Near Surface Absorption Parameter Inversion And Q-compensation:A Case Study In Dagang Oil Field

Seismic waves would suffer from frequency absorption and velocity dispersion when propagating in the near surface,leading to the decrease of the seismic resolution.Q compensation is widely used to eliminate the effect on the seismic resolution via accurate Q factor estimated from near surface,which is an important trial for high resolution seismic exploration in recent years.This paper firstly discusses the dominant factors impacting Q estimation for near surface.Based on the discussion above,a tomography inversion method without source effect has been proposed.From the results,it turns out that Q is not frequency-independent but changes with frequency,which provides reliable evidence for frequency-dependent Q.Afterwards,on the circumstance of the frequency-dependent Q,the analytical expression of estimate error of the Q estimation method based on the linear regression is derived.In addition,the systematic analysis of the estimate error has been done.The analysis shows that the Q estimation method based on the linear regression would introduce a large estimate error.Therefore,a novel non-linear inversion method,called two-parameter regression method(TPM),without the source and geophone coupling effects has been proposed to estimate frequency-dependent Q.By introducing the prior information,TPM could inverse the frequency-dependent Q directly,subtly avoiding the estimate error from the assumption of the frequency-independent Q and improving the inversion reliability.Finally,a case study in Dagang Oil Field has been discussed using TPM method,and its Q factors have been estimated by nonlinearly fitting to seismic attenuation.By applying inverse Q filter,the effect of the weathering layer absorption has been removed and the resolution of the seismic section has been enhanced.