Velocity Estimation in Complex Chalk

M. Sugrue, I. F. Jones, E. J. Evans, S. Fairhead, G. Marsden
2003 EAGE/SEG Summer Research Workshop - Processing and imaging of seismic data   unpublished
Here we consider a North Sea study where our initial approach was to build the subsurface model using interpreted horizons as a guide to the velocity update. This is common practice in the North Sea, where the geology 'lends itself' to a layer-based model representation. In other words, we encourage preconceived bias, as we consider it to be a meaningful geological constraint on the solution. However, in this instance we had a thick chalk sequence, wherein the vertical compaction gradient
more » ... d subtlety, in a way not readily discernable from the seismic reflection data. As a consequence, imposing the explicit top and bottom chalk horizons, with an intervening vertical compaction gradient (of the form v(x,y,z) = vo(x,y) + k(x,y).z), lead to a misrepresentation of the subsurface. To address this issue, a gridded model building approach was also tried. This relied on dense continuous automatic picking of residual moveout in CRP gathers at each iteration, followed by gridded tomography, resulting in a smoothly varying velocity field which was able to reveal the underlying local changes within the chalk. Great Explorations -Canada and Beyond
doi:10.3997/2214-4609.201405912 fatcat:y4rgq6yapbdbbg6twikpuoasrq