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Norsk Hydro Research Centre, Sandsliveien 90, 5020, Bergen, Norway
In heterogeneous reservoirs, an optimal number of large-scale flowunits (here termed building blocks) must be defined prior to detailed geological modelling. For the fluvial-dominated fan-deltaic parts of the Tilje Formation, Mid-Norwegian shelf, four fan-delta-front building blocks have been defined. Quantifications with regard to the geometry and spatial arrangement of these building blocks have been made based on outcrop studies of similar sediments in the Ridge Basin, California. The four building blocks are composite delta-front units (CDF), mouth-bar sandstones (MS), mouth-bar-related mudstones and carbonate-cemented zones (MMC), and distal delta-front mudstones (D). The main reservoir units in the Tilje Formation are the composite delta-front units. These have large lateral extents (tens of kilometres), and occur in three intervals separated by impermeable zones of building block D. Within the CDF units, the main heterogeneity is the alternation between permeable mouth-bar sandstones of building block MS and impermeable zones of building block MMC. The mouthbar sandbodies have width (W)/thickness (T) ratios of 220–525, and constitute a considerably larger percentage of the reservoir volume than the less widespread MMC flow-barriers. Hence, the internal communication within the CDF units is believed to be generally good.
