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Richard A. Eisenberg1, Michael J. Roberts1, Robert Shank1, Mark A. Beeunas1
(1) Chevron USA Production Company, New Orleans, LA

Abstract: Integrated risk assessment in sub-salt exploration, deepwater Gulf of Mexico

Total geologic risk is the product of the individual risk elements: source, reservoir, timing/migration, and trap. Our approach to quantitative assessment of risk elements in sub-salt prospects involves integration of technologies including seismic depth imaging, structural and stratigraphic analysis and basin modeling. Results are combined within a 3-D visualization framework.

To help reduce structural and stratigraphic uncertainty, a significant effort is placed on obtaining improved sub-salt seismic images through the use of pre-stack depth migration. Successful depth imaging requires an accurate description of the overlying velocity structure, an understanding of the shadow zones due to seismic illumination, and the attenuation of coherent noise.

Evaluation of trap and reservoir risk is made through sub-regional mapping of large depth migrated seismic volumes and paleogeographic reconstruction. Detailed salt mapping and analysis of base salt cutoff geometry is used to locate potential sediment fairways and model facies patterns. To complete the risk assessment, the timing of hydrocarbon generation is assessed relative to the development of the other essential geologic risk elements. The regional distribution of source rock facies of various ages and their thermal maturity are mapped based on detailed geochemical typing of produced and seep hydrocarbons. Regional bottom hole temperature and surface heat flow measurements help constrain the models and provide more focused evaluation of the burial and thermal histories within the fetch area of prospects.

Our experience indicates that long term success in the deepwater GOM will increasingly rely on integrated work teams using advanced earth science technologies and sound geologic reasoning to assess prospect risk and reward.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana