Research On Tree-Shaped Optical Fiber Temperature And Pressure Sensing System

Temperature and pressure are vital measurement parameters that need to be obtained in the industrial field.Such as in the oil and gas exploration sector,real-time online monitoring of downhole temperature and pressure fluctuations is of great importance for optimizing oil and gas production and guaranteeing the security of downhole production sites.In the downhole environment,due the circumstances of high temperature,high pressure and corrosion,it is difficult for traditional electronic sensors to operate stably for a long time,while optical fiber sensors can adapt well to this harsh environment due to high temperature resistance,high pressure resistance and corrosion resistance,and have higher accuracy and smaller size.In a word,optical fiber sensor has significant advantages in downhole applications.In order to satisfy the requirements of high-precision monitoring of multi-point and multi-parameter oil and gas downhole pressure and temperature,a tree-shaped optical fiber temperature and pressure sensing system is proposed,including the development of downhole optical fiber temperature and pressure sensor,the light source design and system feasibility study of the tree-shaped optical fiber sensing system.The main research contents of this thesis are as follows:(1)Aiming at the high-precision measurement requirements of downhole pressure and temperature dual parameters,an optical fiber temperature and pressure integrated sensor cascading sensitized Fabry-Perot Interferometer and Fiber Bragg Grating is produced.The test reveals the packaged sensor’s temperature sensitivity in the range of 0～250 ℃ is 10.04 pm/℃,its temperature accuracy in the range of 0～100 ℃ is 0.6%F.S,and at room temperature its pressure sensitivity in the range of 0～15 MPa is 187.3 pm/MPa,its pressure accuracy is 0.175%F.S,and in condition of hightemperature ranging from 55℃ to 200℃ and high-pressure ranging from OMPa to 10MPa,its maximum measurement error is 0.042 MPa,which concludes that the sensor enables high-precision calibration of pressure measurement over a wide temperature range.(2)Aiming at the problem of multi-point tree multiplexing of FPI sensors,a pulsed tree-shaped tunable fiber ring cavity laser is designed to realize the detection of timedivision multiplexed spectral signals in the tree structure of FPI sensors.The study of pulsed tree-shaped tunable fiber ring cavity laser shows that the laser has a side-mode suppression ratio of approximately 50 dB,with 3 dB bandwidth of approximately 0.0842 nm,and capable of achieving 1530～1614 nm(84 nm)tunable laser output in a wide-ranging wavelength range.(3)Aiming at the needs of multi-point and multi-parameter downhole testing,a treeshaped fiber temperature and pressure sensing system is designed and built based on the pulsed tree-shaped tunable fiber ring cavity laser built above as the adjustable wavelength pulse light source.Through experiments,the tree-shaped fiber temperature and pressure sensing system realizes tree multiplexing of two FPI sensors,and there is no crosstalk between the spectra of the two sensors,resulting in accurate acquisition of their spectra.According to the spectral test of the single FPI sensor,it proves that the system also has good stability and can realize the demodulation measurement of external pressure and other parameters through subsequent signal processing.