Characterization of Mississippian Osage Chat in South-Central Kansas

Kansas Geological Survey Open-file Report 2002-50

The Mississippian section within the Hardtner Field is predominantly Cowley Facies, but a section of typical Chat facies occurs at the very top of the Mississippian section just below the Pennsylvanian-Mississippian contact. Porosity is in the low 30's percent, bulk volume water varies from 0.12-0.2 in a transitional pattern, permeability varies from 10-40 millidarcies, and the resistivity varies from only 1-4 ohms-m. The producing section has microporosity, which is typical for the Chat.

Chat interval developed on top of the Mississippian Cowley Formation. Chat characterized by lower gamma ray, low resistivity, high porosity, intermediate BVW

Lies west of Hardtner Field on the west flank of the Pratt Anticline along a separate structural block with an orientation perpendicular to Hardtner Field; Farthest field down the southwestern flank of the Pratt Anticline and represents the southern limit of chat fields.

Boundaries of Aetna Gas Area are not well defined due to the marginal properties of the matrix; Classified as a chat field, but produces from a mixture of chert, limestone, and dolomite which are lithologies representative of unaltered Cowley Formation; Reservoir is relatively clean with little shale, but silicification is not as significant as in the those fields with chat pay such as the nearby Hardtner Field.

Produces from cherty carbonate as the result of induced and probably natural fractures since matrix permeability is negligible. Level of alteration is reduced at this location, perhaps due to lack of thick beds of chert, less local structural deformation, or less subaerial exposure.