GB2492095A - Determining pressure profile in an oil or gas well - Google Patents
Determining pressure profile in an oil or gas well Download PDFInfo
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- GB2492095A GB2492095A GB1110455.1A GB201110455A GB2492095A GB 2492095 A GB2492095 A GB 2492095A GB 201110455 A GB201110455 A GB 201110455A GB 2492095 A GB2492095 A GB 2492095A
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- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000009530 blood pressure measurement Methods 0.000 description 2
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L11/00—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
- G01L11/02—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/06—Measuring temperature or pressure
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/12—Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling
- E21B47/13—Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling by electromagnetic energy, e.g. radio frequency
- E21B47/135—Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling by electromagnetic energy, e.g. radio frequency using light waves, e.g. infrared or ultraviolet waves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
- G01B11/18—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge using photoelastic elements
-
- 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
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Mining & Mineral Resources (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Remote Sensing (AREA)
- Fluid Mechanics (AREA)
- Environmental & Geological Engineering (AREA)
- Geophysics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Measuring Fluid Pressure (AREA)
Abstract
A method for use in determining pressure comprises configuring first and second strain sensors to sense respective strain signals along a common direction in a carrier member, the first and second strain sensors having a different response to pressure exerted on the carrier member. The sensors comprise a central optical fibre 34 and four peripheral optical fibres 36,38,40,42. Each optical fibre is coupled to a strain interrogation system (60 to 68, figure 1) and each system includes a pulsed laser source (70) coupled via an optical coupler (72) to the appropriate optical fibre and an optical detector (74) for monitoring power transmitted by the pulsed laser source (70). The method further comprises determining a pressure from the respective strain signals sensed using the first and second strain sensors. Such a method may permit the effects of pressure exerted on the carrier member to be distinguished from the effects of mechanically-induced strain exerted on the carrier member thus allowing a pressure to be determined. Such a method may be particularly useful for providing a distributed pressure profile in a remote or hostile environment such as a subterranean or subsea oil or gas well.
Description
I
METHOD AND APPARATUS FOR USE IN DETERMINING PRESSURE
FIELD
The present invention relates to a method and apparatus for use in determining pressure and particularly, though not exclusively, for use in determining a pressure profile of a fluid En an oil or gas weil.
BACKGROUND
The measurement of pressure profiles Es of interest in many different fields, induding in the oil and gas industry where knowledge of the pressure profile within a weil can be used to determine weil or formation conditions, assist to optimise yES of the weil and the ilke, It is known to use cables that employ different strain sensor technoloes for the measurement of strain and/or temperature profiles in downhole environments. For example, distributed optical techniques for the independent measurement of strain and temperature are disclosed in WO 98/27406 and WO 2005/106396. Such techniques rely upon the detection of Briilouin backsoattering and the general principle that changes in strain generaHy only affect the frequency of the BriUouin backscattering peak whilst changes in temperature generaily only affect the se of the Briilouin backscattering peak.
WO 98/27406 discloses a method and apparatus for the independent measurement of strain and temperature along a single optical fibre that rely upon the measurement of the amplitude and frequency shifts associated with Brillouin backscattering as a function of time. A reference section of the optical fibre is subjected to a known strain and temperature and the amplitude and frequency shift of the Brillouin peaks for the reference section may be used to calibrate data received from other sensing locations along the optical fibre to obtain strain and temperature measurements at the sensing locations.
WO 2005/106396 discloses a method and apparatus for the measurement of amplitude and frequency shifts associated with Brillouin backscattered light that rely upon the use of a receiver having a frequency to amplitude converter arranged to convert a received signal directly into a signal whose amplitude varies with the instantaneous frequency of the Brfflouin component. Such a converter can avoid the timeconsuming scanning of frequencies to obtain the Brillouin frequency spectrum.
US 7,i540B1 so discloses a quasi.distributed optical technique which uses Bragg gratings for the measurement of strn for the indication of damage or concfltions Hkely to cause damage to a composfte structure such as a coated wire assembly.
Depending on the environment around a cable, the cable may be subjected to changes in temperature, pressureinduced strain and/or mechanicayinduced strain such as residual strain, apped strain, bending4nduced strain and the Uke. However, some techniques for measuring temperature and/or strain profiles are not able to distinguish between the effects of pressureinduced strain and mechanicallyinduced strain and are not, therefore, able to provide a pressure profile.
SUMMARY
According to a first aspect of the present invention there is provided a method for use in determining pressure comprising: configuring first and second strain sensors to sense respective strain signals along a common direction in a carrier member wherein the first and second strain sensors have a different response to pressure exerted on the carrier member; and determining a pressure from the respective strain signals sensed using the first and second strain sensors.
Such a method may be used to discriminate the effects of pressure exerted on the carrier member from the effects of mechanicaVyinduced strain in the carrier member.
The common direction may, for example, comprise an axial direction of the carrier member.
ln general, strain in the carrier member along the common direction may comprise a number of different strain components. For example. strain in the carrier member may comprise one or more of a residual strain component, an applied strain component, a strain component induced by bending of the carrier member about a first bending axis, and a strain component induced by bending of the carrier member about a second bending axis perpendicular to the first bending axis.
The strain signals may be any kind of straindependenI signals such as straiN dependent optical signals or the like. For example, the strain signals may be spectral peak frequency shifts and/or powers associated with optical scattering such as Briflothn, Rayleigh, Reman scattering and/or the like. The strafti signS may be associated with strain-induced bftefringence of an optical waveguide. The strain signals may be associated with Ught reflected from a Bragg grating or the like. The strain signals may be associated with strainnduced birefringence of a Bragg grating or the ke.
The first and second strain sensors may have a known configuration. For example, the first and second strain sensors may have a known arrangement or geometry with respect to the carrier member. The pressure may be determined from strain signals sensed by the first and second strain sensors and the known configuration of the first and second strain sensors.
The pressure may comprise a relative pressure. The pressure may comprise an absolute pressure.
The method may comprise calibrating the pressure against a known absolute pressure value or values to provide an absolute pressure.
The method may comprise: subtracting respecfive strain signals sensed using the first and second strain sensors to determine a derived strain signal; and determining the pressure from the derived strain signal.
Such a derived strain signal may be substantially independent of residual strain in the carrier member because the residual strain components sensed using the first and second strain sensors in the common direction are equal. The residual strain component may, for example, be associated with a process used to manufacture the first and second strain sensors and the carrier member. The residual strain components sensed using the first and second strain sensors in the common direction may be equal, for example, because the first and second strain sensors are nominally identical in structure and function and are embedded in a homogeneous carrier member using a uniform manufacturing process. Such a derived strain signal may also be substantially independent of appUed strain in the carrier member because the applied strain components sensed using the first and second strain sensors in the common direction are equal by definition. Subtraction of strain signals sensed using the first and second strain sensors may, therefore, provide a derived strain signal which is independent of residual and applied strain. Such a method may permit a pressure exerted on the carrier member to be determined. This may, for example, be the case where bending of the carrier member is not possible because the carrier member is mechanically constrained.
The method may corn pdse: configuring one of the first and second strain sensors to sense a strain signal along a neutral axis of the carrier member along which strain induced by bending of the carrier member is substantiafly zero.
Such a method may permit a pressure exerted on the carrier member to be determined. This may, for example, be the case where bending of the carrier member is not possible because the carrier member is mechanicaDy constrained. Such a method may provide enhanced sensitivity to pressure because the strain sensor that is not configured to sense strain along the neutral axis may be closer to an external surface of the carrier member and may, therefore, be exposed to a higher pressure induced strain component than the strain sensor configured to sense strain along the neutral axis.
The method may comprise: configuring a third strain sensor to sense a strain signal along the common direction in the carrier member; and determining the pressure from the respective strain signals sensed using the first, second and third strain sensors.
The first; second and third strain sensors may have a known configuration. For example, the first, second and third strain sensors may have a known arrangement or geometry with respect to the carrier member, The pressure may be determined from strain signals sensed by the first, second and third strain sensors and the known configuration of the first, second and third strain sensors, Such a method may permit a pressure exerted on the carrier member to be determined where the carrier member is subjected to residual strain, applied strain and bending in one dimension.
