Reducing the gap between seismic imaging and geology: Horizon consistent velocity analysis and modelling for pre-stack time and depth migrations

S eismic velocities and migration techniques have great impact in the reservoir imaging at any stage of the exploration for hydrocarbons. The effectiveness of a migration algorithm is commonly measured by the ability to boost the signal continuity, against noise and other disturbances such as diffractions from out-of-plane events (Jones, 2010). By contrast, migration is a process applied to reposition the energy from where it originated, to resolve the geometry and positioning of the events. The success of the process is heavily reliant on the velocity field used. The consistency between the velocity field and events is a quality indicator in seismic inversion exercises, for both the low frequency background and the high frequency intervals identified in velocity logs. The migration itself can be seen as an inversion procedure, with the velocity gradients required to be consistent with vertical trends and amplitude events (Guillaume et al., 2011; Benson et al., 2015). The understanding of geological velocities progresses with exploration and the increasing number of wells and geophysical data available, which gradually establish lithological and rock physics properties, together with tectonic and burial history. Several pre-stack algorithms are available for time migration (PSTM) as well as for depth migration (PSDM), which allow the velocity analysis and modelling sequence to more closely integrate geophysical and geological data. Nowadays, pre-conditioned migration velocities are common in the depth imaging, during the processing of PSDM. The approach is applied for complex geology and relies on seismic and non-seismic data, also combined through different joint inversion techniques (Droujinine et al., 2008; Foss et al., 2008; Houghton et al., 2014). We present a migration workflow, originally designed for regional 2D seismic and applicable to 3D, which links the velocity modelling for PSTM with PSDM, and allows geological constraints to be applied at the PSTM stage (Figure 1).