Enhanced anisotropic model building methodology and pre‐stack depth imaging in deep water Gulf of Mexico: A case history

Abstract

We present a case study of anisotropic model building and the resulting accuracy of event placement and improved image quality. Approximately 660 OCS blocks of the MC Revival survey located in Mississippi Canyon area were imaged using anisotropic Kirchhoff pre-stack depth migration (Figure 1). The goals of this large scale project were accurate event placement and improved imaging of steep dips, salt boundaries, and subsalt events. To accomplish these goals, all available well information was used to calibrate the seismic velocity model from prior isotropic pre-stack WEM imaging. The resulting vertical velocity model was used to generate isotropic PSDM image gathers for use in determination of the anisotropy parameters epsilon and delta. These fields were derived from an automated two-parameter residual curvature analysis. Multiple iterations of migration for picking salt overhangs were a necessity to properly image salt bases and subsalt events. Focusing of events was enhanced through iterations of tomography both supra and subsalt. We achieved significant improvements in defining the salt boundaries and in positioning the reflectors and salt overhangs by properly accounting for the effect of anisotropy.

A case study: Improved subsalt imaging through TTI model building and imaging of a WAZ survey in the Gulf of Mexico

“…The Mississippi Canyon/Atwater Valley area has been extensively imaged using NAZ datasets (Whiteside et al, 2008) and WAZ acquisition (Baldock et al, 2009;Ma et al, 2010). It has been demonstrated that the introduction of anisotropy in the velocity model assuming VTI media, results in more accurate placement of events and general improvement of the image quality.…”

Improved subsalt imaging using TTI anisotropy and reverse time migration scans

“…It is well known that anisotropy must be taken into account for successful imaging of Gulf of Mexico seismic data. Whiteside et al (2008) noted that typical depthing errors using the isotropically derived model in this region ranged from 5% to 12% at a depth of 6 km.…”

Improved time and anisotropic depth imaging in the Appalachian Foothills

“…It is well known that anisotropy must be taken into account for successful imaging (Whiteside et al, 2008). Traditional VTI imaging assumes the velocity changes are symmetric along the vertical axis.…”