Characterization of Mississippian Osage Chat in South-Central Kansas

Kansas Geological Survey Open-file Report 2002-50

Characteristics of chat reservoirs in study area.

• Low resistivity accompanied by low natural gamma ray and high porosity
• Extreme lateral, vertical, microscopic, and macroscopic heterogeneity
• Fields are segmented into pods or compartments of good reservoir quality separated by areas of poor reservoir quality
• Porosities in chert facies range from approximately 20 to 50%
• Routine air permeabilities from 5 to 500 md.
• Often high water saturations, long transition zones and complex fluid contacts
• Incompletely silicified lithofacies or lithofacies associated with tripolitic chert:
  cherty dolomite and sucrosic dolomite
  cherty dolomite reservoirs exhibit characteristics more typical of carbonate reservoirs (e.g., Aetna Gas Area):
  • Relatively low porosity, 10-20%, permeabilities less than 5 md
• Water saturations from 35-70%
• Bulk volume water (BVW) from 0.06-0.10.
  Irregularly distributed sucrosic dolomite in cherty limestone (e.g., Bates Field)
  • porosity ranging from 10-18%
  • permeabilities between 5 and 70 md
  • low irreducible water saturations
  • BVW between 0.05- 0.07.