The method may comprise: configuring one of the first, second and third strain sensors to sense a strain signal along a neutral axis of the carrier member along which strain induced by bending of the carrier member is substantially zero; configuring the other two of the first; second and third strain sensors to sense respective strain signals along respective axes which lie substantially in a common plane with, and are located equidistantly from the neutral axis; averaging the strain signals sensed using the strain sensors having respective axes located equidistantly from the neutral axis to determine an average strain signal; subtracting the average stra signal from the strain signal sensed using the strafri sensor configured to sense straTh along the neutral axis to determine a derhied strain &gnal; and determining the pressure from the derived strain gnaL The average strain signs may be substanVally independent of bending of the carrier member. The strain signal sensed by the strain sensor located on the neutral axis may also be substantiaHy independent of bending of the carrier member. The derived strain signal may be suhstantiay independent of bending of the carrier member and substantiay independent of residual and applied strain in the carrier member, Such a method may permit a pressure exerted on the carrier member to be determined where the carrier member is subjected to residual strain, applied strain and bending in two dimensions.
The method may comprise: configuring a fourth. strain sensor to sense a strain signal along the common direction in the carrier member; and determining the pressure from the respective strain signals sensed using the first, second, third and fourth strain sensors.
The first, second, third and fourth strain sensors may have a known configuration. For example, the first, second, third and fourth strain sensors may have a known arrangement or geometry with respect to the carrier member. The pressure may be determined from strain signals sensed by the first, second, third and fourth strain sensors and the known configuration of the first, second, third and fourth strain sensors.
Such a method may permit a pressure exerted on the carder member to be determined where the carrier member is subjected to residual strain, applied strain and bending in two dimensions, Such a method may also permit a direction and degree of bending to be determined in two dimensions. This may be useful for determining the trajectory of the carrier member, for determining strain sensor signal losses and/or for determining damage or the likelihood of damage to the carrier member.
The method may comprise: configuring two of the first to fourth strain sensors to sense respective strain signals along respective axes which lie substantially in a first common plane with, and are located equidistantly from, a neutral axis of the carrier member along which strain induced by bending of the carrier member is substantially zero; configuring the other two 0 the first to fourth strahi sensors to sense respective strain signals along respective axes which he substantially in a second common plane wIth, and are located equidistantly from, the neutral axis. the second common plane being substantially perpendicular to the first common plane; averaging the strain signals sensed using the strain sensors having respective axes located equidistantly from the neutral axis in the first common plane to determine a first average strain signal; averaging the strain signals sensed using the strain sensors having respective axes located equidistantly from the neutral axis in the second common plane to determine a second average strain signal; subtracting the first and second average strain signals to determine a derived strain signal; and determining the pressure from the derived strain signal.
The first average strain signal may be substantially independent of bending of the carrier member.
The second average strain signal may be substantially independent of bending of the carrier member.
The derived strain signal may be substantially independent of bending of the carrier member and substantially independent of residual and applied strain in the carrier member.
Such a method may permit a pressure exerted on the carrier member to be determined where the carher member is subjected to residual strain, applied strain and bending in two dimensions.
Such a method may also permit a direction and degree of bending to be determined in two dimensions. This may be useful for determining the trajectory of the carrier member, for determining strain sensor signal losses and/or for determining damage or the likelihood of damage to the carrier member.
The method may comprise: configuring a fifth strain sensor to sense a strain signal along the common direction in the carrier member; and determining the pressure from the respective strain signals sensed using *the first, second, third, fourth and fifth strain sensors.
The method may comprise: configuring one of the first to fifth strain sensors to sense a strain signal abng a neutral axis of the carrier member abng which strain induced by bending of the cariler member is substantiay zero; configuring two of the first to fifth strain sensors to sense respective strain S signals abng respective axes which he substantiafly in a first common plane with, and are located equidistantly from the neutral axis; configuring two of the first to fifth strain sensors to sense respective strain signals along respective axes which he substantiahy in a second common plane with, and are located equidistantly from, the neutral axis. the second common plane being substantially perpendicular to the first common plane; averaging the strain signals sensed using the strain sensors having respective axes located in the first common plane equidistantly from the neutral axis and the strain sensors having respective axes located in the second common plane equidistantly from the neutral axis to determine an average strain signal; subtracting the average strain signal from the strain signal sensed using the strain sensor configured to sense strain along the neutral axis to determine a derived strain signal; and determining the pressure from the derived strain signal.
The averace strain signal may be substantially independent of bending of the carrier member.
The derived strain signal may be substantially independent of bending of the carrier member and substantially independent of residual and applied strain in the carrier member.
Such a method may provide a derived strain signal having an improved sensitivity to pressure.
The method may comprise: calibrating a strain signal derived from the respective strain signals sensed using two or more strain sensors as a function of pressure; and determining the pressure from the calibrated strain signal as a function of pressure.
The method may comprise: configuring each of the strain sensors as a distributed strain sensor; using the distributed strain sensors to sense respective strain signals as a function of position along the carrier member; and
B
determining pressure as a funcflon of position along the carrier member from the respectkie sensed strain signals.
The method may comprise: determining r&ative pressure as a function of position along the carrier member from the respective sensed strain signais; measuring an absolute value of the pressure exerted on the carrier member at a position along the carrier member; and using the measured absolute pressure value at the position and the determined r&ative pressure as a function of position along the carrier member to determine the absolute pressure as a function of position along the carrier member.
The method may comprise using waveguide strain sensors. For example, the method may comprise using optical waveguide strain sensors.
The method may comprise using optical fibre strain sensors.
The method may comprise: coupling light into the optical waveguides; and detecting light scattered in the optical waveguides.
The method may comprise detecting light scattered by Brillouin scattering in the optical waveguides.
The method may comprise measuring a frequency shift and/or power associated with the light scattered by Briilouin scattering in the optical waveguides.
The method may comprise comprise detecting light scattered by Rayleigh scattering in the optical waveguides.
The method may comprise detecting light scattered by Raman scattering in the optical waveguides.
The method may comprise measuring straininduced birefringence of the optical waveguides, The optical waveguides may comprise polarisation maintaining optical waveguides.
The polarisation maintaining optical waveguides may comprise polarisation maintaining optical fibres.
The method may comprise using an optical time domain reflectometry (OTDR) technique to determine a pressure value associated with a sensing location along the optica waveguide.
The method may comprise determining pressure values associated with a plurality of sensng locations along the optical waveguide so as to generate a pressure profUe.
The method may comprise arranging a Bragg grating in each of the optical waveguides.
The method may comprise arranging a plurality of Bragg gratings at a corresponding piuraty of discrete sensing locations along each of the optical waveguides.
The method may comprise detecting light reflected from each Bragg grating.
The method may comprise determining a respective wav&ength associated with the Hght reflected from each Bragg grating.
The method. may comprise measuring straininduced birefringence associated with each Bragg grating.
The optical waveguides comprise polarisation maintaining optical waveguides.
According to a second aspect of the present invention there is provided a method for use in delermining the pressure of a fluid comprising: exposing the carrier member to the effects of the fluid; and determining a pressure value according to the method of the first aspect.
U should be understood that any of the optional features described in relation to the first aspect may also apply alone or in any combination in relation to the second aspect.
The method may comprise exposing the carrier member direcfly to the fluid.
According to a third aspect of the present invention there is provided a method for use in determining the pressure of a fluid in a well comprising: instafling the carrier member in the well; and determining a pressure of a fluid according to the method of the second aspect.
It should be understood that any of the optional features described in relation to one or both of the first and second aspects may also apply alone or in any combination in relation to the third aspect.
According to a fourth aspect of the present invention there is provided a method for use in determining pressure comprising: configuring first and secon.d strain sensors to sense respective strain signals along a common direction in a carrier member wherein the first and second strain sensors have a different response to pressure exerted on the carrier member; determining a pressure from the respective strain signals sensed using the first and second strain sensors; and enclosing the carder member and the strain sensors in a casing having a pressure transfer arrangement, wherein the casing defines a space around the carrier member and the pressure transfer arrangement is configured to transfer to the carrier member a pressure associated with an environment external to the casing.
Enclosing the carrier member and the strain sensors in such a casing may serve to reduce applied strain and/or bendinginduced strain acting on the carrier member. This may further enhance discrimination between a pressur&nduced strain component and a residual strain component, an applied strain component and/or a bendinginduced strain component.
it should he understood that any of the optional features described in relation to one or more of the first, second and third aspects may also apply alone or in any combination in relation to the fourth aspect.
