Regional Petrophysical Properties of Mesaverde Low-permeability Sandstones

Byrnes, Alan P.¹, John C. Webb², and Robert M. Cluff^2
1Kansas Geological Survey, Lawrence, KS
²The Discovery Group, Inc, Denver, CO

     Petrophysical properties of Mesaverde Group tight gas sandstones for the range of lithofacies present in the Washakie, Uinta, Piceance, Upper Greater Green River, Wind River, and Powder River basins exhibit consistent trends among lithofacies. Grain density for over 2400 samples averages 2.654±0.033 g/cc (±1sd) with grain density distributions differing slightly among basins. The Klinkenberg gas slip proportionality constant, b, can be approximated using the relation: b(atm) = 0.851 kik^-0.34. Regression provides a relation for in situ Klinkenberg permeability (kik): log kik = 0.282 Φi + 0.18 RC2 – 5.13 (±4.5X,1 sd), where Φi = in situ porosity, and RC2 = a size-sorting index. Artificial neural network analysis provides prediction within ±3.3X. Analysis of 700 paired samples indicates 90% of all samples exhibit porosity within 10%-20% variance. Permeability exhibits up to 40% variance from a mean value for 80% of samples.
     Capillary pressure (Pc) exhibits an air-mercury threshold entry pressure (Pce) versus kik trend of Pce = 30.27 kik^-0.44 and wettingphase saturation at any given Pc (for 350< Pc < 3350 psia air-Hg) and kik of Sw = A kik^-0.138 where A = -13.1*ln(Pcair-Hg)+117. Accuracy of the Leverett J function is poorer. Hysteresis Pc analysis indicates that residual nonwetting-phase saturation to imbibition (Srnw) increases with increasing initial nonwetting phase saturation (Snwi) consistent with the Land-type relation: 1/Snwr-1/Snwi = 0.8+0.2. Electrical resistivity measurements show that the Archie cementation exponent (m) decreases with decreasing porosity (Φi) below approximately 6% and can be generally described by the empirical relationship: m = 0.95-0.092 Φi +0.635 Φi^0.5. These relationships are still being investigated. The Mesaverde Project website is (http:// www.kgs.ku.edu/mesaverde).

AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah