CA2436813C - Circumferential strain attenuator - Google Patents
Circumferential strain attenuator Download PDFInfo
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- CA2436813C CA2436813C CA002436813A CA2436813A CA2436813C CA 2436813 C CA2436813 C CA 2436813C CA 002436813 A CA002436813 A CA 002436813A CA 2436813 A CA2436813 A CA 2436813A CA 2436813 C CA2436813 C CA 2436813C
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- pipe
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
- G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
- G01L1/246—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using integrated gratings, e.g. Bragg gratings
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/268—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light using optical fibres
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging
- G01V1/52—Structural details
- G01V1/523—Damping devices
Abstract
An apparatus for varying the gain of a fiber optic sensor that non-intrusively senses the strain response of a pipe includes a circumferential strain attenuator that has a annular land portion that mechanically couples the attenuator to the pipe. An annular web extends coaxially from the land portion and has a reduced cross sectional area relative to the land and an annular mandrel portion extends coaxially from the web portion and forms a gap between the pipe and the mandrel. The fiber optic sensor is wound on the circumferential strain attenuator. The web and mandrel cooperate to reduce the strain response of the fiber optic sensor relative to the strain response of the pipe.
Description
"Circumferential Strain Attenuator"
This invention relates to fluid flow sensing devices that use fiber optics and more particularly to those devices that measure the speed of sound, flow velocity, and other parameters within a pipe using acoustic signals, and local short duration pressure variations within the flow.
In the petroleum industry, there is considerable value in the ability to monitor the flow of petroleum products in the production pipe of a well in real time.
Historically, flow parameters such as the bulk velocity of a fluid have been sensed with venturi type devices directly disposed within the fluid flow. These type devices have several drawbacks including the fact that they provide an undesirable flow impediment, are subject to the hostile environment within the pipe, and typically provide undesirable potential leak paths into or out of the pipe. In addition, these type devices are also only able to provide infonnation relating to the bulk fluid flow and are therefore unable to provide information specific to constituents within a multi-phase flow.
Some techniques utilize the speed of sound to determine various parameters of the fluid flow within a pipe. One technique measures the amount of time it takes for sound signals to travel back and forth between ultrasonic acoustic transmitters/receivers (transceivers). This is sometimes referred to a "sing-around" or "transit time" method.
United States Patent numbers 4,080,837, 4,114,439, 5,115,670 disclose variations of this method. A disadvantage of this type of technique is that gas bubbles and/or particulates in the fluid flow can interfere with the signals travelling back and forth between the transceivers. Another disadvantage of this type of technique is that it considers only the fluid disposed between transceivers during the signal transit time.
Fluid flow within a well will very often be non-homogeneous, for example containing localized concentration variations ("slugs") of water or oil. Localized concentration variations can affect the accuracy of the data collected.
This invention relates to fluid flow sensing devices that use fiber optics and more particularly to those devices that measure the speed of sound, flow velocity, and other parameters within a pipe using acoustic signals, and local short duration pressure variations within the flow.
In the petroleum industry, there is considerable value in the ability to monitor the flow of petroleum products in the production pipe of a well in real time.
Historically, flow parameters such as the bulk velocity of a fluid have been sensed with venturi type devices directly disposed within the fluid flow. These type devices have several drawbacks including the fact that they provide an undesirable flow impediment, are subject to the hostile environment within the pipe, and typically provide undesirable potential leak paths into or out of the pipe. In addition, these type devices are also only able to provide infonnation relating to the bulk fluid flow and are therefore unable to provide information specific to constituents within a multi-phase flow.
Some techniques utilize the speed of sound to determine various parameters of the fluid flow within a pipe. One technique measures the amount of time it takes for sound signals to travel back and forth between ultrasonic acoustic transmitters/receivers (transceivers). This is sometimes referred to a "sing-around" or "transit time" method.
United States Patent numbers 4,080,837, 4,114,439, 5,115,670 disclose variations of this method. A disadvantage of this type of technique is that gas bubbles and/or particulates in the fluid flow can interfere with the signals travelling back and forth between the transceivers. Another disadvantage of this type of technique is that it considers only the fluid disposed between transceivers during the signal transit time.
Fluid flow within a well will very often be non-homogeneous, for example containing localized concentration variations ("slugs") of water or oil. Localized concentration variations can affect the accuracy of the data collected.
2 Multiphase flow meters can be used to measure the flow rates of individual constituents within a fluid flow (e.g., a mixture of oil, gas, and water) without requiring separation of the constituents. Most of the multiphase flow meters that are currently available, however, are designed for use at the wellhead or platform. A
problem with utilizing a flow meter at the wellhead of a multiple source well is that the fluid flow reaching the flow meter is a mixture of the fluids from the various sources disposed at different positions within the well. So although the multiphase meter provides the advantage of providing information specific to individual constituents within a fluid flow (which is an improvement over a bulk flow sensors), the information they provide is still limited because there is no way to distinguish sources.
Acquiring reliable, accurate fluid flow data downhole at a particular source environment is a technical challenge for at least the following reasons.
First, fluid flow within a production pipe is hostile to sensors in direct contact with the fluid flow.
Fluids within the production pipe can erode, corrode, wear, and otherwise compromise sensors disposed in direct contact with the fluid flow. In addition, the hole or port through which the sensor makes direct contact, or through which a cable is run, is a potential leak site. There is great advantage in preventing fluid leakage out of the production pipe. Second, the environment in most wells is harsh, characterized by extreme temperatures, pressures, and debris. Extreme temperatures can disable and limit the life of electronic components. Sensors disposed outside of the production pipe may also be subject to environmental materials such as water (fresh or salt), steam, mud, sand, etc. Third, the well environment makes it difficult and expensive to access most sensors once they have been installed and positioned downhole.
What is needed, therefore, is a reliable, accurate, and compact apparatus for sensing fluid flow within a pipe, one that can sense fluid flow within a pipe in a non-intrusive manner, over a broad range of conditions, one that is operable in an environment characterized by extreme temperatures and pressures and the presence of debris, one that can operate remotely, and one that is not likely to need replacement or recalibration once installed.
problem with utilizing a flow meter at the wellhead of a multiple source well is that the fluid flow reaching the flow meter is a mixture of the fluids from the various sources disposed at different positions within the well. So although the multiphase meter provides the advantage of providing information specific to individual constituents within a fluid flow (which is an improvement over a bulk flow sensors), the information they provide is still limited because there is no way to distinguish sources.
Acquiring reliable, accurate fluid flow data downhole at a particular source environment is a technical challenge for at least the following reasons.
First, fluid flow within a production pipe is hostile to sensors in direct contact with the fluid flow.
Fluids within the production pipe can erode, corrode, wear, and otherwise compromise sensors disposed in direct contact with the fluid flow. In addition, the hole or port through which the sensor makes direct contact, or through which a cable is run, is a potential leak site. There is great advantage in preventing fluid leakage out of the production pipe. Second, the environment in most wells is harsh, characterized by extreme temperatures, pressures, and debris. Extreme temperatures can disable and limit the life of electronic components. Sensors disposed outside of the production pipe may also be subject to environmental materials such as water (fresh or salt), steam, mud, sand, etc. Third, the well environment makes it difficult and expensive to access most sensors once they have been installed and positioned downhole.
What is needed, therefore, is a reliable, accurate, and compact apparatus for sensing fluid flow within a pipe, one that can sense fluid flow within a pipe in a non-intrusive manner, over a broad range of conditions, one that is operable in an environment characterized by extreme temperatures and pressures and the presence of debris, one that can operate remotely, and one that is not likely to need replacement or recalibration once installed.
3 It is, therefore, an object of the present invention to provide an apparatus for non-intrusively sensing fluid flow within a pipe that is reliable, accurate, compact, and remotely operable, one that can sense fluid flow parameters within a pipe in a non-intrusive manner, over a broad range of conditions, one that is operable in an environment characterized by extreme temperatures and pressures, and one that is not likely to need replacement or recalibration once installed.
In an embodiment, an apparatus for varying the gain of a fiber optic sensor that non iritnzsively senses the strain response of a pipe is provided. The apparatus includes a circumferential strain attenuator that has a annular land portion that mechanically couples the attenuator to the pipe. An annular web extends coaxially from the land portion and has a reduced cross sectional area relative to the land and an annular mandrel portion extends coaxially from the web portion and forms a gap between the pipe and the mandrel. The fiber optic sensor is wound on the circumferential stTain attenuator. The web and mandrel cooperate to reduce the strain response of the fiber optic sensor relative to the strain response of the pipe.
Fiber -optic flowmeter limitations are constrained by, among other things, the structural compliance of the pipe, optical. tinnin.g issues for: a given length of fiber, and slew rate limitations based on the rate of change of the length of the fiber sensors. It is often desirable to select a fiber length per sensor and sensor spacing to provide an optimum level of gain for the broadest level of sensing environments for the acoustic environment anticipated, fluid type and consistency flowing within the pipe and the anticipated flow rate of the fluid.
An ad.vantage of at least the preferred embodiments of the present invention is that it provides the ability to selectively modify, or otherwise attenuate, the gain of a flowmeter while keeping other constraints constant. Pref;rred embodiinents result in a flowmeter having a fixed fiber length having the capability to measure a wide range of pressure levels in various acoustic environments. It will be appreciated by those skilled
In an embodiment, an apparatus for varying the gain of a fiber optic sensor that non iritnzsively senses the strain response of a pipe is provided. The apparatus includes a circumferential strain attenuator that has a annular land portion that mechanically couples the attenuator to the pipe. An annular web extends coaxially from the land portion and has a reduced cross sectional area relative to the land and an annular mandrel portion extends coaxially from the web portion and forms a gap between the pipe and the mandrel. The fiber optic sensor is wound on the circumferential stTain attenuator. The web and mandrel cooperate to reduce the strain response of the fiber optic sensor relative to the strain response of the pipe.
Fiber -optic flowmeter limitations are constrained by, among other things, the structural compliance of the pipe, optical. tinnin.g issues for: a given length of fiber, and slew rate limitations based on the rate of change of the length of the fiber sensors. It is often desirable to select a fiber length per sensor and sensor spacing to provide an optimum level of gain for the broadest level of sensing environments for the acoustic environment anticipated, fluid type and consistency flowing within the pipe and the anticipated flow rate of the fluid.
An ad.vantage of at least the preferred embodiments of the present invention is that it provides the ability to selectively modify, or otherwise attenuate, the gain of a flowmeter while keeping other constraints constant. Pref;rred embodiinents result in a flowmeter having a fixed fiber length having the capability to measure a wide range of pressure levels in various acoustic environments. It will be appreciated by those skilled
4 in the art that the environment surrounding a flowmeter may produce too much acoustic energy and tliereby overtax the highly sensitive fiber optic sensors. Such environments are those that include pumps, venturis, choke valves, or any other source that causes noise that is orders of magnitude above that of normal pipe flow.
Preferred embodiments of the present invention also include a compliant material positioned between the circumferential strain attenuator and the pipe. As a result the relatively high natural frequencies of the device that might otherwise cause a signal-processing problem are dampened out.
According to an aspect of the invention there is provided a strain attenuator for attenuating the gain of a sensor sensing the strain response of a pipe, the attenuator comprising: an annular land adapted to mechanically couple to the pipe; an annular web extending coaxially from the land and having a reduced cross sectional area relative to the land; an annular mandrel extending coaxially from the web.
According to another aspect of the invention there is provided a variable gain fiber optic sensor assembly for non-intrusively sensing the strain response of a pipe, the assembly comprising: the attenuator as previously described herein, and a fiber optic sensor mounted to the attenuator.
According to a further aspect of the invention there is provided an apparatus having a variable gain for non-intrusively sensing fluid flow within a pipe, the apparatus comprising: a plurality of strain attenuators as previously described herein;
an acoustic signal sensing array having a plurality of sensors, each sensor including a coil of optical fiber wrapped a plurality of turns around a circumference of a respective strain attenuator; the apparatus being adapted to receive optical power from a source, the optical power being arranged to travel into the acoustic signal sensing array, and the acoustic signal sensing array is arranged to produce a first signal relating to an acoustic signal within the fluid; a local pressure variation sensing array having a plurality of sensors, each sensor including a coil of optical fiber wrapped a plurality of turns around the circumference of a respective strain attenuator; the optical power being arranged to travel into the local pressure variation sensing array, and the local pressure variation sensing array is arranged to produce a second signal relating to a local pressure variation 4a within the fluid; and a housing for enclosing the acoustic signal sensing array and the local pressure variation sensing array.
According to a further aspect of the invention there is provided a system comprising: a strain attenuator as previously described herein; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
According to a further aspect of the invention there is provided a system comprising an assembly as previously described herein, and a pipe, wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
According to a further aspect of the invention there is provided an apparatus for attenuating the gain of a sensor used to sense the strain response of a pipe having an axis, comprising: a land coupled to the pipe and extending radially therefrom; a web extending from the land parallel to the axis of the pipe, wherein the web has a smaller cross sectional area than the land; a mandrel extending from the web parallel to the axis of the pipe, wherein the mandrel forms a gap with respect to the pipe; and a sensor coupled at least to the mandrel.
According to a further aspect of the invention there is provided an apparatus for attenuating the gain of a sensor used to sense the strain response of a pipe having an axis, comprising: a land coupled to the pipe and extending radially therefrom; a web extending from the land parallel to the axis of the pipe; a mandrel extending from the web parallel to the axis of the pipe, wherein the mandrel forms a gap with respect to the pipe, and wherein the mandrel is thicker than the web; and a sensor coupled at least to the mandrel.
According to a further aspect of the invention there is provided an apparatus for attenuating the gain of a sensor used to sense the strain response of a pipe having an axis, comprising: a land coupled to an outside surface of the pipe and extending radially therefrom; a mandrel disposed around the outside surface of the pipe parallel to the axis of the pipe, the mandrel coupled to and extending from the land, wherein the land and 4b mandrel define a mounting surface; and a sensor coupled at least to the mandrel, wherein the sensor comprises a fiber optic sensor coupled to at least a portion of the mounting surface.
According to a further aspect of the invention there is provided an apparatus for attenuating the gain of a sensor used to sense the strain response of a pipe having an axis, comprising: a land coupled to an outside surface of the pipe and extending radially therefrom; a mandrel coupled to and extending from the land along the axis of the pipe, wherein the mandrel forms a gap with respect to the pipe, wherein the land and mandrel define a mounting surface; and a sensor coupled at least to the mandrel, wherein the sensor comprises a fiber optic sensor coupled to at least a portion of the mounting surface.
According to a further aspect of the invention there is provided a method for sensing the strain response of a pipe having an axis, comprising: attenuating the strain response by coupling the strain through a mandrel coupled to an outside diameter of the pipe; and detecting the attenuated strain by at least one sensor coupled to the mandrel.
According to a further aspect of the invention there is provided an apparatus for sensing the strain response of a pipe having an axis, comprising: a pipe having a strain response; a mandrel coupled to an outside diameter of the pipe and extending parallel to the axis of the pipe, wherein the mandrel defines a mounting surface; and a sensor coupled at least to the mandrel, wherein the sensor comprises a fiber optic sensor coupled to at least a portion of the mounting surface.
The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments given, by way of example, with reference to the accompanying drawings, in which:
Figure 1 is a diagrammatic view of a well having acasing and a pipe, and flow meters positioned at various locations along the pipe inside the casing;
4c Figure 2 is a diagrammatic view of an apparatus for non-intrusively measuring fluid flow parameters within a pipe;
Figure 3 is a diagrammatic view of an embodiment of a sensing device;
Figure 4 is a diagrammatic view of an embodirnent of a sensing device;
Figure 5 is a diagrammatic view of an embodiment of a sensing device;
Figure 6 is a diagrammatic view of an apparatus for non-intrusively measuring fluid flow parameters incorporating the circumferential strain attenuators in accordance with the present invention within a pipe;
M&C Folio No P51856W0 5 Figure 7 is a cross sectional side view of a circumferential strain attenuator in accordance with the present invention;
Figure 8 is a graphical representation of the attenuation characteristics of an embodiment of the present invention;
Figure 9 is a graphical representation of the attenuation characteristics of an embodiment of the present invention;
Figure 10 is a graphical representation of the attenuation characteristics of an embodiment of the present invention;
Figure 11 is a perspective view in partial section of a circumferential strain attenuator in accordance with the present invention; and Figure 12 is a cross sectional side view of an alternative embodiment of the circumferential strain attenuator of the present invention.
Referring to Figure 1 there is shown an intelligent oil well system 10 containing one or more production pipes 12 that extend dowuward through a casing 14 to one or more petroleum sources 16. An annulus 18 -is formed between the pipe 12 and the casing 14. Each production pipe 12 may include one or more lateral sections that branch off to access different petroleum sources 16 or different areas of the same petroleum source 16. Fluid mixtures flow 'from the sources 16 to the platform through the production pipes 12. The fluid mixtures consist predominantly of petroleum products and water. The production pipe 12 includes one or more the present invention apparatus 22 for non-intnlsively sensing fluid flow within a pipe (also referred to hereinafter as a "flow meter") to monitor various physical parameters of the fluid mixtures as they flow through the production pipes 12.
Flow meter 22 includes a first sensing array 24 for sensing acoustic signals travelling at the speed of sound (SOS) through the fluid within the pipe 12 (hereinafter AMENDED SHEET
M&C Folio No P5I856W0 5A
also referred to as the "SOS sensing array"), a second sensing array 26 for sensing short duration local pressure variations travelling with the fluid flow (hereinafter also referred to as the "flow velocity sensing array"), and a housing 28 - = >
l ennI=nlni=n qHFFT
affached to the pipe 12 for enclosing the sensing arrays 24,26. Each flow meter 22 can be incorporated into an existing section of production pipe 12, or can be incorporated into a specific pipe section that is inserted in line into the production pipe 12. The distributed scheme of flow meters 22 shown in Figure 2 perrniits an operator of the intelligent well system 10 to deternzine the extent and location of breab~through of water into the petroleum reserve. The availability of this type of information pennits the user to monitor and intelligently control the production of the petroleum reserve.
The sensing arrays 2426 receive optical povwer and pmduce optical signals via fiber optic cables 30 that extend between the flowmeter 22 and ins-uumentatio:n residing on the platform 20 or at a remote location in communication with the platform 20. Optical fiber pressure sensors 32 within each sensing array 24,26 may be connected individually to the platforni instnamentation, or may be multiplexed along one or more optical fibers using known techniques including, but not limited to, wavelength division multiplexing (WDM) and time division multiplexing (TDM). In those embodiments where the optical fiber pressure sensors 32 are not connected individually to the instrumentation, the sensors 32 of a sensing array 24,26 may be connected to one another in series or parallel. The optical signals produced by the sensing arrays 24,26 provide infornnation relating to the fluid flow characteristics within the pipe 12 (e.g., local flow disturbances, acoustic wave propagation within the flow, flow pressure magnitude and changes, etc.).
Interpretation of the optical signals, which can be done using methods well known in the art, enables the determination of the speed of sound (SOS) of the fluid mixture aud the velocity of the fluid flow within the pipe 12. Once the SOS, the flow velocity, the pressure, and the temperature of the m.ia.'tmre are lnown, other desirable data such as the phase fraction of the constituents within the mixture can be determined. The optical signals from the sensing arrays 24,26 may also be interpreted using previously known methods.
Figure 2 shows an exemplary embodiment of the present invention wherein the SOS
sensing array 24 and the flow velocity sensing array 26 are positioned adjacent one another on a common length of pipe 12. Further details of this embodiment are provided below. Figures 3-5 diagrammatically illustrate sensing array embodiments and attributes that can be used with either or both sensing arrays 24,26.
To avoid interference from outside sources and to protect from the harsh environment within the well, the sensing arrays 24,26 are enclosed within a housing 28 that is attached to an exterior surface of the pipe section I.Z. The housing 28 includes an outer sleeve 34 extending between a pair of bosses 36. T'he fzber'optic cable(s) 30 that extends between the flow meter 22 and the instrumentation passes through a sealable port 38 in one or both bosses 36 aind connects with the sensing arrays 24,26.
Outside the housing 28, the sensor cable 30 is housed in a protectiive conduit 40 that is attached to the pipe 12. In the preferred embodiment, the housing 28 and the pipe 12 together form a pressure vessel. The pressure within the pressure vessel may be greater than or less than the ambient pressure within the annulus 18 between the casing 14 and the pipe 12. In other embodiments, the housing 28 is sealed to protect the sensing arrays 24,26, but does not act as a pressure vessel. In all embodiments, the size and structure of the housing 28 are chosen to withstand the pressure gradients present in the well environment, to accommodate the size of the sensing arrays 24,26, and to allow the sensi:ng arrays 24,26 to be positioned a distance away from the housing 28 such that heat transfer via the pipe 12 andlor the housing 28 is non-disabling for the application at hand. In a preferred embodiment, the housing 28 is filled with a gas such as, but not limited to, air, nitrogen, argon, etc. The gaseous envirojnment within the housing 28 advantageously acts as an acoustic isolator that helps reduce pressure wave interference that might otherwise travel into the housing 28 from the annulus 18 and undesirably influence the sensing arrays 24,26. T'he gaseous environment also thermally insulates the sensing arrays 24,26.
In some applications, there is advantage in placing a plurality of bumpers within the housing to help maintain separation between the outer sleeve of the housing and the pipe. Bumpers that can be used in this manner are known.
The pipe section 12 has a compliancy selected to suit the application at hand.
The pipe 12 must have sufficient structural integrity to handle the pressure gradient across the pipe 12, and yet must also be able to def lect (i.e_, change in circumference) an amount that will yield useful infornaation. The amount the pipe 12 will change in circumference for a given pressure distribution is determined by the thickness of the pipe wall 42 and the physical properties of the pipe material (e.g., modulus of elasticity, etc.). Thus, the thickness of the pipe wall 42 and the pipe material can be chosen to help produce a favorable sensor sensitivity for the present apparatus. The characteristics of the pipe section 12 contiguous with each present apparatus may be the same as or different than the characteristics in other sections of the production pipe 12.
The optical pressure sensors 32 used in the SOS and flow velocity sensing arrays 24,26 each include a plurality of optical fiber coils 32. Each coil 32 is wrapped one or more turns around the circumference of the pipe section 12 in a manner that allows the length of the optical fiber within the coil 32 to change in response to a change in the circumference of the pipe 12. l.f, for example, a pipe 12 can be expected to see a maxinum circumferential change of "y", then a one-turn coil will be subject to a maximum potential change in length of "y" (or some known function of "y"). If an optical measurement technique is not sensitive enough to register a change in distance equal to "y", then the coil 32 can be wrapped to include "n" number of tums.
The change in fiber length "y" per tum is therefore multiplied by "n" turns, and a change in fiber length great enough to produce a useful signal (i.e., "n = y") is provided. In fact, the same technique can be used to not only provide a minimum useful signal, but also to increase the sensitivity of the sensor 32 and therefore the range of detectable changes in the circumference of the pipe 12. In all cases, the length of the optical fiber in each coil 32 is kkn.own and is chosen to produce the sensitivity required to sense the disturbance(s) of interest for that particular sensor... The preferred embodiment, as described above, includes coils 32 wrapped around the circumference of the pipe 12.
.Alterraatively, the optical fiber lengths can be arranged around a portion of the circumference of the pipe 12.
The turns of optical fiber in a sensor 32 are preferably laid next to one another to minimize the axial component of each turn, and thereby keep each turn to a known, constant length. Alternatively, some or all the turns of a coil 32 could be separated from adjacent turns. A coil 32 can consist of a single layer of optical fiber turns, or multiple layers of optical fiber turns depending on the application. The coil 32 of optical fiber in each sensor 32 may be attached to the pipe 12 by a variety of attachment mechanisms including, but not limited to, adhesive, glue, epoxy, or tape. In a preferred embodiment, a tape having an adhesive substance attached to opposite surfaces of a substrate is used. The tape adheres to both the pipe 12 and the fiber and provides a smooth surface on which the fiber can be laid. It is our experience that tape used on a rough surface helps to decrease micro-bend losses within the optical fiber.
In most embodiments, the optical pressure sensors 32 used in the SOS and flow velocity sensing arrays 24,26 further include one or more optical reflective devices 46 disposed between coils 32 that are wavelength tunable. rn a preferred embodiment, the optical reflective devices 46 are fiber Bragg Gratings (FBGs). An FBG, as is known, reflects a predetermined wavelength band of light having. a central peak reflection wavelength Qb), and passes the remaining wavelengths of the incident light (withi.n a predeternzined wavelength range). Accordingly, input light propagates along the cable 30 to the coils 32 and the FBGs reflect particular wavelengths of light back along the cable 30. It is our experience that in most applications there is advantage in placing an isolation pad between each optical reflective device and the outer surface of the pipe to accommodate pipe growth and/or vibrations.
