# Patent

## Title
System and method for sensing pressure using an inductive element

## Abstract

Exemplary systems and method are directed to a sensing device, and to a pressure sensing system and method. An exemplary method includes supplying electromagnetic energy to a transducer which is configured to reflect the electromagnetic energy at a ring frequency determined by an inductance of the transducer, wherein the inductance changes in response to compression of the inductive element. The ring frequency of electromagnetic energy reflected by the transducer is correlated to a pressure value.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation of U.S. patent application Ser. No. 11/882,104, filed Jul. 30, 2007, the contents of which are incorporated herein by reference in its entirety.


BACKGROUND
1. Field
Pressure transducers are disclosed, such as transducers that shift the frequency of a reflected signal based on a response to pressure.
2. Background Information
Devices have been used for monitoring downhole conditions of a drilled well, where environmental conditions can be relatively harsh. These downhole conditions include temperature and pressure, among others.
SUMMARY
An exemplary sensing device is disclosed. The sensing device includes a shaped elastomer and ferromagnetic material embedded as discrete particles within the shaped elastomer, wherein a percentage by weight of the ferromagnetic particles is selected such that an inductance of the shaped elastomer will vary a predetermined amount for a given compression of the shaped elastomer.
An exemplary system for sensing pressure in a borehole is also disclosed. The system comprises means for generating electromagnetic energy, and means for modulating the electromagnetic energy. The modulating means includes an inductive element comprising a shaped elastomer and ferromagnetic material embedded as discrete particles within the shaped elastomer, wherein a percentage by weight of the ferromagnetic particles is selected such that an inductance of the shaped elastomer will vary a predetermined amount for a given compression of the shaped elastomer.
An exemplary method of sensing pressure uses a transducer that includes a compressible inductive element. The method comprises supplying electromagnetic energy to a transducer which is configured to reflect the electromagnetic energy at a ring frequency determined by an inductance of the transducer, wherein the inductance changes in response to compression of the inductive element. The ring frequency of electromagnetic energy reflected by the transducer is correlated to a pressure value.



BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages and features described herein will be more readily apparent to those skilled in the art when reading the following detailed description in connection with the accompanying drawings, wherein:
FIG. 1 shows an exemplary inductive sensor for sensing pressure;
FIG. 2 is a flowchart illustrating an exemplary process of manufacturing the exemplary inductive sensor of FIG. 1;
FIG. 3 shows an exemplary system for sensing pressure in a well;
FIG. 4 is a flowchart illustrating an exemplary process of sensing pressure in a well;
FIG. 5 is a flowchart illustrating a system for sensing pressure in a compressible vessel; and
FIG. 6 shows an exemplary inductive sensor and housing for sensing pressure.



