Research On Vibration Sensing Technology Based On Fiber Bragg Gating

With the rapid development of economy and industry in recent years,the global energy demand is greatly increased.Among the many energy sources,oil is the blood of modern industry and a strategic resource indispensable for the survival and development of the country.Petroleum exploration is in the upstream link of the oil and gas industry chain,and petroleum exploration is the first key link of oil and gas exploitation.Among many petroleum exploration technologies,seismic exploration technology is the most common in petroleum exploration.Most of the seismic exploration technologies currently used use electrical sensors,but in the complex environment of oil exploration,electrical sensors are vulnerable to electromagnetic interference,large size and other defects in the practical application of oil exploration caused many problems.Fiber Bragg Gating(FBG)vibration sensors are expected to be of great value in future oil exploration due to their strong anti-electromagnetic interference capability,small size,good insulation,high temperature resistance,and multiplexing.Therefore,this paper is based on FBG vibration sensors.The main work is as follows:(1)The current status of oil and gas exploration and commonly used sensor types are analyzed through research,several common fiber optic sensors are briefly outlined,and different FBG sensors are briefly introduced as well as an overview summary of their research status.The sensing principle of FBG to stress and temperature is analyzed by FBG coupled mode theory,and the mechanical model of FBG vibration sensor is established.(2)Design of a fiber-optic grating vibration sensor with an equal-strength beam as an elastic structure that can be self-compensated for temperature.The sensitivity is improved by changing the sticky grating method so that the vibration direction is parallel to the fiber grating direction.The working principle of the sensor is analyzed,the inherent frequency and sensitivity of the sensor are derived by equations,the structural parameters of the sensor are optimized,and the good response characteristics are demonstrated experimentally.It is proved that the flat frequency range of the sensor is: 1 Hz～200 Hz,the intrinsic frequency is: 330 Hz,the sensitivity is 149.8 pm/g,and the effect on temperature is only 0.17 pm/°C.(3)A two-dimensional fiber grating vibration sensor with a rod as the elastic structure is proposed.Firstly,the two-dimensional fiber grating vibration sensor is analyzed theoretically and the equations of its intrinsic frequency and sensitivity are derived.Secondly,the optimization simulation of the sensor structure is carried out to determine the final values of each parameter.Finally,the theoretical analysis and simulation were verified by experiments,which showed that the sensor has an intrinsic frequency of 493 Hz,sensitivity of 54 pm/g,and linearity of 99.9% in the x-direction,and an intrinsic frequency of 466 Hz,sensitivity of 5pm/g,and linearity of 97.5% in the y-direction.The dual fiber grating is also used to eliminate the influence of temperature on the vibration signal measurement,with a temperature sensitivity of 0.1 pm/°C.