SLOPE APRONS-A KEY RESERVOIR TYPE IN THE BROOKIAN, NORTH SLOPE, ALASKA

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.