JOHNSON, JEFFREY D., BP-Amoco
Abstract: The Challenge of Subsalt Imaging - Past, Present and Future Capabilities
Exploration for economic reservoirs beneath salt structures has been a frontier activity throughout the 1990's, particularly in the Gulf of Mexico.The major challenge for explorers has been obtaining reliable structural and stratigraphic interpretations from seismic data. Contorted salt bodies often act as complex lenses that refract, distort and scatter propagating seismic energy. These effects require extraordinary, interpretive seismic processing efforts, typically 3D prestack depth migration, to image subsalt geology. Today many oil companies and seismic contractors have implemented computational and velocity model building systems that effectively produce mappable depth images. However, project costs and cycle times are high, and image data quality remains a problem in many situations.
Challenges and problems faced
in current seismic subsalt imaging include:
- Velocity model resolution
and tomographic updating
- Algorithm amplitude fidelity
and resolution using standard Kirchhoff or other travel time methods
- Subsurface illumination
due to refraction or critical angle effects
- Multiple reflection and
converted wave interference with primary subsalt reflections
Despite current economic
conditions R&D progress within oil companies and seismic contractors,
coupled with steady increases in computer price/performance, show promise
of meeting these challenges and producing reliable subsalt predictions
of fluid and lithology as well as structural images. Future subsalt depth
imaging developments or applications should include:
- Practical implementation
of wavefield extrapolation/processing approaches including multiple and
converted wave subtraction or imaging.
- Increased use of multi-component
sea bottom recording, vertical cables, and long/wide offsets to improve
illumination and wavefield sampling, particularly in exploitation projects.
- Advanced visualization/virtual
environments for interpretive velocity modeling and processing as well
as for interpretive integration with other subsurface data.
AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England