Distributed temperature sensing technology for oil and gas Wells based on weak reflection Fiber Bragg Grating

For the down-hole distributed temperature measurement problem in the oil industry, the paper uses femtosecond laser direct-written weak reflection fiber Bragg grating (FBG) to construct a down-hole distributed temperature measurement system. The paper analyzes the principle and technical advantages of weak reflection FBG to form a large-scale distributed temperature sensing array; proposes a dual optical path noise suppression method, which effectively eliminates the influence of optical power fluctuations on the measurement results and improves the accuracy and stability of the system temperature measurement; uses self-developed strongly coupled multi-core optical fiber to build a ramp filter, which solves the key problem of fast demodulation of the output of the weak reflection FBG array. The technical problems of fast demodulation of the output of weak FBG arrays were solved by using self-developed strong-coupled multi-core optical fiber. Finally, the developed temperature measurement system was experimentally calibrated and tested in a simulated well, and the test results showed that the accuracy of the system reached 0.5°C with a spatial resolution of 50 cm. The down-hole experimental tests showed that the system has good resistance to high pressure and can operate stably for a long time under high temperature and pressure.