for receiving a sensor and enable it to fluidly contact the sample fluid as it passes through the sample channel.

[0008] According to another embodiment, a method for evaluating a sample fluid is described. The method comprises: drawing a fluid from a borehole location into a sample chamber in a borehole tool; allowing the fluid to pass through a sample chamber, wherein the sample chamber comprises an inlet and an outlet located along the sample channel, wherein the sample chamber comprises three cylindrical chambers comprising a central resonator cavity surrounded by two outer resonator cavities, wherein one of the two outer resonator cavities comprises a sensor inlet for receiving a sensor and enabling it to fluidly contact the sample fluid as it passes through the sample channel; and evaluating the sample fluid with the sensor as it passes through the sample chamber.

[0009] According to another embodiment, a transducer comprising a biased adapter with a sleeve part and an end and a housing comprising a seat part and a shaft part extending from the seat part is described. In this embodiment, the transducer further comprises a piezoelectric element housed entirely within a chamber defined by the sleeve portion and the shaft portion and a diaphragm coupled to an external side of the end such that movement of the piezoelectric element causes movement of the diaphragm.

[0010] According to another embodiment, an instrument for measuring properties of a borehole fluid is described which comprises a body, a fluid chamber formed inside the body and which provides a fluid path at least partially through the instrument and a transducer which is mounted in the body and which has a movable membrane located at least partially inside the fluid chamber. The transducer in this embodiment comprises a biased adapter having a sleeve portion and an end, a housing comprising a seat portion and a shaft portion extending from the seat portion, and a piezoelectric element housed entirely within a chamber defined at least in part by the sleeve portion and the shaft portion. The membrane in this embodiment is connected to an external side of the end so that movement of the piezoelectric element causes movement of the membrane. [0011] According to yet another embodiment, a transducer is described comprising a sleeve part having an end, a housing comprising a seat part and a shaft part extending from the seat part and a piezoelectric element housed at least partially within a chamber that is at least partially defined of the sleeve part and the shaft part so that the piezoelectric element does not touch a fluid during a sampling operation. The transducer in this embodiment also comprises a diaphragm which is coupled to an external side of the end such that movement of the piezoelectric element causes movement of the diaphragm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The following descriptions should not be considered limiting in any way. Referring to the attached drawings, like elements have like numbers:

[0013] FIG.1 illustrates an instrument placed in a borehole;

[0014] FIG. 2 is a perspective drawing of the transducer according to one embodiment;

[0015] FIG.3 is a cross-section of the transducer shown in FIG.2;

[0016] FIG. 4 shows a side cross-section of the transducer shown in FIG. 2 installed in an instrument;

[0017] FIG. 5 is a perspective drawing of an example of a diaphragm that may be used with one embodiment of a transducer;

[0018] FIG. 6 is a cross section of the instrument showing one embodiment of a sample channel; and

[0019] FIG. 7 illustrates the sample channel according to claim 6 having a sensor placed therein.

DETAILED DESCRIPTION

[0020] A detailed description of one or more embodiments of the described apparatus and the manufacturing method is presented here by way of example and not limitation with reference to the figures. In particular, a transducer that can be used to measure one is described here

of or all of the density, viscosity and sound speed of a fluid. In the following description, the fluid under investigation shall be assumed to be a fluid found in or extractable from a wall of the borehole which penetrates the earth, but the transducer described here can be used for other fluids as well. Also, although a transducer is specifically described, it is to be understood that embodiments of this invention may apply to any instrument that carries a transducer as described herein or in equivalents thereof.

[0021] Now referring to FIG. 1, fluid sampling in the borehole environment generally involves placing an instrument 10 in a borehole 5 via a wireline 8. Located opposite on the outer part of the instrument 10 is a sample port 14 and a press device 12. When the sample port 14 is in the vicinity of a formation of interest 6, the press device 12 extends towards the inner surface of the borehole 5 by thereby connecting the test port 14 to the formation 6. The connection of the test port 14 pierces the outer diameter of the borehole 5 and enables fluid communication between the fluid in the formation 6 and the test port 14. The instrument 10 can also comprise a sample channel 15 through which the fluid touching the sample port 14 can be drawn by means of a pump or other device in such a way that it flows through the sample channel 15. Measurements of the fluid properties can be measured by one or more measuring instruments placed in or around the sample channel 15. As it is described in more detail below, a transducer according to one embodiment can be arranged in relation to the sample channel 15 in a way that enables it to be used to measure one or more of the density, viscosity and sound speed of the fluid.

[0022] It should be understood that the wireline 8 can be connected to a drilling rig and comprise a tension element and various conductors to transmit commands to the instrument 10, to receive data from the instrument 10 and to provide power. To that end, the wireline 8 can be connected to an electronic module (eg, a data device), enabling the transmission of required operating commands to the instrument 10 for bidirectional data transmission. The data can be recorded on an archive storage medium of any desired type for simultaneous or later processing. The data can be transmitted in analogue or digital form. Data processors such as a suitable computer can be provided to perform data analysis within the area in real time or the recorded data can be sent to a processing center or both for post processing of the data.

[0023] FIG. 2 is a perspective drawing of a transducer 20 according to one embodiment. The transducer 20 may be provided within or on the instrument 10 shown in FIG. 1 so that it can

perform measurements on the fluid passing through the sample channel 15. In one embodiment, the transducer 20 is a piezoelectric transducer as described in more detail below. In general, a piezoelectric transducer is a transducer that comprises one or more piezoelectric elements.

[0024] The transducer 20 illustrated in FIG. 2 comprises a housing 22. As illustrated, the housing 22 comprises a shaft part 23 which is connected to a seat part 24. The shaft part 23 extends away from an adaptation surface 25 on the seat part 24. The shaft part 23 can be cylindrical as illustrated in FIG. 2 or take any other form. The shaft part 23 surrounds at least one part of a piezoelectric element in one embodiment. As illustrated, the shaft part 23 has an outer diameter which is smaller than the diameter of the seat part 24. In this way, the shaft part 23 can extend into the hole in a measuring instrument while the seat part 24 (and especially the upper surface 25) is secured rotating in relation to a surface surrounding the hole. In one embodiment, the seat part 24 comprises one or more fastening holes 30 through which a bolt (preferably unthreaded) or other rigid element can pass to prevent rotation of the housing 22 relative to the surface surrounding the hole. The hole into which the shaft part 23 extends can provide access, for example, to a fluid passing through a test channel 15 (FIG.1).

[0025] The shaft part 23 comprises one or more access holes 27 through which a cable or other conductor can pass to carry a voltage or current to the piezoelectric element inside the housing 22. In one embodiment, the access holes 27 also enable a cable or other conductor to carry a voltage or current away from the piezoelectric element. Naturally, the number of holes 27 in the shaft part 23 may vary from that shown in FIG. 2 depending on the particular implementation and can be omitted in certain situations. In one embodiment, the holes 27 can be moved to another location in the housing 22. The shaft part 23 can alternatively comprise a sealing groove 32 onto which a sealing o-ring or other sealing mechanism can be inserted.

[0026] The transducer 20 also includes a prestressed adapter 34. The prestressed adapter 34 provides a mechanism through which the piezoelectric element inside the shaft portion 23 can be loaded in compression. To this end, the biased adapter 34 may be threaded or otherwise adapted to the shaft portion 23 to impart a biased compressive force on the piezoelectric element within the housing 22. The biased adapter 34 includes a mating surface 35 configured to conform to an internal shoulder in the hole where the shaft part 23 is inserted.

[0027] The transducer 20 also includes a sensor adjustment device 40. The sensor adjustment device includes adaptation features shown as threads 42 which enable it to force the housing 22 against the biased adapter 34.

[0028] The transducer further comprises a membrane 50. In operation, the membrane 50 is exposed to a fluid in the sample channel 15 (FIG. 1). The membrane 50 serves to transmit an oscillation formed by the piezoelectric element inside a fluid in the sample channel 15 (FIG. 1) without the piezoelectric element being exposed to or otherwise in contact with the fluid. Also, in one embodiment, the membrane 50 can be used to sense the fluid's resistance (impedance) to the oscillation of the piezoelectric element. Further details of the membrane 50 are discussed below.