Such an isolation pad is previously known. _ In the embodiment of the present invention shown in Figure 3, the sensors 32 are connected in series and a single FBG 46 is used between each of the sensor 32, and each FBG 46 has a common reflection wavelength XI. In the embodiment shown in Figure 4, the sensors 32 are connected in series and pairs of FBGs 46 are located along the fiber at each end of each of the sensors 32, respectively_ I'he FBG pairs 46 are used to multiplex the sensed signals to identify the individual sensors 32 from optical return signals. The pair of FBGs 46 on each end of the first sensor 32A have a common reflection wavelength 11, and the second pair of FBGs 46 on each end of the second sensor 32B have a common reflection wavelength X2, but different from that of the first pair of FBGs 46. Similarly, the FBGs 46 on each end of the third sensor 32C
have a common reflection wavelength 13, which is different from 11,X2, and the FBGs 46 on each end of the fourth sensor 32D have a common reflection wavelength X4, which is different from 44~.3. The- sensors 32 within either sensing array 24,26 may alternatively be connected to one another in parallel by using optical couplers (not shown) that are positioned upstream of each sensor 32 and coupled to a common fiber.
Referring to Figures 2, 3, and 4, the sensors 32 with the FBGs 46 disposed therebetween may be configured in numerous known ways to precisely measure the fiber length or change in fiber tength, such as an interferometric, Fabry Perot, time-of-flight, or other known arrangements. An example of a Fabry- Perot technique is described in US Patent. No. 4,950,883 "Fiber Optic Sensor Arrangement Having Reflective Gratings Responsive to Particular Wavelengths", to Glenn.
Alternatively, a portion or all of the fiber between the optical reflective device 46 may be doped with a rare earth dopant (such as erbium) to create a tunable fiber laser, examples of which can be found in U.S. Patent Nos. 5,317,576; 5,513,913; and 5,564,832.
Referring to Figure 5, in an alternative embodiment the sensors 32 may also be formed as a purely interferometric sensing array by using sensors 32 without FBGs 46 disposed therebetween. In this embodiment, each sensor 32 is independently connected to the instrumentation at the platform 20 and known interferometric techniques are used to determz.ne the length or change in length of the fiber around the pipe 12 due to pressure variations. U.S. Patent 5,218,197, entitled "IV[ethod and Apparatus for the Non-invasive Measurement of Pressure Inside Pipes Using a Fiber Optic Interferometer Sensor", issued to Carroll discloses such a technique. The interferometric wraps may also be multiplexed in a manner si.milar to that described in Dandridge, et al, "Fiber Optic Sensors for Navy Applications", IEEE, Feb. 1991, or Dandridge, et al, "Multiplexed Interferometric Fiber Sensor Arrays", SPIE, Vol. 1586, 1991, pp.176-183.
Other techniques to determin.e the change in fiber length may also be used. In addition, reference optical coils (not shown) may be used for certain interferometric approaches and may also be located on or around the pipe 12 but may be designed to be insensitive to pressure variations.
Adjacent sensors 32, within either sensing array 24,26, are spaced apart from each another by a known distance or distances. The sensors 32 in an array are preferably equidistant from one another, but not necessarily. In both sensing arrays 24,26, the spacing between adjacent sensors 32 and the number of sensors 32 reflect the nature of the signal being sensed; i.e., the SOS sensing array 24 utilizes acoustic signals having relatively long wavelengths, and the flow velocity sensing array 26 utilizes local pressure variations within the flow having relatively small coherence length.
In relative terms, the sensors 32 in the SOS sensing array 24 are spaced apart from one another substantiatly farther than are the sensors 32 within the flow velocity sensing array 26 because of the intrinsic differences in the. signals being sensed. The exact inter-spacing and number of c ils 32 in a sensing array 24,26 is application dependent and is a function of parameters such as, but not limited to, the spectra of anticipated acoustic signals and local pressure variations, the anticipated SOS of the fluid constituents, the number of sensors 32, the processing technique used, etc. Examples of signal processing techn.iques can be found in the following references : H. Krim, M.
Viberg, "Two Decades of Array Signal Processing Research - The Parametric Approach", IEEE
Signal Processing Magazine, pp.67-94, R. Nielson, "Sonar Signal Processing", Ch. 2, pp.51-59.
Figure 2 shows an exemplary embodiment of the present invention flow meter 22 that can be inserted in-line within a production pipe 12 and disposed at an appropriate position within the well. The flow meter 22 includes a SOS sensing array 24 and a flow velocity sensing array 26 mounted on a section of pipe 12 adjacent one another and enclosed within a housing 28. A fiber optic cable 30 extends through one of the housing bosses 36 and connects to an optical delay line 48. An optical fiber 50, in turn, connects the optical delay line 48 to the SOS sensing device 24. The SOS
sensing device 24 includes six (6) sensors 32 located at six predeternined locations (x1,x2, x3, x4, xs, x6) along the pipe 12, where each sensor 32 is separated from adjacent sensors 32 within the SOS sensing array 24 by an axial length increment equal to "x ".
Each sensor is mounted on a tape that includes adhesive on both faces. A FBG 46 is positioned between the optical delay line 48 and a sensor 32. One FBG 46 is also positioned between and connected to each pair of adjacent sensors 32, such that the optical delay line 48, the FBGs 46, and the sensors 32 in the SOS sensing array 24 are in series with one another. It is preferred, but not required, to skew each between the adjacent sensors 32 to as to minimize the sharpness of the directional changes within the fiber of either sensor 32 or within the FBG 46.
An optical fiber 52 extends from the last sensor 32 in the SOS sensing array over to a first sensor 32 in the adjacent flow velocity sensing array 26. A
FBG 46 is disposed in-line between the two devices. The flow velocity sensing array 46 includes four (4) sensors 32 located at predetermined locations (x7, xg, x9, xlo) along the pipe 12.
Like the SOS sensing array 24, each sensor 32 in the flow velocity sensing array 26 is mounted on tape and is separated from adjacent sensor 32 within the flow velocity sensing array 26 by an axial length increment equal to "x ". The axial distance x separating the sensors 32 in the flow velocity sensing array 26 is, however, substantially shorter than that used in the SOS sensing array 24 because of the difference in the characteristics of the pressure disturbances sought to be measured; i.e., the SOS sensing array 24 senses relatively long wavelength acoustic signals travelling through the fluid flow at the speed of sound, and the flow velocity sensing array 25 senses relatively short coherence length local pressure variations with the fluid flow. One FBG 46 is 09-11-2002 _ GB0105277 M&C Folio No P51856W0 .13 positioned between and connected to each pair of adjacent sensors 32, such that the FBGs 46 and the sensors 32 in the flow velocity sensing array 26 are in series with one another. Here again, it is preferred to skew each FBG 46 between the adjacent sensors 32 so as to minimize the sharp changes within the fiber of either sensor 32 or within the FBG 46. In some applications, it.may be useful to connect an additional optical delay line 48 after the last sensor 32 within the flow velocity sensing array 26.
In a version of the exemplary embodiment of the present invention flow meter 22 shown in Figure 2, the optical delay line(s) 48 are formed by wrapping approximately two hundred and ten meters (210m) of optical fiber around the circumference of a three and one-half inch (9 cm) diameter pipe. Each coil of the SOS
sensing device 24 is formed by wrapping one hundred and two meters (1 02m) of optical fiber around the circumference of the pipe in a single layer. The optical fiber is wrapped using approximately twenty-five grams (25g) of tension on the fiber.
Each turn of the coil is separated from adjacent coils by a fifteen micron (15 ) gap. Adjacent coils in the SOS sensing device are spaced approximately eighteen inches (46 cm) apart, center to center. - The velocity sensing device is formed in like manner, except that each coil comprises seven layers rather than a single layer, and adjacent coils are spaced approximately one and eight tenths of an inch (4.6 cm) apart, center to center. In both sensing devices, the FBGs are spliced in the section of optical fiber that extends in a helical fashion between adjacent coils, or between a coil and a delay line, etc. Each FBG and the splices that tie the FBG into the optical fiber are laid on an isolator.pad.
The flowmeter as described herein above may be designed to accommodate a variety of pressure levels, slew rates, and pressure variations. For any given design the practical limitations of the flowmeter will be controlled by the ability of the fiber to accurately sense the structural response, or the time varying strains, of the pipe to the pressure fluctuations within the pipe. . These limitations are constrained by, among other things, the structural compliance of the pipe, optical fiiming issues for a given length of fiber, and slew rate limitations based on the rate of change of the length of the fiber sensors. As described herein above it is desirable to select a fiber length per sensor and sensor spacing to provide an optimum level of gain for the broadest level of sensing AMFNnFn ';HFET
environments for the acoustic environment anticipated; fluid type and consistency flowing within the pipe and the anticipated flow rate of the fluid.
The method of interrogating the sensors of a give:n flowmeter depends on the fiber length and the practical constraints described herein. The present invention provides the ability to -selectively modify, or otherwise attenuate, the gain of a flowmeter while keeping other constraints constant. The present invention results in a flowmeter having a fixed fiber length having the capabillity to measure a wide range of pressure levels in various acoustic environments. It will be appreciated by those skilled in the art that the environment surrounding a flowmeter inay produce too much acoustic energy and thereby overtax the highly sensitive fiber optic sensors. Such enviromnents are those that include pumps, venturis, choke valves, or any other source that causes noise that is orders of magnitude above that of normal pipe flow.
The flowmeter 22 shown in Figure 2 depicts an embodiment wherein sensor wraps 32 are coupled directly, or closely, to the pipe 12. This configuration provides the highest level of gain or ability to sense the structural response of the pipe 12 to -pressure fluctuations from fluids flowing therethrough. An embodiment of attenuators 100 of the present invention is best described with reference to Figures 6 and 7 wherein the varlous sensors 32 of flowmeter 22 are mounted to the attenuators.
Attenuator 100 is an axisymmetrical ring or collar including a land 102 coupled directly to the outside diameter of the pipe 12. The land may be coupled by providing an interference fit, welding or other methods as described herein after or any other known method.
Fiber 30 of sensor 32 may variously be positioned on land 102, mandrel 104, and web portion 106 as appropriate to obtain the level of desired attenuation. In operation, land 102 has a strain response similar to that of the pipe 12 having a slightly stiffer cross-sectional effect. Because the web 106 and mandrel 104 are cantilevered from the pipe 12, a slight gap 108 is maintained therebetween providing these pori:ions with an attenuated strain response relative to the pipe. The level of attenuation is primarily driven by the geonietries selected for attenuator 100 and in the embodiment shown web 106 is thin compared to the land 102 and the mandrel 104 and provides a low stress transition zone from the land to the mandrel. The mandrel 104 includes a thicker cross section than the web and possesses a higher hoop stiffness than web portion 106 and is able to resist the strain experienced by land 102 in response to pressure fluctuations within pipe 12. In the embodiment shown mandrel 104 exhibits a small negative strain response relative to the pipe 12 and land 102 as a result of the relatively low bending stiffness of the web portion 106. In addition to providing a low stress transition zone from the land to the mandrel, the low bending stiffness of the web portion can be sized to minimize the amount of negative strain imparted to the mandrel portion 104.
The attenuator 100 provides a broad band attenuation of the strain response of the pipe without introducing additional dynamics between the strain in the pipe and the average strain in the fiber that would distort the relation between the attenuated strain and the actual strain response of the pipe. The broad band attenuation provided is essentially flat up to frequencies approaching the ring frequency mode of the attenuator (breathing mode) because of its inherent stiffness in all modes that have a circumferentially averaged strain component. The attenuator 100 will have non-axisymmetric modes, such as yaw, that occur at frequencies significantly below the ring frequency. These modes do not influence or otherwise degrade the transfer function because they do not contain a circumferentially averaged strain component and therefore are not observed by the sensor.
The level of attenuation provided by attenuator 100 is dependant upon many parameters including material type, coupling methods, the number of layers of fibers 30 and geometry including the length, thickness and geometries of the various portions of the attenuator. In addition, the position of the sensor 32 along the various portions of the attenuator 100 will change the ultimate attenuation level for any given combination of parameters. The total level of attenuation may be determined by integrating the hoop strain over the entire length of the attenuator 100 and may be expressed in terms of the ratio of the strain response of the attenuator with the strain response of the pipe 12.
Optical fibers 30 react to the various strain response of the attenuator by producing a commensurate length change similar to that described herein above resulting in a M&C Folio No P51856W0 16 flowmeter 22 which provides attenuated signal responses relative to a flowmeter having sensors 32 coupled directly to pipe 12.
The present invention will now be described with respect to specific embodiments with reference to Figures 7 and 8. In a particular embodiment the configuration of the attenuator 100 is that of an attenuator comprised of Stainless Steel material and includes a nominal inside diameter 120 of the land 102 portion of 2.375 inches (6 cm), outside diameter 122 of 3.225 inches (8.2 cm) and a length 124 of approximately .25 inches (0.6 cm). The length 126 of mandrel portion 104 is nominally 2.0 inches (5 cm) long and includes a sensor 32 comprising a three layer wrap of fibers 30 occupying a width 128 of approximately 1.664 inches (4 cm). With reference to Figure 8 the level of attenuation for this particular embodiment is depicted graphically for sensor 32 having a 1.664 inch (4 cm) width mounted to mandrel portion 104 at different positions thereon from a starting position nearest the land 102 to a starting position near the end of the mandrel portion. As can be seen from the figure the level of attenuation is dependent upon the starting position of the sensor 32 and increases as the sensor starting position moves away from the land 102 portion of the attenuator. The perforrriance of -the attenuator depicted in Figure 8 is based on a nominal hoop strain response of pipe 12 of 0.096 microinch/in/psi (0.014 m/m(kPa) and shows that a sensor 32 starting at a point .19 inches (0.5 cm) along mandrel 104, depicted by point 110, has an attenuated strain response of approximately 0.0103 microinch/in/psi (0.0015 m/m(kPa) or an attenuation of 9.29. Similarly a sensor 32'having starting points at.21, .23, .25 %and .27 inches (0.53, 0.58, 0.64 and 0.69 cm) along mandrel 104 exhibits attenuation levels of 10.09, 11.03, 12.16 and 13.54 respectively.
An alternative embodiment of attenuator 100 is shown with reference to Figures 7 and 9 comprising an attenuator comprised of Stainless Steel material and includes a nominal inside diameter 120 of the land 102 portion of 2.875 inches (7.3 cm) and outside diameter 122 of 3.225 inches (8.2 cm) and having a width 124 of .25 inches (0.64 cm) long. The mandrel portion 104 has a length 126 of nominally 1.8 inches (4.6 cm) and includes a sensor 32 comprising a three layer wrap of fibers 30 occupying a width 128 of approximately 1.414 inches (3.6 cm). The performance of the attenuator AMENDED SHEET
t =
M&C Folio Nb P51856W0 17 depicted in Figure 9 is based on a nominal hoop strain response of pipe 12 of approximately 0.279 microinch/in/psi (0.04 mlm/kPa) and, similar to that described herein above in Figure 8, shows that a sensor 32 starting at a point .22 inches (0.56 cm) along mandrel 104, depicted by point 112, has an attenuated strain response of approximately 0.0308 microinch/in/psi (0.004 rnlm/kPa) or an attenuation of 9.07.
Similarly a sensor 32 having starting points at .21, .23, .25 and .26 inches (0.53, 0.58=, 0.64 and 0.66 cm) along mandrel 104 exhibits attenuation levels of 9.46, 10.33, and 10.88 respectively. Similarly, although not shown in the figure, a sensor 32 having starting points at .30 and .35 inches (0.76 and 0.89 cm) along mandrel 104 exhibits attenuation levels of 13.38 and 18.62 respectively. The performance of an attenuator similar to that described above having a mandrel length of 1.5 inches (3.8 cm) is depicted in Figure 10 showing a similar relationship between sensor starting point and attenuation level.
An alternative embodiment of attenuator 100 is best shown with reference to Figure 11 wherein the 'attenuator includes a circumferential groove 130 positioned on the inside,diameter of mandrel portion 104. Attenuator 100 fizrther includes an o-ring 132 positioried within groove 130. 0-ring 130 is sized such that it is compressed between attenuator 100 and the outside diameter of pipe 12 to provide a predetermined level of compression. In such a configuration o-ring 130 provides a predictable level of damping to high natural frequency vibration modes of the attenuator. In a particular embodiment o-ring 130 is comprised of a nitrile or neoprene material and together with groove 130 is sized to provide a compression level of about 20%.
Yet another alternative embodiment is best shown with reference to Figure 12 wherein attenuator 100 comprises an axisymetrical attenuator ring 140 including mandrel 104- and web portion 106 and fizrther comprises a ramp portion 142.
Attenuator 100 further comprises a split ring 132, comprising two or more partial arc sections as is known, having a ramp portion 146 and an externally threaded potion 148. In operation the sections of split ring 132 are assembled about pipe 12 and attenuator ring portion 140 is assembled over the split ring with ramp 142 cooperating with ramp 146 to provide a force to wedge the split ring and attenuator ring together.
Attenuator 100 onnFnrnFn qNFFT
09-11-2d02 G B0105277 M&C Folio No P51856WO 17A
further includes nut 150 having internal threads 152 which cooperate with the external threads 148 on split ring 132. When engaged and tightened, nut 150 forces intimate contact between ramps 142, 146 and between split ring 132 and pipe 12 thus providing AMENDED SHEET
a land portion similar to that described herein above. This particular embodiment is particularly advantageous for the ability to mount attenuator on a pipe where other methods are difficult or not possible.
Although the invention has been described and illustrated with respect to exemplary embodiments thereof, the foregoing and various other additions and omissions may be made therein and thereto without departirig from the spirit and scope of the present invention.
Preferred embodiments of the present invention also include a compliant material positioned between the circumferential strain attenuator and the pipe. As a result the relatively high natural frequencies of the device that might otherwise cause a signal-processing problem are dampened out.
According to an aspect of the invention there is provided a strain attenuator for attenuating the gain of a sensor sensing the strain response of a pipe, the attenuator comprising: an annular land adapted to mechanically couple to the pipe; an annular web extending coaxially from the land and having a reduced cross sectional area relative to the land; an annular mandrel extending coaxially from the web.
According to another aspect of the invention there is provided a variable gain fiber optic sensor assembly for non-intrusively sensing the strain response of a pipe, the assembly comprising: the attenuator as previously described herein, and a fiber optic sensor mounted to the attenuator.
According to a further aspect of the invention there is provided an apparatus having a variable gain for non-intrusively sensing fluid flow within a pipe, the apparatus comprising: a plurality of strain attenuators as previously described herein;
an acoustic signal sensing array having a plurality of sensors, each sensor including a coil of optical fiber wrapped a plurality of turns around a circumference of a respective strain attenuator; the apparatus being adapted to receive optical power from a source, the optical power being arranged to travel into the acoustic signal sensing array, and the acoustic signal sensing array is arranged to produce a first signal relating to an acoustic signal within the fluid; a local pressure variation sensing array having a plurality of sensors, each sensor including a coil of optical fiber wrapped a plurality of turns around the circumference of a respective strain attenuator; the optical power being arranged to travel into the local pressure variation sensing array, and the local pressure variation sensing array is arranged to produce a second signal relating to a local pressure variation 4a within the fluid; and a housing for enclosing the acoustic signal sensing array and the local pressure variation sensing array.
According to a further aspect of the invention there is provided a system comprising: a strain attenuator as previously described herein; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
According to a further aspect of the invention there is provided a system comprising an assembly as previously described herein, and a pipe, wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
According to a further aspect of the invention there is provided an apparatus for attenuating the gain of a sensor used to sense the strain response of a pipe having an axis, comprising: a land coupled to the pipe and extending radially therefrom; a web extending from the land parallel to the axis of the pipe, wherein the web has a smaller cross sectional area than the land; a mandrel extending from the web parallel to the axis of the pipe, wherein the mandrel forms a gap with respect to the pipe; and a sensor coupled at least to the mandrel.
According to a further aspect of the invention there is provided an apparatus for attenuating the gain of a sensor used to sense the strain response of a pipe having an axis, comprising: a land coupled to the pipe and extending radially therefrom; a web extending from the land parallel to the axis of the pipe; a mandrel extending from the web parallel to the axis of the pipe, wherein the mandrel forms a gap with respect to the pipe, and wherein the mandrel is thicker than the web; and a sensor coupled at least to the mandrel.
According to a further aspect of the invention there is provided an apparatus for attenuating the gain of a sensor used to sense the strain response of a pipe having an axis, comprising: a land coupled to an outside surface of the pipe and extending radially therefrom; a mandrel disposed around the outside surface of the pipe parallel to the axis of the pipe, the mandrel coupled to and extending from the land, wherein the land and 4b mandrel define a mounting surface; and a sensor coupled at least to the mandrel, wherein the sensor comprises a fiber optic sensor coupled to at least a portion of the mounting surface.
According to a further aspect of the invention there is provided an apparatus for attenuating the gain of a sensor used to sense the strain response of a pipe having an axis, comprising: a land coupled to an outside surface of the pipe and extending radially therefrom; a mandrel coupled to and extending from the land along the axis of the pipe, wherein the mandrel forms a gap with respect to the pipe, wherein the land and mandrel define a mounting surface; and a sensor coupled at least to the mandrel, wherein the sensor comprises a fiber optic sensor coupled to at least a portion of the mounting surface.
According to a further aspect of the invention there is provided a method for sensing the strain response of a pipe having an axis, comprising: attenuating the strain response by coupling the strain through a mandrel coupled to an outside diameter of the pipe; and detecting the attenuated strain by at least one sensor coupled to the mandrel.
According to a further aspect of the invention there is provided an apparatus for sensing the strain response of a pipe having an axis, comprising: a pipe having a strain response; a mandrel coupled to an outside diameter of the pipe and extending parallel to the axis of the pipe, wherein the mandrel defines a mounting surface; and a sensor coupled at least to the mandrel, wherein the sensor comprises a fiber optic sensor coupled to at least a portion of the mounting surface.
The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments given, by way of example, with reference to the accompanying drawings, in which:
Figure 1 is a diagrammatic view of a well having acasing and a pipe, and flow meters positioned at various locations along the pipe inside the casing;
4c Figure 2 is a diagrammatic view of an apparatus for non-intrusively measuring fluid flow parameters within a pipe;
Figure 3 is a diagrammatic view of an embodiment of a sensing device;
Figure 4 is a diagrammatic view of an embodirnent of a sensing device;
Figure 5 is a diagrammatic view of an embodiment of a sensing device;
Figure 6 is a diagrammatic view of an apparatus for non-intrusively measuring fluid flow parameters incorporating the circumferential strain attenuators in accordance with the present invention within a pipe;
M&C Folio No P51856W0 5 Figure 7 is a cross sectional side view of a circumferential strain attenuator in accordance with the present invention;
Figure 8 is a graphical representation of the attenuation characteristics of an embodiment of the present invention;
Figure 9 is a graphical representation of the attenuation characteristics of an embodiment of the present invention;
Figure 10 is a graphical representation of the attenuation characteristics of an embodiment of the present invention;
Figure 11 is a perspective view in partial section of a circumferential strain attenuator in accordance with the present invention; and Figure 12 is a cross sectional side view of an alternative embodiment of the circumferential strain attenuator of the present invention.
Referring to Figure 1 there is shown an intelligent oil well system 10 containing one or more production pipes 12 that extend dowuward through a casing 14 to one or more petroleum sources 16. An annulus 18 -is formed between the pipe 12 and the casing 14. Each production pipe 12 may include one or more lateral sections that branch off to access different petroleum sources 16 or different areas of the same petroleum source 16. Fluid mixtures flow 'from the sources 16 to the platform through the production pipes 12. The fluid mixtures consist predominantly of petroleum products and water. The production pipe 12 includes one or more the present invention apparatus 22 for non-intnlsively sensing fluid flow within a pipe (also referred to hereinafter as a "flow meter") to monitor various physical parameters of the fluid mixtures as they flow through the production pipes 12.
Flow meter 22 includes a first sensing array 24 for sensing acoustic signals travelling at the speed of sound (SOS) through the fluid within the pipe 12 (hereinafter AMENDED SHEET
M&C Folio No P5I856W0 5A
also referred to as the "SOS sensing array"), a second sensing array 26 for sensing short duration local pressure variations travelling with the fluid flow (hereinafter also referred to as the "flow velocity sensing array"), and a housing 28 - = >
l ennI=nlni=n qHFFT
affached to the pipe 12 for enclosing the sensing arrays 24,26. Each flow meter 22 can be incorporated into an existing section of production pipe 12, or can be incorporated into a specific pipe section that is inserted in line into the production pipe 12. The distributed scheme of flow meters 22 shown in Figure 2 perrniits an operator of the intelligent well system 10 to deternzine the extent and location of breab~through of water into the petroleum reserve. The availability of this type of information pennits the user to monitor and intelligently control the production of the petroleum reserve.