According to a fifth aspect of the present invention there is provided an apparatus for use in determining pressure comprising: a carrier member: and first and second strain sensors configured to sense respective strain signals along a common threction in the carrier member, wherein the first and second strain sensors are configured to have a different response to pressure exerted on the carrier member.
The one of the first and second strain sensors may be configured to sense a strain signal along a neutral axis of the carrier member along which strain induced by bending of the carder member is substantially zero.
The first and second strain sensors may te configured to sense respective strain signals along respective axes which lie substantially in a common plane with, and are located equidistantly from, a neutral axis of the carrier member along which strain induced by bending of the carrier member is substantially zero.
The apparatus may comprise a third strain sensor configured to sense a strain signal along the common direction in the carrier member.
One of the first, second and third strain sensors may be configured to sense a strain signal along a neutral axis of the carrier member along which strain induced by bending of the carrier member is substantially zeroS The other two of the first, second and third strain sensors may be configured to sense respective strain signals along respective axes which lie substantiaHy in a common pne with, and are located eqwdstanUy from the neutr axis.
The apparatus may comprise a fourth strain sensor configured to sense a strain signal along the common direction in the carrier member.
Two of the first to fourth strain sensors may configured to sense respeothie strain signals along respective axes which lie substantiafly in a first common plane with, and are located equidistanfly from, a neutral axis of the carrier member along which strain induced by bending of the carrier member is substantially zero. The other two of the first to fourth strain sensors may be configured to sense respective strain signals along respective axes which lie substantiafly in a second common plane with, and are boated equidistantly from, the neutral axis, the second common plane being substantially perpendicular to the first common plane.
The apparatus may comprise a fifth strain sensor configured to sense a strain signal along the common direction in the carrier memher One of the first to fifth strain sensors may be configured to sense a strain signal along a neutral axis of the carrier member along which strain induced by bending of the carrier member is substantially zero. Two of the first to fifth stran sensors may be configured to sense respective strain signals along respective axes which lie substantially in a first common plane with, and are located equidistantly from the neutral axis. Two of the first to fifth strain sensors may be configured to sense respective strain signals along respective axes which lie substantially in a second common plane with, and are bcated equidistantly from, the neutral axis, the second common plane being substantially perpendicular to the first common plane.
The first and second strain sensors may he wholly or partially embedded in the carrier member or attached to the carrier member so as to sense strain in the carrier member.
The first and second strain sensors may, for example, be embedded at different positions within or across the carrier member.
The carrier member may be elongate. The carder member may have a uniform crosssection of any shape. For example, the carrier member may have a circular crosssection.
Each of the strain sensors may comprise a distributed strain sensor configured to sense a strain signal as a function of position along the carrier member.
The apparatus may comprise a pressure sensor configured to measure absolute pressure at a position along the carrier member.
Each of the two or more strain sensors may comprise an optical fibre.
The apparatus may comprise a casing having a pressure transfer arrangement.
wherein the casing defines a space around the carrier member and the pressure transfer arrangement is configured to transfer to the carrier member a pressure associated wfth an envfronment external to the casing.
The pressure transfer arrangement may comprise an aperture formed in the casing. The aperture may, for example, be formed in a sidewaU of the casing.
The pressure transfer arrangement may comprise a flexibe membrane configured to seal the aperture so as to contam a fluid or a g& within the space.
The pressure transfer arrangement may comprise a flexible membrane within the space, the flexible membrane containing the carrier member and a fluid or a geL The apparatus may' be configured to avow the signal carrier to move independenfly of the casing.
The apparatus may comprise one or more flexibe or a breakable supports between the carrier member and the casing.
According to a sixth aspect of the present invention there is provided a cable for use in determining pressure comprising: a carrier member; and first and second strain sensors configured to sense respective strain signas along a common direction in the carder member, wherein the first and second strain sensors are configured to have a different response to pressure exerted on the carrier member.
It shouki he understood that any of the optional features described in r&ation to the fifth aspect may also apply alone or in any combination in r&ation to the sixth aspect.
According to a seventh aspect of the present invention there is provided a cable comprising a signal carrier and a casing having a pressure transfer arrangement, wherein the casing defines a space around the signal carder and the pressure transfer arrangement is configured to transfer to the signal carrier a pressure associated with an environment external to the casing.
The pressure transfer arrangement may comprise an aperture formed in the ca&ng. The aperture may, for example, be formed in a sid&wafl of the casing.
The pressure transfer arrangement may comprise a flexible membrane configured to seal the aperture and contain a fluid or a gel within the space.
The pressure transfer arrangement may comprise a flexible membrane within the space, the flexible membrane containing the carrier member and a fluid or a geL The cable may be configured to allow the signal carrier to move independently of the casing.
The cable may comprise one or more flexible or a breakable supports between the signal carrier and the casing.
The signal carrier may comprise an electrical conductor.
The signal carrier may comprise a waveguide. For example, the waveguide may comprise an optical waveguide. The optical waveguide may comprise an optical fibre.
BRIEF DESCRIPTION OF THE FIGURES
The present invention will be further described by nonlimiting example only with reference to the foflowing drawings of which: Figure 1 is a schematic representation of an apparatus for use in determining pressure in a downhole environment; Figure 2 is a schematic representation of a strain sensing cable of the apparatus of Figure 1; Figure 3 is a schematic representation of a strain sensor arrangement of the strain sensing cable of Figure 2; Figure 4 shows the strain sensor arrangement of Figure 3 during bending; Figure 5(a) is a schematic representation of a first alternative strain sensor arrangement for the apparatus of Figure 1; Figure 5(b) is a schematic representation of a second alternative strain sensor arrangement for the apparatus of Figure 1 Figure 6(a) is a schematic representation of a third alternative strain sensor arrangement for the apparatus of Figure 1 Figure 8(b) s a schematic rwresentaUon of a fourth &ternative strain sensor arrangement for the apparatus of Figure 1; Figure 7(a) is a schemafic representation of a fifth aRernative strain sensor arrangement for the apparatus of Figure 1; Figure 7(b) is a schematic representafion of a sixth aternathie strain sensor arrangement for the apparatus of Figure 1; Figure 8(a) is a schematic representation of a seventh alternative strain sensor arrangement for the apparatus of Figure 1; Figure 8(b) is a schematic representation of an eighth alternative strain sensor arrangement for the apparatus of Figure 1 Figure 9(a) is a schematic crosssection representation of the cable of' Figure 2; Figure 9(b) is a schematic crosssection representation of a first alternative cable configuration; and Figure 9(c) is a schematic crosssection representation of a second alternative cable configuration.
DETAILED DESCRPTION OF THE FIGURES
Referring initiay to Figure 1 there is shown an apparatus, generay designated 2, for use in determining pressure within a subterranean well, generaHy designated 4, such as a hydrocarbon production well. The we 4 comprises a casing 8 located b&ow a surface 8 which may be the seabed, During production, a fluid such as oil, gas and/or water enters the casing 6 from formation 9 via casing perforations 10 as indicated by arrows 12 and the fluid is conveyed via production tubing 14 to the surface 8 for coHection via outlet 16 in a production Christmas tree 17.
The apparatus 2 comprises a strain sensor cable generally designated 20 that is exposed to the effects of pressure of the fluids within the production tubing 14 and a strain interrogation apparatus generally designated 22. As shown in Figure 2, in the present exemplary embodiment, the strain sensor cable 20 comprises a strn sensor arrangement 30 comprising a carrier member 32, a central optical fibre 34 and four peripheral optical fibres 36! 36, 40 and 42 embedded in the carrier member 32 between the central optical fibre 34 and an external surface 43 of the carher member 32. The central optica fibre 34 and the four peripheral optical fibres 36; 38, 40 and 42 are nominally identical in structure and function. The strain sensor cable 20 further comprises a casing 44 having a pressure transfer arrangement generally designated 45. The casing 44 is configured to protect the strain sensor arrangement 30 from damage and excessive mechanical strain, In particthar, the casing 44 is configured to reduce the effects of both applied axial strain and bendinginduced axial strain on the strain sensor arrangement 30. The casing 44 defines a space 46 around the strain sensor arrangement 30. The pressure transfer arrangement 45 is configured to transfer to the strain sensor arrangement 30 a pressure associated with an environment external to the casing 44 as indicated by the arrows in Figure 2. In the embodiment shown, the pressure transfer arrangement 45 comprises a plurality of apertures 47 formed in a sidewall of the casing 44 to permit fluid external to the casing 44 to penetrate the space 46. The strain sensor arrangement 30 is configured to move independenfly of the casing 44. For additional strain relief, the strain sensor arrangement 30 has a length marginally greater than a length of the casing 44 and the strain sensor arrangement 30 is forced into the space 46 on assembly of the cable 20 such that the strain sensor arrangement 30 does not extend beyond the length of the casing 44. This may ensure that the strain sensor arrangement 30 either follows a linear path within the space 46 wherein the linear path is angled relative to an axis of the casing 44, or the strain sensor arrangement 30 follows a nonlinear path within the space 46.
