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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Impact of Seismic Loop-Scale Depositional Models on
Reservoir Architecture in a Heavy Oil Accumulation,
Santos Basin, Brazil
By
Several deepwater turbidite discoveries of Eocene age have been made in the northern Santos mobile salt basin, offshore Brazil. The Shell-operated BS-4 NE discovery (2001) shows significantly better reservoir development than in equivalent sections penetrated nearby. Both the discovery and appraisal wells encountered in excess of 100 m of predominantly clean sand.
A 3D seismically-based study covering some 4000 km2 was undertaken to better understand the sub-regional context, paleo-slope position and depositional architecture of the proximal, high net-togross reservoirs penetrated in the BS-4 NE. The main focus was on detailed loop-scale seismic interpretation of internal heterogeneities and understanding aquifer potential, both of which have direct impact on field development planning.
Study results demonstrate that considerable uncertainty remains
with respect to the distribution of discrete heterogeneities within
these highly amalgamated reservoirs, specifically the nature and
configuration of predominantly silty material that drapes over
incision surfaces. Reservoir facies were deposited within a
dominantly channelized environment as part of a fan apron
developed across an inherited stepped slope profile, with a
depositional trend from NW to SE. An Eocene intra-slope break
is evident about 15 km up-dip of the present-day closure, at the
downward limit of several confined feeder canyons, outboard of
which low- to moderate-aggradation channel complexes were
deposited across a lower gradient
slope.
The BS-4 NE reservoir complex is situated
in the outer part of this low
gradient
“step
flat” with a higher
gradient
“exit ramp”
immediately down-dip. Seismic mapping
of complex erosional surfaces with
evidence for multi-phase knick point
migration and significant bypass, also
supported by core and image log data,
provide a framework within which to
better understand the distribution of key
heterogeneities. A key observation is that
the canyon systems and channel complexes
become progressively younger to the NE.
There is a strong interplay between this migrating sedimentary
system and tectonics that can be related to the amount of incision
and bypass. The conceptual models derived from this front-end
work provide key constraints to static reservoir model building in
order to derive realistic infill architecture for testing the dynamic
impact of reservoir heterogeneities. Results from the 2006
appraisal drilling on BS4-NE are consistent with the conceptual
geological model.
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