Depositional Architecture-Based Correlation Techniques for Fluvial and Deltaic Reservoirs in Lacustrine Basins
Yu, Xinghe; Li, Shengli; Shunli, Li; Chen, Bintao
Oil fields in Eastern China are composed of predominately lacustrine deltaic and fluvial deposits which exhibit complex reservoir architectures (cake-layer, jigsaw puzzle, labyrinthine or shingled). The recognition of various reservoirs involves making a well correlation where data are limited to a few, widely spaced cores and well logs. The geologists are therefore required to infer the lateral reservoir character by various means. Depositional architecture-based techniques, represent genetic interpretations of reservoirs depending upon their certain sedimentary environments and architectures, are available to help the geologists make a reliable geological correlation. In certain sedimentary environments, the individual sediment units can exhibit their specific architectural characteristics (geometry, length scale and vertical variation). And the distinctive patterns or group of patterns for reservoirs can be recognized on well logs and cores.
As a generalization, reservoirs with deltaic deposits commonly consist of basin-ward dipping and off-lapping clinoform prograding strata. Reservoirs with fluvial deposits show rapid facies variation and various architectures (lateral accretion, downstream accretion and overbank fills). This study is such one exercise whereby different geological correlation techniques based on various depositional architectures of reservoirs were discussed for their potential impact on hydrocarbon development. Shihezi Formation (Middle Permian) in Sulige oil field (Ordos Basin) and Badaowan Formation (Lower Jurassic) in Cainan oil field (Junggar Basin) have been correlated using well logs and core data. Meandering fluvial deposits were identified in Shihezi Formation with core characteristics (erosional surfaces, trough and planar cross-beddings) and log patterns (bell-like); and fan delta deposits in Badaowan Formation with massive conglomerates and blocky gamma-ray curve. Combined with the thickness of sandbodies, net-to-gross and conceptual guides derived from geometries observed in basin margin outcrops, the Shihezi Formation was correlated as labyrinthine (channel complexes with point bars and clay plugs); and the Badaowan Formation was correlated as shingled geometry with inclined sediment bodies (prograding configuration) instead of lithostratigraphic correlation as cake-layer. The correlations for Badaowan Formation which were verificated by production data exhibited improvement of development efficiency by 12.5%.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013