Modeling Diagenetic Overprint in Both Fluvial and Tidal Influenced Deltaic Deposits, Outcrop Example Form the Eocene Roda Sandstone Formation, Spain

Geoffray Musial and Richard Labourdette
TOTAL S.A./Montpellier 2 University, Pau, France

Early calcite cementation in deltaic depositional settings can highly complicate hydrocarbon recovery and production. This calcite cementation is directly linked to subaerial exposure or non-deposition duration. This leads to a complex distribution of baffles and barriers, strongly dependant on depositional processes involved in deltaic deposition (e.g. fluvial or tide dominated systems).

The Roda Sandstone Formation in Spain is an outcrop example of a lowstand depositional system tract, composed of a succession of fluvial dominated sandy bodies and wide tidally influenced sandy lobes. These units are clearly identified, based on their geometrical characteristics and cementation styles.

This study uses sedimentological descriptions, sequence stratigraphy, geological modeling and fluid flow simulations to better represent cemented level distributions and understand their impact on hydrocarbon recovery.

Eight depositional facies and three cementation levels are distinguished and modeled to characterize the architecture of the two studied units.

The constructed model takes into account the geometrical characteristics of these two reservoir analog types. The resulting stratigraphic grid shows prograding depositional sets typical of the fluvial dominated basal unit and compensation lobes typical of the tidally influenced upper unit. This configuration allows diagenetic products to be integrated deterministically, in conjunction with depositional architecture and processes.

The final model shows a realistic distribution of cementation into the studied sedimentary bodies. Fluid flow simulations performed underline the different effects of calcite cementation in both fluvial and tidal dominated depositional settings. The differences observed reinforce previously observed subsurface production histories and the reliability of the proposed modeling workflow.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas