Attenuation Characteristics Of Near-surface Seismic Wave And Retrieval Methods Of Quality Factor Q

Quality factor,as an important parameter to reflects the energy dissipation during seismic wave propagation in subsurface medium,the Q-factor Quantifies the absorption effect,meanwhile it is also a useful parameter for characterization of reservoirs and detection of hydrocarbons,moreover,the accurate Q estimation of near-surface absorption can be used to improve seismic exploration resolution by inverse filtering,meanwhile it can greatly increase the precision of reservoir prediction and had great significance.According to the great effects of near-surface poses on waveform and amplitude,and the issues related to the estimation of quality factor Q,this paper has established accruate geological model of the near-surface absorption and attenuation,then analyzed the layer thickness,noise,fitting frequency bandwidth and other factors on the application effect of the spectral ratio method and the methods advantages,the application condition and limitations in dealing field seismic data of spectral ratio method in detail.Analysis results show that the spectral ratio method can effectively estimate the change of Q value base on the thick reservoir,be affected by the travel time reading error or velocity estimation error,Q value evaluated by the conventional adjacent trace spectral ratio method is low in precision and discrete.and the method used in the actual data processing is less effective.In this paper,a novel spectral ratio logarithmic integral method is proposed by learning from velocity regression analysis based on the uphole survey data.Velocity stratification constraint,referring the principle of spectral ratio method,this method determines the formation Q value by linear regression between inter-trace travel moveout and integral of the spectral ratio logarithm of non-adjacent trace in effective frequency band.On the basis of the method principle and the algorithm precision theoretical analysis and realize the theoretical model construction,the synthetic uphole survey,the quality factor Q quantitative estimation.The result of model analysis shows that: under the condition of accuate travel moveout pickup,the estimation error of the spectral ratio integral method is close to zero;When the random noise of S/N equal to 10 is added to the theoretical model,the spectral ratio integral method relative error is 20.46%,but the spectral ratio method is up to 128.71%;under the condition of conventional travel pickup error,the maximum relative error of estimation result is about 20%,with the average value of <12%,the spectral ratio method maximum Q estimation error can be as high as 367%,the average error is about 92%.The application result of actual uphole survey shows that: the estimation Q values of low velocity layer,descending layer and high velocity layer by spectral ratio integral method are 43.67,119.71 and 358.52 respectively,but the spectral ratio method maximum of Q estimation of spectral ratio method is 3935.9,the minimum is about 9.02 and the difference is about 4000.At the same time,based on spectral ratio method to calculate the Q value,S transform has the highest accuracy and better noise immunity compared with STFT and WT.The application result by the spectral ratio integral method in the first break picking is satisfied.Comparing to conventional adjacent trace spectral ratio method,Q value estimated by spectral ratio integral method is in high-precision and stable,and the estimation result is in accordance with velocity stratification.This method is also applicable for other uphole survey observation systems and common shot seismic first breaks.At the end of this paper,according to the great effects of near-surface in Hetaoyu coal mine,we processed the original seismic data by compensation of earth absorption,based on the high-resolution of seismic prospecting,the processing abundant seismic attributes information were achieved,conducted the time-frequency analysis of seismic profile with the help of S transform,the seismic wave attenuation character is studied by using the two-phase model,analytical results show that: seismic wave presents obvious low-frequency shadow phenomenon,e.g.,the high frequency energy of seismic waves in coal seam methane concentration area attenuates seriously,contrarily,low frequency components decay slowly.And used to for Hetaoyu mining area predict the coal seam methane concentration area of main mining coal seamof Hetaoyu coal mine.The subsequent drilling results has validated the validity of this method.Using low-frequency shadow effect not only predicts the coal seam methane concentration area but also depicts its boundary and space distribution,which extra reduces the multiple solvability of methane concentration area prediction by 3D seismic data.