Trapping Styles and
Reservoir Architecture of Deep-water
Reservoirs: Comparison of 33 Field Examples
from West Africa, Brazil and Gulf of
Mexico
By Rod Sloan
A
comparison of 33 deep-water turbidite
fields in seven basins from West Africa,
Brazil and Gulf of Mexico reveals recurring
patterns of trapping and reservoir architectural
styles that have implications for exploration
drilling and development plans in passive-margin
basins. The fields are contained mainly
in combination structural-stratigraphic
traps, with 80% showing some element
of stratigraphic closure, principally
depositional pinch-out, which generally
tends to diminish in importance upslope
with increasing structuration and sand
occurrence. Basinwide mobile substrate
(salt or shale) thickness controls regional
deformation style, the likelihood of
structural trapping and the location
of reservoirs. Six principal deep-water
reservoir types are recognized, whose
abundance varies across the continental
slope: (1) channel-dominated reservoirs,
which are commonest on the middle slope;
(2) sheet-dominated reservoirs, commonest
on the middle-lower slope; (3) leveed-channel
reservoirs on the upper slope; (4) canyon-fill
reservoirs on the upper slope-shelf;
(5) debrite reservoirs on the upper slope;
and (6) contourite reservoirs, commonest
on the lower slope-basin floor. The case
histories provide a series of guidelines
for predicting sand-body dimensions and
stacking patterns, together with their
influence on aquifer support, well spacings
and development options. Pre-drill reserves
estimates should take into account the
upside potential for deeper hydrocarbon
pools as virtually all the passive-margin
case studies have at least 2-5 separate
payzones. Passive-margin turbidite fields
are generally of Paleogene age or younger,
so the reservoirs are weakly consolidated/cemented,
porosities exceed 25% in most cases and
excellent well deliverabilities are common.
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