ABSTRACT

The exposed upper parts of the oldest and youngest point bar ridge deposits at Duncan Point south of Baton Rouge, Louisiana, present information about the change in reservoir architecture during their latest stages of development. The youngest point bar deposit is still growing because it becomes inundated yearly and is slightly sandier than the higher oldest point bar, which only receives sediment during an occasional high flood stage. The dense vegetation on the older ridges helps to reduce current velocities.

Although gamma-ray measurements indicate that the sand/mud ratio differs between these two point bars, the sedimentary structures are much the same in type but not in occurrence. Horizontal heterogeneity is rather high in both locations, but vertical connectivity is low in the younger point bar and even lower in the older bars because of some thin interbedded clayey silt layers in between sandy beds.

Together, the exposures reveal the complexity of the upper point bar reservoir characteristics. A very gradual decrease in vertical permeability is typical, but sealing conditions require that fine-grained overbank muds or marine clays overlie the point bar deposits.