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Submarine Fan Stratigraphy Described as a Function of Hydraulic Variables

Abstract

Submarine fans are complex distributive channel systems that represent the final sediment sink for the fluvial/marine system and are prime targets for hydrocarbon reservoirs. As with other types of distributive systems, e.g. deltas and alluvial fans, submarine fans have an internal cyclicity that persists without any external forcing due to non-linear sediment transport mechanics. These mechanics are not included in basin-scale kinematic models and therefore the emanating complexity is absent. A significant amount of heterogeneity is generated over intermediate time and length scales, e.g. channels and lobes and their eventual complexes, that dictate the distribution of porosity and permeability and flow baffles and barriers in reservoirs. That complex internal geometry is generated via intrinsically dynamic processes indicates a clear tie between the formative hydraulics and the resulting stratigraphy. This interrelationship has yet to be fully understood. Herein we present an experimental study aimed at quantitatively explicating mesoscale hydraulics and further tying measured hydraulic properties to stratigraphic architecture. This is done via a calibrated particle tracking velocimetry (PTV) method combined with high frequency bathymetric scans and solution of governing equations. From this data we explore Froude number control on mesoscale submarine processes primarily in the supercritical regime. While supercritical flow may be uncommon in subaerial environments, it is more readily achieved in subaqueous settings due to the effects of the small density contrast between turbidity current and ambient fluid. Given this reality, supercritical architecture is of particular interest to the geologic community and the petroleum industry. We propose a general model for submarine fan deposition predicated on process-based scaling relationships that incorporates the role of the formative hydraulics (e.g. Froude number, velocity, depth, sediment mobility) on the sedimentary product.