As shown in more detail in Figure 3, the carrier member 32 has a circular cross section and an axis of symmetry 50. The carrier member 32 comprises a homogeneous material for the transfer of the effects of pressure of the fluid, as represented by arrows 33, to the central optical fibre 34 and the four peripheral optical fibres 36; 38, .40 and 42. The central optical fibre 34 is arranged to sense strain in the carrier member 32 along the axis 50 of the carrier member 32 and the four peripheral optical fibres 36; 38, 40 and 42 are arranged to sense strain in the carrier member 32 along respective axes 52, 54, 56 and 58 which are generally parallel to hut offset equidistantly from the axis 50 of the carrier member 32. The axes 52 and 56 correspondkig to peripheral optical fibres 38 and 40 respectiv&y are arranged n a first plane that contains the axis 50 of the carrier member 32. The axes 54 and 58 corresponding to peripheral optical fibres 38 and 42 respectively are arranged in a second plane that contains the axls 50 of the carrier member 32, wherein the second plane is perpendicular to the first plane.
Referring again to Figure 1, the strain interrogation apparatus 22 comprIses a strain interrogation system 60 coupled to the central optical fibre 34 and four further strain interrogation systems 62, 64, 66 and 68 coupled to the four peripheral optk fibres 36, 38, 40 and 42 respectively. The further strain interrogation systems 62, 64, 66 and 68 are each identical to the strain interrogation system 60. In the interests of clarity, only strain interrogation system 66 is shown explicifly in Figure 1 endosed within a dotted box and each of the other strain interrogation systems 60, 62, 64, and 68 are represented by respective dotted boxes.
As shown in Figure 1 the strain interrogation system 66 comprises a pulsed laser source 70 coupled via a 2x2 optical coupler 72 to the optical fibre 40 and an optical detector 74 for monitoring power transmitted by the pulsed laser source 70.
The 2x2 optical coupler 72 is also arranged to couple fight backscattered from the further optical fibre 40 towards a 1x2 optical coupler 76 which is arranged to divide a first proportion of the backscattered light towards an optical detector 78 for measuring Rayleigh backscatter and a second proportion of the backscattered light towards an arrangement for measuring Brillouin backscatter comprising a scannable optical filter followed by an optical detector 82. The strain interrogation apparatus 22 further comprises a controller 84 having a processor 86 and a memory 87. As indicated by the dashed lines in Figure 1, the controller 84 is configured for communication with the pulsed laser source 70, the optical detectors 74, 78 and 82 and the scannable optical filter 80 of the strain interrogation system 66. In addition, although not shown explicitly in Figure 1, it should be understood that the controller 64 is also configured for communication with respective pulsed laser sources, optical detectors and scannable optical filters of the other strain interrogation systems 60, 62, 64, and 68.
In use, the controller 84 controls the pulsed laser source 70 so as to transmit pulses along the optical fibre 40. Detectors 78 and 82 detect returning pulses backscattered from different positions along the optical fibre 40. The scannable optical filter 80 is scanned at a slower rate compared to a pulse repetition rate of the pulse laser source 70. A magnitude of the Brillouin backscatter peak and a frequency shift of the Brillouin backscatter peak relative to the Rayleigh backscatter peak is determined for each poson along the optical fibre 40. The Briiiouin peak magnftudes and frequency shifts for each position are referenced against a BrUlouin peak magnftude and frequency shift associated wfth a reference section 68 of cable 20 which is subjected to a known temperature and strain to permit cabraUon of the data received from each sensing location into strain and temperature values.
SimUarly. in use, strain interrogation systems 60, 62, 64, and $8 measure the strain and temperature independenfly along corresponding optic fibres 34, 36, 38 and 42 respectively, As described b&ow wfth reference to Figures 3 and 4, the strain sensor cable 20 and, in paftcular, the strain sensor arrangement 30 is specificay arranged to permit the processor 86 to discriminate between the effects of mechanicayinduced strSn and pressure-induced strain. The axial strain ei sensed at any position along the r optical fibre wifl, in general, comprise axial strain components s5. e, C?11, 842; and s, attributable to residual axial strain, applied axial strain, axial strain induced by bending of the carrier member 32 about a first bending axis, axial strain induced by bending of the carrier member 32 about a second benthng axis perpendicular to the first bending axis, and pressureinduced axial strain respethvely 81 + e, +-842i * Equation I The residual strain component e, may, for example, be associated with a process used to manufacture the 1m optical fibre and/or embed the 1th optical fibre in the carrier member 32. For a uniform manufacturing process, the central optical fibre 34 and the four peripheral optical fibres 36, 38. 40 and 42 may be assumed to be identical in structure and function and the residual strain components s £7 Ej»=4 and s may he assumed to be equal. By definition, the applied strain components e,,, 8A2. e, £44 and 1..45 for the optical fibres 34, 36. 38, 40 and 42 respectively are also equal.
The effects of fluid pressure are transferred by the carrier member material from the external surface 43 of the carrier member 32 to the 1th optical fibre and the strain pressureinduced strain component e. for the r optical fibre will therefore, in general, depend on the geometry of the carrier member 32, the properties of the material from which the carrier member 32 is formed and the configuration of the 1m optical fibre within the carrier member 32.
By vktue of the circuar cross..section of the carrier member 32, the homogeneity of the carrier member material and the circumferent arrangement of the peripheral optical fibres 36, 38, 40 and 42 around the axis of symmetry 50 of the carrier member 32, the pressureinduced strain components SJ?2. s1, 84 and for the different peripheral optical fibres 36, 38, 40 and 42 may be assumed to be equal. The pressureinduced strain component s1 for the central optical fibre 34 is, however, different from the pressure1nduced strain components s3,2, e3, £])4 and g, because the central optical fibre 34 is arranged to sense strain in the homogeneous carrier member 32 along axis 50 which is further from the external surface 43 of the carrier member 32 than the peripheral optical fibres 36. 38, 40 and 42.
Furthermore, because the axis of symmetry 50 of the carrier member 32 is neutral with respect to strain and the central optical fibre 34 is arranged to sense strain in the homogeneous carrier member 32 along the axis 50, the strain s, sensed by the central optical fibre 34 will, in general, comprise no bendinginduced strain components (i.e. e = fl21 = 0) but will comprise residual strain, applied strain and pressureS-induced strain components e, and c1,1 respectively: = 8M1 + 6'Ai + Equation 2 Since peripheral optical fibres 36 and 40 are arranged to sense strain along respective axes that are located in a first plane with the neutral axis 50 and are offset equidistantly in opposite directions from the neutral axis 50, the strain components for peripheral optical fibres 36 and 40 which are attributable to bending of the carrier member 32 about a first bending axis normal to the first plane will be equal but opposite. For example. with reference to Figure 4, the peripheral optical fibre 36 is arranged to have an offset of r from the axis 50 and the optical fibre 40 is arranged to have an offset of r from the axis 50 with the result that. when the carrier member 32 is subjected to a bending radius R in the first plane as shown in Figure 4, the peripheral optical fibre 36 is in tension and is subject to a bendinginduced strain component s2 while the peripheral optical fibre 40 is in compresalon and is subject to a bending induced strain component E44 witch is equal in magnitude but opposite in gn to J312 6R,!4 =B12 Equation 3 Since peripheral opfical fibres 36, 40 e in the same plane as the neutral axis 50, the strain components for peripheral optical fibres 36 and 40 which are attributable to bending of the carrier member 32 about a second bending axis normal to the second plane are both zero: 8A22 = 8/324 = Equation 4 1.5 The average of the strains 2 and 54 sensed by peripheral optical fibres 36 and 40 is then given by: (e2 +84)-(ER2 +8R4)±(C/2 +C.44)+(C.fl2 P4) Equation S Assuming that the pressureinduced strain components are equal (i.e. 8P2 = = that the residual strain components are equal (i.e. 8R2 = e,), and the applied strain components are equal (i.e. ,:2 = A4 = c,) then Equation 5 becomes: i: (2 84 8Ry + + Equation 6 Such a derived strain value is independent of bending strain. Subtracting the strain a, sensed by the central optical fibre 34 given by Equation 2 from the average of the strains for peripheral optical fibres 36 and 40 given by Equation 6 then yields: +(2 +s)--e1 = (e, tfrl)r(6A; -e41 rti -e1) Equaflon I Assumng that the re&dua stran component e, for pedpher optca fibres 36 and 40 S s equa to the resdu stran component si?, for the first opfica fibre 34 and that the appiled stran component s, for perphera optica fibres 36 and 40 s equa to the apped strain component S4 for the first optica fibre 34, Equafion 7 yi&ds: Equaton8 Equation 8 impfles that the processor 86 may determine an average of the strains detected in the corresponding peripheral opdcal fibres 36, $0 and subtract the strain detected in the centr optical fibre 34 to determftie a pressure dependent parameter Sm that is independent of axial and benthng-induced strain components. Such a parameter is only pressure dependent by vfttue of the fact that the central optical fibre 34 has an associated pressur&induced strain component c»=M which is different from the pressurenduced strain component c. associated with penpherai optical fibres 38 and 40 so that e s is nonzero.
