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Hot Dry Rock Geothermal Energy Technology


Right - Schematic of an HDR Site

Diagram of HDR Site

The technology to mine the heat from the hot rock found almost everywhere at some depth beneath the surface of the earth was conceived and developed at Los Alamos between the years of 1970 and 1996. Conceptually, hot dry rock (HDR) heat mining is quite simple. As shown in the drawing (above, left) water is pumped into hot, crystalline rock via an injection well, becomes superheated as it flows through open joints in the hot rock reservoir, and is returned through production wells. At the surface, the useful heat is extracted by conventional processes, and the same water is recirculated to mine more heat.

The key element in successful heat mining is the development of an engineered geothermal reservoir in a hot body, impermeable rock. The point in a hot rock body at which an HDR reservoir is created is determined by the selection of the location on the surface from which the injection well is drilled and the depth within the wellbore at which the water is injected into the hot rock, while the overall size of the reservoir is a direct function of the total amount of water pumped into the rock during its development. Although these parameters can be engineered, the shape, orientation, and internal structure of the reservoir, are entirely functions of the local geologic conditions and are, at present, beyond human control. For this reason, it is important to understand the local geology before attempting to develop an HDR reservoir.

As an HDR reservoir is being formed, rock blocks are moved very slightly by the injected water. These small movements give rise to low frequency stress waves similar to, but much smaller than, those caused by earthquakes. Microseismic technology has been developed to identify these signals and locate their points of origin. The data from many such signals provide a picture of the size, shape, and orientation of the reservoir. With this information in hand, production wells can be drilled into the reservoir to most efficiently tap the superheated water that has been injected.

 

Right - Image of the Fenton Hill Plant - Now Decommissioned

Fenton Hill Geothermal Site

As demonstrated at the Los Alamos Fenton Hill site (above, right) HDR system is operated by circulating water through the engineered reservoirs at a pressure somewhat less than that used during its creation. Under these conditions the overall volume of the engineered reservoir is relatively stable. In the closed-loop operation, the injection pump, working like the human heart, provides the entire motive force for the circulation. Nothing except a small amount of waste heat is released to the environment.

The Fenton Hill test experiment has been completed and HDR technological advances realized at Los Alamos have been incorporated into a broader program encompassing hydrothermal environments. That program is under the leadership of Princeton Economic Research, Inc. (PERI). PERI is working with the US geothermal industry to apply technology developed as part of the Los Alamos HDR effort to problems facing commercial geothermal production which is currently derived entirely from natural hydrothermal resources. PERI is also formulating longer-term plans and designing programs that should eventually lead commercial utilization of HDR resources.

HDR field work is continuing at sites in northern France and on the island of Honshu in Japan. A nascent HDR program is also getting underway in Australia. The experience gained from HDR work at Los Alamos is being utilized in all of these international projects. That experience also provided the basis for a wide range of related activities now underway in EES-11. Relevant points of contact at Los Alamos and elsewhere, a list of related web sites, and references to selected HDR publications are given below.

For more information on our hot dry rock program, contact Don Brown or Don Dreesen or read Hot Dry Rock in the USA, a A 127 KB PDF File.

View a QuickTime movie, The Closing of Fenton Hill

 

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