Characterization and Geostatistical Modeling of Facies and Diagenesis in a Mixed Carbonate-Siliciclastic Reservoir Analog (Ilerdian Alveolina Limestone, Serraduy, NE Spain)
Carbonate sedimentary facies and their related reservoir heterogeneities can be modeled with geostatistical approaches. However, such facies models often reproduce the reservoir petrophysical properties incompletely, as the diagenetic events can alter or improve the reservoir porosity and permeability. The objective of the proposed work is to build a fine grid geological model which reproduces both the sedimentary facies and the diagenetic trends interpreted from outcrop observations.
In NE Spain, the Ilerdian (Early Eocene) Alveolina Limestone Formation is composed of mixed siliciclastic-carbonate facies, outcropping in the Graus-Tremp foreland basin. Sedimentology, petrography and diagenesis analyses were carried out from field and laboratory data in order to constrain the high-resolution architecture of the different sedimentary bodies and the construction of paleogeographic models within a sequence-stratigraphy framework.
This model corresponds to a carbonate ramp (shallow lagoon with important tidal influence closely associated to bioconstructed mounds evolving toward open lagoon and open-marine ramp facies). This system is influenced by siliciclastic continental inputs in its more proximal part (fluvial- and tidal-dominated deltaic complexes).
Results from diagenetic analyses show early diagenetic phases characterized by isopachous calcite cements with marine isotopic signatures; early to shallow burial phases are dominated by drusic cements with concentric zoning; a late stage cement with sector zoning luminescence has been also observed. This study also emphasized the impact of the silty/argillaceous interbedded facies on the distribution and type of cementation in the carbonate reservoirs, by expulsing specific fluids during compaction and further acting as permeability barrier.
In order to reproduce the facies organization of this mixed system, a 3D gridded model has been constructed, based on nine surfaces (sequence boundaries and maximum flooding surfaces) that have been recognized on all sections. The relationships between sedimentary facies and diagenesis have been used to define lithofacies simulation rules for the plurigaussian algorithm, that aims at simulating both the distribution of sedimentary facies and the diagenetic overprint.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009