REFLECTOMETRIC VIBRATION MEASUREMENT SYSTEM AND RELATIVE METHOD FOR MONITORING MULTIPHASE FLOWS

Abstract

Reflectometric vibration measurement system to monitor multiphase flows in production wells or pipelines using multimode fibers comprising: a sensing multimode optical fiber; an optical source with at least one fiber output port, which generates optical pulses which are to be sent to the sensing fiber; an optical receiver with at least one multimode fiber input port; an optical device with at least 3 multimode fiber ports, in which one port is connected to the optical source, one port to the optical receiver, and one port to the sensing multimode fiber; a system for processing the output signals from the optical receiver, further comprising more than one spatial mode filter. A process for reconfiguring an optical reflectometry system which has already been installed in a monitoring structure is also described.

Claims

1. Reflectometric vibration measurement system to monitor multiphase flows by multimode fibers comprising: a sensing multimode optical fiber; an optical source with at least one fiber output port, which generates optical pulses which are to be sent to the sensing multimode optical fiber; an optical receiver with at least one multimode fiber input port; an optical device with at least 3 multimode fiber ports, in which one multimode fiber port is connected to said optical source, one multimode fiber port is connected to said optical receiver, and one multimode fiber port is connected to said sensing multimode optical fiber; a system for processing the output signals from said optical receiver, further comprising more than one spatial mode filter.

2. System according to claim 1, wherein said optical receiver comprises at least one photodiode.

3. System according to claim 2, wherein said optical receiver also includes a fiber with few spatial modes connected between said receiver input and said photodiode.

4. System according to claim 3, wherein the guided modes of fiber with few spatial modes are, counting the degenerate modes, fewer than 17.

5. System according to claim 1, wherein said optical receiver comprises at least two of said photodiodes.

6. System according to claim 5, wherein said optical receiver also includes a multimode fiber power splitter, wherein said multimode fiber power splitter has one input port and a number of output ports substantially equal to the number of said photodiodes, said input port of said multimode fiber power splitter being connected to said input port of said receiver and each output port of said multimode fiber power splitter being connected to each said photodiode by means of a monomode fiber section.

7. System according to claim 6, wherein said monomode fibers are connected to said multimode fibers by means of an adiabatic mode converter.

8. System according to claim 5, wherein said optical receiver also includes a photonic lantern with a multimodal input and a number of monomode fiber outputs substantially equal to the number of said photodiodes, said input of said photonic lantern being connected to said input of said optical receiver and each said monomode output of said photonic lantern being connected to each said photodiode.

9. System according to claim 1, wherein said optical device with at least three said multimode fiber ports is selected from: a directional coupler; power coupler/splitter; a circulator; an optical switch.

10. System according to claim 1, wherein said optical source comprises: a high coherence laser that emits light pulses to the output port of said optical source; a high coherence laser, which generates continuous light, and an optical modulator connected to said laser, where said optical modulator generates optical pulses that are sent to the output port of said optical source.

11. System, heterodyne version, according to claim 1 where: said optical source has two output ports, and a first said output port emits a modulated optical signal at a first frequency and a second said output port emits an optical signal at a second frequency; said optical receiver has two input ports one of which is monomode and the other multimode, where said multimode port is connected by multimode fiber to said optical device with at least three multimode fiber ports and said monomode port is connected to said second port of said optical source.

12. System according to claim 11, wherein the said optical receiver also includes a polarization/coupler beam splitter with two inputs and two outputs and two photodetectors, wherein said polarization beam splitter comprising: a first input connected to said multimode port of said optical receiver and a second input connected to said monomode input of said optical receiver; said two outputs coupled to each of said two photodetectors; said two inputs equipped with optical systems capable of collimating the input optical beams; a collimator of said second monomode input dimensioned to generate a collimated beam that substantially overlaps the fundamental mode of said first multimode input.

13. System according to claim 12, wherein said photodetectors are segmented area photodiodes, and wherein said collimator of said monomode input of said coupler/splitter is dimensioned to generate a collimated beam that illuminates said segmented area photodiodes substantially uniformly.

14. System according to claim 13, wherein said photodiodes have at least two separate measurement segments.

15. System according to claim 13, where a few mode fiber is interposed between said multimode input of said optical receiver and the a relative input of said polarization beam splitter, wherein said few-mode fiber is not monomode.

16. System according to claim 15, wherein the guided modes of said few mode fibers with few spatial modes are, also counting the degenerate modes, fewer than 17.

17. System according to claim 11, wherein said optical receiver includes: a spatial demultiplexer with a multimode input and at least two monomode outputs, wherein said multimode input is connected to said multimode input of said optical receiver; an optical splitter with one input and a number of outputs equal to said monomode outputs of said spatial demultiplexer, wherein said input is connected to said monomode input of said optical receiver; a number of photodetectors equal to the number of said monomode outputs of said spatial demultiplexer; a number of optical couplers equal to the number of said monomode outputs from said spatial demultiplexer, where each said coupler combines each said monomode output of said demultiplexer with a different output from said optical splitter and directs the combined light to one of said photodetectors.

18. System according to claim 17 wherein said spatial demultiplexer includes a multimode fiber power splitter, wherein each said multimode output is connected to a monomode fiber.

19. System according to claim 18, wherein said monomode fibers are connected to said multimode outputs by means of adiabatic mode converters.

