Facies and Flow Units Distribution in Sandy Estuaries

Rojas, Temistocles S.¹, Dr. Deborah S. Lawrence² (1) PDVSA, Maracaibo, Venezuela (2) University of Reading, Reading, England

Estuaries are recognized as depositional systems with high potential for preservation within the geological record, and oil reservoirs formed in such environments are widely reported.

Facies models for estuaries have been developed, but the relationship between facies and the distribution of petrophysical properties, such as porosity and permeability, has not yet been well explained.

We propose a flow units distribution model working with three modern estuarine systems (Severn, Mawddach and Camel estuaries) and three small tidal inlets on the North Norfolk Coast, all located in the United Kingdom. Modern sand deposits were described and sampled at these sites and it was possible to distinguish 14 lithofacies and 7 facies associations. Facies association were related to porosity and permeability analyses, resulting in a characterization of the distribution of flow conditions within the estuary. This revealed the presence of 4 flow units within the sandy deposits of these systems.

More prospective flow units were located towards the mouth of the estuaries and units with poorer flow conditions were found towards the estuary head and along the lateral boundaries of the estuary, parallel to the principle flow directions.

The lateral and vertical distribution of these units have a great significance for exploration and exploitation of reservoirs developed in such environments. Possible distributions of these units under different relative sea level variations are demonstrated in this work.