Research On Low Frequency Geophone With Fiber Grating In Wells

In recent years,with the rapid economic growth in China,the demand for oil and natural gas is also increasing day by day,and the seismic exploration technology in Wells for oil and natural gas exploitation is also becoming more mature,among which the low-frequency seismic detection technology for deep exploration has made great progress.Low-frequency seismic detection is of great significance in the field of seismic exploration.The existing low-frequency seismic exploration technology in Wells mostly relies on the electric geophone,but it has many inevitable defects in practical application,such as easy to be interfered by electromagnetic waves and low temperature resistance.The low-frequency Fiber Bragg Grating(FBG)geophone in Wells have become one of the most widely used geophone in the existing seismic exploration technology due to its strong anti-electromagnetic interference ability,high sensitivity,good electrical insulation,safety and reliability,and multiplex.Therefore,this paper focuses on the research of low-frequency geophone in FBG Wells,and the main work is as follows:(1)The sensing principle and research status of low-frequency geophone in FBG Wells were investigated and analyzed.Based on the strain sensing principle of FBG and the general mechanical model of geophone,the FBG geophone model was established.(2)A Optical Fiber Grating Geophone Assisted With a Hollow Triangle Beam is studied and designed,and its geophone characteristics are theoretically deduced,and its structural parameters and packaging are optimized through simulation.The experimental results show that the geophone has a natural frequency of 61 Hz,a good dynamic response in the range of 0.6 Hz to 50 Hz,a transverse interference degree of 2.8 % in the X direction and 4.6 % in the Y direction,and a sensitivity of 120.12 pm/g.The average linear fitting degree in the repeated experiment is 99.8 %.(3)A three-component FBG geophone was designed.According to the acceleration detection theory,the correlation formula of its natural frequency and sensitivity was theoretically analyzed and derived.The final parameters of the geophone were determined through simulation optimization.The flat region of the geophone is 0.6-50 Hz,the first-order natural frequency of the geophone is 56 Hz,the second-order natural frequency is 59 Hz,and the third-order natural frequency is 63 Hz.The linear sensitivity of the three directions is 284.47 pm/g,218.25 pm/g,249.67pm/g,respectively.The transverse anti-interference degree in three directions is less than 5 %.