Reservoir analog model for oolite-microbialite sequences, Miocene terminal carbonate complex, Spain

Abstract

Static three-dimensional (3-D) reservoir analog models were constructed for the Miocene terminal carbonate complex (TCC) in southeastern Spain. The models used field data collected from two areas containing exceptional 3-D exposures (La Molata; La Rellana-Ricardillo). Four TCC sequences in each area are composed of oolite, microbialite (thrombolites, stromatolites), bioclastic sands, and coralgal reefs deposited over paleotopographic relief of 33–76 m (108–249 ft). The models integrate field, laboratory, and petrophysical data with results providing a workflow and reservoir analogs useful in evaluating oolilte and microbialite reservoir characteristics in relation to paleotopography and sea level change. Results from this study reveal favorable reservoir-quality values with the potential for substantial hydrocarbon storage for many lithofacies. Flow and baffle facies were distinguished for the models based on thickness, lateral distribution, porosity, and permeability values. Trough cross-bedded ooid grainstone is volumetrically the most abundant lithofacies within both models, is laterally extensive across the entirety of sequences, has large storage capacities with good permeability, and has good connectivity with other flow facies. This facies represents the best reservoir-quality facies and would be the primary target for hydrocarbon exploitation. Microbialites act both as reservoir and baffle facies. Thrombolites, in particular, are concentrated downslope and in a more restricted embayment but vary between porous and nonporous facies. Stromatolites and fenestral ooid grainstones are concentrated at sequence boundaries and would create laterally extensive baffles with significant thicknesses at the sequence boundaries. Sea level interacting with both paleotopography and paleogeography were identified as the main controls on sequence development and reservoir heterogeneity. An understanding of these controls can aid in exploitation and identification of oolite-microbialite sequences.