The processor 86 may perform a simHar analysis on strains 6'3 and 55 sensed using peripheral opfical fibres 36 and 42 respecfiv&y to determine: 3(c., +E5)-L = C Equation 9 Equabon 9 implies that the processor 86 may perform a simflar analysis on the strains sensed in peripheral optical fibres 38 and 42 to produce the same pressure dependent parameter e) determined from analysis of the strains sensed in peripheral optical fibres 3$ and 40. Further manipulation of Equation 8 and Equation 9 also $0 yields: quafion 10 Thus, Equatbn 10 ftnpes that the processor 86 may deterrnne the average of the strains for all four peripheral optical fibres 36, 38, 40 and 42 to produce the same pressure dependent parameter (s E:D1) determined from analysis of the strains sensed in either paft of peripheral optical fibres 36 and $0 or 38 and 42. The advantage of the processor 8$ calculafing the pressure dependent parameter e;) from an average of strain values sensed in a four peripheral optical fibres 36, 38, 40 and 42 according to Equafion 10 is that strah signal noise may be reduced.
The use of four peripheral opfical fibres 36, 38, $0 and 42 also aows the processor 8$ to determine a threction and degree of bending of the strain sensor arrangement 30 in two dimensions as a function of position along the strain sensor arrangement 30. For example. a difference between the strain signals sensed by the perIpheral optical fibres 838 and 840 may be subsLantiafly independent of re&dual strain, apped strain and pressure induced strain and may be solely dependent on strain nduced by bending about a first bending axis normal to the first plane. A degree of bending about the first bending axis may be determined by calibration. Similarly. a difference between the strain signals sensed by the sensed by the peripheral optical fibres 836 and 842 may be substantially independent of residual strain, appUed strain and pressure induced strain and may be sol&y dependent on strain induced by bending about a second bending axis normal to the second plane. A degree of bending about the second bending axis may be determined by cahbration, To permit the processor 86 to calibrate or convert a pressure dependent parameter e1) prcfile along the strain sensor arrangement 30 of the cable 20 into an absolute pressure profile, the apparatus 2 comprises a point gauge 90 shown in Figure 1 for use in measuring an absolute value of pressure exerted on the carrier 32.
at a position along the cable 20. As indicated by the dashed lines in Figure 1 the controller 84 is configured for communication with the point gauge 90. In use., the processor 86 determines a ratio of an absolute pressure measured using the point gauge 90 to a value of the pressure dependent parameter (e e) corresponthng to the position of the point gauge 90 determined according to Equation 10. The processor 86 subsequendy sces the pressure dependent parameter (e -s1) profile according to the dete rrmned ratio to provide an absolute pressure profile.
One skified in the art wiU appreciate that modifications of the method and apparatus for use in determining pressure described wfth reference to F9gures I to 4 are possible. For example, Figures 5(a) and 5(b) show two alternative strain sensor arrangements 230 and 330 each comprising two distributed strain sensors. The strain sensor arrangement 230 shown in Figure 5(a) comprises a carrier member 232 and first and second distdbuted strain sensors 234 and 236 arranged to sense strain along respective axes 254 and 256 located at different nonzero radii r&ative to an axis of symmetry 250 of the carrier member 232. The first and second strain sensors 234 and 236 may be nominafly identical in structure and function.
The strain sensor arrangement 230 may permit a pressure to be determined from strain signals sensed using the first and second strain sensors 234 and 236.
Knowledge of the configuration of the first and second strain sensors 234 and 236 may be required to determine the pressure. This may, for example, he possible where bending of the carrier member 232 is not possible because the carrier member 232 is mechanically constrained. For example. subtraction of strain signals sensed using the first and second strain sensors 234 and 236 may prmnde a derived strain which is independent of residual and applied strain. A pressure exerted on the carrier member 232. may then he determined from the derived strain.
The strain sensor arrangement 330 shown in Figure 5(b) comprises a carrier member 332. a central distributed strain sensor 334 arranged to sense strain along an axis of symmetry 350 of the carrier member 332 and a peripheral distributed strain sensor 336 arranged to sense straln along an axis 35$ which lies in a common plane with the axis of symmetry 350.
The strain sensor arrangement 330 may permit a pressure to be determined from strain signals sensed using the strain sensors 334 and 336. This may, for example, he possible where bending of the carrier member 332 is not possible because the carrier member 332. is mechanicafly constrained. For exampie, subtraction of strain signals sensed using the strain sensors 334 and 33$ may provide a derived strain which is independent of residual and applied strain. A pressure exerted on the carrier member 332 may then be determined from the derived strain.
The strain sensor arrangement 330 may provide enhanced sensitivity to pressure because the strain sensor 334 is configured to sense strain along the axis of symmetry 350 whereas the peripheral strain sensor 336 is configured to sense strain along the axis 356 which is relatively dose to an external surface 343 of the carrier member 332.
FigureS 6(a) and 6(b) show two alternative strain sensor arrangements 530 and 630 each comprising three thstributed strain sensors. The strain sensor arrangement 530 shown in Figure 6(a) comprises a carrier member 532 and first, second and third distributed strain sensors 534, 536 and 538 arranged to sense strain abng respective axes 554, 556 and 558 located at different nonzero radH r&ative to an axis of symmetry 550 of the carrier member 532. The first, second and third strain sensors 534, 536 and 538 may be nominay identical in structure and funcuon.
The strain sensor arrangement 530 may permit pressure to be determined from strain signals sensed using the strain sensors 534, 536 and 538. Knowledge of the configuration of the strain sensors 534, 536 and 538 may be required to determine the pressure. This may be possible where bending of the carrier member is not possible, for example, because the carrier member is mechanicafly constrained or where bending of the carrier member is only possible about a single bending axis, for example, because the carrier member is mechanicab constrained to lie within a plane.
The strain sensor arrangement 630 shown in Figure 6(b) comprises a carrier member 632 and a first strain sensor 634 arranged to sense strain along an axis of symmetry 650 of the carrier member $32. The strain sensor arrangement 630 further comprises second and third strain sensors 636 and 638 that are arranged to sense strain along respective axes 656 and 658 located in a common plane with the axis of symmetry 650 of the carrier member 832 and which are offset equidistantly from the axis of symmetry 650. The first, second and third strain sensors 634, 636 and 638 may be nominally identical in structure and function.
The strain sensor arrangement 630 may permit a pressure to be determined from strain signals sensed using the strain sensors 634, 636 and 638. Knowledge of the configuration of the strain sensors 634, 636 and 638 may be required to determine the pressure. For example, since the first strain sensor 634 is configured to sense strain along the axis of symmetry 650 of the carrier member 632, a strain signal sensed using the first strain sensor 634 may be substantially independent of bending of the carrier member 632. Furthermore, the configuration of the second and third strain sensors 636 and 638 may ensure that an average of the strain signals sensed using the second and third strain sensors $36 and 638 is also independent of bending of the carrier member 632. Subtracting the average of the strain signals sensed using the second and third strain sensors 636 and 638 from the strain signal sensed using the first strak sensor 634 may provde derived stran &gna that s substantfly independent of redual strn, apped strain and bending in two dimensions and which is solely a function of pressure. The pressure may be determined from such a derived strain signal by cabration.
