Alan P. Byrnes1, Martin K. Dubois1, Michael Magnuson1
(1) Kansas Geological Survey, Lawrence, KS
ABSTRACT: Western Tight Gas Carbonates: Comparison of Council Grove Group, Panoma Field, Southwest Kansas and Western Low Permeability Sandstones
The Hugoton natural gas area of southwest Kansas has produced over 27 Tcf of gas from the Hugoton, Panoma, Bradshaw, Greenwood, and Byerly fields. Of this total, over 2.7 Tcf have been produced since 1968 from low-permeability carbonates of the Lower Permian Council Grove Group, Panoma Field. Previous research has documented low-permeability gas sandstone properties. Council Grove low permeability carbonates illustrate the universality of certain low-permeability rock properties and provide insight into lithologic controls on reservoir properties.
Like Mesaverde Group and Frontier Formation low-permeability sandstones and siltstones (medium to very fine grained, massive to flasier bedded, litharenite to sublitharenite), Council Grove limestone porosity and permeability decrease with decreasing grain size (grainstone to mudstone) and increasing shalyness. In situ carbonate porosities average 0.5 porosity percent less than routine porosities compared with approximately 0.8 porosity percent less in sandstones. In both groups in situ Klinkenberg permeability (ki) exhibits similar increasing difference from routine air permeability (kair) with decreasing permeability. For kair<1 millidarcy: log10ki=1.5(+0.1) log10kair - 0.3(+0.1). Both also exhibit the characteristic exponential or cube root core permeability decrease with increasing confining stress from routine to in situ stress conditions.
Both groups of low-permeability rocks exhibit decrease in "irreducible" water saturation (Swi) with increasing ki. Differences in the slope of a log Swi-logki correlation are consistent with differences in clay content and distribution. Comparison of carbonate and sandstone rocks indicate that many low-permeability petrophysical properties are "universal" and indicate the moniker "tight gas" isn't just for sandstones anymore.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado