Abstract: Reservoir Facies Architecture of Two Upper Point Bar Deposits

Arnold H. Bouma, Lars O. Bouma

The exposed upper parts of the oldest and youngest point bar deposits along the Mississippi River at Duncan Point south of Baton Rouge, Louisiana, present information about the change in reservoir architecture during their latest stages of development. The youngest and inner one is still growing because it becomes inundated yearly and is sandier than the higher point bar that receives sediment only during the very occasional high flood stage. Maximum inundation of the point bar normally results in a wide and shallow water body across the entire upper point bar, providing conditions that are more favorable for the deposition of fine-grained sediment. The dense vegetation on the older point bars helps reduce current velocities.

Although gamma-ray measurements indicate that the sand:mud ratio differs slightly between these two point bars, the sedimentary structures are much the same in type but not in occurrence. Horizontal heterogeneity can be observed in both locations, but vertical connectivity changes from reasonable in the younger point bar to low in the older one because of silty clay and clayey mud layers in between sandy ones.

The exposures together give more complete information about the upper point bar reservoir characteristics. A gradual decrease in vertical permeability is typical, but sealing conditions require that fine-grained overbank muds cover the point bar deposits.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994