DETAILED DESCRIPTION
FIG. 1 shows an exemplary inductive sensor for sensing pressure. As shown in FIG. 1, the inductive sensor 100 can be configured as a ferrite core in the form of a shaped elastomer that includes ferromagnetic material such that an inductance of the inductive element varies as a function of compression of the shaped elastomer due to a pressure of the surrounding environment. The ferrite core can be formed in the shape of a ring for coupling to production tubing within a drilling well or any other shape suitable for achieving the desired response or performance.
The inductive sensor 100 can be formed of ferromagnetic material that is potted using an elastomeric potting agent, e.g. silicone rubber or any other suitable elastomeric material as desired. The inductive sensor 100 can include a ferromagnetic blend of various ferromagnetic materials (or particles), such as iron oxides, iron powder, or any other suitable materials as desired. The composition by weight of each magnetic material in the ferromagnetic blend determines various parameters of the inductive sensor 100, which can include but are not limited to an impedance value, core loss, frequency response, temperature response, quality (Q) factor, power handling, and any other controllable parameters or characteristics. Due to the physical properties of the ferromagnetic blend, the inductive sensor 100 can be compressed by an external force, e.g., pressure, such that an inductive value of the sensor 100 will vary in response to the external force. Those of skill in the art will recognize that a ferromagnetic material does not have to comprise iron compounds, but can be comprised of other metal-based ceramics.
FIG. 2 illustrates an exemplary method for manufacturing the inductive sensor 100 of FIG. 1.
In a step 200, ferromagnetic materials can be mixed with a liquid elastomeric material to form a ferromagnetic material-elastomer mixture. The ferromagnetic materials can include a blend of various ferromagnetic-based magnetic materials. The materials can be added in various compositions by weight to establish a desired hardness composition of the rubber matrix, and which determine various parameters and characteristics of the inductive sensor 100, such as an inductance value, for example.
The liquid elastomeric material can include any of a number of known elastomers, such as amorphous polymers or other silicone-based materials as desired.
In a step 202, the ferromagnetic material-elastomer mixture is transferred to a mold, such as a ring, cylinder, or any other suitable shape mold as desired. In step 204, the ferromagnetic material-elastomer mixture in the mold is cured at any suitable temperature (e.g., room temperature or greater), to form an inductive structure. The curing temperature is determined by the material composition of ferromagnetic material-elastomer mixture. The curing temperature can be determined by whether the elastomer is a saturated or unsaturated material. For example, saturated elastomers, such as silicones, fluoroelastomers (e.g., Viton®), and perfluoroelastomers (e.g., Kalrez®) can be cured at room temperature absent a catalyst or curing agent for vulcanization. Unsaturated materials, such as polyisoprene (e.g., butyl rubber) and polybutadiene (e.g., nitrile), for example, can require the introduction of a curing agent such as sulfur to promote vulcanization. Based on the material composition of the elastomeric materials, the inductive sensor 100 can be made compatible with temperatures up to 400° F., or greater.
In a step 206, the inductive structure can be deaerated to remove bubbles. Deaerating enables the expansion of the inductive mold to be controlled and reproducible. One of ordinary skill in the art will recognize that any known deaerating technique or process can be used.
If the inductive sensor 100 is to be used in an environment in which contamination may be present, then the inductive sensor 100 can be configured to include a protective coating and/or mounted in a protective casing. In a step 208, the inductive mold can be encapsulated with a protective material such as Teflon®, for example, and/or encapsulated in a vessel, formed as a cylinder, or any other suitable encapsulating means as desired. One of ordinary skill will appreciate that the disclosed method can be performed by a machine.
FIG. 3 shows an exemplary system 300 for sensing pressure in a well using the exemplary inductive sensor. The exemplary system 300 can be a telemetry system as described in U.S. patent application Ser. No., 11/394,186 filed Mar. 31, 2006, and additional details regarding such a telemetry system can be found in that application, the contents of which are hereby incorporated in their entirety by reference.
The telemetry system 300 includes means, such as a signal generator 302, for generating electromagnetic (EM) energy and applying the EM energy to a transmission means (not shown), such as a borehole casing or production tubing. The signal generator 302 can generate the EM energy as a pulse (e.g., a sequence or series of pulses or chirps), or as a continuous wave. The EM energy can be generated in a range defined between a desired low resolution (e.g., 1 pulse/sec) and a desired high resolution (e.g., 20 kHz or greater) signals. Modulating means, such as one or more downhole transducers 304, are coupled to the production tubing for interacting with and modulating at least some of the EM energy of the pulse at a “ring frequency.” Receiving means, such as a receiver 306 located at or near the surface, receives the EM energy that is reflected by the transducer 304 at the ring frequency. The receiver 306 samples the EM energy at a rate much higher than either of the ring frequency or the frequency of the EM energy so that the original signal can be reproduced.
In embodiments wherein the EM energy is in the form of an EM pulse, an EM pulse generator is used. Non-nuclear means for generating EM pulses are well-known to those in the nuclear-weapons community. Such EM pulse generators are typically used to test electronic devices by simulating EM pulses associated with nuclear blasts. See, e.g., U.S. Pat. Nos. 3,562,741 (McEvoy et al.); 4,430,577 (Bouquet); 4,845,378 (Garbe et al.); and 5,150,067 (McMillan).
As shown in FIG. 3, the one or more transducers 304 can include an inductive element 308, such as the inductive sensor 100, and a capacitive element 310. The inductive sensor 100 can be configured to sense a characteristic, e.g. pressure, of the well through an observed range of compression, and modulate the frequency of the EM energy based on the compression. The capacitive element 310 is coupled to the inductive element 308 to form a tank circuit. The capacitive element 310 can be configured to be less sensitive to temperature and pressure than the inductive element 308.
When the telemetry system 300 is configured to include multiple transducers 304, each transducer 304 can be configured to operate at a different “ring” frequency. For example, each transducer 304 can include an inductive element 308 having different formulations (i.e. composition by weight, percentage weight) of ferromagnetic material, which result in varying sensitivities to pressure across the multiple transducers 304.
The receiver 306 can include processing means, such as a processor 312. Those of ordinary skill in the art will appreciate that the processor 312 can be implemented as a computer or other suitable hardware and/or software processing means as desired. Prior to placing the transducer 304 into the well, the modulating (ring) frequency of the transducer 304 can be calibrated using a graphical user interface (GUI) associated with the processor 312. As a result, the processor 312 can be configured to store information (e.g., look-up tables, files, and/or databases) that correlate various ring frequency values to observed compression ranges of the inductive element 308.
FIG. 4 is a flowchart illustrating an exemplary process of sensing pressure using a transducer including the exemplary inductive element 100 in connection with the telemetry system 300. In a step 400, the pulse generator 302 generates EM energy and supplies the EM energy to the transducer 304 via the production tubing. The transducer 304, being coupled to the production tubing, interacts with the EM energy and reflects the EM energy at a ring frequency determined by the inductive element 308 of the transducer 304.
The inductance of the inductive element 308 can vary based on a degree to which the inductive element is compressed by the observed pressure in the borehole. In a step 402, the receiver 306 receives the reflected EM energy. Based on the prior calibration, the processor 312 of the receiver 306 uses means, such as a look-up table, for correlating the ring frequency of the received EM energy to a pressure value (step 404). For example, the processor 312 determines an inductance value of the inductive element 308 based on the ring frequency of the transducer 304. The processor 312 correlates the inductance value of the inductive element 308 to a degree of compression of the inductive element 308. The processor 312 then associates the compression of the inductive element 308 to the pressure in the well.
FIG. 5 shows an exemplary device 500 having an inductive sensor 502 mounted in a housing. As shown in FIG. 5, the inductive sensor 502 is encapsulated within a vessel 504. The inductive sensor 500 can be configured to include the physical properties and characteristics as described with respect to the inductive sensor 100 of FIG. 1. The inductive sensor 500 can also be configured in any shape determined by the vessel 500 and/or a shape suitable to achieving the desired response within the vessel 504. The vessel 504 also includes a load-bearing element 506, such as a piston, and a port 508 for applying a load or force to the load-bearing element 506. A processor 510 can be connected to the vessel to compute the pressure in the vessel based on the inductance of the inductive sensor 502.
FIG. 6 is a flowchart illustrating a method for sensing pressure using the inductive sensor 502 of FIG. 5. In a step 600, pressure is applied to a load-bearing element 506, e.g. piston, of the vessel so that the inductive element 502 is compressed. In a step 602, the processor 510 monitors and records a measurement of an inductance of the inductive sensor 502. In a step 604, the processor 510 determines an observed degree of compression of the inductive sensor 502 based on the measured inductance of the inductive sensor 502. The processor 510 correlates the determined compression to the pressure in the vessel 500 (step 506).
While the invention has been described with reference to specific embodiments, this description is merely representative of the invention by way of example only and is not to be construed as limiting the invention, as numerous variations will exist. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.

