Downhole optical fiber distributed flow monitoring system

Abstract

A downhole optical fiber distributed flow monitoring system, which includes an ultra-narrow linewidth laser, the laser enters a first circulator after passing through an acousto-optic modulator, a first optical amplifier and an ultra-narrow bandwidth first optical filter, and then injects into a sensing fiber , the back-Rayleigh scattered light in the sensing fiber returns to the first circulator and enters the ultra-narrow linewidth second optical filter through the second optical amplifier, and the back-Rayleigh scattered light passes through the polarization controller and enters the After the second circulator, it enters the 3×3 coupler, and splits the beam into the first Faraday rotating mirror, the second Faraday rotating mirror and the fourth photodetector; the fourth photodetector sends the electrical signal to the fiber for distributed flow demodulation System; the back-scattered light enters the second photodetector, the third photodetector and the second circulator through a 3×3 coupler, and the second circulator outputs an optical signal to the first photodetector; the first light The electrical signals of the detector, the second photodetector and the third photodetector simultaneously reach the optical fiber distributed traffic demodulation system.

Description

technical field [0001] The invention relates to the field of optical fiber sensors, in particular to the field of non-immersed downhole optical fiber distributed flow monitoring. Background technique [0002] In the field of oil field, flow measurement can provide extremely important parameters for dynamic monitoring of production and well logging, and oil production and transmission characteristics. Downhole has very harsh environments such as high temperature and high pressure. Traditional electronic flowmeters are prone to failure. Some fiber optic turbines and vortex flowmeters are immersion technologies (such as the invention patent of "Distributed Optical Fiber Flow Measurement Device and Method"), which break the original system flow field and have limitations in measurement results. [0003] The test principle of the invention patent of "Distributed Optical Fiber Flow Measurement Device and Method" is as follows: [0004] By using a sensing optical fiber to connect ...

AI Technical Summary

Problems solved by technology

[0007] (2) Using the scattering principle, the signal-to-noise ratio of the demodulated signal is low, and it is difficult to measure accurately at low flow rates

Its system adopts the principle of optical fiber scattering, resulting in a low signal-to-noise ratio of the system. The scheme in its patent can realize the acoustic wave signal with a relatively large sound pressure directly acting on the optical fiber, and does not have the ability to detect the flow information in the downhole pipe.

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