Figures 7(a) and 7(b) show two afternative strain sensor arrangements 730 and 830 each compri&ng four distributed strain sensors. The strain sensor arrangement 730 shown in Figure 7(a) comprises a carrier member 732 and first, second, third and fourth distributed strain sensors 734, 736, 738 and 740 arranged to sense strain along respective axes 754. 756, 758 and 760 located at different nonzero radii relative to an axis of symmetry 750 of the carrier member 732. The first, second, third and fourth strain sensors 734, 736, 738 and 740 may be nominally identical in structure and function.
The strain sensor arrangement 730 may permit a pressure to be determined from strain signals sensed using the strain sensors 734, 736, 738 and 740. Knowledge of the configuration of the strain sensors 734. 736, 738 and 740 may be required to determine the pressure. For example, the strain sensor arrangement 730 may permit discrimination of a pressureinduced strain component from a residual strain component, an apMed strain component, a strain component induced by bending about a first bending axis and a strain component induced by bending about a second bending axis perpendicular to the first bending axis. The strain sensor arrangement 730 may also permit a degree and direction of bending of the carder member 732 to be determined from the strain signals sensed using the strain sensors 734, 736, 738 and 740.
The strain sensor arrangement 830 shown in Figure 7(b) comprises a carrier member 832 and first, second, third and fourth distributed strain sensors 834, 836, 838 and 840 arranged to sense strain abng respective axes 854, 856, 858 and 860. The axes 854 and $58 are located in a first common plane with an axis of symmetry 850 of the carrier member 832 and are offset equidistantly by a first offset from the axis of symmetry 850. Similarly, the axes 858 and 860 are located in a second common plane with the axis of symmetry 850 of the carrier member 832 and are offset equidistanfly by a second offset from the axis of symmetry 850, wherein the second common plane is perpendicular to the first common. plane, The first, second, third and fourth strain sensors 834, 836, 83$ and 840 may he nominally identical in structure and function.
The strain sensor arrangement $30 may permit a pressure to be determined from strain signals sensed using the strain sensors 834, 836, 838 and 840. Knowledge of the configurafion of the strain sensors S3$. 836, 838 and 840 may be requred to determne the pressure. For exampe, an average of the strain &gnak sensed u&ng the firsL and tthrd strain sensors 34 and 838 may be suhstantfty ndependent of bending of the carher member 832. Simarly, an average of the strain signS sensed using the second and fourth strain sensors 836 and 840 may be substantiay independent of bending of the carrier member 832. The average of the strain signS sensed using the first and third strain sensors 834 and $38 may have a cflfferent dependency on pressure compared wfth the average of the strain signals sensed using the second and fourth strain sensors 836 and 840 as a resuR of a difference between the first and second offsets. Subtracting the average of the strain signals sensed using the first and thftd strain sensors 834 and $38 from the average of the strain signals sensed using the second and fourth strain sensors 83$ and $40 may: therefore, provide a derived strain signal that is substantiSy independent of residual strain, applied strain and bending in two dimensions and is solely a function of pressure. The pressure may be determined from such a derived strain signal by calibration.
The strain sensor arrangement 830 may also permit a degree and direction of bending of the carrier member 832 to be determined. For example, a difference between the strain signals sensed using the first and third strain sensors $34 and 838 may be substantially independent of residual strain, applied strain and pressure induced strain and may be solely dependent on strain induced by bending about a first bending axis normal to the first common plane. A degree of bending about the first bending axis may be determined by calibration, Similarly, a difference between the strain signals sensed using the sensed by the second and fourth strain sensors 836 and $40 may be substantially independent of residual strain, applied strain and pressure induced strain and may be soi&y dependent on strain induced by bending about a second bending axis normal to the second common plane. A degree of bending about the second bending axis may be determined by calibration.
The strain sensor arrangement 930 of Figure 8(a) comprises a central distributed strain sensor 934 arranged to sense strain in the carrier member 932 along an axis 950 of the carrier member 932 and peripheral strain sensors 936, 937, 938, 939, 940: 941. 942 and 943 arranged to sense strain in the carder member 932. along respective axes wherein the axes of each pair of peripheral strain sensors 936 and 940, 937 and 941, 938 and 942, and 939 and 943 are equidistant from and coplanar with the axis 950 of the carrier member 932. The strain sensors 934, 936, 937, 938.
939, 940, 941, 942 and 943 may be nominally identical in structure and function. A pressure may he determined from strain &gnals measured by the strain sensors 934.
936, 937, 938. 939, 940, 941, 942 and 943. Knowledge of the configuration of the strain sensors 934, 936, 937, 938, 939, 940, 941, 942 and 943 may be required to determine the pressure. Such a strain sensor arrangement 930 may permit discrimination of pressureinduced strain from residual strain, applied strain and bending strain in two dimensions. For example, subtracting an average of the strain signals sensed using the peripheral strain sensors 936, 937, 938, 939. 940, 941, 942 and 943 from the strain signal sensed using the central strain sensor 934 may provide a derived strain signal that is substantially independent of residual strain, applied strain and bending of the carrier member 932 and which is solely a function of pressure.
Similady, the strain sensor arrangement 1030 of Figure 8(b) comprises a central strain sensor 1034 arranged to sense strain in the carrier member 1032 along an axis 1050 of the carrier member 1032 and pedpheral strain sensors 1036, 1037, 1038. 1039, 1040, 1041, 1042 and 1043 arranged to sense strain in the carrier member 1032 along respective axes, wherein the axes of peripheral strain sensors 1036, 1040, 1037 and 1041 lie in a first common plane with the axis 1050 of the carrier member 1032 and the axes of peripheral strain sensors 1038, 1042, 1039 and 1043 lie in a second common plane with the axis 1050 of the carrier member 1032, wherein the second common plane is perpendicular to the first common plane. The respective axes of peripheral strain sensors 1036, 1038, 1040 and 1042 are offset equidistanfly from the axis 1050 by a first offset. The respective axes of peripheral strain sensors 1037, 1039, 1041 and 1043 are offset equidistantly from the axis 1050 by a second offset different from the first offset. A pressure may be determined from strain signals sensed using the strain sensors 1034, 1036; 1037, 1038, 1039, 1040, 1041, 1042 and 1043. Knowledge of the configuration of the strain sensors 1034, 1036, 1037, 1038: 1039, 1040, 1041, 1042 and 1043 may be required to determine the pressure. Such a strain sensor arrangement 1030 may permit discrimination of pressureinduced strain from residual strain, applied strain and bending strain in two dimensions. For example.
subtracting an average of the strain signals sensed by the peripheral strain sensors 1036, 1037, 1038, 1039, 1040, 1041, 1042 and 1043 from the strain signal sensed using the central strain sensor 1034 may provide a derived strain signal that is substantially independent of residual strain; applied strain and bending of the carrier member 1032 and which is solely a function of pressure.
Figure 9(a) shows a crosssection of the cable 20 shown in Figure 2 alongside alternative cable configurations 1120 and 1220 in Figures 9(b) and 9(c).
The cable configuration 1120 of Figure 9(b) comprises a casing 1144 having a pressure transfer arrangement generay designated 1145. The casing 1144 is designed to provide protection for the strain sensor arrangement 30 and, in parUcSr, to suppress the effects of bending strain on the strain sensor arrangement 30. The casing 1144 defines a space 1146 around the strain sensor arrangement 30. The pressure transfer arrangement 1145 is configured to transfer to the strain sensor arrangement 30 a pressure associated with an environment external to the casing 1144. The pressure transfer arrangement 1145 comprises a plurality of apertures 1147 formed in a side-wafl of the casing 1144, each aperture 1147 being sealed by a flexible membrane 1148 so as to seal the space 1146. The space 1146 is fluid or gekIlled in order that the effects of pressure of a fluid external to the casing 1144 are transmitted via the flexible membranes 1148 and the fluid or gel to the strain sensor arrangement 30, The strain sensor arrangement 30 is configured to move independenfly of the casing 1144. For additional strain relief, the strain sensor arrangement 30 has a length marginally greater than a length of the casing 1144 and the strain sensor arrangement is forced into the space 1146 on assembly of the cable configuration 1120 such that the strain sensor arrangement 30 does not extend beyond the length of the casing 1144. This may ensure that the strain sensor arrangement 30 either foUows a linear path within the space 1146, wherein the linear path is angled relative to an axis of the casing 1144, or the strain sensor arrangement 30 follows a non-linear path within the space 1146.