[0029] FIG. 3 is a side cross-sectional view of the transducer 20 shown in FIG. 2. In the illustrated embodiment, a piezoelectric element 60 is disposed with a chamber 62 formed within the biased adapter 34 and shaft member 23. The piezoelectric element 60 is completely enclosed within the chamber 62 in one embodiment.

[0030] As illustrated, the biased adapter 34 includes an inner sleeve portion 36 that is configured to extend into an inner diameter of the sleeve portion 23. The depth at which the inner sleeve portion 36 extends into the shaft portion 23 may vary depending on the application. The inner sleeve portion 36 is fixedly installed on the sleeve portion 23 to impart the biased pressure to the piezoelectric element 60. In one embodiment, the inner shaft portion 36 has an outer diameter smaller than the diameter of the sleeve portion 23. However, it should be understood that the biased the adapter 34 would be able to surround part of the sleeve part 23. In such a case, the inner diameter of the inner sleeve part 36 could be larger than the outer diameter of the sleeve part 23.

[0031] The prestressed adapter 34 includes a mating surface 65. An external side 67 of the mating surface 65 is coupled to the membrane 50. In one embodiment, the external side 67 may include a hub 66 or other accessory extending therefrom and which the membrane 50 can be attached to. Naturally, the hub 66 may be omitted and the diaphragm 50 may be coupled directly to the external side 67 of the mating surface 65. Naturally, the mating surface 65 may have different thicknesses across its diameter to accommodate measurement accuracy while maintaining structural integrity.

[0032] The fitting surface 65 of the biased adapter 34 also comprises an inner side 68 which can be used to either directly or indirectly apply pressure to the piezoelectric element 60. The shaft part 23 also comprises an inner shaft element 64. In one embodiment, the piezoelectric element 60 is accommodated between the inner step member 64 and the inner side 68 of the fitting surface 65 of the biased adapter 34.

[0033] Naturally, the exact configuration of the shaft member 23 and the biased adapter 34 may differ from that shown in FIG. 3. Regardless of the exact configuration, the housing 22 and the biased adapter 34 cooperate to impart a compressive force on the piezoelectric element 60.

[0034] A biased spring 70 is displaced between the regulating mechanism 40 and the housing 22. Rotational movement of the regulating mechanism 40 will cause the housing 22 to move towards the inner landing due to threads 42. This movement compressing biased spring 70 presses the housing 22 in the direction indicated by arrow C. This causing a bias to form between the surface 35 and the inner ledge.

[0035] Any type of piezoelectric element 60 may be used. In general, piezoelectricity is characterized by the ability that certain crystals have to develop an electrical charge when subjected to mechanical stress. The behavior is referred to as the direct piezoelectric effect. In the opposite case, these crystals undergo a deformation when exposed to an electric voltage field. The behavior is referred to as the inverse piezoelectric effect. The piezoelectric effect is exhibited by certain ceramic materials belonging to the ferroelectric group (eg, lead zirconate titanate (PbZT) consisting of mixed crystals of PbZrO3 and PbTiO3). The piezoelectric element 60 can be formed from any crystal or crystal combination that exhibits the piezoelectric effect as long as the resulting structure can convert mechanical quantities, such as stress and shape change, into electrical stress and conversely convert electrical stress into mechanical forces and displacements.

[0036] In one embodiment, the opposite piezoelectric effect can be created by connecting a voltage supply 71 to the piezoelectric element 60. Likewise, a current meter 72 can be used to measure the current produced due to compression/expansion of the piezoelectric element 60 due to the piezoelectric effect. In operation, and as described briefly above, the piezoelectric element 60 is biased. The magnitude and frequency of the voltage provided by the voltage supply 71 to the piezoelectric element 60 controls the distance of movement and the frequency with which the membrane 50 moves in the fluid. The current meter 72 can measure

the current flowing (I) from the piezoelectric element 60. The relative displacement of the ends of the piezoelectric element 60 follows the received charge (Q) with good linearity and, as a consequence, the flowing current (I = dQ/dt) is proportional to the relative velocity of the ends (76, 77) of the piezoelectric element 60 (v = ds/dt). Consequently, the steepness (rate of change) of the fluctuations in the current (dI/dt) is proportional to the relative acceleration (a = dv/dt) of the ends 76, 77.