The sensing arrays 2426 receive optical povwer and pmduce optical signals via fiber optic cables 30 that extend between the flowmeter 22 and ins-uumentatio:n residing on the platform 20 or at a remote location in communication with the platform 20. Optical fiber pressure sensors 32 within each sensing array 24,26 may be connected individually to the platforni instnamentation, or may be multiplexed along one or more optical fibers using known techniques including, but not limited to, wavelength division multiplexing (WDM) and time division multiplexing (TDM). In those embodiments where the optical fiber pressure sensors 32 are not connected individually to the instrumentation, the sensors 32 of a sensing array 24,26 may be connected to one another in series or parallel. The optical signals produced by the sensing arrays 24,26 provide infornnation relating to the fluid flow characteristics within the pipe 12 (e.g., local flow disturbances, acoustic wave propagation within the flow, flow pressure magnitude and changes, etc.).
Interpretation of the optical signals, which can be done using methods well known in the art, enables the determination of the speed of sound (SOS) of the fluid mixture aud the velocity of the fluid flow within the pipe 12. Once the SOS, the flow velocity, the pressure, and the temperature of the m.ia.'tmre are lnown, other desirable data such as the phase fraction of the constituents within the mixture can be determined. The optical signals from the sensing arrays 24,26 may also be interpreted using previously known methods.
Figure 2 shows an exemplary embodiment of the present invention wherein the SOS
sensing array 24 and the flow velocity sensing array 26 are positioned adjacent one another on a common length of pipe 12. Further details of this embodiment are provided below. Figures 3-5 diagrammatically illustrate sensing array embodiments and attributes that can be used with either or both sensing arrays 24,26.
To avoid interference from outside sources and to protect from the harsh environment within the well, the sensing arrays 24,26 are enclosed within a housing 28 that is attached to an exterior surface of the pipe section I.Z. The housing 28 includes an outer sleeve 34 extending between a pair of bosses 36. T'he fzber'optic cable(s) 30 that extends between the flow meter 22 and the instrumentation passes through a sealable port 38 in one or both bosses 36 aind connects with the sensing arrays 24,26.
Outside the housing 28, the sensor cable 30 is housed in a protectiive conduit 40 that is attached to the pipe 12. In the preferred embodiment, the housing 28 and the pipe 12 together form a pressure vessel. The pressure within the pressure vessel may be greater than or less than the ambient pressure within the annulus 18 between the casing 14 and the pipe 12. In other embodiments, the housing 28 is sealed to protect the sensing arrays 24,26, but does not act as a pressure vessel. In all embodiments, the size and structure of the housing 28 are chosen to withstand the pressure gradients present in the well environment, to accommodate the size of the sensing arrays 24,26, and to allow the sensi:ng arrays 24,26 to be positioned a distance away from the housing 28 such that heat transfer via the pipe 12 andlor the housing 28 is non-disabling for the application at hand. In a preferred embodiment, the housing 28 is filled with a gas such as, but not limited to, air, nitrogen, argon, etc. The gaseous envirojnment within the housing 28 advantageously acts as an acoustic isolator that helps reduce pressure wave interference that might otherwise travel into the housing 28 from the annulus 18 and undesirably influence the sensing arrays 24,26. T'he gaseous environment also thermally insulates the sensing arrays 24,26.
In some applications, there is advantage in placing a plurality of bumpers within the housing to help maintain separation between the outer sleeve of the housing and the pipe. Bumpers that can be used in this manner are known.
The pipe section 12 has a compliancy selected to suit the application at hand.
The pipe 12 must have sufficient structural integrity to handle the pressure gradient across the pipe 12, and yet must also be able to def lect (i.e_, change in circumference) an amount that will yield useful infornaation. The amount the pipe 12 will change in circumference for a given pressure distribution is determined by the thickness of the pipe wall 42 and the physical properties of the pipe material (e.g., modulus of elasticity, etc.). Thus, the thickness of the pipe wall 42 and the pipe material can be chosen to help produce a favorable sensor sensitivity for the present apparatus. The characteristics of the pipe section 12 contiguous with each present apparatus may be the same as or different than the characteristics in other sections of the production pipe 12.
The optical pressure sensors 32 used in the SOS and flow velocity sensing arrays 24,26 each include a plurality of optical fiber coils 32. Each coil 32 is wrapped one or more turns around the circumference of the pipe section 12 in a manner that allows the length of the optical fiber within the coil 32 to change in response to a change in the circumference of the pipe 12. l.f, for example, a pipe 12 can be expected to see a maxinum circumferential change of "y", then a one-turn coil will be subject to a maximum potential change in length of "y" (or some known function of "y"). If an optical measurement technique is not sensitive enough to register a change in distance equal to "y", then the coil 32 can be wrapped to include "n" number of tums.
The change in fiber length "y" per tum is therefore multiplied by "n" turns, and a change in fiber length great enough to produce a useful signal (i.e., "n = y") is provided. In fact, the same technique can be used to not only provide a minimum useful signal, but also to increase the sensitivity of the sensor 32 and therefore the range of detectable changes in the circumference of the pipe 12. In all cases, the length of the optical fiber in each coil 32 is kkn.own and is chosen to produce the sensitivity required to sense the disturbance(s) of interest for that particular sensor... The preferred embodiment, as described above, includes coils 32 wrapped around the circumference of the pipe 12.
.Alterraatively, the optical fiber lengths can be arranged around a portion of the circumference of the pipe 12.
The turns of optical fiber in a sensor 32 are preferably laid next to one another to minimize the axial component of each turn, and thereby keep each turn to a known, constant length. Alternatively, some or all the turns of a coil 32 could be separated from adjacent turns. A coil 32 can consist of a single layer of optical fiber turns, or multiple layers of optical fiber turns depending on the application. The coil 32 of optical fiber in each sensor 32 may be attached to the pipe 12 by a variety of attachment mechanisms including, but not limited to, adhesive, glue, epoxy, or tape. In a preferred embodiment, a tape having an adhesive substance attached to opposite surfaces of a substrate is used. The tape adheres to both the pipe 12 and the fiber and provides a smooth surface on which the fiber can be laid. It is our experience that tape used on a rough surface helps to decrease micro-bend losses within the optical fiber.
In most embodiments, the optical pressure sensors 32 used in the SOS and flow velocity sensing arrays 24,26 further include one or more optical reflective devices 46 disposed between coils 32 that are wavelength tunable. rn a preferred embodiment, the optical reflective devices 46 are fiber Bragg Gratings (FBGs). An FBG, as is known, reflects a predetermined wavelength band of light having. a central peak reflection wavelength Qb), and passes the remaining wavelengths of the incident light (withi.n a predeternzined wavelength range). Accordingly, input light propagates along the cable 30 to the coils 32 and the FBGs reflect particular wavelengths of light back along the cable 30. It is our experience that in most applications there is advantage in placing an isolation pad between each optical reflective device and the outer surface of the pipe to accommodate pipe growth and/or vibrations.
Such an isolation pad is previously known. _ In the embodiment of the present invention shown in Figure 3, the sensors 32 are connected in series and a single FBG 46 is used between each of the sensor 32, and each FBG 46 has a common reflection wavelength XI. In the embodiment shown in Figure 4, the sensors 32 are connected in series and pairs of FBGs 46 are located along the fiber at each end of each of the sensors 32, respectively_ I'he FBG pairs 46 are used to multiplex the sensed signals to identify the individual sensors 32 from optical return signals. The pair of FBGs 46 on each end of the first sensor 32A have a common reflection wavelength 11, and the second pair of FBGs 46 on each end of the second sensor 32B have a common reflection wavelength X2, but different from that of the first pair of FBGs 46. Similarly, the FBGs 46 on each end of the third sensor 32C
have a common reflection wavelength 13, which is different from 11,X2, and the FBGs 46 on each end of the fourth sensor 32D have a common reflection wavelength X4, which is different from 44~.3. The- sensors 32 within either sensing array 24,26 may alternatively be connected to one another in parallel by using optical couplers (not shown) that are positioned upstream of each sensor 32 and coupled to a common fiber.
Referring to Figures 2, 3, and 4, the sensors 32 with the FBGs 46 disposed therebetween may be configured in numerous known ways to precisely measure the fiber length or change in fiber tength, such as an interferometric, Fabry Perot, time-of-flight, or other known arrangements. An example of a Fabry- Perot technique is described in US Patent. No. 4,950,883 "Fiber Optic Sensor Arrangement Having Reflective Gratings Responsive to Particular Wavelengths", to Glenn.
Alternatively, a portion or all of the fiber between the optical reflective device 46 may be doped with a rare earth dopant (such as erbium) to create a tunable fiber laser, examples of which can be found in U.S. Patent Nos. 5,317,576; 5,513,913; and 5,564,832.
Referring to Figure 5, in an alternative embodiment the sensors 32 may also be formed as a purely interferometric sensing array by using sensors 32 without FBGs 46 disposed therebetween. In this embodiment, each sensor 32 is independently connected to the instrumentation at the platform 20 and known interferometric techniques are used to determz.ne the length or change in length of the fiber around the pipe 12 due to pressure variations. U.S. Patent 5,218,197, entitled "IV[ethod and Apparatus for the Non-invasive Measurement of Pressure Inside Pipes Using a Fiber Optic Interferometer Sensor", issued to Carroll discloses such a technique. The interferometric wraps may also be multiplexed in a manner si.milar to that described in Dandridge, et al, "Fiber Optic Sensors for Navy Applications", IEEE, Feb. 1991, or Dandridge, et al, "Multiplexed Interferometric Fiber Sensor Arrays", SPIE, Vol. 1586, 1991, pp.176-183.
Other techniques to determin.e the change in fiber length may also be used. In addition, reference optical coils (not shown) may be used for certain interferometric approaches and may also be located on or around the pipe 12 but may be designed to be insensitive to pressure variations.
Adjacent sensors 32, within either sensing array 24,26, are spaced apart from each another by a known distance or distances. The sensors 32 in an array are preferably equidistant from one another, but not necessarily. In both sensing arrays 24,26, the spacing between adjacent sensors 32 and the number of sensors 32 reflect the nature of the signal being sensed; i.e., the SOS sensing array 24 utilizes acoustic signals having relatively long wavelengths, and the flow velocity sensing array 26 utilizes local pressure variations within the flow having relatively small coherence length.
In relative terms, the sensors 32 in the SOS sensing array 24 are spaced apart from one another substantiatly farther than are the sensors 32 within the flow velocity sensing array 26 because of the intrinsic differences in the. signals being sensed. The exact inter-spacing and number of c ils 32 in a sensing array 24,26 is application dependent and is a function of parameters such as, but not limited to, the spectra of anticipated acoustic signals and local pressure variations, the anticipated SOS of the fluid constituents, the number of sensors 32, the processing technique used, etc. Examples of signal processing techn.iques can be found in the following references : H. Krim, M.
Viberg, "Two Decades of Array Signal Processing Research - The Parametric Approach", IEEE
Signal Processing Magazine, pp.67-94, R. Nielson, "Sonar Signal Processing", Ch. 2, pp.51-59.
Figure 2 shows an exemplary embodiment of the present invention flow meter 22 that can be inserted in-line within a production pipe 12 and disposed at an appropriate position within the well. The flow meter 22 includes a SOS sensing array 24 and a flow velocity sensing array 26 mounted on a section of pipe 12 adjacent one another and enclosed within a housing 28. A fiber optic cable 30 extends through one of the housing bosses 36 and connects to an optical delay line 48. An optical fiber 50, in turn, connects the optical delay line 48 to the SOS sensing device 24. The SOS
sensing device 24 includes six (6) sensors 32 located at six predeternined locations (x1,x2, x3, x4, xs, x6) along the pipe 12, where each sensor 32 is separated from adjacent sensors 32 within the SOS sensing array 24 by an axial length increment equal to "x ".
Each sensor is mounted on a tape that includes adhesive on both faces. A FBG 46 is positioned between the optical delay line 48 and a sensor 32. One FBG 46 is also positioned between and connected to each pair of adjacent sensors 32, such that the optical delay line 48, the FBGs 46, and the sensors 32 in the SOS sensing array 24 are in series with one another. It is preferred, but not required, to skew each between the adjacent sensors 32 to as to minimize the sharpness of the directional changes within the fiber of either sensor 32 or within the FBG 46.
An optical fiber 52 extends from the last sensor 32 in the SOS sensing array over to a first sensor 32 in the adjacent flow velocity sensing array 26. A
FBG 46 is disposed in-line between the two devices. The flow velocity sensing array 46 includes four (4) sensors 32 located at predetermined locations (x7, xg, x9, xlo) along the pipe 12.
