Sedimentary Structure – Morphology Relationship in Deltas

The connection between the morphology of a delta and its grain-level sedimentary structure was investigated numerically with the aim of extracting sedimentological and depositional history information from seismic data. Such an ability to extract the sedimentary structural information from the gross seismic horizon data will be very valuable, especially for oil exploration from ultra-deep water where the exploratory well cost is exhorbitant. The model developed describes a deltaic system in terms of three main dimensionless parameters which account for (i) the tendency of particles to settle out of the turbidity current or remain suspended in it; (ii) the ratio of the sediment deposit bed thickness to the turbidity current thickness; and (iii) the ratio of the Stokes settling velocity to the inlet velocity of the current. The average grain size of the particles constituting a delta could be explicitly inferred from the match of the model prediction to the measured seismic horizon, and can be used to determine the hydrocarbon bearing capacity of a formation, especially when core data, well and production logs are unavailable.

The results from our simulations suggest that the dominant mechanism for the evolution of a delta is particle transport via convection, contrary to the commonly held assumption that bulk transport processes represented grossly as geomorphic dispersion are responsible for deltaic evolution. Based on our hydrodynamics-based delta progrdation model, an analytical approximation for the progradation velocity of the delta was also derived using material balance arguments. The performance of the model was successfully validated using field data from the Mississippi and the Rhine deltas.