A method for extracting and utilizing geothermal energy present in the earth's interior is based on at least one essentially vertical bore hole into the ground, the bottom zone of which is provided with penetrating passages into the surronding rock. A heat-conducting substance is forced into the penetrating passages. At least one supply and one return line for a heat transmission medium is thermally linked with the heat-conducting substance and the surrounding rock. The heat transmission medium is conveyed in a circuit in which part of its heat content is extracted and industrially utilized before reintroducing the fluid into the ground.

Disclosed are a device and a method for utilizing the thermal energy in the soil to protect against damage to plants, such as citrus trees, from cold weather and to promote the growth of plants. The device comprises a heat pipe having an evaporator section which extends into the soil in the vicinity of the root system of the plants and extracts heat from the soil. The heat is then transferred to a condenser section which extends above ground and radiates and convects the heat to the plant. This also refrigerates the root system of the plant to extend the dormancy period. Also disclosed is a method for providing a supply of water to a plant, comprising the use of a heat pipe to create a temperature gradient around the root system of the plant, whereby water from the surrounding soil is caused to flow toward the plant.

A soil heat exchanger for effecting an energy exchange between earth soil and an energy exchanger and including a thermoinsulated flow duct arranged in a borehole formed in ground, a pump provided at an end of the flow duct, a shroud pipe surrounding the flow duct and the pump, and a return flow region for return water located radially outwardly of the shroud pipe and including return flow pipes and a porous filling, with the return flow pipe means extending down to a bottom of the borehole and having lateral opening means communicating with an interior of the shroud pipe through the inlet openings of the shroud pipe, with the shroud pipe having its lower end spaced from the bottom of the borehole, and with the lateral openings of the return flow pipes being beneath the lower end of the shroud pipe, and with the porous filling extending from the borehole bottom and at least up to a level above the inlet openings of the shroud pipe.

A device and method for recovering heat from the soil and groundwater, comprise heat-exchanging means consisting of an inner tube, an outer tube and partitions forming longitudinal channels between said inner and outer tube. An inlet for heat-exchanging fluid and an outlet for heat-exchanging fluid are present for conveying a heat-exchanging fluid through said longitudinal channels. The heat-exchanging means are preferably placed in a perforated casing allowing passage of liquid but not of soil particles. The casing consists preferably of an outer casing tube and an inner casing tube, casing partitions providing longitudinal casing channels. For allowing passage of groundwater the outer casing tube and the inner casing tube are provided with perforations. Heat is recovered by passing a heat-exchanging fluid through the casing channels.

The method and improvement for recovery of hydrocarbons in situ from subterranean oil shale formations is disclosed by forming generally horizontal electrodes from the injection of molten metal into preheated or unheated fractures of the formation. A nonconductive spacing material is positioned in the casing of the bore hole between the electrodes. A fracture horizontally intermediate between the metallic electrodes is propped with a nonconductive granular material. Unterminated standing waves from a radio frequency (R.F.) generator are passed between the electrodes so as to heat the oil shale formation. The hydrocarbons in the formation are vaporized and are recovered at the surface by their migration through the intermediate fracture and tubing. By this method radial metallic electrodes can be formed at various depths throughout a subterranean oil shale formation so as to vaporize the hydrocarbons contained within the oil shale formation.