Like the SOS sensing array 24, each sensor 32 in the flow velocity sensing array 26 is mounted on tape and is separated from adjacent sensor 32 within the flow velocity sensing array 26 by an axial length increment equal to "x ". The axial distance x separating the sensors 32 in the flow velocity sensing array 26 is, however, substantially shorter than that used in the SOS sensing array 24 because of the difference in the characteristics of the pressure disturbances sought to be measured; i.e., the SOS sensing array 24 senses relatively long wavelength acoustic signals travelling through the fluid flow at the speed of sound, and the flow velocity sensing array 25 senses relatively short coherence length local pressure variations with the fluid flow. One FBG 46 is 09-11-2002 _ GB0105277 M&C Folio No P51856W0 .13 positioned between and connected to each pair of adjacent sensors 32, such that the FBGs 46 and the sensors 32 in the flow velocity sensing array 26 are in series with one another. Here again, it is preferred to skew each FBG 46 between the adjacent sensors 32 so as to minimize the sharp changes within the fiber of either sensor 32 or within the FBG 46. In some applications, it.may be useful to connect an additional optical delay line 48 after the last sensor 32 within the flow velocity sensing array 26.
In a version of the exemplary embodiment of the present invention flow meter 22 shown in Figure 2, the optical delay line(s) 48 are formed by wrapping approximately two hundred and ten meters (210m) of optical fiber around the circumference of a three and one-half inch (9 cm) diameter pipe. Each coil of the SOS
sensing device 24 is formed by wrapping one hundred and two meters (1 02m) of optical fiber around the circumference of the pipe in a single layer. The optical fiber is wrapped using approximately twenty-five grams (25g) of tension on the fiber.
Each turn of the coil is separated from adjacent coils by a fifteen micron (15 ) gap. Adjacent coils in the SOS sensing device are spaced approximately eighteen inches (46 cm) apart, center to center. - The velocity sensing device is formed in like manner, except that each coil comprises seven layers rather than a single layer, and adjacent coils are spaced approximately one and eight tenths of an inch (4.6 cm) apart, center to center. In both sensing devices, the FBGs are spliced in the section of optical fiber that extends in a helical fashion between adjacent coils, or between a coil and a delay line, etc. Each FBG and the splices that tie the FBG into the optical fiber are laid on an isolator.pad.
The flowmeter as described herein above may be designed to accommodate a variety of pressure levels, slew rates, and pressure variations. For any given design the practical limitations of the flowmeter will be controlled by the ability of the fiber to accurately sense the structural response, or the time varying strains, of the pipe to the pressure fluctuations within the pipe. . These limitations are constrained by, among other things, the structural compliance of the pipe, optical fiiming issues for a given length of fiber, and slew rate limitations based on the rate of change of the length of the fiber sensors. As described herein above it is desirable to select a fiber length per sensor and sensor spacing to provide an optimum level of gain for the broadest level of sensing AMFNnFn ';HFET
environments for the acoustic environment anticipated; fluid type and consistency flowing within the pipe and the anticipated flow rate of the fluid.
The method of interrogating the sensors of a give:n flowmeter depends on the fiber length and the practical constraints described herein. The present invention provides the ability to -selectively modify, or otherwise attenuate, the gain of a flowmeter while keeping other constraints constant. The present invention results in a flowmeter having a fixed fiber length having the capabillity to measure a wide range of pressure levels in various acoustic environments. It will be appreciated by those skilled in the art that the environment surrounding a flowmeter inay produce too much acoustic energy and thereby overtax the highly sensitive fiber optic sensors. Such enviromnents are those that include pumps, venturis, choke valves, or any other source that causes noise that is orders of magnitude above that of normal pipe flow.
The flowmeter 22 shown in Figure 2 depicts an embodiment wherein sensor wraps 32 are coupled directly, or closely, to the pipe 12. This configuration provides the highest level of gain or ability to sense the structural response of the pipe 12 to -pressure fluctuations from fluids flowing therethrough. An embodiment of attenuators 100 of the present invention is best described with reference to Figures 6 and 7 wherein the varlous sensors 32 of flowmeter 22 are mounted to the attenuators.
Attenuator 100 is an axisymmetrical ring or collar including a land 102 coupled directly to the outside diameter of the pipe 12. The land may be coupled by providing an interference fit, welding or other methods as described herein after or any other known method.
Fiber 30 of sensor 32 may variously be positioned on land 102, mandrel 104, and web portion 106 as appropriate to obtain the level of desired attenuation. In operation, land 102 has a strain response similar to that of the pipe 12 having a slightly stiffer cross-sectional effect. Because the web 106 and mandrel 104 are cantilevered from the pipe 12, a slight gap 108 is maintained therebetween providing these pori:ions with an attenuated strain response relative to the pipe. The level of attenuation is primarily driven by the geonietries selected for attenuator 100 and in the embodiment shown web 106 is thin compared to the land 102 and the mandrel 104 and provides a low stress transition zone from the land to the mandrel. The mandrel 104 includes a thicker cross section than the web and possesses a higher hoop stiffness than web portion 106 and is able to resist the strain experienced by land 102 in response to pressure fluctuations within pipe 12. In the embodiment shown mandrel 104 exhibits a small negative strain response relative to the pipe 12 and land 102 as a result of the relatively low bending stiffness of the web portion 106. In addition to providing a low stress transition zone from the land to the mandrel, the low bending stiffness of the web portion can be sized to minimize the amount of negative strain imparted to the mandrel portion 104.
The attenuator 100 provides a broad band attenuation of the strain response of the pipe without introducing additional dynamics between the strain in the pipe and the average strain in the fiber that would distort the relation between the attenuated strain and the actual strain response of the pipe. The broad band attenuation provided is essentially flat up to frequencies approaching the ring frequency mode of the attenuator (breathing mode) because of its inherent stiffness in all modes that have a circumferentially averaged strain component. The attenuator 100 will have non-axisymmetric modes, such as yaw, that occur at frequencies significantly below the ring frequency. These modes do not influence or otherwise degrade the transfer function because they do not contain a circumferentially averaged strain component and therefore are not observed by the sensor.
The level of attenuation provided by attenuator 100 is dependant upon many parameters including material type, coupling methods, the number of layers of fibers 30 and geometry including the length, thickness and geometries of the various portions of the attenuator. In addition, the position of the sensor 32 along the various portions of the attenuator 100 will change the ultimate attenuation level for any given combination of parameters. The total level of attenuation may be determined by integrating the hoop strain over the entire length of the attenuator 100 and may be expressed in terms of the ratio of the strain response of the attenuator with the strain response of the pipe 12.
Optical fibers 30 react to the various strain response of the attenuator by producing a commensurate length change similar to that described herein above resulting in a M&C Folio No P51856W0 16 flowmeter 22 which provides attenuated signal responses relative to a flowmeter having sensors 32 coupled directly to pipe 12.
The present invention will now be described with respect to specific embodiments with reference to Figures 7 and 8. In a particular embodiment the configuration of the attenuator 100 is that of an attenuator comprised of Stainless Steel material and includes a nominal inside diameter 120 of the land 102 portion of 2.375 inches (6 cm), outside diameter 122 of 3.225 inches (8.2 cm) and a length 124 of approximately .25 inches (0.6 cm). The length 126 of mandrel portion 104 is nominally 2.0 inches (5 cm) long and includes a sensor 32 comprising a three layer wrap of fibers 30 occupying a width 128 of approximately 1.664 inches (4 cm). With reference to Figure 8 the level of attenuation for this particular embodiment is depicted graphically for sensor 32 having a 1.664 inch (4 cm) width mounted to mandrel portion 104 at different positions thereon from a starting position nearest the land 102 to a starting position near the end of the mandrel portion. As can be seen from the figure the level of attenuation is dependent upon the starting position of the sensor 32 and increases as the sensor starting position moves away from the land 102 portion of the attenuator. The perforrriance of -the attenuator depicted in Figure 8 is based on a nominal hoop strain response of pipe 12 of 0.096 microinch/in/psi (0.014 m/m(kPa) and shows that a sensor 32 starting at a point .19 inches (0.5 cm) along mandrel 104, depicted by point 110, has an attenuated strain response of approximately 0.0103 microinch/in/psi (0.0015 m/m(kPa) or an attenuation of 9.29. Similarly a sensor 32'having starting points at.21, .23, .25 %and .27 inches (0.53, 0.58, 0.64 and 0.69 cm) along mandrel 104 exhibits attenuation levels of 10.09, 11.03, 12.16 and 13.54 respectively.
An alternative embodiment of attenuator 100 is shown with reference to Figures 7 and 9 comprising an attenuator comprised of Stainless Steel material and includes a nominal inside diameter 120 of the land 102 portion of 2.875 inches (7.3 cm) and outside diameter 122 of 3.225 inches (8.2 cm) and having a width 124 of .25 inches (0.64 cm) long. The mandrel portion 104 has a length 126 of nominally 1.8 inches (4.6 cm) and includes a sensor 32 comprising a three layer wrap of fibers 30 occupying a width 128 of approximately 1.414 inches (3.6 cm). The performance of the attenuator AMENDED SHEET
t =
M&C Folio Nb P51856W0 17 depicted in Figure 9 is based on a nominal hoop strain response of pipe 12 of approximately 0.279 microinch/in/psi (0.04 mlm/kPa) and, similar to that described herein above in Figure 8, shows that a sensor 32 starting at a point .22 inches (0.56 cm) along mandrel 104, depicted by point 112, has an attenuated strain response of approximately 0.0308 microinch/in/psi (0.004 rnlm/kPa) or an attenuation of 9.07.
Similarly a sensor 32 having starting points at .21, .23, .25 and .26 inches (0.53, 0.58=, 0.64 and 0.66 cm) along mandrel 104 exhibits attenuation levels of 9.46, 10.33, and 10.88 respectively. Similarly, although not shown in the figure, a sensor 32 having starting points at .30 and .35 inches (0.76 and 0.89 cm) along mandrel 104 exhibits attenuation levels of 13.38 and 18.62 respectively. The performance of an attenuator similar to that described above having a mandrel length of 1.5 inches (3.8 cm) is depicted in Figure 10 showing a similar relationship between sensor starting point and attenuation level.
An alternative embodiment of attenuator 100 is best shown with reference to Figure 11 wherein the 'attenuator includes a circumferential groove 130 positioned on the inside,diameter of mandrel portion 104. Attenuator 100 fizrther includes an o-ring 132 positioried within groove 130. 0-ring 130 is sized such that it is compressed between attenuator 100 and the outside diameter of pipe 12 to provide a predetermined level of compression. In such a configuration o-ring 130 provides a predictable level of damping to high natural frequency vibration modes of the attenuator. In a particular embodiment o-ring 130 is comprised of a nitrile or neoprene material and together with groove 130 is sized to provide a compression level of about 20%.
Yet another alternative embodiment is best shown with reference to Figure 12 wherein attenuator 100 comprises an axisymetrical attenuator ring 140 including mandrel 104- and web portion 106 and fizrther comprises a ramp portion 142.
Attenuator 100 further comprises a split ring 132, comprising two or more partial arc sections as is known, having a ramp portion 146 and an externally threaded potion 148. In operation the sections of split ring 132 are assembled about pipe 12 and attenuator ring portion 140 is assembled over the split ring with ramp 142 cooperating with ramp 146 to provide a force to wedge the split ring and attenuator ring together.
Attenuator 100 onnFnrnFn qNFFT
09-11-2d02 G B0105277 M&C Folio No P51856WO 17A
further includes nut 150 having internal threads 152 which cooperate with the external threads 148 on split ring 132. When engaged and tightened, nut 150 forces intimate contact between ramps 142, 146 and between split ring 132 and pipe 12 thus providing AMENDED SHEET
a land portion similar to that described herein above. This particular embodiment is particularly advantageous for the ability to mount attenuator on a pipe where other methods are difficult or not possible.
Although the invention has been described and illustrated with respect to exemplary embodiments thereof, the foregoing and various other additions and omissions may be made therein and thereto without departirig from the spirit and scope of the present invention.
Claims (137)
1. A strain attenuator for attenuating the gain of a sensor sensing the strain response of a pipe, the attenuator comprising:
an annular land adapted to mechanically couple to the pipe;
an annular web extending coaxially from the land and having a reduced cross sectional area relative to the land;
an annular mandrel extending coaxially from the web.
an annular land adapted to mechanically couple to the pipe;
an annular web extending coaxially from the land and having a reduced cross sectional area relative to the land;
an annular mandrel extending coaxially from the web.
2. The attenuator as set forth in claim 1, wherein the land, the web and the mandrel are concentric about a common axis.
3. The attenuator as set forth in claim 2, wherein the radially outside surfaces of the land, web and mandrel are equidistant from the common axis and from a contiguous sensor mounting surface.
4. The attenuator as set forth in claim 3, wherein the or each sensor is mounted to the sensor mounting surface.
5. The attenuator as set forth in claim 3 or 4, wherein the or each sensor comprises an optical fiber wound circumferentially about the sensor mounting surface.
