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Depositional Reservoir Quality of Deep-Water Channels and Lobes: Aínsa and Jaca Basins, Spain


Deep-water stratigraphic successions reflect the interplay of allogenic and autogenic factors, which controls their depositional architecture and distribution of sedimentary character. Depositional reservoir quality relates to the primary, process-controlled fabric prior to post-depositional modification. The secondary, diagenetic fabric is strongly controlled by the primary texture and mineralogy. Therefore, understanding the primary processes controlling spatial and temporal changes in fabric and mineralogy is critical to improved prediction of reservoir performance at different hierarchical levels. A well-constrained, exhumed lobe complex in the Jaca Basin, and a channel element in the Aínsa Basin, northern Spain, were sampled to characterize the depositional reservoir quality of facies in axial to marginal settings, from bed-scale, to lobe complex and channel complex-set scales respectively. Heterogeneity and primary texture trends from grain- to element-scale were used to populate larger hierarchical levels. A quantified sedimentological and petrological characterization of the successions enables realistic comparison to subsurface datasets. The grain-scale fabric of samples was analysed in thin-section to establish how different depositional processes affect textural properties, at grain- and bed-scale, and therefore reservoir quality of each process-based facies type. High-density turbidites exhibit the best primary textural properties, followed by low-density turbidites, and hybrid event beds respectively. Construction of architectural panels reveals the proportion of each facies at each sub-environment within reservoir-scale geobodies, enabling estimation of, and rates of change in, reservoir quality spatially within submarine channels and lobes.