Characterization of Mississippian Osage Chat in South-Central Kansas

Kansas Geological Survey Open-file Report 2002-50

• Approximately 22 km2 in size with chat thickness ranging from 0 to 37 m
• Chat abruptly thins on the northern and northeast edges of the field which are structurally higher on the surface of the Mississippian
• Trapping of gas and oil is associated with loss of permeability at these edges of the chat (Zajic, 1956; Curtis, 1968)
• Northern field boundaries are orthogonal, residing along similarly oriented basement lineaments that pass through Glick Field located 8 km to the southeast
• New log correlation within the field delimits four low resistivity, generally high porosity chat intervals. These chat beds are separated by thin, tight zones that can be correlated through much of the field. The chat layers have similar gamma ray values and thicknesses while porosity varies. Lowest chat layer overlies the dense lower Mississippian carbonates
• Correlation of the lower carbonates across the northern edge of the field indicates approximately 24 m of vertical uplift over the distance of 200 m (40-acre well spacing) suggesting faulting.
• A basal chat layer, with apparently low permeability, persists beyond the field boundaries, but is not productive in the vicinity. Reservoir development is greatest below the sub-Pennsylvanian unconformity and diminishes to the south away from the unconformity abruptly grading into unweathered chert-rich Cowley Formation
• Interbedding of chert-rich intervals and crinoidal wacke-grainstones in Nichols Field closely resembles the stratigraphic succession in Tjaden 1-A WIW from Spivey-Grabs field and suggest regional correlation of the unconformity surfaces on the top of the crinoidal wacke-grainstones, which would then qualify as sequence boundaries.

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