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Languages : en
Pages : 145
Book Description
In geothermal energy technology, the hydrothermal systems rely on volcanic hot rocks being fortuitously co-located with an adequate supply of natural ground water, usually at some considerable depth within the earth. This represents essentially two accidents in the same place, and the occurrence is relatively rare. Yellowstone Park and the desert valley of southern California are the most noteworthy US. examples. Since the heat is the energy needed, if we could just get the water down to it and back. Well, that's what is being done with the hot dry rock program. A well is drilled down to where there is adequate heat in the rocks. The well is then pressurized until the rock fractures creating what amounts to a reservoir full of hot, shattered rock. Finally, a well is drilled into the reservoir and water is pumped in one well, heated by the rock, and taken out through the other well at useful temperatures and pressures. We are getting ready to run significant long-term flow tests at the Fenton Hill Hot Dry Rock site west of Los Alamos, New Mexico. We expect the operational information to provide the data to forecast the energy life of the wells as a production facility. This kind of resource is much more common than regular geothermal resources. Robert H. Hendron described the Long Term Flow Test and reservoir studies for which the project is preparing. A shortfall of available funding has slowed preparations, delaying the start of that test. The test is planning to gather data for more definitive reservoir modeling with energy availability or reservoir lifetime of primary interest. Other interests include geochemistry and tracer studies, microseismic response, water requirements and flow impedance which relates directly to the pumping power required. Progress has been made in modeling studies, chemically reactive tracer techniques, and in improvements in acoustic or microseismic event analysis. Donald W. Brown discussed reservoir modeling as it relates to production management of the HDR well. For wells which are fracture dominated rather than matrix-permeability controlled, a knowledge of the pressure-dependent permeability of the interconnected system of natural joints (or pre-existing fractures is critical to long-term power production from the wells) through optimized pressure management. It was mentioned that a knowledge of the pressure-dependent joint permeability could aid in designing more appropriate secondary recovery strategies in petroleum reservoirs, or reinjection I procedures of geothermal reservoirs. Dr. Bruce A. Robinson discussed the development of fluid flow and transport models for simulation of HDR geothermal reservoirs. These models are also expected to provide accurate predictions of long-term behavior and help in the development of strategies for reservoir improvement and operation. Two approaches were discussed. The discrete fracture approach is based on a random fracture network subject to prescribed statistical properties of the fracture set. It is used to simulate steady state fluid flow and solute transport. The other approach used the continuum approximation. This type of model is appropriate when the reservoir consists of many interconnected fractures, as is the case at Fenton Hill.
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Author: Catherine Fairhurst
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Author: A. S. Batchelor
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Author: Donald W. Brown