Print this pageSequence Stratigraphic Architecture and Energy Resources of Bartlesville Sandstone
YE, LIANGMIAO
The Pennsylvanian Bartlesville Sandstone, a main oil producer in Oklahoma and Kansas, is traditionally interpreted as part of a large deltaic complex deposited in essential as a single regressive interval. However, regional scale to reservoir scale investigation in both outcrop and subsurface in an area over 2000 square miles in northeastern Oklahoma reveals that Bartlesville Sandstone is mainly fluvial incised valley-fill deposited in a transgressive manner from a lower braided fluvial to an upper tidal-influenced meandering fluvial depositional systems.
Outcrop survey illustrates that a type-I sequence boundary exits at the base of Bartlesville Sandstone, indicated by subaerial erosion of underlying Savannah Shale and basinward facies shift from marine shale below to braided fluvial deposits above. Core facies and log facies interpretation validates the facies shift. Well log correlation shows Bartlesville Sandstone thickens at the expense of the Savannah Shale. The incised valley exits from north to south over a distance of 120 miles within Oklahoma, and is 4-5 miles wide in Washington County to over 40 miles wide in the Eufaula Lake area. The thickness of Bartlesville Sandstone interval varies from 120-250 ft within the valley to less than 20 ft outside the valley.
Depositional environment interpretation based on outcrop, core, and log curves demonstrates that the whole Bartlesville Sandstone incised valley-fill section consists of two sequence stratigraphic architectural elements: (1) the lower lowstand system tract 80-150 ft, composed of braided fluvial deposits and distal lowstand delta; (2) the upper transgressive system tract 70-100 ft, composed of meandering fluvial, estuarine tidal, and shallow marine deposits. The regional Inola Limestone marker, capping the Bartlesville Sandstone interval, is equivalent to a condensed section which represents maximum flooding.
The lowstand systems tract (LST), holding about 75 percent of OOIP discovered in Bartlesville Sandstone, played a key role in the past 90 year development and is almost depleted. The transgressive systems tract much more complex and heterogeneous and less developed in comparison with LST, offers the main potential for further reservoir development.