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The AAPG/Datapages Combined Publications Database

Kansas Geological Society


Transactions of the 1999 AAPG Midcontinent Section Meeting (Geoscience for the 21st Century), 1999
Pages 103-103

ABSTRACT: Prediction of Previous HitEffectiveNext Hit Porosity and Permeability in Mississippian Carbonates, Kansas

Willard J. Guy1, Alan P. Byrnes2, John H. Doveton3, Evan K. Franseen4

The integration of saturated and desaturated NMR responses and air-mercury and air-brine capillary pressure analyses with more conventional petrophysical techniques allows the exploration and development geologist to predict better the Previous HiteffectiveNext Hit porosity and permeability of producing reservoirs. The Schaben field in western Kansas, which has produced about 9 million bbls of oil primarily from the Mississippian Osage carbonate, has been studied extensively as a Class 2 USDOE project.

The primary reservoir is a coarsening-upward spicule-rich dolomite wackestone-packstone-grainstone deposited on a shallow southwestward dipping ramp. The dominant grain type is sponge spicules and their molds intermixed with a dolomite mudstone. The porosity primarily is moldic, intercrystalline, and intergranular, but may contain a significant number of vugs. Grain or crystal sizes are fine (<100 μm to <2 μm) resulting in very fine microcrystal line pores. Determination of Previous HiteffectiveNext Hit porosity requires additional data than that available through typical well log suites.

The oil column in the Schaben field is between 35–50 feet and is discontinuous because of a heterogeneous reservoir. The integration of NMR responses, which predominantly measures the size of the pores, and the capillary pressure data (which predominantly measures the size of the pore throats), allows an excellent evaluation of the pore geometry of the reservoir. The critical component of the NMR evaluation is the T2 relaxation-time cutoff, which divides the Previous HiteffectiveTop and ineffective pore sizes. The T2 cutoff within the Schaben field is typically about 20–25 ms as defined by the point of divergence of the desaturated and saturated cumulative porosity curves. As the T2 values increase, there is an increase in pore size and permeability.

Acknowledgments and Associated Footnotes

1 Kansas Geological Survey, Lawrence, Kansas

2 Kansas Geological Survey, Lawrence, Kansas

3 Kansas Geological Survey, Lawrence, Kansas

4 Kansas Geological Survey, Lawrence, Kansas

Copyright © 2006 by the Kansas Geological Society