[0037] In operation, when driven by the voltage displacement 71, the resulting displacement response of the piezoelectric element 60 is a complex function of the applied voltage and the coupled interaction of interfacial reaction forces. The interface reaction forces are based, at least in part, on one or more of the density, viscosity and sound speed of a liquid to which the membrane 50 is exposed. In more detail, the interfacial reaction forces develop a counteracting shape change that changes the relative displacement of the ends 76, 77 from the expected idle (direct piezoelectric effect) response. The change in relative displacement of the ends 76, 77 of the piezoelectric element 60 due to the combination of applied voltage and reaction force moves relative to the reaction force from the idle condition. In this way, the voltage provided by the voltage source 60 and the current read by the current meter 72 can be used to analyze one or more of the density, viscosity and sound speed of a fluid.

[0038] In previous patent applications, piezoelectric sensors have been used to determine the physical properties of a fluid. For example, acoustic wave sensors based on mechanical resonance have been developed, including thickness-shear mode (TSM) resonators or surface acoustic wave (SAW) resonators. All these resonators were in contact with the fluid that was sampled. In contrast, according to one or more embodiments of this invention, the piezoelectric element does not touch the fluid being collected. This can be advantageous because the impedance response of a piezoelectric resonator is strongly affected by the fluid conductivity when its electrodes are placed on the surface of the fork and the fork is immersed in the conductive fluid. This happens because the conductive fluid is connected to the piezoelectric resonator as a low-impedance parallel component in a circuit. The impedance response is still affected even when the electrodes are coated with a thin (tens to hundreds of microns) layer of dielectric materials. Consequently, they are only capacitively coupled to the fluid. In such cases it is almost impossible to accurately measure the densities and viscosities of conductive or ionic fluids. By separating it

piezoelectric element from the fluid being sampled, the inaccuracies caused by contact between the element and the fluid can be reduced or eliminated.

[0039] FIG. 4 shows a side cross-section of a transducer 20 having its membrane 50 displayed within a fluid chamber 15 of an instrument 10. As illustrated, the instrument comprises an inner ledge 100 which is in contact with the fitting surface 35. As described above, the control mechanism 40 comprises adaptation functions 42 which are adapted to the instrument 10 and which allow it to press the housing 22 against the inner landing 100 and thus place a pressure force on surface 35 which is adapted to the shoulder 100. Application of a voltage to the piezoelectric element 60 causes the membrane 50 to oscillate in the fluid chamber 15 Naturally, the fluid in the chamber will resist such fluctuations. The resistance will result in a current change that can be measured as described above. In one embodiment, the upper surface 25 is not in contact with a surface 75 surrounding a hole 76 into which the transducer 20 is inserted.

[0040] FIG. 5 is a perspective drawing of one embodiment of a diaphragm 50. As described generally above, magnetization of a piezoelectric element 60 (FIGS. 3-4) imparts linear motion to the diaphragm 50 when coupled to the biased adapter 34 and a fluid under investigation resists this movement. The amount by which the linear motion is resisted can, in some situations, be measured and used to determine the viscosity, density and sound speed of the fluid in the flow chamber. In viscosity measurements, the diaphragm 50 is preferably shaped so that it imparts a shear force on the fluid while minimizing the turbulence it imparts as turbulence can produce undesirable effects on the linear motion of the diaphragm. In one embodiment, this can be accomplished if the Reynolds number for the boundary layer flow across the membrane 50 can be maintained at a sufficiently low value over the range of fluid density and viscosity values to be measured. This is carried out if the product of the shear surface's transverse characteristic length and fluid viscosity is below the threshold value. In practice, this can be accomplished by providing a recess area 102 and double-sided shear disturbances 110 formed inside the membrane 50. In order to promote fluid flow and have the least possible obstruction due to sedimentation through the membrane 50, it can include holes 104 formed in its side 108. But sufficient viscous function in the fluid must be developed to establish high correlated feedback in the measurement of fluid viscosity. At this end, the recessed area 102 may include one or more disturbances 110 formed on its surface and extending through the membrane 50 as indicated in FIG. 4.

