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The AAPG/Datapages Combined Publications Database

Earth Science Bulletin (WGA)


Earth Science Bulletin
Vol. 15 (1982), No. 1. (Annual), Page 131

Abstract: Reservoir Characteristics of Selected Low-Permeability Sandstones, Late Cretaceous Age, Uinta Basin, Utah, and Green River Basin, Wyoming

C. W. Keighin1

Joint Meeting: University of Wyoming Department of Geology and Geophysics Wyoming Geological Association Geological Survey of Wyoming: April 2-4, 1982 Laramie, Wyoming: Subsurface Practices in Geology and Geophysics Abstracts of Papers - Compiled by James R. Steidtmann

Examination of core samples of low-permeability sandstones from the Upper Cretaceous Mesaverde Group, Uinta Basin, Utah, and the Upper Cretaceous Lance Formation. Green River Basin, Wyoming, indicates that porosity and permeability characteristics are significantly altered by physical and chemical diagenetic processes. The effects of these processes are magnified by the fine-grained nature of the sandstones examined. The effects of physical processes such as fractures produced by compaction are, in the depth range examined (6,000 ft - 12,000 ft), generally much less pronounced than the chemical processes of precipitation or dissolution. Much of the present porosity in-these rocks is secondary due to dissolution of earlier formed cements and, to a lesser degree, rock fragments and other framework grains. Many of the secondary pores are lined with, or at least partially filled with, authigenic kaolinite or illite. The generally small (< 10/hm) size of the pores, and the common presence of authigenic clays with high surface areas produce a tortuous pathway for fluid migration. The clays, in addition, contribute to a disproportionately high content of irreducible absorbed water in the sandstones, probably accounting for the high water saturations (Sw) calculated from well logs.

Permeability measurements show that permeability is severely reduced by increasing confining stress and by partial water saturation, although porosity is reduced only slightly. Although most low-permeability sandstones which have been examined exhibit similar—and significant—loss of permeability under confining stress, there is no general formula which quantitatively relates permeability loss to increases in confining pressure.

Acknowledgments and Associated Footnotes

1 C. W. Keighin: U.S. Geological Survey, Denver, Colorado

© Wyoming Geological Association, 2015