Study On Key Technique Of Marine Electro-magnetic Vibrator

With the development of marine seismic exploration , marine high-resolution seismic exploration has become the hotspot of current research in the field of seismic exploration. Marine high-resolution seismic exploration is a systemic project, and the rule of high-resolution exploration must be followed by bestir of seismic wave, arrangement of geophones, collection of data, process and explanation of data. As the source of seismic signal, the seismic excitation can give direct influence to the effect of exploration. In marine seismic excitation market , air gun is the most important , but in practical work, air gun wavelet's energy is inconsistent with bandwidth. Vibrator is a new type of seismic source which will not bring the danger and destructibility of dynamite and can bestir repetitious sweeping signal. Vibrator is used broadly in land , but in marine seismic exploration , it is not used now. Electro-magnetic vibrator is a new type of non-destructive vibrator which frequency is adjustable. Its design ideas come from radar and sonar echo ranging technology, and its applications were mainly located in the shallow high-resolution seismic exploration. It not only can enhance the high frequency components by nonlinear sweep in accordance with the pre-determined frequency, but also could achieve the desired amplitude spectrum by variable frequency sweep.Marine electro-magnetic vibrator is not same as marine source, it has high frequency, but the output energy is less, so it need long time sweep to achieve high energy output, we need think nether problems in design :First, the electro- magnetic vibrator has a high working frequency, and vibration in a small Vibration amplitude. The tenet of Vibrator seismic exploration is outputting as much energy through a continuous bestirring in a period of time as that outputted by other sources in an instantaneous time. The realization of this goal needs that Vibrator can output a same sweeping signal in many times continuously, then overlap the reflect signal to eliminate the noise from the exploration background, finally visualize the structure of the stratum. Secondly, the electro-dynamic Vibrator has a comparatively light coupling weight and its output is not forceful, so a best transmission of energy must be realized between Vibrator and water. The depth and resolution of seismic exploration depend heavily on the magnitude of seismic reflecting wave, so under a ideal condition a Vibrator should work in a fully loaded state to output its most power to meet the need of seismic exploration.. In practical work , the coupling with water is better than ground, but because of linearity damp and linearity restoring force, different period of frequency in different exploration target will pick corresponding sweeping parameters to lead a tight couple between Vibrator base-plate and water , which realizes best transmission of limited energy.The dissertation, which was supported by the state 863 project "Study on key technology of marine electro-dynamic vibrator", aims to design a suitable seismic vibrator system. Working on marine vibrator system design , controlling sweep signal and system working in field, and the main work and conclusions are as follows:1.As a main participator, I developed the first marine electro-dynamic Vibrator of our country. The system performance can catch up with the internal world level.2.The composition and structure of present seismic instruments were compared and the advantage of the marine electro-dynamic Vibrator was analyzed. Present seismic instruments have a problem of energy and bandwidth, electro-dynamic Vibrator can solve this problem by adding sweep frequency bandwidth and time , therefore marine electro-dynamic Vibrator system and sweep method is the key technologies, which leads to the focus of this study.3.Analyzing marine electro-dynamic Vibrator configuration , developing controlling cell , power amplifier and excitation, realizing marine electro-dynamic Vibrator system . In marine electro-dynamic Vibrator system , designing the sweeping signal card, based on DDS(Digital Direct Synthesize), is used to output signal with choice magnitude, comparatively wide frequency band and random waveform to meet the need of different kind of seismic explorations, studying configuration of excitation, designing power amplifier based on excitation.4.Study coupling of excitation with water by marine electro-dynamic Vibrator excitation and the difference of water and ground, because of water's specialty , considering excitation contacting well with water, emulating excitation, getting its system equation , analyzing vibration instances of system by simple harmonic wave power , gained four working state such as anti-main resonance vibration based on system respond in every frequency segment, studying the influence of system resonance frequency and respond signal range by excitation quality, gained energy absorbability changing curve with frequency in same character factor and differ character factor, at last studying non-linearity of excitation, gained the influence of system stability by inspirit signal's frequency and range.5.Developing marine vibrator system incepting cell, developing MEMS seismic accelerometer, bringing forward problems based on design of accelerometer, reforming accelerometer by noises interference rejection , dynamic revising , improving linearity and so on, introducing EMC design of accelerometer and gained results, developing accelerometer frequency-domain integral based on accelerometer physical speciality and base plate displacement.6.Vibrator sweep mode was studied, basing on ground vibrator sweep mode, bringing forward pseudo-random encoding sweeps first time, investigating pseudo-random encoding character , and sampled pseudo-random encoding , numerical modeling this sweep mode, gained auto-correlation of pseudo-random encoding, validating this sweep mode ; gained marine vibrator short time sweep mode , developing short time sweep mode , gained emulation result , numerical modeling short time sweep mode , analyzing auto-correlation results , processing vibrator experiment based by emulation , gained correlation results , validating this sweep mode .7.Instruments experiments in lab and field were carried out. Instruments assembly were carried out. Excitation was airproofed, target test was carried out , at last instruments was test in trough. Vibrator seismic exploration computer emulation was carried out. Emulation gave method for vibrator experiments in field. The geographical position, natural and cultural condition and the noise of the test site is analized.Output power of excitation and base plate signal were measured , the result is content, vibrator seismic section chart was gained by lots of sweep experiments.The key innovative points are as follows:1.Aiming at marine seismic exploration ,marine electro-magnetic vibrator was developed based on idea of electro-magnetic vibrator2.Aiming at working specialty , pseudo-random encoding sweeps was bringed forward based on vibrator sweep mode.3.Aiming at marine vibrator , marine electro-magnetic vibrator short time sweep mode was designed.4. Excitation-water coupling module was design based on water speciality, non-linearity analyzing of excitation was carried out, excitation configuration was designed , excitation that fitting base plate and water coupling was developed.