The shape of the disturbances 110 may vary, and in some cases they may be in line with the holes 104. As illustrated, the disturbances 110 are in a cell configuration with a multi-finger resonator. Regardless of the shape, in one embodiment, the disturbances 110 are formed so that the maximum Reynolds number is kept below 100 for the extreme values expected for fluid test parameters (eg, density = 300 - 1500 kg/m<3>, viscosity =0 .1 - 100 centipoise). In one embodiment, the disturbances 110 pass completely through the membrane 50.

[0041] In the description above, reference was made to the sample channel 15 the space in an instrument 10 which receives fluid from a borehole via a sample port 14 (FIG. 1). The transducer 20 shown above is mounted so that the membrane 50 is placed inside the same channel 15 so that it can make measurements. In this sense, the transducer 20 can also be referred to here as a sensor because it provides output data that includes information about one or more properties of the fluid passing through the sample channel 15.

[0042] It has been discovered that in some situations, the shape of the sample channel 15 in the region on which the membrane 50 of the sensor 20 is mounted, can improve the sensor 20's measurement capacity. Now referring to FIG.6 where a cross section of a part 200 of the instrument 10 is shown. The part 200 comprises some or all of the sample channels 15 shown in FIG. 1. In particular, the part 100 comprises a sample cavity 202 through which the sample fluid can flow and into which a part of a sensor can be introduced. In one embodiment, the sensor is the sensor 20 described above. Of course, other sensors may be provided within or otherwise in fluid communication with the sample cavity 202 without departing from the scope of this invention.

[0043] The illustrated sample cavity 202 comprises three resonator cavities 204, 206 and 208 which are all in fluid communication with each other. In one embodiment, each resonator cavity 204, 206, 208 defines a substantially cylindrical volume having a respective radius r104, r106, r108. In more detail, the central resonator cavity 206 is surrounded by two outer resonator cavities 204, 208 which will sometimes be referred to as first and second resonator cavities, respectively. In one embodiment, the radius r106 of the central resonator cavity 206 is greater than the radii (r104, r108) of one or both of the outer resonator cavities 204, 208. In one embodiment, r104 is approximately equal to r108.

[0044] As illustrated, the resonator cavities 204, 206, 208 are concentric about a vertical center line Y. Each resonator cavity 204, 206, 208 also has a respective height h204, h206,

h208. In one embodiment, the height h206 of the central resonator cavity 206 is greater than the height (h204, h208) of one or both of the outer resonator cavities 204, 208. In one embodiment, h204 is approximately equal to h208.

[0045] The sample cavity 202 comprises an inlet 220 where the fluid enters the sample cavity 202 and an outlet 222 where the fluid leaves the sample cavity 202. The inlet 220 is connected to an inlet pipe 224 and the outlet 222 is connected to an outlet pipe 226. As illustrated, forming both the inlet 220 and the outlet 222 in the central resonator cavity 206. In one embodiment, the inlet 220 and the outlet 222 are offset on opposite sides of a center line X of the central resonator cavity 206. Naturally, the exact location of the inlet 220 and the outlet 222 may be different. In one embodiment, the inlet 220 and the outlet 222 are offset from each other so that the fluid entering the sample cavity 202 through the inlet pipe 224 must change direction before entering the outlet pipe 226.

[0046] One of the outer resonator cavities 204, 208 also comprises a sensor inlet 230 where some or all of the sensors can be introduced into the sample cavity 202 so that it can interact with a fluid passing through the sample cavity 202. In the illustrated embodiment, the sensor inlet 230 is formed in the second resonator cavity 208 but could alternatively be formed in the first resonator cavity 204.

[0047] Now referring to FIG. 7, where the sample cavity 202 illustrated in FIG. 6 is illustrated comprising a sensor 240 comprising a membrane 242 introduced into the sample cavity 220 through the sensor inlet 230. In one embodiment, the sensor inlet 230 defines the inner ledge 100 (FIG. 4) described above.

[0048] The illustrated sensor 240 may be the same or similar to one of the sensors/transducers described herein or may be any other sensor type. The area inside the second resonator cavity 208 that is not filled with the sensor 240 in general, and the membrane 242 in particular, shall be referred to herein as the baffle opening and generally denoted by the reference numeral 244. In one embodiment, the membrane 242 is adapted and mounted inside the sample cavity 202 such that it is enclosed in the volume defined by both the central 206 and the second resonator cavity 208 .

