Clastic Facies Development under Unsteady Flow Conditions and Consequences over Petrophysical Properties: An Experimental Approach

Temistocles S. Rojas¹ and Deborah S. Lawrence^2
1 Petroleos de Venezuela (PDVSA), Maracaibo, Venezuela
² The University of Reading, Reading, England

Experimental simulations, which seek to identify the variables controlling sedimentary facies, can be a powerful tool in reservoir characterization as this information aids in understanding and predicting the distribution of petrophysical properties within a hydrocarbon reservoir. The simulations presented consider the behavior of bedforms under unsteady flow conditions, which mimic a tidal cycle. The resultant depositional facies are described in terms of the internal and external physical structures of the deposits. The development of porosity and permeability is related to the described sedimentary facies and the flow conditions under which such facies were originated. The experimental runs were conducted in a recirculating flume using three different types of sandy sediments, with and without a mud fraction, and cyclically varying the flow conditions.

In some cases, a lag in the response of the bedforms to changes in flow conditions was observed, and this was considered a consequence of insufficient sediment transport during the flow cycle. Different values of permeability were obtained within samples of the same grain size but developed under different flow cycles, implying that flow conditions control the packing of the sediments and packing is a variable with a strong influence on porosity and permeability, then flow conditions influence permeability and porosity. Variations in porosity and permeability were found to be related basically to flow-conditions (packing), grain-size, sorting and mud content.