SLOPE APRONS-A KEY RESERVOIR
TYPE IN THE BROOKIAN, NORTH SLOPE, ALASKA
MORRIS, William R., ConocoPhillips Co, Houston, TX 77095, [email protected]
Slope aprons form an important, yet rarely recognized type of deep-marine
reservoir
. They commonly form stratigraphic traps and are a key reservoirs type
in "sand-poor" basins or as "coarser-grained" lateral systems in longitudinal
basins. These systems occur near the base of slope and form where sediment
supply is relatively low and are most commonly sourced by longshore drift,
shelfal currents or via small/ephemeral fluvial systems. Our studies of modern
and ancient systems recognize five basic types of slope apron systems.
The Cenomanian Tarn and Meltwater Fields consist of a number of separate
slope apron systems that form a slope apron bajada within the Brookian Foreland
basin. These slope apron systems include all five main types. Debris flow/
slump/ slurry flow dominated slope apron systems form during incision of the
slope during falling sea level and have limited reservoir
potential. The second
type is channelized to lobate HDT slope aprons systems. These systems occur were
either mixed sediment is supplied to the system or where the largest volume
slope apron systems occur. The third type of system consists of lobate HDT slope
aprons, which typically has the best por/perm and N/G ratios. Comparison to
modern systems indicates that these systems are fed by longshore drift or small
sandy fluvial systems. The forth type of system is similar to the previous type
except that it can contain 10% to 50% slurry flows.
Reservoir
properties can be
quite good but the slurry flows increase
reservoir
compartmentalization and can
significantly lower recovery efficiencies. Slope incision, slumping of shelf
deltas or mixed sediment feeder systems are the most likely
mechanisms
for
initiation of this type of system. The last type is LDT slope aprons, which in
the Brookian, occur during late lowstand when coarse grained feeder systems have
transgressed landward and they typically have very little
reservoir
potential.