Study On The Fiber Grating Sensing Technology

The information of pressure and temperature in downhole environments offers an important foundation for analysis of oil and gas reserves in different stratum in a well. However the electronic sensing method for these information often suffers electromagnetic interference, and has low measure precision and transmission rate. Also it can but operate for a short term because of high pressure and high temperature in downhole. Since fiber grating sensor can permanently detect the pressure and temperature of different stratum in a well in real time, it has been a breakthrough in solving the above problems.This thesis focuses on the basic theoretical and technical researches on the optical fiber grating sensors, including the sensing mechanism of fiber gratings, the increasing of temperature and pressure sensitivity of optical fiber gratings, the temperature and mechanics characteristic; the sensing principle of optic fiber grating sensor with polymer package, the coating and solidifying technology of polymer. A simple and practical method for the measurement of temperature and pressure aim at the measurement the high temperature and pressure at oil and gas bottom line is proposed, its feasibility is proved through a great deal of experiments.Finally, FBG temperature sensor and FBG pressure sensor are proposed by a elastic cylinder to resist the high temperature and pressure in the oil/gas down-hole. The FBG temperature sensor is tested from 27°C to 196°C and FBG pressure sensor is tested from 0MPa to 44MPa. Fromhe experimental results ,the temperature response sensitivity of FBG temperature is 0.0112nm/°C and presicion is±1°C ,the pressure response sensitivity of FBG pressure is 0.0302nm/MPa and presicion is±0.1MPa.