Prestack depth migration at the Frade field, Deepwater Brazil, for high-resolution subsurface characterization

The utility of prestack depth migrated seismic data is well-established in obviously complex geologic and geophysical environments, such as subsalt.  Rising costs of data acquisition and drilling necessitate a more robust characterization of risk, and more recently the benefit of prestack depth migration has been realized in areas in which time migrated data were traditionally deemed acceptable.  Advances in computer efficiencies combined with an evolving knowledge base enable high-resolution seismic imaging techniques that preserve and recover amplitude fidelity and optimize frequency bandwidth.  The resulting increased confidence in interpretation can lead to a reduction in uncertainty, impacting static and dynamic models and ultimately project economics.

The Chevron-operated Frade field in the deep water of the Campos Basin was discovered in 1986 by Petrobras, followed by a successful appraisal well in 1989.  Because of technical and economic challenges, comprehensive efforts toward appraisal and development planning were not commenced until 1998 by Texaco.  (Chevron merged with Texaco in 2001.)  Consequently, the field’s development was delayed by more than two decades after its discovery.  The Frade structure is only ~1 km beneath the seafloor, but the overlying complexities create geophysical challenges that demand a prestack depth migration:  a deep incised seafloor canyon with associated buried stacked channels, shallow gas, and a laterally varying anisotropic velocity structure.  Near the end of the Appraisal phase of the project, Chevron delivered a reservoir-scale prestack depth migrated dataset.  The imaging effort drove a reevaluation of the structure maps, which significantly impacted estimates of original oil in place and prompted changes to proposed development well placement.  A depth migration is an inherently interpretative product, and continual and close interaction between the geologist and the geophysicist is an iterative and integral element of success.  As Frade enters the Production Operations phase and offers new insight into the subsurface, the depth migration will be reworked and recalibrated to further impact business decisions.