Research about northern Great Plains

USGS1985

The occurrence of extractable elements in soils from the northern Great Plains

The modes of occurrence of extractable elements from 21 A and C horizon samples of uncultivated soils were examined using R-mode factor analysis. The extractants (DTPA, EDTA, HCl, hydroquinone, magnesium nitrate, and ammonium oxalate) cover a wide range of chemical attack. Four major elements (Ca, K, Mg, and Na) and eight trace elements (Cd, Co, Cu, Fe, Mn, Ni, Pb, and Zn) were determined in each extractant solution. A variety of chemical, mineralogical, and physical variables were also determined on each sample. Four varimax factors (clay, organic, Fe and Mn oxides, and soluble-Na) accounted for 74.2% of the total variance of the 90 variables for the A horizon. Seven varimax factors (Fe and Mn oxides, clay, CEC, soluble-Na, organic, Fe and Mn, and plagioclase) accounted for 77.2% of the total variance of the 79 variables for the C horizon. A and C horizon extractable trace elements are most generally related to Fe and Mn oxides, as indicated by loadings on the Fe and Mn oxide factor for both the A and C horizons. Each extractant generally operates on different modes of occurrence of an element in soil. For example, substantial differences occur between the HCl-, oxalate-, and hydroquinone-extractable trace elements. However, the modes of occurrence for trace elements removed by DTPA and EDTA were very similar, suggesting strong relationships between elements dissolved by these two extractants. The modes of occurrence for each individual major element are similar with each of the six extractants. A horizon Ca and Mg, and C horizon K and Mg are strongly related to a clay factor. C horizon Ca and A horizon K are strongly related to the CEC and organic factors, respectively. Both A and C horizon extractable Na are very strongly related to the soluble-Na factor. These results suggest that extractable major elements are water-soluble and are associated with the constituents that are responsible for that factor. Consequently, strong relationships should occur for any individual major element dissolved by any pair of extractants.

northern Great Plains↗

USGS1980

Shallow, low-permeability reservoirs of northern Great Plains: Assessment of their natural gas resources.

Major resources of natural gas are entrapped in low-permeability, low-pressure reservoirs at depths less than 4,000 ft (1,200 m) in the northern Great Plains. This shallow gas is the product of the immature stage of hydrocarbon generation and is referred to as biogenic gas. Prospective low-permeability, gas-bearing reservoirs range in age from late Early to Late Cretaceous and include most of the section from the base of the Mowry Shale to the top of the Judith River Formation. For detailed examination, the potential reservoir section was divided into five intervals represented by one or more formations and their correlatives. The intervals selected correspond to (1) Mowry Shale, (2) Belle Fourche Shale and Greenhorn Formation, (3) Carlile Shale, (4) Niobrara and Telegrap Creek Formations and Eagle Sandstone, and (5) Claggett Shale and Judith River Formation and their equivalents. Within each interval, several different facies are developed. The following facies were identified and mapped for each interval: nonmarine rocks, coastal sandstones, shelf sandstones, siltstones, shales, and chalks. Two types of shelf sandstone were differentiated but generally not mapped separately because of lack of well log control. The "sand ridge" type has reservoir properties comparable to coastal sandstones and occurs as isolated tongues as much as 75 ft (23 m) thick. The second type of shelf sandstone is in beds commonly less than 1 in. (3 cm) thick which are interbedded with shale and contain a high content of allogenic silt- and clay-size material. It is impossible to differentiate these individual beds on conventional well logs. The siltstone and shale facies are grouped to ether because conventional logs cannot distinguish between these two rock types, particularly when they are interbedded. For future evaluation of natural gas resources from low-permeability reservoirs, it will be necessary to differentiate between the siltstone and shale facies and to identify individual beds, particularly very thin ones, within the shelf sandstone facies. Each facies contains distinct reservoir types, some of which are low in permeability. The most promising low-permeability reservoirs are developed in the shelf sandstone, siltstone, and chalk facies. Reservoirs within these facies are particularly attractive because they are enveloped by thick sequences of shale which serve as both a source and a seal for the gas. When naturally fractured, these shales also may be low-productivity gas reservoirs similar to the Devonian shales of the Appalachian basin. In addition, facies with low-permeability reservoirs are present over most of the study area when maps for all of the intervals are combined. Natural gas is produced from low-permeability reservoirs in the northern Great Plains in the southern part of western Canada. Established production covers an area of approximately 8,000 sq mi (20,700 sq km) where reported recoverable reserves average as much as 2 Bcf sq mi. Using these reserve data as an analog, the United States portion may contain resources of natural gas in excess of 100 Tcf. The volume of recoverable gas in the United States will depend on the development of improved recovery technology and higher gas prices relative to costs.

northern Great Plains↗