Illumination Using RTM & Kirchhoff Depth Processing to Enlighten the Geoscientists in Subsalt Domain

Fabre, Gregori¹; Gaillot, Jeremie; Collin, Magali; and Lalande, Severine
¹[email protected]

In deep offshore exploration, seismic imagery is generally the key to better understand how complex turbidite depositional systems are organized. In compressive domains, salt-cored anticlines or thrusts associated with allochtonous salt diapirs often create potential traps for hydrocarbons, but also induce great challenges to imagery teams and interpreters. Therefore, seismic processing algorithms are continuously improved and fine-tuned to increase the image quality, to track all sedimentary information, to remove noise, and to relocate the signal at the right place. Tailor-made workflows are built for each project, in order to represent the salt content, and track the weak signals to give to interpreters the best datasets possible.

In this example, a Common Azimuth Wave Equation (CAWE) reprocessing has been challenged 6 years later by a most recent state-of-the-art reprocessings using Kirchhoff and Reverse Time (RTM) algorithms for migrations, with an iterative process on velocity model building, and involving interpretation geoscientists in each step.

This poster shows in a complex subsalt setting the importance of working in parallel on different seismic outputs in order to refine the interpretation and the understanding of the tectono-sedimentary architecture, leading to a proper evaluation of the reservoir prospectivity. Those migrations allow a better understanding of depositional evolution: channel type, sand content and location related to the salt movement.

In this example of a thrusted anticline associated with a salt diapir, turbidite fairways were evidenced in the hanging-wall and were suspected in the footwall below the salt diapir. The Fullsalt velocity model RTM migration is mainly used to image the turbidite fairways below the salt body, and the thrust surface. The Sediment flood Kirchhoff migration is used to properly image sediments and faults on the edge of the salt diapir flanks. Finally, the Fullsalt Kirchhoff migration is used to reconciliate the other migration interpretations, and also for semi-regional seismic amplitude extractions for turbidite fairway mapping.

In this complex subsalt setting there is no ‘best’ reprocessing for the whole prospect. It is an evolving process; out of the many seismic migrations performed, some of them contribute to enhance the seismic imaging in a specific area while others are used for the overall prospect understanding, all leading to the most reliable depositional system.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013