Velocity Determination in 3D Seismic

Velocity analysis still remains a weak link of 3D seismic inheriting the profiling (2D) technologies. The development of modern 3D seismic resulted in significant growth of number of channels in acquisition systems and use of migration of raw seismograms, that making it possible to enhance the resolution provided that a velocity model of medium is specified adequately. However it is difficult to count upon a noticeable increase in detail level of a survey where velocities are determined and, hence, smoothed, over several-kilometer-long arrays.<br>The proposed approach to determining seismic velocities is based upon two principles: Controlled Directional Reception (CDR) – i.e. slant stacking along a plane and the theory of diffraction by aperture. Amplitude analysis on sets of stacked traces computed with increasing aperture makes it possible to measure the first Fresnel zone radius of any regular wave that is proportional to its effective velocity. The ray parameters and effective velocities of all regular waves measurable at any point of a single 3D seismogram make it possible to construct more detailed depth-velocity model. Robustness of the first Fresnel zone radius measurement is discussed here.<br>