Anisotropic P-P and P-Sv Pre-Stack Depth Migration of 4-C Seismic Data, Offshore Trinidad

Tony D. Johns¹*, Carmen Vito¹, and Raul Sarmiento^2
1WesternGeco, USA
²EOG Resources Inc., USA
*[email protected]

In 2004, EOG Resources acquired an ocean-bottom cable (OBC) 4-component swath survey across the Pamberi-1 well location in the Columbus Basin, offshore Trinidad. The motivation from EOG was because a previously acquired conventional 3-D towed-streamer survey failed to adequately image the potential reservoir under the main fault. Details of the P-P and P-Sv processing of this dataset through anisotropic pre-stack time migration were previously described by Johns et al. (2006) in which it was demonstrated there existed a qualitative correlation between derived parameters and attributes from P and Sv anisotropic migration velocities, overpressure and known regional geology. This observation was quite remarkable considering that only a limited effort to validate and constrain the parameters was performed. Under the Future Work section of the previous publication, it was suggested that further data quality enhancement in preparation for more quantitative rock-property classification could only be achieved after pre-stack depth imaging. In this presentation, we discuss that next phase in the 4C processing, advancing the P-P and P-Sv data through anisotropic pre-stack depth migration. The Pamberi-1 well was used to constrain the anisotropy in the shallow section, with the deeper spatial trend guided by the anisotropy derived previously in the time processing with further updates from detailed event registration. Prior to the depth tomography, the nature of birefringence from the presence of azimuthal anisotropy was first examined to assess its potential impact on the radial P-S signal. The shear splitting analysis revealed polarization alignment with the regional stress direction delineated by fault blocks acting as pressure seals.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain