THREE-DIMENSIONAL ARCHITECTURE OF BEDROCK
LITHOLOGY, WEATHERING, AND PRODUCED WATER
MOVEMENT AT THE USGS OSAGE SKIATOOK PETROLEUM
ENVIRONMENTAL RESEARCH (OSPER) SITE A, NORTHEAST OKLAHOMA
James K. Otton*
Robert A. Zielinski
U.S. Geological Survey
MS 939 Box 25046
Lakewood, CO 80225
Voice: 303-236-8020
Fax: 303-236-0459
E-mail: jkotton@usgs.gov
Drillcore description and analysis of aqueous extracts of core samples from the USGS' OSPER Site A provide a three-dimensional view of the complex sequence of variably weathered Pennsylvanian sandstone, mudstone, and shale beds, and the movement of saline produced water through them. Aqueous extracts of core samples show that Cl-rich salts extend north and west from two pits that are the primary source for Cl-rich produced water releases at the site. Saline rock extends for a distance of at least 125 meters and to depths of as much as 13 meters. Surface releases of produced water from the pits initially followed the surface topography to the north and west and more permeable zones and channels in the local colluvium to the northwest and west (Otton and others, IPEC, 2003), but releases from the pits also directly entered or moved down into the underlying bedrock. Immediately underlying the two pits, a sheet-like sandstone up to 5 m thick forms the local bedrock. This sandstone dips gently (about 1°) to the west-northwest and is underlain by 2-3 m of mudstone and shale that, in turn, are underlain by a second sandstone 5-8 m thick, second mudstone-shale 2-4 m thick, and third sandstone sequence not fully penetrated. The upper sandstone is intensely weathered as indicated by its friable character and heavy iron-staining, and was probably a favored conduit for movement of produced waters. Shale and mudstone directly below the upper sandstone also contain Cl-rich salts indicating that permeability of these finer-grained rocks was sufficient to allow produced water infiltration. The second sandstone is variably weathered and variably contaminated by salt suggesting that produced water migrated into it locally. Deeper, unweathered, dolomite-cemented sandstone and mudstone, identified by their generally gray color and hard, dense character in core specimens, are generally devoid of salt and were apparently sufficiently impermeable to be the limiting factor for downward salt penetration at the site.