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