The cable configuration 1220 of Figure 9(c) comprises a casing 1244 having a pressure transfer arrangement generay designated 1245. The casing 1244 is designed to provide protection for the strain sensor arrangement 30 and, in particular, to suppress the effects of bending strain on the strain sensor arrangement 30. The casing 1244 defines a space 1246 around the strain sensor arrangement 30. The pressure transfer arrangement 1245 is configured to transfer to the strain sensor arrangement 30 a pressure associated with an environment external to the casing 1244. The pressure transfer arrangement 1245 comprises a plurality of apertures 1247 formed in a side-wall of the casing 1244 to permit fluid external to the casing 1244 to penetrate the space 1246 and a fluid or gel-filled flexible membrane 1249 in the space 1246, wherein the flexible membrane 1249 contains the strain sensor arrangement 30.
Pressure from the external fluid is transmitted to the strain sensor arrangement 30 via the fluid or gel-filled flexible membrane 124g. For additional strain relief, the strain sensor arrangement 30 has a length marginally greater than a length of the casing 1244 and the strain sensor arrangement 30 is forced into the space 1246 on assembly of the cable configuration 1220 such that the strain sensor arrangement 30 does not extend beyond the length of the casing 1244. This may ensure that the strain sensor arrangement 30 either follows a ftear path within the space 1248, wherein the linear path is angled relative to an axis of the casing 1244, or the strain sensor arrangement follows a nonlinear path within the space I 24$..
One skilled in the art wi also understand that the cable configurations 20, 1120 and 1220 shown in Figures 9(a), 9(b) and 9(c) respectively may comprise strain sensor arrangements other than strain sensor arrangement 30 for the purposes of protecting and reducing the effects of bending strain on such strain sensor arrangements.. For example, the cable configurations 20, 1120 and 1220 shown in Figures 9(a) to 9(c) may comprise one or more of the strain sensor arrangements 230, 330, 530, 630, 730, 830, 930 and 1030 shown in any of Figures 5 to 8. The cable configurations 20, 1120 and 1220 shown in Figures 9(a) to 9(c) may comprise a strain sensor of any kind. In a further variant, the cable configurations 20, 1120 and 1220 shown in Figures 9(a) to 9(c) may comprise a signal carrier of any kind.
in an alternative embodiment of the apparatus for measuring pressure, rather than using multiple independent interrogation systems 60, 62, 64, 66 and 68 as shown in Figure 1 wherein each interrogation system 60, 62, 64, 66, 68 is coupled to a different optical fibre strain sensor 34, 36, 38, 40 and 42, a single interrogation system may be used in conjunction with an optical switch that cyclically couples the interrogation system to each of the optical fibre strain sensors 34, 36, 38, 40 and 42 in turn.
Rather than comprising a scannable optical filter, the interrogation apparatus may comprise a receiver having a frequency to amplitude converter arranged to convert a received signal directly into a signal whose amplitude varies with the instantaneous frequency of the Briilouin component.
It should be understood that rather than using a point gauge 90 to determine an absolute pressure value along the cable 20 to convert a pressure dependent parameter -s4 profile into an absolute pressure profile, th.e reference section 88 of the cable 20 may be exposed to or subected to a known absolute pressure.
It should also be understood that for pressure measurement it is not necessary to calibrate the strain signals sensed by the optical fibre strain sensors in terms of absolute strain values using reference section 88 of cable 20. Instead, the methods described hereinbefore may be applied to st.rain signals such. as Brillouin peak frequency shifts and such rSative strain signals may he caUbrated directly against pressure. The strns c, and their various respective strain components appearing in Equation I through Equation 10 may, therefore, he Briflouh peak frequency shifts in the central optical fibre 34 and the peripheral optical fibres 36, 36, 40 and 42 or functions thereof. The pressure dependent parameter (se, **c,,) may, therefore, also be a difference between 8riouin peak frequency shifts or a function of Briilouin peak frequency shifts.
R should also be understood that the r&ationships between the different strain components in Equation I through Equation 10 are intended to be merely illustrative and that the relationships may be different from these, The relationships may, in particular, involve products or more complex functions of the different strain components.
The apparatus 2 may comprise more than one point gauge. For example, the apparatus 2 may comprise a plurality of point gauges for measuring absolute pressure at a corresponding pluraty of positions along the cable 20. The processor 86 may then determine an average of the ratio of absolute pressure reading to the corresponding pressure dependent parameter (e e4) value for each of the plurality of point gauges. The processor may subsequently scale the pressure dependent parameter s1) profile according to the determined average ratio to provide an absolute pressure profile.
A pressure dependent parameter (e, -) may also be converted into an absolute pressure value using a calibration procedure. During such a calibration procedure a location along the cable 20 may be exposed to a series of different known pressures and the processor 86 may determine values of the pressure dependent parameter according to Equation 10 from the corresponding strain signals sensed in the central optical fibre 34 and each of the peripheral optica.i fibres 36, 38, 40 and 42 respectively. The processor 86 stores the values of the pressure dependent parameter 6n e) determined during the calibration procedure along with the corresponding known pressure values in a iookup table in the memory 87.
When the cable is exposed to the effects of fluid pressure to be measured, strain signals are sensed by the central optical fibre 34 and each of the peripheral optical fibres 3$, 38, 40 and 42 and the processor 66 determines a value for the pressure dependent parameter (L,, - according to Equation 10. The processor 86 identifies a value of the pressure dependent parameter in the lookup table that corresponds to the pressure dependent parameter value determined from the strahi signals according to EquaUon 10 and the processor 86 determines the fluid pressure as the pressure vakie in the lookup table that corresponds to the identified pressure dependent parameter value. Where the pressure dependent parameter (ei>, determined by the processor 86 from the strain &gnals according to Equation 10 does not correspond exacfiy to a value of the parameter measured during the calibration procedure, interpolation of the calibration data may be used to determine the fithd pressure.
Rather than using Briflouin scattering for sensing strain, one skiHed in the art wi also understand that any strain sensing technique may be used in conjunction with the pressure measurement method and apparatus disdosed above. For example, an distributed optical strain sensing technique based on Briiiouin scattehng, Rayleigh scattering., Raman scattering or any combination thereof could be used. A distributed optical strain sensing technique that comprises a measurement of straininduced hirefringence in an optical sensing waveguide may be used. The optical waveguide may, for example, comprise a polarisation maintaining optical waveguide such as a polarisation maintaining optical fibre. A plurality of Bragg gratings may be located at a corresponding plurality of discrete sensing locations along an optical waveguide and a strain value at the location of each Bragg grating may be determined from a measurement of the wavelength of the peak reflectance from each Bragg grating. A straininduced birefringence associated with each Bragg grating may be determined.
The Bragg gratings may also be formed in a polarisation maintaining optical waveguide such as a polarisation maintaining optical fibre.
One skiHed in the art wl also understand that the method and apparatus disclosed herein are not restricted to the use of optical fibre strain sensors but may be applied when using an apparatus comprising distributed or quasidistributed strain sensors of any kind. The apparatus may, for example, comprise waveguides of any kind. The apparatus may comprise electrical strain sensors.
Claims (4)
- CLAIMS1. A method for use in determining pressure corn prng: configuring first and second strain sensors to sense respective strain signals along a common direction in a carrier member wherein the first and second strain sensors have a different response to pressure exerted on the carrier member; and determining a pressure from the respective strain signals sensed using the first and second strain sensors.
- 2. The method according to claim I comprising: subtracting the respective strain signals sensed using the first and second strain sensors to determine a derived strain signal; and determining the pressure from the derived strain signal.
- 3. The method according to claim I or 2, comprising: configuring one of the first and second strain sensors to sense a strain signal along a neutral axis of the carrier member along which strain induced by bending of the carrier member is substantiaHy zero.
