Key Technology And Experiment Of Metal Mine Seismic Exploration Based On Vibroseis

The metal mine seismic exploration technology is a new developing and graduallyimproving metallic ore exploration method. Over the years, traditional methods suchas gravity, electric and magnetic methods are the main methods for metallic mineralexploration, but the ability and precision of exploration dramatically reduces sharplywith the increase of exploration depth. The vertical resolution of gravity and magneticexploration methods is low, and the field intensity is decaying with inverselyproportional to the square of distance. There is serious lack in detecting deep metalore body. The exploration depth of DC electric method is too shallow and theresolution of electromagnetic method in deep exploration is low. Currently, the metalmining depth has reached one kilometer around, and because of the characteristics ofhigh precision, large detecting depth, high resolution and reliable detection result ofseismic method, it has become the most promising technology in deep exploration ofmineral resources, and especially made up for the lack of heavy magneto-electricmethod in search for deep concealed deposits.Currently, we mostly adopt explosive as the seismic source in metal mineralseismic exploration, but explosive is dangerous and destructive. Compared withexplosive, the security of vibroseis is greatly improved, and the excitation waveformis controlled, so it can improve the resolution of seismic signal, and control thegeneration of random disturbance with the help of related technologies. Earlydeveloped vibroseis is mainly used for oil-gas exploration, and adopts hydraulic drivemode. Its frequency range is narrow, and the output force is large and it’s in the formof vibrator vehicle. And metal mine is mostly located in mountainous areas, thesurface and topography of which is complex. Hydraulic source is relatively heavy sothat it is difficult to develop work, and its frequency is restricted. Therefore, this paper presented portable vibroseis instead of explosive andhydraulic source excites seismic waves in seismic exploration. Impact rammer sourcepowered by gasoline adopts the internal combustion engine. With the characteristicsof portable carry, simple operation, safe and reliable, portable vibroseis has greatdevelopment potential in seismic exploration. To solve the related interferenceproblems caused by single vibration frequency of impact rammer source, pseudorandom coding method is adopted to make optimization design on the impact rammersource signals in this paper. The output energy of electromagnetic drive vibroseis issmall, but because of the wide frequency band and high dominant frequency ofexcitation signals, the resolution of seismic exploration is improved, and the scanningsignal parameters can be identified according to the practical geological situation offield and it is preferably applied in shallow seismic exploration. The interference withseismic wavelet caused by the single vibration frequency of impact rammer sourceseriously restricts the resolution of exploration, so we will do further study on theelectromagnetic drive vibroseis as effictive supplement for impact rammer source inshallow high resolution seismic exploration.Combining with National “863” Plan Project “Key Technology and Equipment ofMetal Mine Seismic Exploration”(project number:2007AA060801) and PublicWelfare Scientific Research Special of Ministry of Land and Resources “Cable-freeSelf-location Seismic Prospecting System Development"(project number:201011081), the research on seismic exploration technology based on portablevibroseis is presented in this paper, which is carried on in several aspects such asseismic wave excitation, receiving and acquisition, data processing and the field testapplication, and aimed at achieving high resolution seismic exploration. Our mainwork includes several aspects as follows:1）According to the problem that the interference with correlation wavelet caused bythe periodicity of continuous impact signal of impact rammer source in relatedprocessing reduces the resolution in seismic exploration, we adopted pseudo randomcoding method to design impact rammer source signals, this method makes the ratioof mainlobe to sidelobe of seismic wavelet increased, and at the same time, the ratioof mainlobe to related interference is correspondingly increased, the interference withseismic wavelet produced by single vibration frequency of impact rammer source canbe effectively decreased, and the resolution of seismic exploration is improved. 2）According to the problem that the autocorrelation function sidelobe of sweep signalusing linear scan by electromagnetic drive vibroseis makes the weak signals difficultto be found in seismic section and high resolution seismic exploration unable torealize, we used the amplitude taper mode to suppress the autocorrelation functionsidelobe of sweep signal, which makes the side-lobe amplitude decrease and the tailamplitude decay quickly.3）According to the problem that the large noise intensity in metal mines leads to thedecrease of signal-to-noise ratio and seriously affects the resolution of seismicexploration, the scanning parameters of electromagnetic drive vibroseis have beenstudied in detail. To meet the needs of high resolution seismic exploration, vibroseis isrequired to work in the mode of broadband, long time, multiple stacking,and manysets of source array.4）According to the problem of electromagnetic drive vibroseis exploration depth, themethod of directional lighting is applied in the metal mine seismic exploration,directional seismic signals are equivalently compounded by delaying and overlayingthe single source, strengthen the energy of seismic signal in the needed direction,improve the signal-to-noise ratio of seismic records and raise the exploration depth.5）According to the characteristics of metal mine seismic prospecting data based onvibroseis, we analyzed the data acquisition parameters one by one such as the recordlength, sampling rate, group interval, offset and stacking fold and so on, and achievedthe result that the fieldwork method with small group interval, short offset andmultiple coverage is suitable for vibroseis seismic prospecting.6）The characteristics of seismic prospecting based on vibroseis determine the dataprocessing flow is different from that of conventional pulse source, based on thecharacteristics of metal mine seismic exploration, we designed the data preprocessingmethod of metal mine seismic exploration based on vibroseis, and designed the wholeprocessing flow of vibroseis in metal mine seismic exploration according to thefeatures of noise.7）Using electromagnetic drive vibroseis, we did research on seismic explorationexperiment of Jinchang nickel-copper mining area in Gansu, and verified thefeasibility and effectiveness of electromagnetic drive vibroseis in seismic explorationcompared with the hydraulic source of America and the impact rammer source ofCanada. Using the electromagnetic drive vibroseis and impact rammer source, we did applied research on metal mining goaf detection of Luanchuan molybdenum mine, thereflection seismic and seismic image methods prove that using electromagnetic drivevibroseis and impact rammer source can obtain the prospecting effect similar toexplosive source.The innovation points existing in this paper are as follows:1）According to the interference with seismic wavelet caused by the single vibrationfrequency of impact rammer source, based on the impact rammer controlled source,we put forward a pseudo random coding method, which can effectively improve theresolution of seismic exploration.2）According to the problem of electromagnetic drive vibroseis exploration depth, themethod of directional lighting is applied in the metal mine seismic exploration,directional seismic signals are equivalently compounded by delaying and overlayingthe single source, it effectively improved the exploration depth of electromagneticdrive vibroseis.3）Based on the characteristics of metal mine seismic exploration, we designed thedata preprocessing method of metal mine seismic exploration based on vibroseis,which effectively improved the signal-to-noise ratio of vibroseis seismic data and theresolution of seismic section.