For the past four years, the Los Alamos Scientific Laboratory (LASL) has been investigating a method for extracting geothermal energy from hot, but essentially impermeable, rocks at moderate depths. The concept is to drill a hole into the hot, relatively impermeable rock and create a large hydraulic fracture that serves as a downhole heat exchanger. A second hole is drilled to intersect the fracture, creating a circulation loop for the injected water.

Two deep holes (GT-2 and EE-1) have been drilled at the Fenton Hill site in northern New Mexico. The first hole, GT-2, has a depth of 2,928 m and a bottom-hole temperature of 197 °C. The second hole, EE-1, has been temporarily halted at at depth of 3,062 m, where the temperature is 205.5 °C. Hydraulic fractures have been created in both holes, and fluid communication between the holes was established in October 1975. Circualtion experiments are now being conducted between the two holes.

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