Tomography Static Correction Method And Its Engineering Application

With the continuous expansion of China's seismic exploration area,the topography of the exploration area has become increasingly complex.Static correction has always been a problem that is difficult to completely solve.Because the near-surface velocity profile is generally uniform,which would make First picked up by the seismic wave to the time there is a delay,the reflected waves will be distorted,so that the stacked section deformed and distorted.Static correction work is to eliminate this delay and lay a solid foundation for subsequent processing of seismic data.Traditional static corrections usually use shallow refraction and surface survey methods to determine the near-surface velocity and establish near-surface velocity models to calculate static corrections.The former is only applicable to the layered uniform media area with flat terrain,flat ground surface,or small inclination.Based on the principle of refracted waves,a stable refractive interface is required when using this method,and the formation velocity is not allowed to reverse.The latter is mainly applicable to the difficult-to-implement stage of intense shallow refractometry.Although this method can accurately obtain the local near-surface velocity,it also increases the surface survey(such as microwell logging)if the surface is relatively complicated.With density,the cost becomes very high.Using the above two methods may cause certain errors in the calculation of the static correction amount.Seismic tomography statics is a research hotspot in recent years,and it is also the current development direction of static correction technology at home and abroad.At the core of tomography is the use of first-arrival travel time to model block-like near-surface velocity structures without making any assumptions about the formation,allowing for intense fluctuations in the formation and lateral changes in velocity and even inversion of the formation.Tomography is to get near surface statics chromatography by the method of high-speed position and the velocity distribution of the top layer of the interface,and then can complete the calculation of the statics.This paper first summarizes the principle of static correction method,and introduces the theory and method of tomography in this foundation,and carries out detailed analysis and research.Comparing various forward and inverse algorithms,we finally selected improved Vidale finite difference algorithm and back projection technique(BPT)to perform tomography,and calculated the static correction based on the tomographic results,and applied it to the processing of actual seismic data.Among them,good results have been achieved.