20. System according to claim 24 wherein said spatial demultiplexer is a photonic lantern.

21. System according to claim 11, wherein said optical source includes a laser that emits continuous light and a 3-port acoustic-optical modulator, wherein the input port of said modulator is connected to the laser and the two output ports of said modulator are the output ports of said optical source, and wherein said modulator is configured to send short pulses to a first port and substantially longer pulses to the second port, wherein said second port is connected to said monomode port of said optical receiver.

22. Method for measurement of vibration along a structure by means of a system according to claim 1 comprising: finding said sensing multimode optical fiber installed along the structure to be monitored; delivering a pulse of light to said sensing multimode optical fiber; selecting more than one speckle of backscattered light from said sensing multimode optical fiber due to Rayleigh scattering induced by the launched pulse; generating a signal indicative of the vibrations along the monitored structure from the multiple speckle collected from said sensing multimode optical fiber.

23. Method according to claim 22 also comprising the use of a multimode fiber to convey the backscattered light towards said optical receiver.

24. Method according to claim 22 wherein in order to collect the multiple speckles there is used: either a segmented area photodiode;. or a multimode fiber power splitter with at least two output ports, where each is connected to a photodiode; or a photonic lantern.

25. Method for the measurement of vibration along a structure by means of a system, heterodyne version, according to claim 11 comprising: dividing the light produced bye said optical source into two different paths; modulating the light in the first path to form the optical pulse to be delivered to said sensing multimode optical fiber, while the light in the second optical path has an optical frequency different from that in the first; the light of the second path is combined with each of the multiple speckles collected from said sensing multimode optical fiber; detecting only the signal at a frequency equal to the difference between the frequency of light in said first path and that of the light in said second path.

26. Method for reconfiguring an optical reflectometry system already installed in a structure to be monitored, comprising a sensing multimode optical fiber installed along said structure, a source for delivering pulses to said sensing multimode optical fiber, an optical receiver for receiving backscattered light from said sensing multimode optical fiber due to Rayleigh scattering induced by the delivered pulse, characterized in that it comprises placing a device for spatially separating multiple speckles of the light backscattered due to Rayleigh scattering between said sensing multimode optical fiber and said optical receiver.

27. Process according to claim 26 wherein the device for spatially separating multiple speckles comprises: either a multimode fiber power splitter, in which each output is connected to a photodiode; or a multimode fiber coupled to a segmented area photodiode; or a photonic lantern, in which each output is connected to a photodiode.

28. Process according to claim 26 further comprising also generating a signal indicative of the vibration along the monitored structure by means of an analysis system based on multiple recorded speckles.

Description

EXAMPLE 1

[0081] The diagram is illustrated in FIG. 1.

[0082] A high coherence laser 101 with an emission wavelength lying typically between 800 and 1650 nm (preferably between 1300 and 1650 nm) controlled by an electrical signals generator (pulse generator) 102, emits optical pulses typically lasting 3-200 ns (preferably 20-100 ns) with a repetition frequency of approximately at least 1 kHz which enter an input port of a 3 dB directional coupler (multimode directional coupler) 103 connected to the multimode measurement fiber multimode fiber) 104 through an optical connector 105. The signal backscattered from the installed multimode fiber enters coupler 103 via optical connector 105 and a fraction of the signal enters the second coupler 106, all made using multimode fibers of preferably the same type as the measurement multimode fiber to reduce coupling losses and spurious reflections. 2 receivers 108 with a single mode tail (single mode fiber) 107 which measure two different portions of the multimode speckle are connected to the output of coupler 106. Downstream from the two photodiodes (PD) 108 connected to generator 102 there is a board 109 for processing the backscattered optical signals and the control signal from the electrical signals generator (electrical signal processing).

EXAMPLE 2

[0083] The diagram shown in FIG. 2 is similar to that in FIG. 1 in which coupler 103 is replaced by a 3 port optical circulator (multimode optical circulator) 201, with insertion losses of typically 1 dB and a directivity of more than 40 dB,

EXAMPLE 3

[0084] The diagram shown in FIG. 3 is similar to that in FIG. 1 in which the multimode outputs from coupler 106 are connected to single mode patch cord 107 by means of tapers 301 (see FIG. 6). The tapers may be provided in 2 ways: [0085] i) Limited intensity discharges are made after the fusion splicing of the single mode fibers with the multimode fiber in order to facilitate the diffusion of doping agents from the core to the cladding. [0086] ii) A very short length of fiber having few modes which has geometric characteristics and refractive index differences between the core and cladding, intermediate between those of the single mode fiber and the multimode fiber is placed in between.

[0087] Both solution i) and ii) make it possible to reduce coupling losses.

EXAMPLE 4

[0088] The diagram illustrated in FIG. 4 is similar to that in FIG. 2 with the insertion of two tapers 301.

EXAMPLE 5

[0089] The diagram illustrated in FIG. 5 is similar to that in FIG. 2 with the insertion of short sections of few mode fibers, preferably 2, in front of the photodiodes.

EXAMPLE 6

[0090] The diagram illustrated in FIG. 6 is similar to that in FIG. 1 with the insertion of an acoustic-optical modulator (modulator) to produce a coherent receiver system which is possibly also sensitive to polarization.

EXAMPLE 7

[0091] The diagram illustrated in FIG. 7 is similar to that in FIG. 1 with the insertion of a segmented area photodiode (segmented area photodiode) (2 or more independent sensitive areas) in the reception portion so as to produce an array of 2 or more receivers, each of which are sensitive to one speckle. The segmented area photodiode is sensitive to wavelengths between 800 and 1700 nm.