Submarine levees: form, process and reservoir prediction

Submarine channel levees commonly show a regular decay in thickness away from their parent channel. The form of this decay (power-law or exponential) is governed by the flow processes over the levee(1), in particular by the rate of entrainment of ambient seawater, which is a function of the flow Richardson number. This in turn depends on the local slope on which the levees are built(2). Using characteristic scaling parameters(3,4) it is possible to generalize the form of the levee independently of its size. Calibrating with field data from an ancient slope channel system(5) one can deduce the exponent in the thickness scaling law, which is theoretically dependent only on the grain-size of the sediment.
The shape of the levee reflects the mean shape of the individual beds within it, which decay away from the channel; however, since mud and sand respond differently to the flow, the proportion of sand to mud in individual beds (and resulting net-to-gross) also decreases away from the channel. A similar scaling and calibration procedure using outcrop data can be applied to net-to-gross decay across the levee, in order to derive the exponent in the net-to-gross scaling law. This approach can be used to reduce substantially the uncertainty in reservoir prediction in levees.