6. The attenuator as set forth in any one of claims 3 to 5, wherein the or each sensor is positioned at a predetermined axial position along the sensor mounting surface.
7. The attenuator as set forth in any one of claims 3 to 6, wherein the or each sensor is wound in a predetermined number of layers along the sensor mounting surface.
8. The attenuator as set forth in claim 1, 2 or 3, further comprising:
a circumferential groove positioned on the inside diameter of the mandrel; and a compliant o-ring disposed within the groove.
a circumferential groove positioned on the inside diameter of the mandrel; and a compliant o-ring disposed within the groove.
9. The attenuator as set forth in any one of claims 1 to 4, further comprising:
an axially projecting wedge section positioned on the inside of the land;
a split ring comprised of a plurality of partial circumferential are sections sized to fit about the pipe, the split ring further comprising:
a set of external threads positioned on the outside diameter about a first end; and a wedge section positioned about the outside diameter at a second end;
a nut having a set of internal threads and a shoulder; and wherein the shoulder contacts an end of the land and the threads and wedge portions cooperate to couple the land to the pipe.
an axially projecting wedge section positioned on the inside of the land;
a split ring comprised of a plurality of partial circumferential are sections sized to fit about the pipe, the split ring further comprising:
a set of external threads positioned on the outside diameter about a first end; and a wedge section positioned about the outside diameter at a second end;
a nut having a set of internal threads and a shoulder; and wherein the shoulder contacts an end of the land and the threads and wedge portions cooperate to couple the land to the pipe.
10. A variable gain fiber optic sensor assembly for non-intrusively sensing the strain response of a pipe, the assembly comprising:
the attenuator as set forth in any one of claims 1 to 7 or 9; and a fiber optic sensor mounted to the attenuator.
the attenuator as set forth in any one of claims 1 to 7 or 9; and a fiber optic sensor mounted to the attenuator.
11. An assembly of claim 10, wherein the attenuator comprises:
a circumferential groove positioned on the inside diameter of the mandrel; and a compliant o-ring disposed within the groove.
a circumferential groove positioned on the inside diameter of the mandrel; and a compliant o-ring disposed within the groove.
12. A variable gain fiber optic sensor assembly for non-intrusively sensing the strain response of a pipe, the assembly comprising:
the attenuator as set forth in claim 8; and a fiber optic sensor mounted to the attenuator.
the attenuator as set forth in claim 8; and a fiber optic sensor mounted to the attenuator.
13. An apparatus having a variable gain for non-intrusively sensing fluid flow within a pipe, the apparatus comprising:
a plurality of strain attenuators as set forth in any of claims 1 to 7 or 9;
an acoustic signal sensing array having a plurality of sensors, each sensor including a coil of optical fiber wrapped a plurality of turns around a circumference of a respective strain attenuator;
the apparatus being adapted to receive optical power from a source, the optical power being arranged to travel into the acoustic signal sensing array, and the acoustic signal sensing array is arranged to produce a first signal relating to an acoustic signal within the fluid;
a local pressure variation sensing array having a plurality of sensors, each sensor including a coil of optical fiber wrapped a plurality of turns around the circumference of a respective strain attenuator;
the optical power being arranged to travel into the local pressure variation sensing array, and the local pressure variation sensing array is arranged to produce a second signal relating to a local pressure variation within the fluid; and a housing for enclosing the acoustic signal sensing array and the local pressure variation sensing array.
a plurality of strain attenuators as set forth in any of claims 1 to 7 or 9;
an acoustic signal sensing array having a plurality of sensors, each sensor including a coil of optical fiber wrapped a plurality of turns around a circumference of a respective strain attenuator;
the apparatus being adapted to receive optical power from a source, the optical power being arranged to travel into the acoustic signal sensing array, and the acoustic signal sensing array is arranged to produce a first signal relating to an acoustic signal within the fluid;
a local pressure variation sensing array having a plurality of sensors, each sensor including a coil of optical fiber wrapped a plurality of turns around the circumference of a respective strain attenuator;
the optical power being arranged to travel into the local pressure variation sensing array, and the local pressure variation sensing array is arranged to produce a second signal relating to a local pressure variation within the fluid; and a housing for enclosing the acoustic signal sensing array and the local pressure variation sensing array.
14. An apparatus of claim 13, wherein the attenuator comprises:
a circumferential groove positioned on the inside diameter of the mandrel; and a compliant o-ring disposed within the groove.
a circumferential groove positioned on the inside diameter of the mandrel; and a compliant o-ring disposed within the groove.
15. An apparatus having a variable gain for non-intrusively sensing fluid flow within a pipe, the apparatus comprising:
a plurality of strain attenuators as set forth in claim 8;
an acoustic signal sensing array having a plurality of sensors, each sensor including a coil of optical fiber wrapped a plurality of turns around a circumference of a respective strain attenuator;
the apparatus being adapted to receive optical power from a source, the optical power being arranged to travel into the acoustic signal sensing array, and the acoustic signal sensing array is arranged to produce a first signal relating to an acoustic signal within the fluid;
a local pressure variation sensing array having a plurality of sensors, each sensor including a coil of optical fiber wrapped a plurality of turns around the circumference of a respective strain attenuator;
the optical power being arranged to travel into the local pressure variation sensing array, and the local pressure variation sensing array is arranged to produce a second signal relating to a local pressure variation within the fluid; and a housing for enclosing the acoustic signal sensing array and the local pressure variation sensing array.
a plurality of strain attenuators as set forth in claim 8;
an acoustic signal sensing array having a plurality of sensors, each sensor including a coil of optical fiber wrapped a plurality of turns around a circumference of a respective strain attenuator;
the apparatus being adapted to receive optical power from a source, the optical power being arranged to travel into the acoustic signal sensing array, and the acoustic signal sensing array is arranged to produce a first signal relating to an acoustic signal within the fluid;
a local pressure variation sensing array having a plurality of sensors, each sensor including a coil of optical fiber wrapped a plurality of turns around the circumference of a respective strain attenuator;
the optical power being arranged to travel into the local pressure variation sensing array, and the local pressure variation sensing array is arranged to produce a second signal relating to a local pressure variation within the fluid; and a housing for enclosing the acoustic signal sensing array and the local pressure variation sensing array.
16. The apparatus of any one of claims 13 to 15, wherein the acoustic signal sensing array further includes at least one reflective element disposed between sensors.
17. The apparatus of claim 16, wherein the reflective element is a fiber Bragg grating.
18. A system comprising:
a strain attenuator of any one of claims 1 to 7 or 9; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
a strain attenuator of any one of claims 1 to 7 or 9; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
19. A system of claim 18, wherein the attenuator comprises:
a circumferential groove positioned on the inside diameter of the mandrel; and a compliant o-ring disposed within the groove.
a circumferential groove positioned on the inside diameter of the mandrel; and a compliant o-ring disposed within the groove.
20. A system comprising:
a strain attenuator of claim 8; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
a strain attenuator of claim 8; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
21. A system comprising:
an assembly of claim 10; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
an assembly of claim 10; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
22. A system comprising:
an assembly of claim 11 or 12; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
an assembly of claim 11 or 12; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
23. A system comprising:
an apparatus of claim 13; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
an apparatus of claim 13; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
24. A system comprising:
an apparatus of claim 14 or 15; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
an apparatus of claim 14 or 15; and a pipe;
wherein the or each annular land is mechanically coupled concentrically about the pipe, and wherein a gap is formed between the pipe and the or each mandrel.
25. A system of claim 19, 20, 22 or 24, wherein the o-ring is disposed against the outside diameter of the pipe.
26. An apparatus for attenuating the gain of a sensor used to sense the strain response of a pipe having an axis, comprising:
a land coupled to the pipe and extending radially therefrom;
a web extending from the land parallel to the axis of the pipe, wherein the web has a smaller cross sectional area than the land;
a mandrel extending from the web parallel to the axis of the pipe, wherein the mandrel forms a gap with respect to the pipe; and a sensor coupled at least to the mandrel.
a land coupled to the pipe and extending radially therefrom;
a web extending from the land parallel to the axis of the pipe, wherein the web has a smaller cross sectional area than the land;
a mandrel extending from the web parallel to the axis of the pipe, wherein the mandrel forms a gap with respect to the pipe; and a sensor coupled at least to the mandrel.
27. The apparatus of claim 26, wherein the web is thinner than the mandrel.
28. The apparatus of claim 26 or 27, wherein the land, web, or mandrel are annular.
29. The apparatus of claim 28, wherein the land, web, and mandrel are annular.
30. The apparatus of claim 29, wherein the land, web, and mandrel are concentric about pipe axis.
31. The apparatus of claim 30, wherein the land, web and mandrel have outside diameters that are equidistant from the pipe axis.
32. The apparatus of claim 31, wherein the outside diameters form a mounting surface for the sensor.
33. The apparatus of any one of claims 26 to 32, wherein the sensor comprises a fiber optic sensor.
34. The apparatus of claim 33, wherein the fiber optic sensor comprises a winding of fiber optic cable wound around the mounting surface.
35. The apparatus of claim 29, further comprising a circumferential groove on an inside diameter of the mandrel, and an o-ring disposed between the groove and the pipe.
36. The apparatus of any one of claims 26 to 35, wherein the land comprises:
a first wedge having first threads coupled to the pipe; and a second wedge coupled to a nut having, second threads, wherein the second wedge is coupled to the web, wherein coupling the first and second threads wedges the first wedge and second wedge into contact.
a first wedge having first threads coupled to the pipe; and a second wedge coupled to a nut having, second threads, wherein the second wedge is coupled to the web, wherein coupling the first and second threads wedges the first wedge and second wedge into contact.
37. The apparatus of claim 36, wherein the first wedge comprises a split ring comprising a plurality of partial circumferential arc sections.
38. The apparatus of any one of claims 26 to 37, wherein the land, web, and mandrel define a mounting surface, wherein the sensor comprises a fiber optic sensor, and wherein the sensor is coupled to at least a portion of the mounting surface.
39. The apparatus of claim 38, wherein the fiber optic sensor comprises a winding of fiber optic cable wound around the mounting surface.
40. The apparatus of claim 38, wherein the attenuation of the sensor varies depending on the axial position of the fiber optic cable on the mounting surface.
41. The apparatus of claim 38, further comprising tape coupled between the fiber optic cable and the external surface.
42. The apparatus of claim 38, wherein the web is thinner than the mandrel.
43. The apparatus of claim 38, wherein the mounting surface is annular.
44. The apparatus of claim 43, wherein the mounting surface is concentric about pipe axis.
45. The apparatus of claim 44, wherein the mounting surface comprises a uniform diameter.
46. The apparatus of claim 38, further comprising a circumferential groove on an inside diameter of the mandrel, and an o-ring disposed between the groove and the pipe.
47. An apparatus for attenuating the gain of a sensor used to sense the strain response of a pipe having an axis, comprising:
a land coupled to the pipe and extending radially therefrom;
a web extending from the land parallel to the axis of the pipe;
a mandrel extending from the web parallel to the axis of the pipe, wherein the mandrel forms a gap with respect to the pipe, and wherein the mandrel is thicker than the web;
and a sensor coupled at least to the mandrel.
a land coupled to the pipe and extending radially therefrom;
a web extending from the land parallel to the axis of the pipe;
a mandrel extending from the web parallel to the axis of the pipe, wherein the mandrel forms a gap with respect to the pipe, and wherein the mandrel is thicker than the web;
and a sensor coupled at least to the mandrel.
48. The apparatus of claim 47, wherein the web has a smaller cross sectional area than the land.
49. The apparatus of claim 47 or 49, wherein the land, web, or mandrel are annular.
50. The apparatus of claim 49, wherein the land, web, and mandrel are annular.
51. The apparatus of claim 50, wherein the land, web, and mandrel are concentric about pipe axis.
52. The apparatus of claim 51, wherein the land, web and mandrel have outside diameters that are equidistant from the pipe axis.
53. The apparatus of claim 52, wherein the outside diameters form a mounting surface for the sensor.
54. The apparatus of any one of claims 47 to 53, wherein the sensor comprises a fiber optic sensor.
55. The apparatus of claim 54, wherein the fiber optic sensor comprises a winding of fiber optic cable wound around the mounting surface.
56. The apparatus of claim 50, further comprising a circumferential groove on an inside diameter of the mandrel, and an o-ring disposed between the groove and the pipe.
57. The apparatus of any one of claims 47 to 56, wherein the land comprises:
a first wedge having first threads coupled to the pipe; and a second wedge coupled to a nut having second threads, wherein the second wedge is coupled to the web, wherein coupling the first and second threads wedges the first wedge and second wedge into contact.
a first wedge having first threads coupled to the pipe; and a second wedge coupled to a nut having second threads, wherein the second wedge is coupled to the web, wherein coupling the first and second threads wedges the first wedge and second wedge into contact.
