2D wave equation pre‐stack reverse‐time migration for complex geology structures with rugged topography by finite‐element method

Abstract

In order to acquire satisfying seismic images, the pre‐stack depth migration should be used, and the perfect way is the migration directly from rugged surface without static correction. This paper discusses a finite‐element pre‐stack reverse‐time migration method which accomplishes migration of a common‐shot dataset from irregular surface. Because static correction is automatically realized during migration, the error resulted from static correction is avoided. Since accurate wave equation is adopted as the migration operator, it has not restriction of imaging dips, and is able to imaging steep reflectors. Finite‐element method uses triangle elements to fit the topography. Velocity and wave field in an element is regarded as a quadratic function, thus migration operator can adapt for arbitrary velocity distributions. Several model experiments are conducted to verify the validity of this migration method. Four imaging conditions (excitation‐time imaging condition, U/D imaging condition, maximum amplitude imaging condition and correlation imaging condition) are investigated in the migration of Marmousi datasets to compare their imaging qualities. The results indicate that the imaging effect of correlation imaging condition is the best. The Topspline model including rugged topography and near‐surface velocity variations is another test model. The imaging results in two migration conditions (direct migration from rugged topography and migration from plane datum after static correction) are compared. The results indicate that direct migration from rugged topography can image precisely, while the conventional image obtained after static correction has the phenomenon of excessive migration or less migration.