| Oil and natural gas are important energy sources for human development.Its scientific exploration and rational development are of great significance to the development of the national economy.However,after many years of exploration,some large structural oilfields with shallow burial and simple geological conditions have been discovered.The current exploration task is to search for some small structural oilfields with deep burial and complicated geological conditions.The performance requirement for geophone is gradually improved,and the difficulty of exploration is increasing.On side,the signal pickup in the existing cross-well seismic exploration systems mainly rely on electromagnetic geophone,which is vulnerable to electromagnetic interference.Meanwhile,it has the shortcomings of high temperature resistance and is not conducive to network distribution,which has become the bottleneck of cross-well seismic exploration technology.For another,in the exploration of oil and gas resources,the frequency band of the excitation seismic wave signals is very wide,and the high-frequency component is the key to improve the resolution of exploration.However,due to the low-pass filtering of the ground,the high-frequency component is attenuated seriously.The high-frequency and high-sensitivity geophone is the first step to improve the resolution of exploration.In recent years,Fiber Bragg Grating?FBG?has been applied in many fields owing to its advantages including non-electromagnetic interference,high temperature resistance and easy networking.The application of FBG sensors to seismic wave detection can make up for these shortcomings of traditional detection methods and has important research value.This paper is based on the application background of seismic wave vibration detection in oil and gas exploration.Based on the sensing principle of FBG,an FBG-sensing two-dimensional acceleration sensor based on multi-axis flexible hinge and a FBG-sensing accelerometer based on diaphragm and diamond structure are proposed for the vibration detection of seismic wave in wells with the high temperature environment.The sensing characteristics and high temperature resistance of the two sensors have been studied in depth.The main work and research results are as follows:1.The conventional seismic geophones in seismic exploration are summarized in this paper,the principles and characteristics of all kinds of geophones are sum up.The difficult problems in the exploration field are presented.And the application status of optical fiber seismic sensors and the research status of optical fiber accelerometer are summarized,and the research works are proposed.2.Starting from the formation mechanism and propagation theory of seismic wave,the factors affecting the amplitude and velocity of seismic reflection wave are analyzed and studied in detail.And the frequency requirements of the sensor in this paper are derived from the spectrum characteristics of seismic wave and the relationship between seismic exploration resolution and frequency.3.In view of the seismic wave vibration detection of underground high temperature environment in oil and gas exploration,and the weak high-frequency signal of seismic reflection wave caused by the low-pass filtering of the earth.A high frequency and high sensitivity FBG accelerometer with temperature self-compensation was designed.The strain model and vibration model of the sensor are established.Then the sensor structure parameters are determined by numerical analysis and finite element simulation.Finally,the sensing characteristics of the sensor are tested.The study verified the correctness of the theoretical model and simulation analysis.The experimental results show that the first natural frequency of the sensor is about 681.4 Hz,which is basically consistent with the theoretical calculation value?696.7 Hz?and the finite element simulation result?686.04 Hz?.In the range of 0Hz-500Hz,the sensitivity of the sensor has a good linear relationship with the frequency of the vibration signal.The sensitivity can be expressed as?0.066f+63.164?pm/g at different frequencies.The transverse interference of the sensor is less than 5%,and it has a good temperature self-compensation effect.4.Aiming at the detection of multi-dimensional seismic wave signals in oil and gas exploration,an FBG-sensing two-dimensional vibration sensor based on multi-axis flexible hinge was designed.The structural model and theoretical model of the sensor are established.The numerical analysis and finite element simulation of the sensing model were carried out.Two different sizes of sensors were identified.Finally,the sensing characteristics were studied by experiments.The experimental results are in good agreement with the theoretical calculations and simulation results.The experimental results show that the stable operating frequency band of the sensor Max is 5Hz-170Hz,the acceleration sensitivity is up to 220 pm/g,the cross interference in the two measurement directions is less than 4%,and the resonant frequency is 280 Hz.The stable working frequency band of the sensor Min is 20Hz-600 Hz,The acceleration sensitivity is 40 pm/g,the cross interference in the two measurement directions is less than 3.5%,and the resonance frequency is 815 Hz.5.The temperature experiment system was designed to study the high temperature resistance characteristics and the self-compensation characteristics for the high temperature of FBG sensors.The acceleration resolution of each FBG sensor is 4.5×10-4g?Max-sensor?,2.5×10-3g?Min-sensor?,1.04×10-3g1.6×10-3g?diaphragm FBG sensor?,and the dynamic range can reach 86 dB.And the impact vibration experiment system is set up.The FBG sensors and the conventional moving coil detectors and piezoelectric sensors are used simultaneously to collect the impact signal,and the amplitude and frequency characteristics of each vibration sensor are compared and analyzed.The experimental results show that the FBG sensors are free from electromagnetic interference and can accurately respond to the amplitude of impact vibration signals.The acceleration calculated by FBG wavelength variation are basically consistent with the measured value by piezoelectric acceleration. |
PDF Full Text Request