58. The apparatus of claim 57, wherein the first wedge comprises a split ring comprising a plurality of partial circumferential arc sections.
59. The apparatus of any one of claims 47 to 58, wherein the land, web, and mandrel define a mounting surface, wherein the sensor comprises a fiber optic sensor, and wherein the sensor is coupled to at least a portion of the mounting surface.
60. The apparatus of claim 59, wherein the fiber optic sensor comprises a winding of fiber optic cable wound around the mounting surface.
61. The apparatus of claim 59, wherein the attenuation of the sensor varies depending on the axial position of the fiber optic cable on the mounting surface.
62. The apparatus of claim 59, further comprising tape coupled between the fiber optic cable and the external surface.
63. The apparatus of claim 59, wherein the web has a smaller cross sectional area than the land.
64. The apparatus of claim 59, wherein the mounting surface is annular.
65. The apparatus of claim 64, wherein the mounting surface is concentric about pipe axis.
66. The apparatus of claim 65, wherein the mounting surface comprises a uniform diameter.
67. The apparatus of claim 59, further comprising a circumferential groove on an inside diameter of the mandrel, and an o-ring disposed between the groove and the pipe.
68. An apparatus for attenuating the gain of a sensor used to sense the strain response of a pipe having an axis, comprising:
a land coupled to an outside surface of the pipe and extending radially therefrom, a mandrel disposed around the outside surface of the pipe parallel to the axis of the pipe, the mandrel coupled to and extending from the land, wherein the land and mandrel define a mounting surface; and a sensor coupled at least to the mandrel, wherein the sensor comprises a fiber optic sensor coupled to at least a portion of the mounting surface.
a land coupled to an outside surface of the pipe and extending radially therefrom, a mandrel disposed around the outside surface of the pipe parallel to the axis of the pipe, the mandrel coupled to and extending from the land, wherein the land and mandrel define a mounting surface; and a sensor coupled at least to the mandrel, wherein the sensor comprises a fiber optic sensor coupled to at least a portion of the mounting surface.
69. The apparatus of claim 68, wherein the land or mandrel are annular.
70. The apparatus of claim 69, wherein the land and mandrel are annular.
71. The apparatus of claim 70, wherein the land and mandrel are concentric about the pipe axis.
72. The apparatus of claim 71, wherein the land and mandrel have outside diameters that are equidistant from the pipe axis.
73. The apparatus of claim 72, wherein the outside diameters form a mounting surface for the sensor.
74. The apparatus of claim 73, wherein the sensor comprises a fiber optic sensor.
75. The apparatus of claim 74, wherein the fiber optic sensor comprises a winding of optical fiber wound around the mounting surface.
76. The apparatus of claim 70, further comprising a circumferential groove on an inside diameter of the mandrel, and an O-ring disposed between the groove and the pipe.
77. The apparatus of claim 68, wherein the land comprises:
a first wedge having first threads coupled to the pipe, and a second wedge coupled to a nut having second threads, wherein the second wedge is coupled to the mandrel, wherein coupling the first and second threads wedges the first wedge and second wedge into contact.
a first wedge having first threads coupled to the pipe, and a second wedge coupled to a nut having second threads, wherein the second wedge is coupled to the mandrel, wherein coupling the first and second threads wedges the first wedge and second wedge into contact.
78. The apparatus of claim 77, wherein the first wedge comprises a split ring comprising a plurality of partial circumferential arc sections.
79. The apparatus of claim 68, wherein the fiber optic sensor comprises a winding of optical fiber wound around the mounting surface.
80. The apparatus of claim 68, wherein the attenuation of the sensor varies depending on an axial position of the optical fiber on the mounting surface.
81. The apparatus of claim 68, further comprising tape coupled between the optical fiber and the mounting surface.
82. The apparatus of claim 68, wherein the mounting surface is annular.
83. The apparatus of claim 82, wherein the mounting surface is concentric about pipe axis.
84. The apparatus of claim 83, wherein the mounting surface comprises a uniform diameter.
85. The apparatus of claim 68, further comprising a circumferential groove on an inside diameter of the mandrel, and an o-ring disposed between the groove and the pipe.
86. An apparatus for attenuating the gain of a sensor used to sense the strain response of a pipe having an axis, comprising:
a land coupled to an outside surface of the pipe and extending radially therefrom;
a mandrel coupled to and extending from the land along the axis of the pipe, wherein the mandrel forms a gap with respect to the pipe, wherein the land and mandrel define a mounting surface; and a sensor coupled at least to the mandrel, wherein the sensor comprises a fiber optic sensor coupled to at least a portion of the mounting surface.
a land coupled to an outside surface of the pipe and extending radially therefrom;
a mandrel coupled to and extending from the land along the axis of the pipe, wherein the mandrel forms a gap with respect to the pipe, wherein the land and mandrel define a mounting surface; and a sensor coupled at least to the mandrel, wherein the sensor comprises a fiber optic sensor coupled to at least a portion of the mounting surface.
87. The apparatus of claim 86, wherein the land or mandrel are annular.
88. The apparatus of claim 87, wherein the land and mandrel are annular.
89. The apparatus of claim 88, wherein the land and mandrel are concentric about the pipe axis.
90. The apparatus of claim 89, wherein the land and mandrel have outside diameters that are equidistant from the pipe axis.
91. The apparatus of claim 90, wherein the outside diameters form a mounting surface for the sensor.
92. The apparatus of claim 91, wherein the sensor comprises a fiber optic sensor.
93. The apparatus of claim 92, wherein the fiber optic sensor comprises a winding of optical fiber wound around the mounting surface.
94. The apparatus of claim 88, further comprising an O-ring disposed between the groove and the pipe.
95. The apparatus of claim 86, wherein the land comprises:
a first wedge having first threads coupled to the pipe; and a second wedge coupled to a nut having second threads, wherein the second wedge is coupled to the mandrel, wherein coupling the first and second threads wedges the first wedge and second wedge into contact.
a first wedge having first threads coupled to the pipe; and a second wedge coupled to a nut having second threads, wherein the second wedge is coupled to the mandrel, wherein coupling the first and second threads wedges the first wedge and second wedge into contact.
96. The apparatus of claim 95, wherein the first wedge comprises a split ring comprising a plurality of partial circumferential arc sections.
97. The apparatus of claim 86, wherein the fiber optic sensor comprises a winding of optical fiber wound around the mounting surface.
98. The apparatus of claim 86, wherein the attenuation of the sensor varies depending on an axial position of the optical fiber on the mounting surface.
99. The apparatus of claim 86, further comprising tape coupled between the optical fiber and the mounting surface.
100. The apparatus of claim 86, wherein the mounting surface is annular.
101. The apparatus of claim 100, wherein the mounting surface is concentric about pipe axis.
102. The apparatus of claim 101, wherein the mounting surface comprises a uniform diameter.
103. The apparatus of claim 86, further comprising a circumferential groove on an inside diameter of the mandrel, and an O-ring disposed between the groove and the pipe.
104. A method for sensing the strain response of a pipe having an axis, comprising:
attenuating the strain response by coupling the strain through a mandrel coupled to an outside diameter of the pipe; and detecting the attenuated strain by at least one sensor coupled to the mandrel.
attenuating the strain response by coupling the strain through a mandrel coupled to an outside diameter of the pipe; and detecting the attenuated strain by at least one sensor coupled to the mandrel.
105. The method of claim 104, wherein the mandrel extends parallel to the axis of the pipe.
106. The method of claim 104, wherein the mandrel couples to the pipe at a location of smaller cross-sectional area than the mandrel.
107. The method of claim 104, wherein the mandrel couples to the pipe at a location that is thinner than the mandrel.
108. The method of claim 104, wherein the mandrel is annular.
109. The method of claim 108, wherein the mandrel is concentric about the pipe axis.
110. The method of claim 109, wherein the outside diameter of the mandrel forms a mounting surface for the sensor.
111. The method of claim 110, wherein the sensor comprises a fiber optic sensor.
112. The method of claim 111, wherein the fiber optic sensor comprises a winding of optical fiber wound around the mounting surface.
113. The method of claim 104, further comprising an O-ring disposed between the mandrel and the pipe.
114. The method of claim 104, wherein the mandrel defines a mounting surface, wherein the sensor comprises a fiber optic sensor, and wherein the sensor is coupled to at least a portion of the mounting surface.
115. The method of claim 114, wherein the fiber optic sensor comprises a winding of optical fiber wound around the mounting surface.
116. The method of claim 114, wherein the attenuation of the sensor varies depending on an axial position of the optical fiber on the mounting surface.
117. The method of claim 114, further comprising tape coupled between the optical fiber and the mounting surface.
118. The method of claim 114, wherein the mandrel is coupled to the pipe by a web, and wherein the web has a smaller cross sectional area than the land.
119. The method of claim 114, wherein the mounting surface is annular.
120. The method of claim 119, wherein the mounting surface is concentric about pipe axis.
121. The method of claim 120, wherein the mounting surface comprises a uniform diameter.
122. The method of claim 114, further comprising a circumferential groove on an inside diameter of the mandrel, and an O-ring disposed between the groove and the pipe.
123. An apparatus for sensing the strain response of a pipe having an axis, comprising:
a pipe having a strain response;
a mandrel coupled to an outside diameter of the pipe and extending parallel to the axis of the pipe, wherein the mandrel defines a mounting surface, and a sensor coupled at least to the mandrel, wherein the sensor comprises a fiber optic sensor coupled to at least a portion of the mounting surface.
a pipe having a strain response;
a mandrel coupled to an outside diameter of the pipe and extending parallel to the axis of the pipe, wherein the mandrel defines a mounting surface, and a sensor coupled at least to the mandrel, wherein the sensor comprises a fiber optic sensor coupled to at least a portion of the mounting surface.
124. The apparatus of claim 123, wherein the mandrel is annular.
125. The apparatus of claim 124, wherein the mandrel is concentric about pipe axis.
126. The apparatus of claim 125, wherein the mandrel has an outside diameter that is equidistant from the pipe axis.
127. The apparatus of claim 126, wherein the outside diameter forms a mounting surface for the sensor.
128. The apparatus of claim 127, wherein the sensor comprises a fiber optic sensor.
129. The apparatus of claim 128, wherein the fiber optic sensor comprises a winding of optical fiber wound around the mounting surface.
130. The apparatus of claim 124, further comprising a circumferential groove on an inside diameter of the mandrel, and an O-ring disposed between the groove and the pipe.
131. The apparatus of claim 123, wherein the fiber optic sensor comprises a winding of optical fiber wound around the mounting surface.
132. The apparatus of claim 123, wherein attenuation of the sensor varies depending on an axial position of the optical fiber on the mounting surface.
133. The apparatus of claim 123, further comprising tape coupled between the optical fiber and the mounting surface.
134. The apparatus of claim 123, wherein the mounting surface is annular.
135. The apparatus of claim 134, wherein the mounting surface is concentric about pipe axis.
136. The apparatus of claim 135, wherein the mounting surface comprises a uniform diameter.
137. The apparatus of claim 123, further comprising a circumferential groove on an inside diameter of the mandrel, and an O-ring disposed between the groove and the pipe.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US09/726,061 | 2000-11-29 | ||
| US09/726,061 US6550342B2 (en) | 2000-11-29 | 2000-11-29 | Circumferential strain attenuator |
| PCT/GB2001/005277 WO2002044658A1 (en) | 2000-11-29 | 2001-11-29 | Circumferential strain attenuator |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2436813A1 CA2436813A1 (en) | 2002-06-06 |
| CA2436813C true CA2436813C (en) | 2007-08-14 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002436813A Expired - Fee Related CA2436813C (en) | 2000-11-29 | 2001-11-29 | Circumferential strain attenuator |
Country Status (5)
| Country | Link |
|---|---|
| US (2) | US6550342B2 (en) |
| EP (1) | EP1340051A1 (en) |
| AU (1) | AU2002223909A1 (en) |
| CA (1) | CA2436813C (en) |
| WO (1) | WO2002044658A1 (en) |
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2003
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| US20030217605A1 (en) | 2003-11-27 |
| EP1340051A1 (en) | 2003-09-03 |
| US6868737B2 (en) | 2005-03-22 |
| AU2002223909A1 (en) | 2002-06-11 |
| WO2002044658A1 (en) | 2002-06-06 |
| US6550342B2 (en) | 2003-04-22 |
| CA2436813A1 (en) | 2002-06-06 |
| US20020064330A1 (en) | 2002-05-30 |
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