Interferometric Fiber Optic Sensors And Their Quasi-distributed Sensing Research

High-resolution Fiber-optic Seismic System is an advanced seismic wave detection system based on fiber-optic geophone array,which is used to provide real-time detection on oil and gas reservoir structure and migration with high precision.HR-FOSS is the research highlight in several petroleum exploration countries,as well as the tendency and direction of oil exploring on land and sea in the next few years.It will gradually replace the existing traditional technology,becoming ancillary equipment of oil exploration and production.This paper developed a small-scale HR-FOSS prototype system,laying the foundation of technology and process for the future commercial high resolution fiber optic oil and gas layer monitoring system.The technical requirements of small-scale HR-FOSS are the same as the large one,except that the small-scale HR-FOSS has only 64 sensors.It has 6 parts,including multi-wavelength laser light source,optical modulation and demodulation part,optical sensing part,electrical data processing part,the control computer and system power part.In the dissertation,optical modulation and demodulation part and optical sensing part are designed and developed.A discrete phase modulation and demodulation method and a wavelength division multiplexing technology are proposed.This paper also studies the difference between the traditional oil data and the output data of the system,and compiles a large-scale dynamic reading and writing database used to regulate the data format.In the project,a discrete phase modulation and demodulation method is used.Three output signals of interference light are received to calculate the optical phase change caused by the vibration signal.The phase of the optical beam has a good agreement with the vibration signal.Wave division multiplexing(WDM)and time-division multiplexing(TDM)technology are used in the system,the output signals are dislocation coupled while de-multiplexing in order to reduce the system crosstalk.64 geophones and the sensing network are tested during the development of the system.It shows that:the sensitivity of the detector is 1028rad/g@60Hz,the linearity is 0.997,the resonant frequency is 300Hz-350Hz which is higher than the working frequency.Except 4 detectors,the start-up times of the others are the same.The noise of the optical fiber sensing system is about 50ng/?Hz@200Hz,time division multiplexing crosstalk are less than-76dB,wavelength division multiplexing crosstalk are less than-59dB.Experiments show that the system can achieve seismic wave detection,but also has the advantages of high detection sensitivity,small environmental noise and small system crosstalk.