Spatial and Temporal Evolution of Densimetric Froude Number in Deep Water Distributive Systems

Hoyal, David¹, Benjamin Sheets¹ (1) ExxonMobil Upstream Research Company, Houston, TX

An important control on the performance of deep-water hydrocarbon reservoirs involves autocyclic structure associated with the formation, migration and filling of channels. This heterogeneity is often below seismic resolution, and is commonly modeled statistically based on reservoir analogs. One reasonable basis for selecting appropriate analogs is an understanding of the physics underlying channel initiation and evolution. Dimensional analysis indicates that an important control in all turbulent open channel flows, including turbidity currents, is the Froude number, which characterizes important flow properties, as well as important states in flow energetics.

Here we describe detailed laboratory experiments designed to elucidate the role of the densimetric Froude number (Fr) in the morphodynamic initiation and evolution of deep water channels in a distributive setting. In order to optimize for the formation of channels the experiments decouple the density flow and sediment transport dynamics by using salt (NaCl) as a densifying agent and crushed plastic as sediment. In particular we focus on the role of the Fr in determining the length scale of the channel segments in a distributive system. In addition we quantify, for the first time, the evolution in Fr associated with the growth of a mouth bar, subsequent channel bifurcation, channel backfilling and avulsion. Bifurcation over a channel mouth bar represents a state when the effluent inertia is diminished by lifting over the bar and is linked to a Fr threshold. We propose that the Fr has important implications for landscape evolution and morphodynamic structure in deep-water depositional systems.