Fluvial reservoir architecture, directional heterogeneity and continuity, recognizing incised valley fills, and the case for nodal avulsion on a distributive fluvial system: Kern River field, California

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Abstract Kern River field of California contains a succession of Upper Miocene fluvial deposits more than 1000 ft thick that represents a distributive fluvial system (DFS). Well spacing is so tight (100–200 ft) that well logs can be used to create images that appear similar to seismic sections that can be readily interpreted. Directional heterogeneity and continuity are associated with orientation of the channelized geobodies: parallel to paleocurrent direction, sandstone continuity is measurably higher. Larger channelized geobodies at Kern River field are on average 46 ft thick and 1.4 mi wide (perpendicular to paleocurrent flow). They possess a mappable lower erosional surface and internally, consist of high net-to-gross, multistory sandstone bodies. These large channelized geobodies are interpreted to represent the fills of incised valleys. Incised valley deposits are produced by punctuated incision and aggradation typically related to falls in base level, from whatever origin. The valleys are then filled during subsequent periods of aggradation, first resulting in the filling of the valleys and then allowing the floodplain to aggrade as well. Two systems tracts can then be defined (after Shanley and McCabe, 1994): the incised valley tract, representing the typically high net-to-gross fill of the incised valley, and the aggradation tract, representing the aggradation of the floodplain as well as associated single- and multistory sandstone bodies that are not contained within incised valleys. The high frequency of these geobodies may be associated with changes in Late Miocene climate, base level, eustacy, and autocyclic nodal avulsions on a DFS.

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