Timothy A. Cross¹, Margaret A. Lessenger¹
(1) Colorado School of Mines, Golden, CO

Abstract: 3-D stratigraphic model of deep-water systems based on energy and rheology

We have written a 3-D simulation of deep-water sediment-gravity flow deposition that: (1) creates elongate fans with terminal lobes; (2) fills topographic lows between previously deposited lobes; (3) creates topographic compensation at all scales (individual flows, lobes and coalescing fans); and (4) creates flow conduits (“channels”) with levee-like forms at seismic scales. Model simulations may be converted to a petrophysical which may be input for reservoir simulation.

A mass of sediment of specified concentration, grain-size distribution, volume and position is released, approximating a slump failure or other point source. The potential energy (slope), rheology and flow mass determine the acceleration. Resisting forces are from friction. The flow velocity is the balance among these forces acting on a sediment/water mass of specified concentration.

The sediment mass flows downhill, perpendicular to seafloor contours. Flows are funneled through lows between topographic highs. Flows are deflected around topographic highs; the amount and angle of deflection is a function of the flow thickness and and inertial energy relative to the relief of the high. The dimension and aspect ratios of the flow are determined by the flow strength. As flow strength increases, flow thickness may increase up to a maximum thickness determined by the flow strength. If the flow becomes confined, it thickens. If it thickens above the rheologically determined value, it thins down the contours until it has the rheologically determined aspect ratio. If unconfined, the flow thins.

Deposition is determined by a critical value of the dimensionless Hampton number. The model changes the rheological behavior of flows as sediment is deposited. Deposition reduces the sediment concentration in the remaining flow and reduces the flow strength. The petrophysical properties of the sediment are those at the time the flow freezes.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana