Lithofacies and Petrophysical Properties of Mesaverde Tight-Gas Sandstones in Western U.S. Basins
Alan P. Byrnes1, John C. Webb2, Robert M. Cluff2, Daniel A. Krygowski2, and Stefani D. Whittaker2
1Kansas Geological Survey, University of Kansas, Lawrence, KS
2The Discovery Group, Inc., Denver, CO
The relationship between core and log petrophysical properties and lithofacies sedimentary characteristics is examined in Mesaverde Group tight gas sandstones from forty cores in the Washakie, Uinta, Piceance, Greater Green River, Wind River, and Powder River basins.
Shaly intervals of the Mesaverde Group are dominated by mudstones and silty shales; burrowed, lenticular and wavy-bedded very shaly sandstones; and wavy-bedded to ripple cross-laminated shaly sandstones. Sandstone intervals are dominated by ripple cross-laminated , cross-bedded, planar laminated, and massive, very-fine to fine-grained sandstones .
For 2200 core plugs measured, grain density averages 2.654+0.033 g/cc (error of 1 std dev) with distributions differing slightly among basins. Core porosity ranges from 0-25%, averaging 7.2%. 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 improved sorting, with secondary influences including sedimentary structure and the nature of cementation. Multivariate and neural network permeability prediction methods exhibit a standard error of 4.5X and 3.3X respectively. 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 Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas