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Development of hydrothermal geothermal resources associated with volcanic fields of the Circum-Pacific region is progressing at an accelerating pace. This valuable energy resource base can be greatly expanded by forming artificial reservoirs in rock that is hot but contains insufficient permeability and fluid for hydrothermal development. The formation of significant in-situ heat transfer systems and subsequent testing of these man-made geothermal reservoirs have indicated the technical and economic feasibility of the hot dry rock (HDR) geothermal concept. Extended production history and heat-extraction data obtained during the period of 1978-1980 have confirmed heat transfer, chemical, water loss, and thermal drawdown models of the systems. Closed-loop heat extraction op rations during a 9-month test, during which 15 × 106 kwh of thermal energy were produced, have demonstrated growth of the reservoir's effective heat-transfer area and volume due to secondary fracturing caused by thermal contraction and sustained pressurization. Drilling, fracturing, and testing of a larger reservoir system, are underway, which will demonstrate a HDR geothermal reservoir of commercial size. HDR projects within the Circum-Pacific area include the Los Alamos experiments supported by the U.S. Department Energy and of the governments of Japan and Federal Republic of Germany. A small-scale field test has been carried out at Yakedake, Japan, since 1979. This project will be continued until 1983 and a candidate site chosen for the construction of a several megawa t pilot plant.
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