Prestack depth migration of an Alberta Foothills data set—The Husky experience

Abstract

We produce depth images for an Alberta Foothills line by iteratively using a number of migration and velocity analysis techniques. In imaging steeply dipping layers of a foothills data set, it is apparent that thrust belt geology can violate the conventional assumptions of elevation datum corrections and common midpoint (CMP) stacking. To circumvent these problems, we use migration from topography in which we perform prestack depth migration on the data using correct source and receiver elevations. Migration from topography produces enhanced images of steep shallow reflectors when compared to conventional processing. In addition to migration from topography, we couple prestack depth migration with the continuous adjustment of velocity depth models. A number of criteria are used in doing this. These criteria require that our velocity estimates produce a focused image and that migrated depths in common image gathers be independent of source‐receiver offset. Velocity models are estimated by a series of iterative and interpretive steps involving prestack migration velocity analysis and structural interpretation. Overlays of velocity models on depth migrations should generally show consistency between velocity boundaries and reflection depths. Our preferred seismic depth section has been produced by using prestack reverse‐time depth migration coupled with careful geological interpretation.

2-D traveltime and waveform inversion for improved seismic imaging: Naga Thrust and Fold Belt, India

“…Besides the inherent goal of time migration, which is to obtain the 'best' subsurface image, depth migration also requires simultaneous development of a geologically valid velocity model. In complex geological terrains such as thrust belts where adjustments in the velocity field may span several iterations (Wu et al 1998;Yan & Lines 2001), the process of velocity-model building may become interpretive. This 'interpretion', which is common to databased methods of velocity-model building, can be reduced to a certain extent by model-based methods such as traveltime and waveform inversion that honor the physics of wave propagation.…”

Imaging of complex fault-fold structures in a mountainous setting

“…In such environments, pre-stack migration from topography is found to produce the best images of steeply dipping, shallow reflectors (e.g. Gray & Marfurt 1995;Lines et al 1996;Wu et al 1998).…”