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Fiber-optic Grating Sensing Technology And Its Application On The Measurement Of Oil/gas Down-hole

Posted on:2005-08-26Degree:DoctorType:Dissertation
Country:ChinaCandidate:X D ZhangFull Text:PDF
GTID:1118360152965094Subject:Optics
Abstract/Summary:PDF Full Text Request
This paper focused into the fiber-optic grating sensing technology and its applications on the pressure and temperature measurement for the oil/gas down-hole, including the basic theory and characters of fiber-optic gratings; the sensing mechanism of fiber-optic gratings; the fabrication technologies of sensing fiber-optic gratings; the demodulating and multiplexing technologies of the sensing fiber-optic Bragg gratings; the theoretical and experimental researches on the pressure and temperature sensing systems.Firstly, the recent developments in the technologies of sensing fiber-optic gratings are reviewed. Then, several different fiber-optic sensing technologies, particularly for the oil/gas down-hole are analyzed in a comparing way, and it indicates that the fiber-optic grating sensing method is the best one in all our discussion and has a brilliant application foreground.After analyzing the photosensitivities of the optical fibers and their mechanisms of forming fiber-optic gratings, the mechanical and thermal properties of the fiber-optic gratings are studied in a theoretical way, several instructive conclusions for enhancing the reliability of the fiber-optic grating sensing system are deduced. The polarized coupled mode theory for the fiber-optic gratings is built. The birefringent properties of the fiber grating is also studied.Then, the sensing mechanisms of the fiber-optic Bragg gratings and the long-period fiber gratings are analyzed in a systemic way. This paper focuses on the sensingbirefringent characters of the two kings of gratings, and their applications on the dual and multi-parameters measurements simultaneously.The fabrication technologies particularly for the sensing fiber-optic gratings are studied in this paper. The most applying three kinds of fiber grating sensors such as resisting super-high temperature, high mechanical intensity and enhancing/weakening sensitivities are generalized in comparing with the communicating ones.After analyzing the demodulating technologies and multiplexing technologies for the sensing fiber-optic Bragg gratings, two actual demodulating systems are designed by cooperation, one is an economical demodulating system based on a matched-grating filter tuned by a cantilever and a micro-computer, another is a all digital demodulating system based on a tunable fiber Fabry-Perot filter and a digital signal processor(DSP). For the purpose of using in the birefringent fiber-optic sensing systems, two new demodulating systems working on polarization separating technology are also given, one is based on a polarization-maintaining(PM) tunable fiber Fabry-Perot filter and a DSP, the other is based on a wallaston prism for separating and a charged coupled device(CCD) for detecting.Finally, the pressure and temperature sensing technologies for the oil/gas down-hole application based on fiber-optic Bragg grating sensors are studied. Using finite element analyzing(FEA) theory, the optimization of structured parameters of the side-hole high-birefringent(Hi-Bi) fiber for hydrostatic pressure sensing are deduced. An experimental pressure and temperature sensing system for the oil/gas down-hole application is founded, in which the pressure sensitivities of the pressure fiber grating sensors are enhanced by a thick-wall elastic cylinder, while their temperature sensitivities are weakened by a temperature compensation structure, the fiber Bragg grating sensors shielded temperature from pressure are used only sensing for temperature. Having calibrated by the designed multiplexing and calibrating devices, the sensing system is also tested in a simulated oil down-hole, the primary testing results are obtained.
Keywords/Search Tags:fiber-optic gratings, temperature measurement, pressure measurement, oil/gas down-hole
PDF Full Text Request
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