OPTICAL FIBER VIBRATION MEASUREMENT SYSTEM IN MULTIPHASE FLOWS WITH RELATED METHOD TO MONITOR MULTIPHASE FLOWS

Abstract

A vibration measurement system and relative method to monitor multiphase flows in extraction wells or conduits, by analysis of backscattered multimode fiber light comprising: • a sensing multimode optical fiber; • an optical source, containing a high coherence laser that emits optical pulses to be sent in said sensing fiber; • a photonic lantern with 3 or more single-mode optical fiber ports and one multimode fiber port that is connected to the sensing multimode fiber; • an optical receiver, comprising a number of photodetectors equal to the number of the single-mode optical fiber ports of said photonic lantern minus 1, wherein each photodetector is connected to each of said single-mode ports; • a system for processing output signals from the optical receiver, the optical source being connected to one of the single-mode optical fiber ports and the other single-mode fibers being connected to the optical receiver. A process is also described for reconfiguring an optical reflectometry system already installed at a facility to be monitored.

Claims

1. Reflectometric system for vibration measurement to monitor multiphase flows by analysis of the light backscattered by multimode fiber comprising: a sensing multimode optical fiber; an optical source, containing a high coherence laser that emits optical pulses to be sent in said sensing multimode optical fiber; a photonic lantern with 3 or more single-mode optical fiber ports, and one multimode fiber port connected to said sensing multimode optical fiber; an optical receiver, comprising a number of photodetectors equal to the number of said single-mode optical fiber ports of said photonic lantern minus 1, wherein each said photodetector is connected to each of said single-mode optical fiber ports; a system for processing output signals from said optical receiver, wherein, said optical source is connected to one of said single-mode optical fiber ports and other single-mode fibers are connected to said optical receiver.

2. System according to claim 1, wherein: said optical source has two output ports, emitting at a first optical port an optical signal at a first frequency and at a second optical port an optical signal at a second frequency, different from said first frequency; said optical receiver includes a light splitter with 1 input and a number of outputs equal to the number of photodetectors, and also includes a number of optical combiners equal to the number of photodetectors: the input port of said light splitter is connected to said second port of said optical source; each output port of said splitter is connected to each said combiner; each said combiner is connected to each of said photodetectors.

3. Method for vibration measurements 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; launching an optical signal in said sensing multimode optical fiber; selecting more than one speckle of the light backscattered from said sensing multimode optical fiber by Rayleigh scattering induced by the launched pulse; generating from the multiple speckles collected from said sensing multimode optical fiber a signal indicative of the vibrations along the monitored structure.

4. Method according to claim 3 further comprising also the use of said sensing multimode optical fiber to convey the backscattered light towards said optical receiver.

5. A method for reconfiguring said reflectometric system, according to claim 1, already installed at a facility to be monitored, comprising said sensing multimode optical fiber installed along said structure, said optical source for launching pulses in said sensing multimode optical fiber, said optical receiver for receiving the light backscattered by said sensing multimode optical fiber by Rayleigh scattering induced by the impulse launched, characterized in that it comprises the interposition between said sensing multimode optical fiber and said optical receiver of said photonic lantern to spatially separate multiple speckles of the light backscattered by Rayleigh scattering.

6. Process according to claim 5 comprising also generating a signal indicative of the vibration along the monitored structure, by means of an analysis system based on the multiple speckles recorded.

Description

EXAMPLE 1

[0042] The diagram is shown in FIG. 1.

[0043] A high coherence laser 101 with emission wavelength typically comprised between 800 and 1650 nm (preferably between 1300 and 1650 nm), controlled by an external pulse generator 102, emits optical pulses typically lasting 3-200 ns (preferably 20-100 ns) with repetition frequency of at least 1 kHz, is coupled to one of the input ports of a “photonic lantern”; the other input ports of the photonic lantern are connected to 1 or more photodiodes (PDs), which give out electrical signals proportional to the respective optical input speckles. The multimode output port of the photonic lantern is connected to the multimode sensing fiber.