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