3D Diffraction Imaging Using a Vertical Traveltime Difference Gather with Prestack Time Migration

We have built a vertical traveltime difference gather to image diffractions in 3D time domain. This significantly contributes to 3D seismic data interpretation in detecting small-scale faults and heterogeneities. The vertical traveltime difference gather is obtained using 3D Kirchhoff prestack time migration based on the traveltime-related inline and crossline dip anlges, which is closely related to the 2D dip-angle gather. In the vertical traveltime difference gathers, diffraction events exhibit flattening while reflection events have convex upward sloping shapes. Different from 2D dip-angle gather, Fresnel zones related specular reflections are precisely focused on the given positions in spite of offsets and data azimuths, thus leaving more diffraction energy after muting. To image linear diffractors, such as faults in 3D, the vertical traveltime difference gather can be extended into 2D by adding a dimension with respect to dip-azimuth. This makes it possible to correct phases of edge diffractions and detect the orientations of the linear diffractors. We can store the gathers at each lateral position and then correct the phase and enhance the weak diffractions in 3D cases. Field data tests demonstrate the effectiveness of the proposed 3D diffraction imaging method.