Lithofacies and Petrophysical Properties of Mesaverde Tight-Gas Sandstones in Western U.S. Basins
John C. Webb1, Alan P. Byrnes2, Robert M. Cluff1, Dan A. Krygowski1, and Stefani D. Whittaker1
1The Discovery Group, Inc., Denver, CO
2Chesapeake Energy, Oklahoma City, OK
The relationship between core and log petrophysical properties and lithofacies are examined in Mesaverde Group tight gas sandstones from forty cores in the Washakie, Uinta, Piceance, Greater Green River, Wind River, and Powder River basins. Fine-grained intervals of the Mesaverde Group include mudstones and silty shales; burrowed, lenticular and wavy-bedded very shaly sandstones; and wavy-bedded to ripple cross-laminated shaly sandstones. Sandstone intervals include ripple cross-laminated and cross-bedded, very fine to fine-grained sandstones, low-angle cross-laminated to planar laminated sandstones, and massive sandstones. Lithofacies were deposited in nonmarine, paludal, marginal marine and marine environments. For all lithofacies undifferentiated in the cores sampled, grain density averages 2.654+0.033 g/cc (error of 1 std dev) with grain density distributions differing slightly among basins. Core porosity ranges from 0-25%, averaging 7.2% (n=2200). In situ Klinkenberg permeability ranges from 0.0000001-200 millidarcies, averaging 0.002 millidarcies. Characteristic of most sandstones, permeability at any given porosity increases with increasing grain size and increasing sorting though this relationship is further influenced by the nature of cementation. Cements include chlorite, ML-IS and illitic clays, quartz, calcite and ferroan calcite. Capillary threshold entry pressure and pore characteristric length are well correlated with permeability. Archie cementation exponent, m, can be modeled with a dual porosity matrix-fracture model with m approaching one as porosity approaches zero. Critical gas saturation is generally less than 5% but increases with increasing bedform complexity. Integration of wireline log analysis and core petrophyscial relationships provides guidelines and equations for predicting reservoir properties. The Mesaverde Project website is (http://www.kgs.ku.edu/mesaverde).
AAPG Search and Discovery Article #90092©2009 AAPG Rocky Mountain Section, July 9-11, 2008, Denver, Colorado