Research And Application Of Special High Precision Seismic Acquisition Method In Complex Surface Area

The purpose of oil and gas seismic exploration is to find the important national strategic resources of oil and gas.At present,the level of seismic exploration in the relatively simple surface areas in China has been very high,and the complex surface areas have become the strategic substitute areas for oil and gas resources exploration.Complex surface refers to the very shallow surface of the earth's crust,which is characterized by large surface fluctuations,seismic wave propagation velocity significantly lower than that of the underlying strata,and complex and changeable lithology.Common types include complex mountains,deserts,Gobi,Yadan landforms,giant loess tableland,tidal flats,etc.The complex earth surface brings great difficulties to the field acquisition of seismic exploration,and the seismic data acquisition is also seriously affected,which is manifested as serious attenuation of high frequency seismic wave,narrow wavelet band,low resolution,insufficient,uneven,asymmetric and poor continuity of seismic wave field collection,resulting in low imaging accuracy of seismic wave.At present,many years of research on surface structure survey and static correction of complex surface area,illumination of geological targets by seismic waves,optimization design of observation system,and suppression of"collecting footprints"have been carried out in China,and good results have been achieved.The expansion of seismic wave frequency band is also studied in terms of excitation and reception,but the effect is not obvious.The research progress of wave field recovery of inhomogeneous and insufficient seismic data is slow,so it is necessary to widen the frequency band of seismic wave,improve the resolution of seismic wave,and improve the recovery precision of wave field and the imaging precision of wave field.Aiming at the problems of narrow frequency band and multiple side lobes of seismic wavelet,low resolution,low imaging and low inversion accuracy of seismic waves caused by complex earth surface,this paper studies the variation law between frequency band width,amplitude spectrum shape and wavelet resolution,and points out the decisive effect of maximum frequency,frequency band width and amplitude spectrum shape on wavelet resolution.This paper also studies the effect of wavelet frequency band width and frequency components on the inversion accuracies of seismic reflection coefficient and wave impedance,and the influence of wavelet frequency band width on the random noise suppression in deconvolution processing.It especially emphasizes the importance of the low frequency components below 3 Hz and the frequency band widths in wave impedance inversion and the influence of band widths in reflection coefficient inversion and deconvolution processing.The correctness of theoretical analysis on seismic wave inversion is verified by Marmousi modelling.In order to improve the resolution of seismic wavelet and the imaging accuracy of seismic waves,this paper systematically studies the acquisition theory of seismic acceleration signal with wide frequency band,high imaging resolution,high sensitivity in response to medium changes and high signal fidelity.The wave equation and the staggered grid finite difference equation of seismic acceleration signal are derived.The velocity signal and the acceleration signal in the relationship between signal and medium physical properties,signal geometry and wave characteristics,signal spectrum,signal noise,signal-to-noise ratio?SNR?and resolution are compared.Two geological models of Hession and Marmousi,which have shallow thin layer,medium thin layer and deep thin layer,wedge,overthrust nappe tectonics,anticline,unconformity,oil-water interface,toplap,pinch-out and other geological phenomena,are used to simulate seismic waves of velocity signal and acceleration signal and compare their imaging accuracy.And the correctness of the theoretical analysis about acceleration signal and velocity signal is verified.In order to better receive acceleration signal,the high-sensitivity land piezoelectric geophone and laser fiber optic acceleration geophone were developed,and their application results are good in2D seismic acceleration signal acquisition tests and 3D seismic acceleration signal acquisition applications.The test and application results of acceleration signal show that acceleration signal can effectively improve the imaging accuracy of geological targets.In order to improve the recovery precision of wave field,this paper explores the development history and the basic principles of compressed sensing?CS?sparse seismic acquisition,the layout design method,and the CS data wave field reconstruction and processing technology.The application effect of CS sparse seismic acquisition is also analyzed by taking the first three-dimensional?3D?CS sparse seismic acquisition and wave field reconstruction test conducted by Sinopec in TFT area of Xinjiang Province as an example,which lays a foundation for further research on sparse seismic data acquisition technology.Through the research,this paper has mainly obtained the following three achievements:?1?The optimization principle of seismic wave excitation method is summarized:Increasing the maximum frequency of seismic waves is the premise of broadening the frequency band of seismic waves,and expanding the excitation frequency below 3 Hz is very important for wave impedance inversion.When the frequency band of seismic wave is relatively narrow?the highest frequency is around or below 70 Hz?,the excitation method to broaden low-frequency band should be adopted to suppress the side lobes of seismic wavelet.When the seismic wave frequency band is relatively wide?the highest frequency is greater than 70 Hz?,the seismic wave should be excited by the method of increasing the highest frequency to improve the resolution of seismic wave.The amplitude spectrum of the excited seismic wave should have a slow transition zone?It is mainly about the design of vibroseis reference signal?,and the shape of amplitude spectrum should be symmetrical or inclined to low frequency side.Furthermore,combined with the domestic development and mature seismic excitation technologies,the explosive source broadband excitation method based on near-surface multi-parameter model and the vibroseis nonlinear broadband excitation method are summarized,which broaden the frequency band of seismic waves in complex surface area.?2?The theory of seismic acceleration signal acquisition is researched and summarized.According to the theory,acceleration signal has small distortion,high fidelity,high frequency,wide frequency band,higher sensitivity to Young's elastic modulus,shear modulus and density changes than velocity signal,and acceleration signal can effectively improve the precision of seismic exploration in complex surface areas.The high sensitivity land piezoelectric acceleration geophone and laser fiber optic acceleration geophone have been developed and their performance indexes have reached the level of similar products abroad.The 2D acquisition test and 3D acquisition application of seismic acceleration signal and new types of acceleration geophones show that acceleration signal significantly improves the imaging accuracy of seismic wave,which has won wide recognition and praise in the industry.Based on the results of the study,we wrote an article published in Applied Geophysics journal?SCI?,two papers,respectively,in 2019 the United States SAN Antonio 89th SEG annual meeting and China institute of petroleum geophysical exploration technology seminar in Yichang of Hubei province in 2015.We obtained three national invention patents and two utility model patents.?3?In this paper,the research on the theory of CS seismic acquisition and the analysis result of 3D CS seismic acquisition and wave field reconstruction test conducted by Sinopec in TFT area of Xinjiang Province show that the random sparse layout design method under the greedy sequential strategy and the wave field reconstruction techniques based on the joint iteration of the l₀ and l₁ norms have effectively improved the SNR and the resolution of seismic waves in the complex surface area.The integration of CS sparse seismic acquisition technology,wireless telemetry node acquisition technology,5G technology and satellite remote sensing real-time positioning technology will be the future development direction of high-precision seismic acquisition technology in complex surface areas.