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Heat-flow and temperature-gradient measurements indicate a correlation between subsurface structures, regional ground-water flow, and heat flow in the Great Plains. Throughout the province, thick Cretaceous shales act as confining layers to aquifers, e.g., the Dakota (Cretaceous) and the Madison (Mississippian), which flow generally eastward in accord with the declivity of the plains. The vertical component of ground-water flow on the margins of the Denver, Kennedy, and Williston basins evidently exceeds the thermal diffusion rate in the confining layers overlying the aquifers, and causes significant disturbances in the surface heat flow. Heat flow along the eastern margin of the Denver basin in Nebraska may be about 50% higher than normal due to the water flow; the effec in the Kennedy basin in South Dakota and Nebraska may have doubled the surface heat flow. The Williston basin has anomalous heat flow on its eastern margin and may also show effects of intrabasin structures such as the Nesson anticline. These ground-water systems constitute a significant low-temperature geothermal resource that is estimated to exceed 20 × 1018 J of energy. Recognition of this geothermal resource and accurate estimation of the amount of available energy is best achieved by heat-flow studies. For example, estimates of geothermal resources in Nebraska based on heat-flow data and bottom-hole temperature data differ by 80%.
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