Deciphering Heterogeneous Reservoirs: Insights from Integrated Modern Analogues, Ancient Outcrops, and Subsurface Data, Key to Unlocking Opportunities

Mixed aeolian-fluvial successions are known to form major hydrocarbon reservoirs in many places worldwide, often forming excellent reservoirs or pathways. However, heterogeneities inherent to these settings can pose significant challenges, requiring advanced reservoir characterization techniques. This study aims to investigate the impact of temporal and spatial variations on the preserved stratigraphic architecture of mixed aeolian-fluvial reservoirs resulting from morphological changes in depositional systems, leveraging insights from modern analogues, ancient outcrop, and subsurface datasets. This workflow involves investigating data from three primary sources: (i) analyzing high-resolution satellite imagery data from modern systems to examine geomorphological relationships and quantify the geometry, orientation, and morphology of depositional elements in both settings. (ii) conducting detailed observations of preserved successions from ancient outcrops, and (iii) describing and interpreting subsurface core and reservoir data. The results were integrated and validated against actual data to evaluate stratigraphic heterogeneity in subsurface reservoirs. Ultimately, multiple depositional models were constructed, explaining various reservoir quality and behavioral scenarios. This comprehensive integrative approach of modern, ancient and subsurface reservoir data revealed the intricate dynamics of interacting aeolian-fluvial systems. Reservoir lithofacies consist mainly of moderate-well-sorted, fine-medium-grained sandstones, exhibiting vertical and lateral juxtaposition, thus creating a complex depositional architecture with multi-scale heterogeneities. Geomorphologic analysis of modern analogues highlights common occurrences of aeolian-fluvial interactions at the margin of aeolian deposits, where fluvial drainages frequently penetrate tens to hundreds of kilometers into the aeolian dune fields. On other areas, fluvial systems dammed or ponded near the margin of aeolian system. Long-standing fluvial channels may partition dune fields, whereas ephemeral pathways occasionally connect isolated dune fields during periods of migrating sands, in addition to the influence on the water table. Such dynamic system interactions yield crucial controls on fluid migration, forming key flow barriers represented by flood surfaces and sequence boundaries. Two main categories of reservoirs identified based on their geometric relationships: (a) reservoirs displaying excellent lateral continuity of aeolian facies coupled with straightforward stratigraphic correlations, and (b) highly compartmentalized reservoir facies subject to intricate stratigraphic correlations and truncations by fluvial sediments. At a higher resolution, generated models reveal that heterogeneous reservoir attributes to the interaction of lithofacies patterns, sedimentary structures, and depositional architectures. This study presents a comprehensive, integrative approach combining modern analogues, ancient outcrops, and subsurface data to decipher the complexities of mixed aeolian-fluvial reservoirs. By unveiling the intricate dynamics of interacting depositional systems, this work yields novel insights into the occurrence of heterogeneous reservoirs. The developed models provide valuable inputs for understanding the vertical and lateral variability of these systems, enabling more precise predictions of reservoir behavior and unlocking new opportunities for exploration and field development.