Research On Optical Fiber Vibration Sensing Technology In Micro Seismic

With the development of unconventional oil and gas in oil field in china.Micro seismic monitoring technology has become a reliable basis for judging the formation and development trend of fracturing fractures.The result of monitoring provides an important guarantee for improving the level of shale gas extraction and unconventional oil and gas recovery.At the same time,micro seismic monitoring is of great significance for the prediction of the risk structure of the mine,the engineering structure and the stability of the geological structure.The detector as the key device of micro seismic monitoring technology,its performance is very important.Compared with electric type sensors,optical fiber vibration sensor with high sensitivity,wide bandwidth,immunity to electromagnetic interference,easy-to-large-scale networking and so on.The main research of this paper is the optical fiber vibration acceleration sensor in the micro seismic monitoring technology.The main work of this paper is as follows:1.The development trend of the micro seismic monitoring technology is studied,and the basic principle of the technique is analyzed.On this basis,the theory and method of FBG vibration acceleration sensor used in micro seismic monitoring technology are presented.The development and research status of fiber optic vibration sensor are summarized.The FBG strain and temperature sensing model and the FBG coupled mode theory are studied.The mechanical model of fiber optic accelerometer is improved,and the response characteristic function is analyzed.2.An acceleration vibration sensor based on the structure of the compliant cylinder is studied and designed,including the basic principle of the sensor,packaging production method and its dynamic characteristics.Experimental results show that the natural frequency of the sensor is 400 Hz,the frequency range is 30~300Hz,the sensitivity is 42.7pm/G,the linearity is 0.999.On this basis,the research and design of a FBGs vibration acceleration sensor based on the push pull structure,its natural frequency is 610 Hz,frequency range is 40~480Hz,the sensitivity is 50pm/G.3.A two dimensional vibration acceleration sensor based on FBGs is developed,which is based on the hinge structure.The stress and strain theory model of the sensor is established,and the finite element method is used to simulate the model.Experimental results show that the resonant frequency of the sensor in X/Y direction respectively 1050 Hz ? 1060 Hz,frequency range for 50~900Hz and sensitivity of the sensor respectively for 13.1pm/G 12.0pm/G.Theoretical analysis of the sensitivity of the sensor can reach 20pm/G.4.An optical fiber vibration sensor based on MZI structure is studied for borehole micro seismic detection.The strain characteristics of the sensor were tested,the experimental results show that the strain sensitivity of the sensors are 2.6pm/?? and 0.0027dB/?? in the strain range of 0~1920??,the linearity is 0.9971.