- 4. The method according to any of claims I to 3, comprising: configuring a third strain sensor to sense a strain signal along the common direction in the carrier member; and determining the pressure from the respective strain signals sensed using the first, second and third strain sensors.5, The method according tc claim 4, comprising: configuring one of the first, second and third strain sensors to sense a strain signai along a neutral axis of the carrier member along which strain induced by bending of the carrier member is substantially zero; configuring the other two of the first, second and third strain sensors to sense respective strain signals along respective axes which lie substantially in a common plane with, and are located equidistantly from the neutral axis; averaging the strain signals sensed using the strain sensors having respective axes located equidistantly from the neutral axis to determine an average strain signal; subtracting the average strain signal from the strain signal sensed using the strn sensor configured to sense strain abng the neutral axis to determine a derived strain &gnal; and determining the pressure from the derived strain signaL 6. The method according to claim 4 or 5, compri&ng: configuring a fourth strain sensor to sense a strain signal along the common direction in the carrier member; and determining the pressure from the respective strain signals sensed using the first, second, third and fourth strain sensors.7, The method according to claim 6, comprising: configuring two of the first to fourth strain sensors to sense respective strain signals along respective axes which lie substantially in a first common plane with, and are located equidistantly from, a neutral axis of the carrier member along which strain induced by bending of the carder member is substantially zero; configuring the other two of the first to fourth strain sensors to sense respective strain signals along respective axes which lie substantially in a second common plane with, and are located equidistantly from, the neutral axis, the second common plane being substantially perpendicular to the first common plane; averaging the strain signals sensed using the strain sensors having respective axes located equidistantly from the neutral axis in the first common plane to determine a first average strain signal; averaging the strain signals sensed using the strain sensors having respective axes located equidistantly from the neutral axis in the second common plane to determine a second average strain signal; subtracting the first and second average strain signals to determine a derived strain signal; and determining the pressure from the derived strain signal.8. The method according to claim $ or 7, comprising: configuring a fifth strain sensor to sense a strain signal along the common direction in the carder member; and determining the pressure from the respective strain signals sensed using the first, second, third, fourth and fifth strain sensors.9. The method according to daim 8, comprising: configunng one of the first to fifth strahi sensors to sense a strain signal along a neutral axis of the carrier member abng which strahi induced by bending of the carrier member is substantiafly zero; configuring two of the first to fifth strain sensors to sense respective strain signals along respective axes which lie substantiaUy in a first common plane with, and are located equidistanfly from the neutral axis; configuring two of the first to fifth strain sensors to sense respective strain signals along respective axes which lie substantially in a second common plane with, and are located equidistantly from, the neutral axis, the second common plane being substantiay perpendicular to the first common plane; averaging the strain signals sensed using the strain sensors having respective axes located in the first common plane equidistantly from the neutral axis and the strain sensors having respective axes located in the second common plane equidistantly from the neutral axis to determine an average strain signal; subtracting the average strain signal from the strain signal sensed using the strain sensor configured to sense strain along the neutral axis to determine a derived strain signal; and determining the pressure from the derived strain signal.1 ft The method according to any of claims I to 9 comprising calibrating a strain signal derived from the respective strain signals sensed using two or more strain sensors as a function of pressure; and determining the pressure from the calibrated strain signal as a function of pressure.II. The method according to any of claims Ito 10, comprising: configuring each of the strain sensors as a distributed strain sensor; using the distributed strain sensors to sense respective strain signals as a function of position along the carrier member; and determining pressure as a function of position along the carrier member from the respective sensed strain signals.12. The method according to claim II, comprising: determining r&ative pressure as a function of positon along the carrier member from the respective sensed strain signas; measuring an absolute value of the pressure exerted on the carrier member at a position along the carder member; and using the measured absolute pressure value at the posftion and the determined relative pressure as a functbn of po&Uon along the carder member to determine the absolute pressure as a function of position along the carrier member.13. A method according to any preceding claim, comprising: enclosing the can-icr member and the strain senscra in a casing having a pressure transfer arrangement, wherein the casing defines a space around the carrier member and the pressure transfer arrangement is configured to transfer to the carrier member a pressure associated with an environment external to the casing.14. A.n apparatus for use in determining pressure comprising: a carrier member: and first and second strain sensors configured to sense respective strain signals along a common direction in the carrier member, wherein the first and second strain sensors are configured to have a different response to pressure exerted on the carrier member.15. The apparatus according to claim 14, wherein one of the first and second strain sensors is configured to sense a strain signal along a neutral axis of the carrier member along which strain induced by bending of the carrier member is substantiaUy zero.16. The apparatus according to claim 14, wherein the first and second strain sensors are configured to sense respective strain signals along respective axes which lie substantially in a common plane with, and are located equidistantly from, a neutral axis of the carrier member along which strain induced by bending of the carrier member is substantially zero.17 The apparatus according to any of claims 14 to 16, comprising a third strain sensor configured to sense a strain signal along the common direction in the carrier member 18. The apparatus according to daim 17 wherein one of the first, second and third strain sensors is configured to sense a strain signal along a neutral axis of the carrier member along which strain induced by bending of the carder member is substantiaHy zero and the other two of the first, second and third strain sensors are configured to sense respecfive strn signals along respective axes which e substantiay in a common plane wth, and are located equidistantly from the neutral axis.19? The apparatus according to daim 17 or 18, compri&ng a fourth strain sensor configured to sense a strain signal along the common direction in the carrier member.20. The apparatus according to claim 19, wherein two of the first to fourth strain sensors are configured to sense respective strain signals along respective axes which e substantiaHy in a first common plane with, and are located equidistantly from, a neutral axis of the carrier member along which strain induced by bending of the carrier member is substantiay zero, and the other two of the first to fourth strain sensors are configured to sense respective strain signals along respective axes which lie substantially in a second common plane with. and are located equidistantly from, the neutral axis, the second common plane being substantially perpendicular to the first common plane.21. The apparatus according to daim 19 or 20, comprising a fifth strain sensor configured to sense a strain signal along the common direction in the carrier member.22. The apparatus according to claim 21, wherein one of the first to fifth strain sensors is configured to sense a strain signal along a neutral axis of the carrier member along which strain induced by bending of the carrier member is substantially zero, two of the first to fifth strain sensors are configured to sense respective strain signals along respective axes which lie substantially in a first common plane with, and are located equidistantly from the neutral axis: and two of the first to fifth strain sensors are configured to sense respective strain signals along respective axes which lie substantially in a second common plane with, and are located equidistantly from, the neutrai axis: the second common plane being substantially perpendicular to the first common plane 23. The apparatus according to any of ciaims 14 to 22, wher&n the carrier member is elongate and has a uniform crosssection, 24. The apparatus according to caim 23, wherein the carrier member has a circthar crosssection, 25. The apparatus according to any of daims 14 to 24, wherefti each of the strain sensors comprises a distributed strain sensor configured to sense a strain signa as a function of position along the carrier member.26. The apparatus accorthng to claim 25, compdsing a pressure sensor configured to measure absolute pressure at a position along the carrier member.27. The apparatus according to any of claims 14 to 26. wherein each of the two or more strain sensors comprises an optical fibre.28. The apparatus according to any of daims 14 to 27, comprising a casing having a pressure transfer arrangement, wherein the casing defines a space around the carrier member and the pressure transfer arrangement is configured to transfer to the carrier member a pressure assodated with an environment external to the casing.29. The apparatus according to claim 25. wherein the pressure transfer arrangement comprises an aperture formed in the casing.30. The apparatus according to claim 29, wherein the aperture is formed in a sidewail of the casing.31 The apparatus according to daini 30, wherein the pressure transfer arrangement comprises a flexible membrane configured to seal the aperture so as to contain a fluid or a g& within the space.32. The apparatus according to claim 30, wherein the pressure transfer arrangement comprises a flexible membrane within the space, the flexibie membrane containing the carrier member and a fluid or a get 33. A cabe compr&ng the apparatus of any of danis 14 to 32.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1110455.1A GB2492095A (en) | 2011-06-21 | 2011-06-21 | Determining pressure profile in an oil or gas well |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1110455.1A GB2492095A (en) | 2011-06-21 | 2011-06-21 | Determining pressure profile in an oil or gas well |
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| GB201110455D0 GB201110455D0 (en) | 2011-08-03 |
| GB2492095A true GB2492095A (en) | 2012-12-26 |
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| WO2015067931A3 (en) * | 2013-11-05 | 2015-09-17 | Optasense Holdings Limited | Fibre optic monitoring of steam injection |
| RU2634490C1 (en) * | 2016-05-12 | 2017-10-31 | Публичное акционерное общество "Уфимское моторостроительное производственное объединение" ПАО "УМПО" | Quasi-distributed fiber-optical information-measuring system |
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|---|---|
| GB201110455D0 (en) | 2011-08-03 |
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