Characterization of Mississippian Osage Chat in South-Central Kansas

Kansas Geological Survey
Open-file Report 2002-50

Rock Petrophysics

Modified Pickett crossplot (PfEFFER)

A modified Pickett crossplot (PfEFFER) was used to analyze patterns in porosity, resistivity, and saturation in the reservoir. Each data point on these plots represents a half-foot interval and points are linked together in sequence by depth to reveal trends through the reservoir. From the Archie relations, saturation contours and bulk volume water contours are superimposed. Details of the methodology in using the modified Pickett plots are described in Doveton et al. (1996).

On the modified Pickett plots shown to the right the chat in cycles D and B exhibit very contrasting and distinctive patterns. Cycle D, above 4322 ft (1317.7 m)`is the chert conglomerate with lower BVW, porosity and water saturation. BVWs values are considerably higher than typical carbonates or sandstones suggesting finer pores. Clustering of values in the uppermost portion of cycle D in the chert conglomerate is followed by a transition and a second clustering of values in the upper chat zone of cycle D. The dual clusters suggest the presence of two intervals at or near irrreducible BVW, but with somewhat larger pore sizes in the chert conglomerate than the upper chat. The lower chat zone in cycle B shows a steady decline at nearly constant porosity, interpreted as a transition zone to the oil-water contact. The lower zone appears to reach the water line (Ro), where Sw = 100% for Archie parameters of m=1.7 and n=2.0.

Lithology solution from Pe-Density-Neutron logs

Mississipppian Chat is typically predominately chert with variable amounts of clay, calcite, and dolomite. The depth plot above shows location of zonation and proportion of lithology.

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Last updated January 2003