Abstract

Prestack Depth Migration (PSDM) is one of the most reliable seismic techniques for imaging subsurface structures because of its ability to focus and position reflections in areas with strong lateral velocity variations. The comparison between velocity sections obtained initially by velocity analysis in time domain on CMP gathers and the same obtained by horizon velocity analysis shows the latter to be more coherent and geologically meaningful. Techniques based on model ray tracing, such as coherency inversion allows more precise estimates of interval velocity to produce superior velocity models for PSDM. This paper is an attempt to study the methodology and application of Kirchoff PSDM through model based interval velocity estimation using coherency inversion technique followed by interval velocity depth model refinement using horizon based tomography and subsequent Pre-Stack Depth Migration. The CMP gathers of an arbitrary 2D seismic line and the Pre-Stack time migrated gathers generated from it were first analysed and by applying the above technique, PSDM sections showed considerable improvement in imaging the subsurface picture in this particular case suggesting that in structurally complex areas, this methodology can be suitably applied to derive much better geological result.