[0049] It has been discovered that certain geometries of the resonator cavities 204, 206, 208 can be varied to allow impedance matching between the membrane 242 of the sensor 240 and the fluid in the sample cavity 202. Now referring to both FIGURES 6 and 7, it has

It has been discovered that the relative diameters, heights and locations of the resonator cavities can improve measurements made by the sensor 242. The baffle 244 size can also help to match the impedance of the diaphragm 242 to the fluid in the cavity 202. In particular, the baffle 244 size can control the phase regulation of forward baffle reflections (f .eg, between the bottom 243 of the membrane 242 and the outer part 245 of the sample chamber 202) which can contaminate external surface reflections. In one embodiment, baffle plate 244 size may be based on relative height of opening between bottom 243 of diaphragm 242 and outer portion 245 compared to resonator heights h204, h206, h208 and diaphragm 242 diameter.

[0050] In more detail, in operation, standing wave patterns can be formed in the fluid in the sample chamber 202 due to movement of the membrane 242 due to the application of voltage to a piezoelectric element inside the sensor 240 as described above. The standing wave pattern in the fluid sample interacts with membrane 242 to create impedance feedback in the form of perturbations in the electrical admittance-frequency response. The electrical admittance properties tend to change in a highly structured manner with variations in density, viscosity and speed of sound.

[0051] The acoustic wave pattern velocity υ is governed by the underlying physics associated with the non-linear Navier-Stokes equation shown in equation 1 below:

and the constancy of mass ratio for pressure P, temperature τ, and pattern velocity υ:

there:

γ = heat density ratio of the fluid (constant pressure, constant volume)

α= coefficient of thermal expansion

c0 = bulk fluid sound speed

ω = Equilibrium angular frequency of influence function

ρ0 = bulk fluid mass density

μ = shear viscosity coefficient

η = bulk viscosity coefficient

[0052] These pattern trends have been observed to closely follow functions for cylindrical harmonic type solutions and simple exponential decay responses (Bessel functions, and natural logarithms).

[0053] Elements of the embodiments have been introduced with either the article "an" or "an." The articles are meant to mean that there is one or more elements. The words "comprising" and "having" are intended to be inclusive so that there may be additional elements other than those listed. The conjunction "or" when used with a list of at least two words is intended to mean any word or combination of words. The words "first," "second," and "third" are used to distinguish elements and are not used to denote a particular order.

[0054] It will be clear that the various components or technologies may provide certain necessary or useful functionalities or features. Accordingly, these functions and characteristics, as may be required in support of the appended patent claims, will be understood as naturally included as part of the teachings herein and part of the described invention defined by the appended patent claims.

[0055] Although the invention has been described with reference to exemplary embodiments, it will be understood that various changes can be made and equivalents can be replaced with elements thereof without deviating from the scope of the invention defined by the appended patent claims. Moreover, many changes will be understood to adapt a particular instrument, situation or material to the teachings of the invention without deviating from the scope defined by the appended

the patent requirements. Therefore, it is intended that the invention shall not be limited to the particular described embodiment as the best method contemplated for implementing this invention, but that the invention shall include all embodiments defined by the appended patent claims.

Claims (19)

