Fox Hills, Lower Hell Creek, Powder River Basin

General Setting

The Powder River Basin is a Rocky Mountain foreland basin in northeastern Wyoming and southeastern Montana. It is a highly asymmetrical basin, with a gently sloping eastern margin and steeply dipping western and southern margins, where folding and overturned strata are common. The Powder River Basin contains fewer structurally defined fields than other basins of western and southwestern Wyoming. The major gas-productive reservoirs, occurring in the Sussex and Shannon Sandstones, the Frontier Formation, and the Dakota Sandstone, contain abundant stratigraphic traps (Mullen and Barlow and Haun, Inc., 1993)

Information Search and Selection

Subsurface formations in the Powder River Basin are well documented, with the majority of the hydrocarbon-producing zones from numerous stratigraphic Cretaceous intervals, with additional zones in the Jurassic, Permian, and Pennsylvanian (Gluskoter and others, 1991). A variety of studies have been made of individual formations and groups, both hydrocarbon and nonhydrocarbon productive, in the Powder River Basin (Cloverly Group [Hooper, 1961], Tekla Sandstone [George, 1974], Fort Union Formation [Ayers and Kaiser, 1984], Sussex and Shannon Sandstones [Tillman and Martinsen, 1984; 1987], Muddy Sandstone [Gustason, 1988], and Lance Formation [Connor, 1991], but many of these studies have focused on potential for hydrocarbon production or coal distribution, with only minor attention paid to brine disposal or aquifer geometry.

Several formations contain permeable and continuous sandstone bodies in the Powder River Basin. Of these formations, the Lower Cretaceous Lakota Formation was initially considered to be a potentially excellent candidate because it contains continuous sandstone bodies, is deeply buried (more than 2,500 ft [>762.2 m]) in most of the Powder River Basin, and contains relatively little hydrocarbon production (Gluskoter and others, 1991). However, critical information such as gross sandstone, formation isopach, top-seal thickness, and potentiometric surface on a regional scale is lacking for the Lakota Formation, and the Upper Cretaceous Fox Hills Sandstone was therefore chosen for characterization.

The Fox Hills Sandstone contains regionally continuous, marine and marginal-marine sandstones overlain by muddy, lower-coastal-plain sandstones of the Lance Formation (Connor, 1991). Because the Fox Hills Sandstone has little or no hydrocarbon production in the Powder River Basin, its characteristics as a hydrogeologic unit have been relatively well described (Henderson, 1985). However, there are some limitations of the Fox Hills Sandstone that may decrease its potential for CO2 sequestration. Although the upper Cretaceous Fox Hills Sandstone meets the minimum depth criterion of 800 m for suitability as a formation for injection of CO2, it may be marginally suitable from the standpoint of salinity. For a large part of the Powder River Basin, the salinity of the Fox Hills Sandstone is less than 3,000 ppm, reaching brackish conditions in the deep, western part of the basin.

The major sources of data for the Fox Hills Sandstone in the Powder River Basin are derived from Lewis and Hotchkiss (1981) and Henderson (1985) in studies of the Upper Cretaceous Hell Creek and Lance-Fox Hills aquifers. Major parameters for the Fox Hills Sandstone are briefly described, with notes pertaining to the suitability of this stratigraphic unit for being included as a data source.


Asquith, D. O., 1970, Depositional topography and major marine environments, Late Cretaceous, Wyoming: American Association of Petroleum Geologists Bulletin, v. 54, no. 7, p. 1184-1224.

Ayers, W. B., Jr., and Kaiser, W. R., 1984, Lacustrine interdeltaic coal in the Fort Union Formation (Paleocene), Powder River Basin, Wyoming and Montana, U.S.A., in Rahmani, R. A., and Flores, R. M., eds., Sedimentology of coal and coal-bearing sequences: International Association of Sedimentologists, Special Publication 7, p. 61-84.

Connor, C. W., 1991, The Lance Formation-petrography and stratigraphy, Powder River Basin and nearby basins, Wyoming and Montana: U. S. Geological Survey, Bulletin 1917-I, 17p. and 8 plates.

George, G. R., 1974, Poison Draw field, Converse County, Wyoming: Wyoming Geological Association, Earth Science Bulletin, v. 7, no. 3, p. 3-19.

Gluskoter, H. J., Rice, D. D., and Taylor, R. B., 1991, eds., The Bureau of Economic Geology, The Geology of North America: The Geological Society of America, v 2.

Gustason, E. R., 1988, Depositional and tectonic history of the Lower Cretaceous Muddy Sandstone, Lazy B field, Powder River Basin, Wyoming: Wyoming Geological Association, Guidebook to 39th Field Conference, p. 129-146.

Henderson, T., 1985, Geochemistry of ground-water in two sandstone aquifer systems in the northern Great Plains in parts of Montana and Wyoming: U. S. Geological Survey, Professional Paper 1402-C, p. C1-C84.

Hooper, W. F., 1961, Lower Cretaceous of Casper Arch, Wyoming: American Association of Petroleum Geologists Bulletin, v. 45, no. 8, p. 1523-1544.

Lewis, B. D., and Hotchkiss, W. R., 1981, Thickness, percent sand, and configuration of shallow hydrogeologic units in the Powder River Basin, Montana and Wyoming: U. S. Geological Survey, Miscellaneous Investigations Series, Map I-1317, 6 sheets.

Mullen, D. M., and Barlow and Haun, Inc., 1993, Powder River Basin (Section FS-1), in Hjellming, C. A., ed., Atlas of major Rocky Mountain gas reservoirs: New Mexico Bureau of Mines and Mineral Resources, Geological Survey of Wyoming, Colorado Geological Survey, Utah Geological Survey, Barlow and Haun, Intera, and Methane Resources Group, Ltd., p. 70.

National Imagery and Mapping Agency, 2000, Digital terrain elevation data (DTED Level 0)

Tillman, R. W., and Martinsen, R. S., 1984, The Shannon shelf-ridge sandstone complex, Salt Creek Anticline area, Powder River Basin, Wyoming: Society of Economic Paleontologists and Mineralogists, Special Publication 34, p. 85-142.

___________ 1987, Sedimentological model and production characteristics of Hartzog Draw field, Wyoming, a Shannon shelf-ridge sandstone: Society of Economic Paleontologists and Mineralogists, Special Publication 40, p.15-112.

U. S. Geological Survey, 1996, Ground water atlas of the United States: Segment 8: Montana, North Dakota, South Dakota, and Wyoming, p. 117.

Van Horn, M. D., and Shannon, L. T., 1989, Hay reservoir field: a submarine fan gas reservoir within the Lewis Shale, Sweetwater County, Wyoming: Wyoming Geological Association, Guidebook to 40th Field Conference, p. 155-180.

Prepared by William Ambrose.

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