Study On The Inverse Q Filtering Method For Seismic Wave Energy Compensation

Energy attenuation and velocity dispersion occur in the process that seismic wavepropagate in the non-perfect elastic quality of underground rock stratum. Energyattenuation makes the energy of deep-seated stratum geted from the detector weak,and we can not pick up the deep-seated stratum information, which reduces thelongitudinal resolution of seismic data. Velocity dispersion caused by the velocitydifference of different frequency components, and it results in seismic wave phasedistortion, makes phase axis continuation worse. With the pressing demand of thehigh-resolution seismic data, reseachers put emphasis on the reduction of thelongitudinal resolution of seismic data as a result of stratum absorption. To improvethe seismic resolution, we must compensate the earth attenuation, and recover thephase distorted by velocity dispersion.Inverse Q filtering is an effective method for compensating stratum absorption. Itcan compensate amplitude attenuation and frequency loss for seicmic wave, andimprove phase characteristic of sesmic record. Consequently, it improves phase axiscontinuation, and enhances the energy of weak refletion wave, and then improvessignal to noise ratio and resolution of seismic data. Nowadays, inverse Q filteringmainly concludes three main categories, using series expansion approximates inverseQ filtering to compensate high-frequency component, inverse Q filtering based onwave-field continuation, and other inverse Q filtering. Inverse Q filtering based onwave-field continuation is a conventional method for seismic wave compensation.However, the amplitude compensation operator belongs to high-pass filter, which willamplify high-frequency interference, and then it results in poor stability ofcompensation result in deep-seated stratum seismic record. Aimed at computationunstability, reseachers propose the gain-limited method and the method added stabilityfactor to suppress high-frequency interference. We make deep study andcomprehensive analysis for the two methods. The results showed that the compensation operater of the gain-limited method also amplities high-frequencyinterference to a certain degree, and energy compensation for deep department stratumseismic wave is quite limited. The highest degree of amplitude compensation forseismic wave using the method added stability factor is only related to the stabilityfactor2. That is to say, however the energy of seismic wave attenuate, thecompensation ability of the method for seismic record is only restricted by2, and itis obvious that the method can not improve the resolution of deep-seated stratumseismic wave.Aimed at the disadvantage that the convetional methods can not compensatedeep-seated stratum seismic record, we present two new methods, the regularationfiltering method and the iteration filtering method. Regularation filtering is aconventional method to solve ill-posed problem of potential-field downwardcontinuation, and we introduce that into inverse Q filtering based on wave fieldcontinuation to suppress the high-frequency interference. The principle of the iterationfiltering method is as follows, the spectrum of seismic record multiplies lowpass filterwhich can effectively suppress high frequency components, and then we use theiteration filtering method to make up the low and medium frequency componentswhich is cutted down by lowpass filter. Simultaneity, convergence of this method isproved, and general formula of the iterative method is given. Model tests andcomparative analyses on the filter characteristics of amplitude compensation operatorindicate that the regularation filtering method and the iteration filtering method havebetter abilities to overcome the noise and compensate deep-seated strata seismic waveamplitude in comparison with the common inverse Q filtering methods. Theconventional methods and the proposed methods are applied to the actual data, theresults further show that the regularation filtering method and the iteration filteringmethod can compensate deep-seated stratum seismic record better, and improve themedium-and deep-seated strata seismic data resolution effectively.The quality factor is not only a precondition of inverse Q filtering energycompensation for seismic wave, but also an important physical parameter describing stratigraphic absorption and joint inversion of PP-and PS-waves, which plays animportant role in the prediction of subsurface petrophysical parameter and oil and gas.Herein, we take the physical mechanism of wave-field continuation in modifiedKolsky model as the base, in combination with the method of calculating travel timein every layer proposed by Zhang and Ulrych, present a method of estimating P-andS-waves quality factors based on the formula of the wave-field continuation inmodified Kolsky model. We can achieve estimating a different stratum Q values bylinear-fitting between the frequency and the logarithm of the amplitude spectrum ratio.Model tests shows that the Q values estimated by this method are correct and theestimated results are accurate. We apply the method to real seismic data, and obtainthe reasonable results of P-waves Q value estimation.