Geophysical Basin Modeling: Velocity Modeling for Seismic Imaging in Complex Geology Settings 1

Abstract

Abstract

Geophysical Basin Modeling, a novel velocity modeling method, is designed to mitigate seismic data limitations by exploiting geological and geophysical knowledge. The geologic information is quantified using basin model simulations to model primary control fields for rock properties, temperature, and effective stress. Transformation of the basin model fields is made by universally calibrated rock models.

Seismic velocity modeling is a challenging task when present time subsurface geology includes highly varying salt body movements and rapid sedimentation. Present time temperature and effective stress under such conditions are severely affected and deviate strongly from traditional assumptions of a simple depth dependent function. Variations in deposition source mineralogy and texture, temperature, and effective stress over time add even more complexity to this scenario. As seismic velocities at present time are products of the above “geo-history”, knowledge of this “non-seismic” piece of information in a quantified form, typically classified as a basin model, has an obvious potential in assisting seismic velocity model building. Basin modeling in various forms has been used with reported success to build velocity models.

Rock physics models form a link between the basin model (geo-history) and the seismic domain. Appropriately designed, the rock model honors the time dependency of deposition source, temperature, and effective stress allowing transformation of this information to elastic properties. We may call the above scheme of using non-seismic information Geophysical Basin Modeling (GBM).

The 3D GBM scheme has been applied to a geologically complex area of the deep water Gulf of Mexico. Conventional model building methods rely solely on the information contained by the seismic data and can suffer limitations due to poor subsalt seismic signal and limited angular illumination at subsalt depths. GBM attempts to mitigate the seismic data limitations and uncertainty by taking advantage of the constraints provided by geological and geophysical inputs. The direct application of the GBM workflow to subsalt imaging has shown that high quality seismic images are produced in areas of geological complexity where it is challenging to define these properties from seismic data alone. This multi-disciplinary operation is therefore of high value in exploration as it gives high quality results from fast generation of an initial velocity model.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016