Oomoldic Reservoirs of Central Kansas, Controls on Porosity, Permeability, Capillary Pressure and Architecture
Kansas Geological Survey
Open-file Report 2002-48
To understand Kansas Pennsylvanian oolite shoal architectures and their position within the stratigraphic framework. To understand textural controls on petrophysical properties in oomoldic limestones and develop quantitative tools for improved reservoir properties.
Cyclic carbonate strata of the Pennsylvanian Lansing-Kansas City groups represent important enhanced oil recovery targets on the Central Kansas Uplift and thus require understanding of controls on reservoir properties and architecture.
Interaction of changing sea level and local episodic processes, such as tidal currents along a broad topographically high shelf area, led to accumulation and local reworking and redeposition of elongate stacked, shingled, and cross-cutting oolite sand bars (0.5-10 m thick). Subaerial exposure and meteoric water percolation led to microporous cementation around the aragonite ooids and often dissolution of the ooids and variable development of vuggy porosity. Resulting oomoldic grainstones, the principal reservoir lithofacies, underwent variable degrees of early or later fracturing and crushing, providing connection between otherwise isolated oomolds.
Grain size variation, location on oolite buildups and local topography, and interbedded carbonate mud (aquitards) influenced the nature and extent of diagenetic overprinting and resulting permeability-porosity, and capillary pressure properties.
The relation between permeability (0.01-400 md) and porosity (5-35%) is significantly influenced by:
The influence of these variables complicates the use of porosity as an effective predictor of permeability without information about lithology. For "average" connectivity:
logk(md)=0.16 f (%) - 2.32
Vug and fracture enhanced connectivity and oomold isolation can respectively increase and decrease permeability by a factor of up to 25X.
Irreducible water saturation (Siw) and residual oil saturation after waterflooding (Sor,w) are also strongly controlled by connectivity and correlate highly with permeability:
Siw(%) = 35.7exp(-0.46 logk (md))
Sor,w(%) = -20.9 logk (md)+ 59
These oomoldic reservoirs provide insight into the interactions of rock fabric-architecture-diagenesis on reservoir properties.
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Last updated March 2004