PATENT CLAIMS 1. Piezoelectric transducer (20) comprising: a biased adapter (34) having a sleeve part (36) and an end; a housing (22) comprising a seat part (24) and a shaft part (23) extending from the seat part (24); a piezoelectric element (60) completely housed in a chamber (62) defined by the sleeve portion (36) and the shaft portion (23); and a diaphragm (50) coupled to an outer side of the end, such that movement of the piezoelectric element (60) causes movement of the diaphragm (50), where the piezoelectric transducer (20) further comprises: an adjustment mechanism (40) on an opposite side of the seat part (24) from the shaft part (23); and a biased spring (70) placed between the adjustment mechanism (40) and the seat part (24). 2. Piezoelectric transducer (20) according to claim 1, wherein the regulation mechanism (40) comprises adjustment functions (42) which are configured to be adjusted according to corresponding adjustment functions in an instrument (10). 3. The piezoelectric transducer (20) of claim 1, wherein the biased adapter (34) and housing (22) are arranged and configured to apply a compressive force to the piezoelectric element (60). 4. Piezoelectric transducer (20) according to claim 3, wherein the housing (22) comprises an internal ledge formed within the sleeve portion (36) defining a first end of the chamber (62), and wherein the end of the biased adapter (34) defines a second end of the chamber (62), and wherein variation of a distance between the first end and the second end causes the compressive force to be applied. 5. Piezoelectric transducer (20) according to claim 1, in combination with a voltage supply (71) configured to provide a voltage to the piezoelectric element (60). 6. A piezoelectric transducer (20) according to claim 1, in combination with a current meter (72) configured to measure a current produced by the piezoelectric element (60). 7. Piezoelectric transducer (20) according to claim 1, wherein the membrane (50) comprises a recessed area (102) formed therein. 8. Piezoelectric transducer (20) according to claim 7, where the recessed area (102) comprises one or more perturbations (110) that go from a surface of the recessed area (102) to an external side of the membrane (50). 9. Piezoelectric transducer (20) according to claim 1, where the membrane (50) comprises one or more holes (104) formed in a side wall (108) thereof. 10. Piezoelectric transducer (20) according to claim 9, where the membrane (50) comprises a recessed area (102) which comprises one or more perturbations (110) formed on a surface thereof, and where at least one of the perturbations (110) is formed over one of the holes (104). 11. Piezoelectric transducer (20) according to claim 1, wherein the end of the biased adapter (34) has at least two different thicknesses. 12. Instrument (10) for measuring properties of a borehole fluid from a downhole location in a basic formation (6) that has been penetrated by a borehole (5), where the instrument (10) comprises: a body; a fluid chamber (15) formed within the body and providing a fluid path at least partially through the instrument (10); and a piezoelectric transducer (20) which is mounted on the body and which has a movable membrane (50) located at least partially inside the fluid chamber (15), where the piezoelectric transducer (20) comprises: a biased adapter (34) having a sleeve part (36) and an end; a housing (22) comprising a seat part (24) and a shaft part (23) extending from the seat part (24); and a piezoelectric element (60) housed entirely within a chamber (62) defined at least in part by the sleeve portion (36) and the shaft portion (23); wherein a membrane (50) is connected to an external side of the end, such that movement of the piezoelectric element (60) causes movement of the membrane (50). 13. Instrument according to claim 12, wherein the body comprises an inner ledge (100) which touches the biased adapter (34). 14. Instrument according to claim 13, where the piezoelectric transducer (20) further comprises: an adjustment mechanism (40) on an opposite side of the seat part (24) from the shaft part (23) and comprising adjustment functions (42) configured to be adapted to the body; and a bias spring (70) located between the adjustment mechanism (40) and the seat part (24); wherein mating of the adjusting mechanism (40) with the body causes the biased spring (70) to press the biased adapter (34) against the inner ledge (100) to form a compressive force between them. 15. Instrument according to claim 12, which further includes: a voltage supply (71) coupled to the piezoelectric element (60). 16. Instrument according to claim 12, wherein the end of the biased adapter (34) has at least two different thicknesses. 17. Instrument according to claim 12, where the body comprises: a sleeve part (36) having an end; a housing (22) comprising a seat part (24) and a shaft part (23) extending from the seat part (24); a piezoelectric element (60) that is accommodated at least partially inside a chamber (62) that is defined at least partially by the sleeve part (36) and the shaft part (23), so that the piezoelectric element (60) does not touch a fluid sampled during a sampling operation; and a diaphragm (50) coupled to an outer side of the end such that movement of the piezoelectric element (60) causes movement of the diaphragm (50). 18. An instrument according to claim 17, wherein the sleeve portion (36) is part of the biased adapter (34), and the housing (22) is arranged and configured to apply a compressive force to the piezoelectric element (60). 19. Instrument according to claim 17, which further includes: an adjustment mechanism (40) on an opposite side of the seat part (24) from the shaft part (23) and comprising adjustment functions (42) configured to be adjusted according to the instrument (10); and a biased spring (70) located between the adjustment mechanism (40) and the seat part (24); wherein matching the adjustment mechanism (40) with the instrument (10) causes the biased spring (70) to press the biased adapter (34) against an internal ledge (100) inside the instrument (10) and creates a compressive force between them.