Genetic Stratigraphy and Reservoir Characterization of the Spiro Sandstone, Red Oak Field, Arkoma Basin, Southeastern Oklahoma
Brian W. Horn
The Lower Atokan Spiro sandstone is a mixed carbonate-silicilastic reservoir that produces hydrocarbons from three discrete stratigraphic intervals at the Red Oak Field. Reservoir-quality sandstones develop in the seaward stepping sub-Spiro sequence (highstand system tract), landward stepping Foster "channel," and upper Spiro depositional sequences (transgressive and highstand system tract). The sub-Spiro and Foster "channel" sequences are separated by regional unconformity interpreted as a sequence boundary. Regressive marine shoreface cycles, genetically related to the sub-Spiro shale, comprise the lowermost producing interval. Fluvial/estuarine valley-fill (Foster channel) sandstones progressively onlap the sequence boundary overlying the regressive shoreface cycles an juxtapose reservoir-quality sandstones of different sequences, creating a complex reservoir architecture. Upper Spiro reservoir sandstones are developed within marine shoreface cycles that are deposited in a landward-stepping succession (highstand systems tract) following the drowning of incised paleovalleys. These aggradational / retrogradational successions downlap onto the valley-fill and sub-Spiro sequences representing the final stages of Spiro deposition prior to the high stand of sea level during Middle Atokan time.
Regional stratigraphic correlations demonstrate progressive basinward truncation of the sub-Spiro regressive shoreface cycles by an erosional surface, creating a network of incised paleovalleys across the Pennsylvanian shelf. Based on core, well log, and outcrop interpretations, the magnitude of the facies offset across this sequence boundary indicates that a significant volume of reservoir-quality sediment has been partitioned basinward of the current producing areas. High-resolution correlations reveal that reservoir compartments are created by stratigraphic discontinuities resulting from the incisement of the sub-Spiro shoreface and deposition of the overlying Foster channel reservoir facies. This stratigraphic architecture explains reservoir geometry, compartmentalization, and res rvoir heterogeneity of the Spiro sandstone at Red Oak Field. Further development of this regional correlation and detailed stratigraphic analysis will result in both a better understanding of other Spiro sandstone reservoirs and the identification potential Spiro reservoirs in untested geographic locations.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California