4 research outputs found
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1978 USGS Geothermal Resource Assessment
The author distinguishes between geothermal resource base, accessible geothermal resource base, geothermal resource, and geothermal reserve. Conditions for periodically updating the assessment of geothermal energy resources include: increased data from expanded exploration and drilling; development of improved and new technologies for exploration, evaluation, extraction, and use; rapid evolution of geothermal knowledge; and the increased role of geothermal energy in response to changing economic, social, political, and environmental conditions, particularly an increasing awareness of the limits to petroleum and natural gas resources. Accordingly, the U. S. Geological Survey (USGS) plans by the end of 1978 to update its 1975 assessment of the United States’ geothermal resource, with increased emphasis on several items. The USGS’s joint evaluations of geothermal resource-assessment techniques in the last year with the National Electric Agency of Italy (ENEL) under U. S. Energy Research and Development Agency sponsorship identified a number of problems, one of which was how to formulate geothermal recovery factors for systems producing by intergranular vaporization and by intergranular flow. The first formulation is fairly rigorous; the author solicits the reservoir engineering community’s help in improving the estimate of the second. 3 figs., 11 refs
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Are there significant hydrothermal resources in the US part of the Cascade Range?
The Cascade Range is a geothermal dichotomy. On the one hand, it is an active volcanic arc above a subducting plate and is demonstrably an area of high heat flow. On the other hand, the distribution of hydrothermal manifestations compared to other volcanic arcs is sparse, and the hydrothermal outflow calculated from stream chemistry is low. Several large estimates of undiscovered geothermal resources in the U.S. part of the Cascade Range prepared in the 1970s and early 1980s were based fundamentally on two models of the upper crust. One model assumed that large, partly molten, intrusive bodies exist in the upper 10 km beneath major volcanic centers and serve as the thermal engines driving overlying hydrothermal systems. The other model interpreted the coincident heat-flow and gravity gradients west of the Cascade crest in central Oregon to indicate a partly molten heat source at 10 {+-} 2 km depth extending {approx}30 km west from the axis of the range. Investigations of the past ten years have called both models into question. Large long-lived high-temperature hydrothermal systems at depths <3 km in the U.S. part of the Cascade Range appear to be restricted to silicic domefields at the Lassen volcanic center, Medicine Lake volcano, Newberry volcano, and possibly the Three Sisters. Federal land-use restrictions further reduce this list to Medicine Lake and Newberry. Dominantly andesitic stratocones appear to support only small transitory hydrothermal systems related to small intrusive bodies along the volcanic conduits. The only young caldera, at Crater Lake, supports only low- to intermediate-temperature hydrothermal systems. Most of the Cascade Range comprises basaltic andesites and has little likelihood for high-level silicic intrusions and virtually no potential for resultant large high-temperature hydrothermal systems. Undiscovered hydrothermal resources of the Cascade Range of the United States are substantially lower than previous estimates. The range does have potential for intermediate-temperature hot dry rock and localized low- to intermediate-temperature hydrothermal systems