## Claims

1. A system for sensing pressure in a borehole, comprising:
means for generating electromagnetic energy; and
means for frequency modulating the electromagnetic energy, wherein the
modulating means includes an inductive element positioned remotely from the means for generating electromagnetic energy and which comprises:
a shaped elastomer; and
ferromagnetic material embedded as discrete particles within the shaped elastomer, wherein a percentage by weight of the ferromagnetic particles is selected such that an inductance of the shaped elastomer will vary a predetermined amount for a given compression of the shaped elastomer.

2. The system of claim 1, further comprising:
means for receiving the modulated electromagnetic energy; and
means for processing the modulated electromagnetic energy to determine pressure.

3. The system of claim 1, wherein the means for generating electromagnetic energy comprises an electromagnetic pulse generator.

4. The system of claim 1, wherein the modulating means comprises:
a capacitive element coupled to the inductive element.

5. The system of claim 4, wherein the capacitive element is less sensitive to temperature and pressure than the inductive element.

6. The system of claim 2, wherein the means for receiving the modulated electromagnetic energy comprises a surface RF receiver.

7. The system of claim 2, wherein the means for processing the modulated electromagnetic energy to determine pressure involves use of a lookup table of known pressure-modulation correlations.

8. A method of sensing pressure using a transducer having a compressible inductive element, the method comprising:
supplying electromagnetic energy to a transducer which is configured to reflect the electromagnetic energy at a ring frequency determined by an inductance of the transducer, wherein the inductance changes in response to compression of the inductive element; and
correlating the ring frequency of electromagnetic energy reflected by the transducer to a pressure value.

9. The method of claim 8, wherein the electromagnetic energy is emitted as a continuous wave.

10. The method of claim 8, wherein the electromagnetic energy is emitted as a pulse.

11. The method of claim 8, wherein the ring frequency is correlated to the pressure value using a look-up table.

12. A system for sensing pressure in a borehole, comprising:
a signal generator electrically coupled to borehole tubing and configured to generate an electrical signal for transmission via the borehole tubing;
a downhole transducer coupled to the borehole tubing and configured to at least modulate at least a portion of the electrical signal, the downhole transducer including an inductive element having a shaped elastomer with a ferromagnetic material embedded therein as discrete particles, wherein a percentage by weight of the ferromagnetic particles is selected such that an inductance of the shaped elastomer will vary a predetermined amount for a given compression of the shaped elastomer.

13. The system of claim 12, further comprising a receiver positioned at or near a ground surface and configured to receive and sample electromagnetic energy reflected by the downhole transducer, the electromagnetic energy representing the modulated portion of the electrical signal.

14. The system of claim 12, wherein the downhole transducer is configured to modulate a portion of the electrical signal at a ring frequency.