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ABSTRACT In offset VSP surveys, downgoing and upgoing waves do not travel along vertical path, and the raypath is often bended due to vertical inhomogeneities. If homogeneous straight ray-path is used for velocity inversion, the velocity obtained from near horizontal ray paths will be higher than the velocity obtained from near-vertical raypaths. Further more, if the lower vertical velocity is used for moveout correction of the upgoing waves in offset-VSPs, the moveout will not be aligned properly and the resulted imaging will be distorted as shown in Figure 1, where the horizontal events are bended after applying NMO with the vertical velocities. The functions and their solutions of equivalent velocity and slowness were studied and the results of real data processing with the methods were shown in this paper.
ABSTRACT This paper advances two equations of absorption for Common Middle Point (CMP) gather in multi-layer horizontal media, which based on crooked ray path and Snell''s law, one equation for offset, the other for traveling time. We compare the two equations with approximate absorption equation based on straight ray path, and results show that the equation about time based on crooked ray path has more precision than other equations. Therefore, this equation is well suited to high precision inversion of value.
ABSTRACT Based on attenuation equation with high accuracy, interval inversion method is developed by using main frequency of reflection wave from CMP records. This method adopts Ricker wavelet to describe seismic wavelet and to calculate main frequency of reflection wave, utilizes multiple traces to calculate average attenuation factor, interval value is obtained by layer stripping method. Theoretical model test proves the method valid.
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.34)